y 

William Dean David Peters 

Frank Pilotte 

ARTHUR D. LITTLE, INC. 

C-73 91 2 

USBM CONTRACT FINAL REPORT (Contract No. H0122026) 

JANUARY 1974 

DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

WASHINGTON, D. C. 
USBM Contract No. H0122026 

SURVEY OF ELECTROMAGNETIC AND SEISMIC NOISE 

RELATED TO MINE RESCUE COMMUNICATIONS 

VOLUME I1 

SEISMIC DETECTION AND LOCATION OF ISOLATED MINERS 

Robert L. Lagace - Project Leader 

John J. Ginty, Martyn F. Roetter, Richard H. Spencer 

Special Seismic Consultants 

Robert Crosson Roy Greenfield 

Francis Crowley John Kuo 

William Dean David Peters 

Frank Pilotte 

ARTHUR D. LITTLE, INC. 

C-73912 

The views and conclusions contained in this document 

are those of the authors and should not be interpreted 

as necessarily representing the official policies or 

recommendations of the Interior Department's Bureau of 

Mines or the U.S. Government. 

USBM CONTRACT FINAL REPORT (Contract No. H0122026) 

JANUARY 19 7 4 

DEPARTMENT OF THE INTERIOR 

BUREAU OF MINES 

WASHINGTON, D. C. 

Arthur D Little. Inc 
FOREWORD 

This report was prepared by Arthur D, Little, Inc., Cambridge, Massachusetts 

under USBM Contract No. H0122026, The contract was initiated under the 

Coal Mine Health and Safety Research Program. It was administered under 

the technical direction of the Pittsburgh Mining and Safety Research Center 

with Mr, Howard E. Parkinson acting as the technical project officer. 

Mr. Francis M. Naughton was the contract administrator for the Bureau of 

Mines . 

This report is a summary of the work recently completed as part of this 

contract during the period August 1971 to December 1973. This report was 

submitted by the authors in January 1974. 

Arthur D Little, Inc 
VOLUME I1 

SEISMIC DETECTION AND LOCATION OF ISOLATED MINERS 

TABLE OF CONTENTS 

INTRODUCTION 

PART ONE EXECUTIVE SUMMARY * 

PART TWO DETECTION RANGE AND ARRIVAL TIME ESTIMATES 

PART THREE ESTIMATES OF MINER LOCATION ACCURACY: ERROR 

ANALYSIS IN SEISMIC LOCATION PROCEDURES FOR 

TRAPPED MINERS 

PART FOUR ESTIMATES OF MINER LOCATION ACCURACY: 

WESTINGHOUSE .LOCATION PROGRAM "MINER" 

PART FIVE THE REFERENCE EVENT METHOD OF SEISMIC 

LOCATION FOR MINE RESCUE SYSTEMS 

PART SIX FIELD UTILIZATION OF SEISMIC SYSTEMS 

PART SEVEN THEORETICAL SIGNAL SOURCE AND TRANSMISSION 

CHARACTERISTICS 

PART EIGHT EARTH MODELS 

PART NINE SEISMIC NOISE CHARACTERISTICS 

PART TEN SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

PART ELEVEN SEISMIC DETECTION/LOCATION INSTRUMENTATION 

PART TWELVE BRIEFING CHARTS 

Page 

v 

iii 

Arthur D Little, Inc 
INTRODUCTION 

PART ONE 

PART TWO 

PART THREE 

PART FOUR 

PART FIVE 

PART SIX 

PART SEVEN 

PART EIGHT 

PART NINE 

VOLUME I 

EMERGENCY AND OPERATIONAL MINE COMMUNICATIONS 

TABLE OF CONTENTS 

ASSESSMENT OF ELECTROMAGNETIC NOISE DATA 

AND DEFINITION OF A NEW MEASUREMENT PROGRAM 

ELECTROMAGNETIC THROUGH-THE-EARTH MINE 

COMMUNICATIONS 

LEAKY COAXIAL CABLE FOR GUIDED WIRELESS 

MINE COMMUNICATION SYSTEMS 

THEORY OF WIRELESS PROPAGATION OF UHF RADIO 

WAVES IN COAL MINE TUNNELS 

HOIST SHAFT MINE COMMUNICATIONS 

TROLLEY WIRE MINE COMMUNICATIONS 

MINE PAGER PHONE TO PUBLIC TELEPHONE 

INTERCONNECT SYSTEM 

TECHNOLOGY TRANSFER SEMINARS ON MINE 

COMMUNICATIONS AND THROUGH-THE-EARTH 

ELECTROMAGNETIC WORKSHOP 

ADDITIONAL TECHNICAL SUPPORT AND CONSULTING 

SERVICES RELATED TO MINE COMMUNICATIONS AND 

MINER LOCATION 

Page 

v 

Arthur D Little, lnc. 
INTRODUCTION 

This final report documents the work done by Arthur D. Little, Inc. (ADL) 

on behalf of the U.S. Bureau of Mines, Pittsburgh Mining and Safety Research 

Center (PMSRC) , on Contract H0122026 (which began in August of 19 71) . Under this contract ADL provided technical assistance to the Bureau on a 

task basis on virtually all aspects of the ~ureau's programs related to 

present and planned emergency and operational communications and miner 

location systems for underground coal mines. The work consisted of independent investigations, analyses, experiments, breadboard and prototype 

hardware development, workshops and technology transfer seminars on mine 

communications, and on-going evaluations and guidance related to the 

~ureau's contracted programs on electromagnetic noise, mine communications systems, and trapped miner location. This final report documents 

the work in two volumes, Volume I, "Emergency and Operational Mine Communications," and Volume 11, "seismic Detection and,Location of Isolated Miners." 

The Tables of Contents of both Volumes are included in each Volume. 

Phase I of the contract was devoted to performing an in-depth assessment 

of electromagnetic noise measurements taken by several contractors and 

other investigators, and then defining a new noise measurement program 

and instrumentation system tailored to obtain the necessary but missing 

noise data. These data are required for use in the design of new emergency 

and operational communication systems. This work, and the follow-on 

coordination and guidance activities of ADL on this noise measurement 

program in subsequent phases of the contract, are treated in Part One of 

Volume I. 

The latter part of Phase I and part of Phase I1 included preliminary performance predictions related to through-the-earth electromagnetic communication systems. These predictions were based on available theoretical 

signal propagation results and on recently acquired noise data at several 

coal mines. This work is treated in Part Two of Volume I. 

In Phases 11, IV and V, investigations were conducted related to wire, 

guided-wireless and wireless communications systems for communicating 

with roving vehicles and personnel underground. This work is documented 

as follows. Part Three of Volume I treats guided wireless communications 

via leaky coaxial cable; Part Four treats wireless communications in mine 

tunnels at UHF frequencies; Part Five treats guided wireless communications 

down deep hoist shafts; Part Six treats aspects of trolley wire communications; and Part Seven treats a new mine pager telephone to public telephone 

interconnect system. 

Arthur D Little Inc 
Another aspect of Phase V included tasks for providing assistance related 

to technology transfer seminars on mine comunications and to a workshop 

on through-the-earth electromagnetics. Part Eight of Volume I treats 

this work. Under Phases 11, IV, and V, ADL also provided a wide variety 

of short-term technical support and consulting services not discussed in 

the above mentioned Parts. This short-term work is treated in Part Nine 

of Volume I. 

In Phase 111 of the contract, ADL performed another in-depth assessment 

on a compressed time schedule, to provide PMSRC with independent technical judgments regarding the potentials and limitations of seismic 

methods and systems for detecting and locating isolated miners. Volume I1 

of this report is devoted entirely to the treatment of this work. 

During the course of this contract we prepared over forty working memoranda, technical reports, seminar papers, and workshop summary reports, 

in addition to many informal memoranda and the monthly technical reports, 

to keep PMSRC informed of the progress and findings of our work as they 

developed. This final report is based on these previous memoranda and 

reports. 

Arthur D Little, Inc. 
PART ONE 

EXECUTIVE SUMMARY 

Arthur D Little, lnc 
PART ONE 

EXECUTIVE SUMMARY 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. PURPOSE AND APPROACH 

11. SUMMARY OF RESULTS 

A. DETECTION OF A MINER 

B. LOCATION OF A MINER 

C . FIELD UTILIZATION 

111. CONCLUDING REMARKS 

Page 

1. iii 

Arthur D Little, Inc 
PART ONE 

EXECUTIVE SUMMARY 

LIST OF TABLES 

Table No. Title 

1 Seismic Detection and Location 

General Ground Rules 

2 Task Areas 

3 Maximum Slant Ranges (In Feet) for 

Detection-Under Natural Noise Conditions 

4 Signal-to-No ise Improvement Techniques 

5 Hardvsre Requirements for Seismic 

Detection/~ocation System 

6 Expected Impact on Investments on System 

Performance and Cost 

Page 

1, iii 

Arthur D Little, lnc. 
Figure No. 

1 

PART ONE 

EXECUTIVE SUMMARY 

LIST OF FIGURES 

Title 

Composite Plot for Estimating Detection 

Ranges Under Natural Noise Conditions 

Example of Location Error Contour Maps 

Alternatives 

Page 

Arthur D Little, lnc. 
PART ONE 

EXECUTIVE SUMMARY 

Arthur D. Little, Inc. 

I. PURPOSE AND APPROACH 

This Volume documents the Phase 111 effort on the Seismic Detection 

and Location of Isolated Miners on Contract H0122026 undertaken during 

the fall of 1972 by a task team composed of ADL staff and several seismic 

consultants. The team was assembled specifically to work together on 

complementary tasks, at an accelerated level of effort for four months, 

to meet the Bureau of ~ines' time schedule for obtaining independent, 

objective, technical judgments regarding seismic methods and systems for 

detecting and locating isolated miners. The impetus for this work resulted from a compilation and analysis, during the first half of 1972, 

of new experimental data obtained from a series of in-mine field tests 

conducted by Westinghouse Corp .+ using the CMRSS* interim seismic location 

system. The Bureau of Mines took advantage of the availability of these 

new data to reassess the potential and limitations of various seismic 

methods and systems, and to direct its seismic system improvement program 

accordingly. 

ADL assisted the Bureau in this reassessment by drawing on the skills 

of seismic consultants from industry, universities and government, to 

supplement the skills of the ADL project team. The consultants were principal resources of broadly-based and detailed technical expertise in the 

areas of seismic signal-source and signal-propagation characteristics, 

natural and cultural seismic noise, seismic sensors and field instrumentation, seismic signal and data processing for detection and location, and 

overall seismic system utilization in the field under operational emergency 

conditions. Specifically, the participating consultants were: F. Crowley, 

Air Force Cambridge Research Laboratories ; W. Dean, Teledyne Geotech, 

Alexandria Laboratories; R. Greenfield, Pennsylvania State University; 

J. Kuo, Columbia University; D. Peters and R. Crosson, University of 

Washington; and F. Pilotte, U.S. VELA Seismological Center. The principal 

ADL participants were J. Ginty, R. Lagace, M. Roetter, and R. Spencer. 

Westinghouae Contract H0210063 with the Bureau of Mines. 

* Coal Mine Rescue and Survival System, 

Arthur Il Little, Inc 
Guidance and assistance related to the general suitability and applicability of recommended techniques and procedures to actual mine environments were provided by H. Parkinson and J. Powell of U.S. Bureau of Mines 

Pittsburgh Mining and Safety Research Center. 

The overall objective of the Phase I11 effort was to perform a short 

intensive study to identify what could be done by seismic methods and 

systems, and how well, to: 

detect live signaling miners 

locate such miners to within the confines of a 

600-by-600 foot section; and 

a locate such miners to within a 15-foot entry width. 

Both general and specific ground rules were established, with the assistance of the Bureau, to focus the study on the primary and fundamental 

aspects of the miner detection/location problem. The general ground 

rules are listed in Table 1 below for convenient reference. The specific 

ground rules related to the miner and his signal, the signal transmission 

path and noise environment, and the signal detection/location activity 

on the surface, are given in Part Twelve of this Volume. 

Table 1 

SEISMIC DETECTION AND LOCATION SYSTEM 

General Ground Rules 

. System hardware field suitable and rapidly deployable. 

. System constrained to present state-of-the-art techniques 

and hardware. 

. System operation from the surface. 

. System self-contained in its operation and calibration. 

. System capable of producing timely location estimates. 

. System operation compatible with and complementary to overall 

rescue effort. 

. Signal sources readily available and reasonable - no special 

devices carried by the miners. 

. No wide-area search required by the surface team - likely areas 

for trapped miners given. 

. Surface team will have benefit of mine maps. 

Arthur D Little, Inc. 
Specific task areas, including output objectives and corresponding 

input components, were also defined, as outlined in Table 2, and assigned 

to the study participants. These ground rules and tasks allowed the 

project team to: 

. obtain "best" estimates, based on available data, of the 

ability to detect and locate miners trapped beneath real 

mine overburdens; 

. define the requirements imposed on the surface seismic 

system by operational field conditions for successfully 

executing the detection and location operations; 

. assess how the above estimates are iafluenced by system 

complexity and cost; and 

. determine what is still needed in terms of basic data, 

analyses, and experiments to improve and/or verify these 

estimates. 

Parts Two through Six of this Volume address in detail the major 

output objectives of detection, arrival time estimation, location, and 

field utilization. Similarly, Parts Seven through Eleven treat the input components -- seismic signal source and transmission characteristics, 

earth models, seismic noise, signal-to-noise improvement techniques, and 

seismic detection/location instrumentation, which influence the ability 

to achieve the above output objectives. Part Twelve presents copies of 

the visual aids used in the initial ADL briefing given to the seismic 

consultants regarding the relevant background, ground rules, major problem components, and identification of specific tasks to be addressed; and 

those used in the ADL oral presentation of results of this study to PMSRC. 

The authorship of each Part is designated to appropriately acknowledge the 

major contributions of each seismic consultant. Consultant F. Crowley 

also provided key assistance to ADL in its role of overall definition, 

coordination, and integration of the study effort within the compressed 

time schedule. The following sections of this Part briefly summarize 

the principal findings and conclusions of the study regarding the main 

objectives of detection and location of isolated miners. These findings 

and conclusions are supported in the subsequent Parts of this Volume. 

Arthur D Little, Inc 
TABLE 2 TASK AREAS 

PARAMETER ESTIMATION LOCATION 

* 

EFFECTIVE 

UTII$ZATION FIELD ' 

SIGNAL SOURCES 

Fn of: Type 

: Man 

: Impact Area 

: Tunnel 

TRANS. MEDIUM. 

CH ARAC . Fn of: Layers 

(Type, Thick, 

Angle, etc.) 

NOISE 

Fn of: Sources 

- Sig. Induced 

- Rescue Sources 

- Basic Bgrd. 

- A1 tered Mine 

- Message 

- System I 

SENSORS 

Fn of: Depth 

: Coupling 

S I GNAL PROCESSING 

DATA PROCESS1 NG 

AND COMPUTATION 

OUTPUT I 

COMPONENTS 11 BJECTIVE 

DETECT1 ON 

MAJOR INPUT 

a Strength 

a Directional and 

Coherence Charac. 

a Pulse Shape 

a Rep. Rate 

a Attenuation 

a Signal Modification 

- Freq. Response 

- Time Domain 

- Spatial Coh. 

a Spectrum Levels 

a Time Charac. 

i .e. Stationari ty 

Impul si veness 

a Spatial Coherence 

a Sensitivity 

a Array Gain/ 

Di rectional i ty 

a Dynamic Range 

a Polarization 

a Candidate 

Detection Methods 

a 

OBJECTIVES 

a Site 

Envi ronmen t 

- Physical 

- Operational 

a Field Crew 

' a Hardware 

a Deployment 

and Operati on 

Procedures 

a Overall 

Rescue 

I 

Operations 

COMPONENT CHARACTERISTICS 

, a Strength 

a Directional and 

Coherence Charac. 

a Pulse Shape 

a Rep. Rate 

a Attenuation 

a Signal Modificatior 

.. - Freq. Response '- Time Domain 

- Spatial Coh. 

a Spectrum Levels 

a Time Charac. 

i .e. Stati onari ty 

Impul si veness 

a Spatial Coherence 

a Sensi ti vi ty 

a Array Gain/ 

Di rectional i ty 

a Dynamic Range 

a Pol ari zati on 

a Candidate 

Estimation Methods 

AFFECTING OUTPUT 

9 Directional 

Charac. 

a Earth Model 

(Detailed) 

a Noise Weighting 

of Parameters 

I 

a Array Geometry 

and Location 

a Location 

A1 gori thms 

a Mine Maps 
11. SUMMARY OF RESULTS 

A. DETECTION OF A MINER 

A surface deployed seismic system utilizing conventional signal-tonoise ratio improvement techniques can provide the capability of detecting miners signaling with timber or sledge sources, to slant ranges on 

the order of 1000 feet, under most natural seismic noise conditions in 

which no man-made noise sources are present. Under such noise conditions, 

these ranges should allow more than adequate coverage of typical mine 

sections. However, to obtain these noise conditions, surface rescue 

operations and activity in the vicinity of the detection area must be 

severelyrestricted and possibly prohibited. This may not be compatible 

with present mine rescue operations. Though more experimental noise 

data must be obtained and analyzed before definitive estimates can be 

made of the reduced detection ranges in the presence of man-made noise 

of the type and level present during uncontrolled rescue operations, it 

is highly likely that the presence of such noise will make the detection 

of a signaling miner impossible wi.th a surface seismic system. 

The dependence of detection range on the type of signaling source 

and on the levels of naturally occurring seismic noise is shown in Figure 1. 

Figure 1 depicts the variation of received signal strength with type of 

source and slant range above the source, derived from data taken at 

several mines. The horizontal lines denote signal detection thresholds 

for three representative natural noise conditions, with and without the 

benefit of a conservative 10 dB improvement in signal-to-noise ratio. 

These natural noise conditions are based on published data taken at 

several locations other than above mines. Only a limited sample of 

suitable noise data taken above mines at quiet times was available for 

comparison. These noise levels at mines were not inconsistent with the 

more comprehensive natural noise data used. 

Arthur D Little, Inc 
Arthur D Little, lr 

0.1 I I I I 1 1 I 

200 400 600 800 1000 1 200 1400 

Slant Range (Feet) 
Detection ranges are obtained by noting the intersection of the 

signal curves with the corresponding detection thresholds of interest in 

Figure 1. Noise levels and corresponding detection thresholds for uncontrolled rescue operations are expected to far exceed those for the 

very high natural noise condition, thereby drastically reducing detection 

ranges to unacceptable levels. Table 3 presents, for convenient reference, 

a summary of detection ranges derived from the curves of Figure 1. Table 4 

summarizes those signal-to-noise improvement techniques judged most and 

least useful for detecting and locating i.solated miners. 

To improve these detection range estimates and to better evaluate 

the utility of the signal-to-noise improvement techniques identified as 

most useful, a series of careful seismic noise and signal strength 

measurements should be performed in Eastern coal mining regions by field 

crews well-experienced in seismic and geophysical field work. This work 

should be supported by theoretical analyses to better understand the 

generation and propagation behavior of signals produced by practical 

signaling sources available to miners during emergencies in coal mines. 

Detailed treatments on detection ;ange estimation and signal-to-noise 

improvement techniques are found in Parts Two and Ten, respectively. 

B. LOCATION OF A MINER 

The above described detection process, being inherently limited to 

slant ranges on the order of 1000 feet, in itself provides a coarse location of a trapped miner that in many cases may be sufficient to direct the 

efforts of a rescue team. However, should greater accuracy be required, 

location of a miner to within a section is a realistic objective. In 

fact, location accuracies to within 100 feet for miners down to depths 

of 1000 feet appear attainable with surface deployed systems, but only 

when the required conditions are met. Namely, when an adequate seismic 

representation (model) of the earth beneath the surface seismic system 

is available, the depth of the miner is known from a good mine map, and 

as in the case of detection, the surface rescue operation and activity 

Arthur D Little, lnc 
TABLE 3 

MAXIMUM SLANT RANGES (In Feet) FOR DETECTION-UNDER 

NATURAL NOISE CONDITIONS** 

* W/O - SIN I = Without 10dB Signal-to-Noise lmprovement 

W - SIN 1 = With 10dBSignal-to-Noise lmprovement 

"* No obvious manmade noise sources 

Source 

Strong 

Thumper 

Strong 

Timber 

Sledge 

Weak 

Timber 

Sledge 

Low Noise High Noise 

I' 

I 

W/O-SIN I 

1400 

WIO-SIN I * 

>2OOO 

>2000 

> 1 500 

1100 

900 

W-SIN 1 

>2000 

W-SIN I 

>2000 

>2000 

>2000 

>I500 

>I400 

d 

1050 

900 

550 

450 

J 

Very High Noise 

1050 

900 

550 

450 

WIO SIN 1 

950 

W-SIN I 

1400 

>I 500 

1250 

650 

550 

375 

300 

800 

625 

d 

1 
Table 4 

SIGNAL-TO-NOISE IMPROVEMENT TECHNIOUES 

Most Useful 

For Detection For Arrival Time Estimation 

. Bandpass Filtering 

Burial of Sensors 

Subarrays: 

- size optimization 

- delayed or direct sum 

- weighted sum 

Least Useful 

Same as for Detection 

. Summing (Stacking) of 

Repeated Signals 

For Detection and Arrival Time Estimation 

Remode Processing 

Linear Phase Filtering of Multicomponent Data 

. Matched Filtering 

Multichannel Maximum Likelihood Array Processing 

Multichannel Wiener Filtering 

Single and Multichannel Prediction Error Filtering 

Arthur D Little, Inc 
in the vicinity of the location area has been severely restricted and 

possibly prohibited, which again may not be compatible with present 

rescue operations. Indeed, for accurate miner location, signals will 

have to be received on several seismometers surrounding the miner's 

location, and signal-to-noise ratios well in excess of those for 

detection will also be required to adequately estimate to sufficient 

accuracy the signal arrival times needed for computing location coordinates. Specifically, the above estimate of location accuracy applies 

only to favorable, controlled conditions: 

. when the signals are strong enough to allow arrival times 

to be measured to within 1-5 milliseconds, and 

. when the earth at the local mine site can be adequately 

represented by a set of laterally homogenous horizontal 

layers with different seismic velocities, and these parameters can be specified to within about 5% by refraction 

surveys from the surface. 

Though available geological information tends to support the reasonableness of the type of seismic earth model assumed, data from refraction 

surveys performed directly over representative coal mines, together with 

controlled location experiments using strong signal sources, are still 

needed to confirm the general applicability of this kind of model. 

Figure 2 is an example of the location error contour maps generated 

during the study to form a basis for drawing conclusions on attainable 

location accuracy with surface seismic arrays. These contours are based 

on an error analysis applied to the well-established location method of 

non-linear, least squares iterative inversion. The contours in each 

square represent the estimated standard location errors in x, y, and z 

(one standard deviation, o , of a normal distribution) for a source so 

located relative to the array geometry. 

The location results indicate that earth model errors of 5% will be 

the dominant contributors to miner location errors when arrival time 

errors fall between 1-5 milliseconds, but that arrival time errors become 

the major contributors and seriously degrade location accuracy when these 

Arthur D Little, In( 
FIGURE 2 EXAMPLE OF LOCATION ERROR CONTOUR MAPS 

Depth Known 

from Mine Map 

4 Layer Model 

0, = 5% 

ot = .001 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

7-ELEMENT HEXAGONAL ARRAY 

Arthur D Little, Inc 
timing errors reach 15-20 milliseconds. Errors of this magnitude can be 

introduced by low signal-to-noise ratios and by the variable thickness of 

low-velocity weathered layers under different seismometers in the location 

array. Hence it is important to account for such sources of large timing 

errors in the field. 

The further objective of directly locating a signaling miner to 

within an entry width with a surface seismic system appears to be an unrealistic goal. Only under the most favorable but improbable circumstances, 

namely, noise conditions similar to or better than those described above, 

and an even more accurate representation of the earth or shallower mine 

depth (300 feet or less), do location accuracies of about 30 feet appear 

attainable. With the aid of a good mine map, these accuracies could allow 

the surface team to identify the entry in which the miner is located. 

However, the only method that is likely to produce accuracies of this 

order in practice is a more costly reference event method. This method 

relies on the prior calibration of the seismic-properties of the earth 

over the mine by initiating and recording seismic reference events on a 

regular periodic basis. Detailed.treatments of the location algorithms 

examined in this study; namely, non-linear least squares iterative 

inversion, Westinghouse program "Miner", and reference events, together 

with the suggestion of even more advanced algorithms that allow iterative 

improvement of the earth model as well as the predicted location, are 

found in Parts Three, Four, Five and Seven. 

C. FIELD UTILIZATION 

The nature of mine emergencies, the experience gained with the 

present interim seismic location system, and applicable experience of 

our consultants related to the deployment of small, highly mobile, operational seismic teams, lead to several guidelines and recommendations 

regarding the field utilization of the seismic equipment and the composition of the seismic team. The seismic system should be transportable 

and deployable in various configurations, depending on the mine location 

and on the needs of the detection and/or location operations. The range 

Arthur D Little, In1 
of field requirements extend from the need for simple detection processes 

in quiet remote locations, to complex detection and location processes 

in areas of relatively easy access with unfavorable noise environments. 

Therefore, the system should be configured in modular form that 

allows deployment in phases. For example, on notification of a mine 

emergency, the initial deployment could include only a simple portable 

detection system capable of being easily transported by commercial or 

private aircraft, automobile, or a small truck to the mine, and backpacked to specific locations over the mine workings if necessary. This 

simple detection system would be composed of a small array subsystem, 

an array control unit, an oscilloscope, and possibly a multichannel 

strip chart recorder. These units are sufficient to obtain not only 

initial detection of miners, but also first-order location of these 

miners in the vicinity of the sites chosen for initial investigation. 

A more comprehensive, easily transportable, van processing center and 

additional subsystems could be deployed shortly thereafter, or as required by the particular emergency situation. 

The equipment must be made simple, weather tight, rugged, modular, 

and temperature insensitive. In addition, because the location of miners 

requires calibrated signals and test and repair facilities may not be readily 

available, calibration and check-out of the system must be easy to do on site. 

Since power may not be available, battery operation is a must for the 

portable field equipment. Furthermore, because emergency conditions require quick response, not only must the equipment be quickly and easily 

deployable at the site, but speed in the acquisition and processing of 

the seismic data is essential once the system has been deployed. Indeed, 

overall processing times of received data should be measured in minutes 

rather than hours. Table 5 summarizes some of the important hardware 

requirements for a flexible, fieldable seismic detection and location 

system. These requirements can be met by appropriately integrating and 

packaging present off-the-shelf components and equipment. 

Arthur D Little, Inc 
Table 5 

HARDWARE REQUIREMENTS FOR SEISMIC DETECTION/LOCATION SYSTEM 

Compact light-weight, rugged, modular, proven hardware 

Simple and easily deployable 

Combination vertical seismometer/amplifier unit capable 

of burial 

Water proof non-ambiguous cabling and array control unit 

Seismometer calibration device 

12-channel tape recorder 

Multichannel hard-copy-output recorder 

Accurate, recoverable time codes on tape, or paper output 

Continuous time reference on tape, or paper output 

Selectable time base displays 

Variable filtering and gain 

Battery operation of portable subsystems 

Radio communication for crew 

Tools 

Van processing center with disk pack and mini-computer 

The final essential element required to ensure the successful utilization of the system during a mine emergency is the composition and 

experience of the seismic team. The minimum requirement is a three-man 

cadre that is trained to work together under such emergency conditions, 

being completely familiar with all aspects of the system and its operation and each others duties. This cadre should include an operator/analyst 

an electrical technician, and a field technician. The operator/analyst 

will be the team chief and should also be an experienced geophysical 

engineer. This cadre would utilize additional but inexperienced mine 

personnel at the site to expedite deployment of the system. The key man 

of this cadre is the team chief who should also be a mature individual 

who is thoroughly familiar with mining operations and practices, can 

interface effectively with the overall resuce coordinators, and successfully direct the seismic detection/location operation in the face of confusion and possibly conflicting rescue requirements. Detailed treatment 

of the instrumentation and its field utilization requirements will be 

found in Parts Six and Eleven. 

Arthur D ~ittle, lncl 
I1 I. CONCLUDING REMARKS 

As stated in the Purpose and Approach Section of this Part, the 

purpose of this study was to provide results to help the Bureau of Mines 

in the formulation of future policy and plans of action related to the 

detection and location of isolated miners by the application of seismic 

methods. In this regard, an additional.question was posed by the Bureau, 

for consideration by the ADL seismic team during the course of this task. 

Namely, which of the following alternative courses of action appear to be 

most feasible and appropriate at this time: 

Abandon the seismic system and rely on electromagnetic 

or other methods? 

Change the performance requirements of the seismic system - 

for example, by only requiring positive location to within 

the dimensions of a working section? 

Improve the system and seismic methods employed? 

Figure 3 summarizes the three alternatives and the corresponding ADL 

responses in a graphic format. Expansions on these responses follow. 

No, it would not be appropriate to abandon seismic detection and 

location methods at this time, in spite of their shortcomings. Until 

viable electromagnetic miner location equipment is developed, produced in 

quantity, and utilized by the mining industry, seismic methods still 

remain the only means presently available for detecting the presence of 

live signaling miners and determining their location from the surface. 

Yes, it is definitely feasible and appropriate to change the performance requirements for a seismic system, particularly regarding the 

required accuracy of location. Location accuracies to within one or two 

coal pillars, and even to within dimensions of a working section, when 

used in conjunction with a good mine map, will be extremely valuable and 

in many cases, be more than sufficient to direct the efforts of both inmine rescue teams and surface drilling crews. However, it should be 

remembered that rescue operations and activity in the vicinity of the 

location area may have to be severely restricted, and possibly prohibited 

temporarily, to achieve these location results. 

Arthur D Little, Inc 
FIGURE 3 ALTERNATIVES 

REQUIREMENTS? 

Arthur D Little, Inc 
Yes, it is definitely required, feasible, and appropriate to improve 

the system and seismic methods employed to detect and locate isolated 

miners. However, the type and extent of these improvements need to be 

determined by the Bureau in the context of its overall plans and associated 

time frames related to its miner location programs. In this regard, the 

Bureau will find that some quick-fix and minor improvements will be suited 

to 3-6 month schedules, while others that are major or that require additional fundamental investigations may require schedules of 1 to 3 years. 

Each of the improvements referred to above will require investments 

of one kind or another that will impact on both cost and performance. 

Table 6 briefly summarizes the expected impact on system performance and 

cost for several possible kinds of investments. Finally, in order to more 

accurately estimate the performance limits and potentials of seismic miner 

detection and location systems, further investigations are still required 

to characterize the following items in a more quantitative manner: 

a Seismic signals from sources available to miners. 

a Seismic noise in coal mine regions. 

a Seismic propagation attributes of coal mine overburdens. 

These investigations will be largely based on experimental work in the 

field." Several of these are described in more detail in the body of this 

Volume. 

* Selected improvements in the seismic system hardware have since been 

made by PMSRC, and experimental investigations related to the above 

three areas have been conducted by Continental Oil Co. for the Bureau 

of Mines under Contract H0133112. 

Arthur D Little, Inc 
Table 6 

EXPECTED IMPACT OF INVESTMENTS 

ON SYSTEM PERFORMANCE AND COST 

IMPACT 

of 

t 

on -+ 

Truly Fieldable Hardware 

Trained Experienced 

Field Crews 

Site Pre-Calibration 

Preparation* 

Improved Seismic 

Earth Models* 

Conventional S/N 

Enhancement Methods 

Sophisticated S/N 

Enhancement Methods 

Controlling Site ManMade Noise 

Improving 

Overall 

Performance 

High 

High 

High 

High 

High 

Low 

High 

Increasing 

Overall 

Cost 

Low 

Moderate 

High 

Low 

Low 

High 

Low 

* Applicable mainly to miner location, as opposed to miner 

detection and location. 

1.18 

Arthur D Little, Ir 
PART TWO 

DETECTION RANGE AND ARRIVAL TIME ESTIMATES 

Arthur D Little, Inc. 
PART TWO 

DETECTION RANGE AID ARRIVAL TIME ESTIMATES 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. SUMMARY 

I1 . INTRODUCTION 

111. NOISE LEVELS 

IV . SIGNAL LEVELS 

V. DETECTION RANGES - BASED ON EXPERIMENTAL DATA 

Page 

2. iii 

2.iv 

2.1 

2.3 

2.3 

VI. EFFECT OF NOISE LEVELS ON ARRIVAL TIME ESTIMATION 

ACCURACY - BASED ON EXPERIMENTAL DATA . 2.18 

VII. EFFECT OF ALLUVIUM ON ARRIVAL TIME ESTIMATION ACCURACY 2.24 

VIII. RECOMMENDED PROJECTS 2.25 

IX. REFERENCES 2.28 

APPENDIX A - RELATION OF PEAKS OF NOISE ENVELOPE TO RMS LEVELS 2.29 

Arthur D Little, lr 
PART TWO 

DETECTION RANGE AND ARRIVAL TIME ESTIMATES 

LIST OF TABLES 

Table No. Title 

1 Maximum Range (in Feet) at Which a Miner 

Could be Detected 

2 RMS Noise Output and Detection Threshold 

of a 25 to 100 Hz Filter 

3 Source Pattern Effects (Copper Queen Mine) 

4 Maximum Slang Range for Detection (Feet) - For a Single Sensor-Before Single-to-Noise 

Improvement Techniques 

5 Maximum Slant Range for Detection (Feet) - 

Including Effects of Signal-to-Noise 

Improvement Techniques 

6 Legend for Tracings of Actual Summed Signals 

Shown in Figure lOa,. b, & c 

2. iii 

Page 

Arthur D Little, Inc. 
PART TWO 

DETECTION WGE AND ARRIVAL TIME ESTIVATES 

LIST OF FIGURES 

Figure No. Title 

1 Natural Seismic Noise Levels: Based on 

Frantti Data When Man-Made Noise is 

Present (at 25 Hz) 

2 Natural Seismic Noise Levels: Based on 

Frantti Data When No Man-Made Noise is 

Present (at 50 HZ)- 

Natural Seismic Noise Levels: Based on 

Frantti Data When Xc Plan-Made Noise is 

Present (at 100 HZ~ 

Page 

2.5 

Natural Seismic Noise Levels Based on 

Frantti Data When Mo Obvious Man-Made 

Noise is Present (ZS Amplitude S.pectra) 2.8 

Seismic Signal Amplitude Plotted Versus 

Slant Range From Typical Sources 

Source-Receiver Locations for Copper Queen 

Mine Westinghouse Signal Strength Experiment 2.12 

Plot 38 From Westinghouse Field Report No. 8 

(Uplink Velocity and Attenuation - Thumper 

on 900 Level - 17 Blows) 2.13 

Plot 39 From Westinghouse Field Report No. 8 

(Downlink Velocity and Attenuation - Thumper 

on Surface - 10 Blows) 2.15 

Composite Plot for Estimating Detection Ranges 2.17 

Schematic Generalized Seismic Signal (Applicable 

to Mine Data Obtained to Date) 2.19 

Tracings of Actual Summed Signals From 

Wes tinghouse Field Reports 

Tracings of Actual Summed Signals From 

Westinghouse Field Reports 

Arthur D Little, Inc. 
PART TWO 

Figure No. 

DETECTION RANGE AND ARRIVAL TIME ESTIMATES 

LIST OF FIGURES 

(Continued) 

Title 

1o(c) Tracings of Actual Summed Signals From 

Westinghouse Field Reports 

11 Example of Time Delay Caused by Surface 

Weathered Alluvium Layer 

Page 

2.22 

2.26 

Arthur D Little, lnc. 
PART TWO -- 

DETECTION RANGE AND ARRIVAL TIME ESTIMATES 

Roy Greenfield 

Pennsylvania State University 

I. SUMMARY 

Estimates are given for the distance from a seismometer at which a miner 

can probably be detected. The procedure in making these estimates was to 

first establish the natural noise levels at the output of a surface seismometer 

for the 25 to 100 Hz frequency passband. The noise levels give the range of 

values which may be expected in areas with no man-made noise. For each noise 

level, we give the detection threshold which, when exceeded, indicates that 

a signal has been received. Based on the signals recorded by Westinghouse, 

curves are given which show the peak signal amplitude as a function of sourceto-receiver distance (slant range). Curves are given for the Westinghouse 

seismic thumper, a 50-pound timber, and a sledge. For a given type of source, 

the receive signal strength depends more strongly on slant range than on any 

other factor. However, there is approximately a five-to-one scatter in the 

amplitudes. Thus, further study of factors affecting the signal amplitude 

might allow better estimates to be made for any particular geological setting. 

Combining the signal amplitude ' with the detection thresholds for the different noise conditions gives the distances at which a miner should be detected. 

These are given in Table l* below. 

Table 1 

Maximum Range (in Feet) at Which a Miner Could be Detected 

For a Single Sensor--Before Signal-to-Noise Improvement Techniques 

(Natural Noise and Average Signal Strength Assumed) 

Natural Noise Condition 

Source Type - Low High Very High 

Thumper 1600 1000 700 

Timber 1400 800 500 

Sledge 1200 700 400 

The text also gives the increase in detection ranges which should occur 

if steps are taken to increase S/N by 10 dB. We feel that 10 dB is a conservative estimate of the improvement possible. 

During an actual rescue operation, the seismic crew and system should be 

capable of making on-site estimates of their detection capability, based on 

measurements of the site noise, and upon the best available estimates of the 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

2.1 

Arthur D Little, Jnc. 
signal strengths to be expected. This will allow the seismic rescue crew to 

estimate the likely coverage area of the seismic system, for detection of a 

signalling miner under the prevailing noise conditions, which will in turn 

assist the rescue team to determine appropriate search strategies for the 

entrapped miners. 

The effects of noise on the estimates of signal arrival times are also 

discussed. The arrival times should be picked by an analyst from stacked signals from all available signal repetitions. It is shown that for low to moderate noise situations, the signal arrival time at each subarray can be determined to within a few milliseconds. However, when the noise is comparable to 

the signal, errors of 10 to 15 milliseconds can occur, and in some cases, it 

might be possible to pick a signal arrival time which is 50 to 100 milliseconds 

after the true arrival time. 

Arthur D Little, lnc 
11. INTRODUCTION 

In this Part estimates, based on experimental data, are made of the 

natural noise levels encountered for surface seismometers, and a model for 

signal levels, based on Westinghouse data,*is developed as a function of 

slant range and source type. The natural noise level estimates are applicable 

to the range of conditions encountered when - no man-made noise sources are 

present. These natural noise levels may be representative of the levels 

experienced during a mine emergency rescue operation at those times when 

care has been taken to control the rescue activity's seismic disturbances. 

Further experimental data is needed in order to characterize the man-made 

noise environment created by rescue operations. 

Using the above results, estimates have been made for the detection range 

whicn can be obtained. All work is done for a 25 to 100 Hz bandpass. Most 

of the signals observed by Westinghouse have most of their energy in that band. 

It remains (as noted in Part Nine) to determine the noise levels above 

100 Hz before it is possible to determine if the band above 100 Hz will aid 

in detection. Initially detection ranges are determined for a single sensor 

with no signal processing. Some estimates also are made of detection ranges 

if signal enhancement is successful. After the detection discussion,a chapter 

will consider how noise levels affect estimates of signal arrival times for 

use in the subsequent location process. 

111. NOISE LEVELS 

We desire to determine a detection threshold, which when exceeded indicates that a signal is present at the output from a single sensor. In the 

Appendix to this Part, we show a reasonable detection threshold level as 

3 times the noise RMS level. This will lead to approximately 1 false alarm 

each 100 seconds on a single trace, and very rare false alarms if coincidence 

detection is used on the outputs of several subarrays. 

To estimate, within the time available, the surface noise levels to be 

expected, we concentrated on the noise data of rantt ti(') 1963 rather than 

the noise measurements made by Westinghouse. This was done because the contamination of the Westinghouse earth noise data by system noise weakened our 

confidence in their noise data (see Parts Nine, Ten). The Frantti data 

are for locations free of obvious man-made noise sources. Frantti measured 

peak-to-peak average envelope values at the output of a 113 octave filter. 

In cases where this envelope average was compared to the RMS noise level, the 

* Westinghouse Contract H0210063 with Bureau of Mines. 

2.3 

Arthur D Little, Inc 
envelope average was slighly higher. In (A 6) of the Addendum we show 

this is to be expected, but the difference, a factor of 1.7, is not important 

because RMS noise levels can be expected to fluctuate over more than an order 

of magnitude at different times and locations. 

We used 47 of Frantti's noise curves (data for deep mines and a site near 

the ocean were excluded). For each curve the spectral level was read at 25, 

50, and 100 Hz. Histograms (Figures 1, 2, and 3) were formed for each frequency. The RMS noise levels exceeded 75% of the time (low noise) were determined for each frequency, and marked on the histograms. This was also done 

for the RMS noise levels exceeded only 25% of the time (high noise). As a 

comparison, the range of levels found by Westinghouse during their mine field 

test program are also included on these Figures. The Westinghouse levels are 

not inconsistent with the levels predicted by Frantti. 

To proceed from the RMS noise spectral estimates to the noise RMS output 

level of a 25 to 100 Hz filter, we used 

RMS75% = [/ii" (f) dfI1l2 

for the "low noise" level condition. The RMS (amplitude) spectrum, ~(f), 

used is plotted on Figure 4. The signal detection threshold was then set at 

3 times the noise RMS output level. The same calculations were made for the 

(25%) "high noise" level condition. The results are given in Table 2. 

Table 2 

RMS Noise Output and Detection Threshold 

Of a 25 To 100 Hz Filter 

RMS Level Exceeded 75% of Time 

(Low Noise) 

RMS Level Exceeded 25% of Time 

(High Noise) 

Detection Threshold (Low Noise) 

Detection Threshold (High Noise) 

IV, SIGNAL LEVELS 

The basis of our estimates of the seismic signal levels is the Westinghouse data. The maximum zero-to-peak amplitude levels for the signals are 

plotted as a function of slant range in Figure 5. The sources of data are 

given in the Figure. Curves have been drawn as estimates of the strong 

Arthur D Little, lnc. 
Noise RMS IPSIm 

Histogram of Number of Occurrences of Noise RMS Levels 

Natural Noise Levels Exceeded 75% and 25% of the Time are Indicated 

For Frequency = 25 Hz 

Westinghouse data for individual mines are included for comparison, and maximum and minimum noise levels are shown 

as open circles connected by lines. Ignore the vertical axis in relation to these data. Arrows pointing to the left indicate 

that system noise limited noise estimates for low noise periods. The Westinghouse data are taken from the Westinghouse 

Report Table 2-4. The order of the mines, going from the top of the figure to the bottom data points, corresponds to the 

field report numbers for the mines. 

FIGURE 1 NATURAL SEISMIC NOISE LEVELS: BASED ON FRANTTI 

DATA WHEN NO MAN-MADE NOISE IS PRESENT 

a 

7 6 0 

- 

2 0 - 1 

,5^ 

- 8 0 0 0 

a 

J I I I I I I I I I I a la I, 

- 9 

0 75% 

- 

G 

- 9 

25% 
Noise RMS IPSIG 

Westinghouse data for individual mines are included for comparison, and maximum and minimum noise levels are shown 

as open circles connected by lines. Ignore the vertical axis in relation to these data. Arrows pointing to the left indicate 

that system noise limited noise estimates for low noise periods. The Westinghouse data are taken from the Westinghouse 

Report Table 2-4. The order of the mines, going from the top of the figure to the bottom data points, corresponds to the 

field report numbers for the mines. 

FIGURE 2 NATURAL SEISMIC NOISE LEVELS: BASED ON FRANTTI 

DATA WHEN NO MAN-MADE NOISE IS PRESENT 
Arthur D Little, lnc. 
0 25 50 75 100 

Frequency (Hz) 

FIGURE 4 NATURAL SEISMIC NOISE LEVELS BASED ON FRANTTI 

DATA WHEN NO OBVIOUS MAN-MADE NOISE IS PRESENT 

(RMS AMPLITUDE SPECTRA) 
Slant Range (feet) 

SIGNAL DATA 

(Largest Zero to Peak Amplitude on Vertical Traces, Plotted for Three Sources, 

Thumper, Timber, Sledge Hammer.) 

1000 

Signal Data from Westinghouse 1972 Report, Estimated Detection Thresholds also 

shown for Natural Seismic Noise Background (Noise Data from Frantti, 1963). 

- 

- 0 Thumper Table 2-3 

- 0 Timber - I Westinghouse '72 Report 

- 

- 0 Thumper 7 Field RPT 8 

FIGURE 5 SEISMIC SIGNAL AMPLITUDE PLOTTED VERSUS 

SLANT RANGE FROM TYPICAL SOURCES 

Arthur D Little, lnc. 
and weak signals for the thumper, timber, and sledge sources. These curves 

enclose the majority of the data, and are the basis of the detection range 

discussion i2 the next chapter. We believe that Figure 5 represents the 

best estimates of signal level that we can make at this time, based on 

experimental data available to us. 

A scatter of a factor approximately 5 exists in the amplitude data. However this is not unexpected. Scatter of this magnitude is quite common in 

seismic data around 1 Hz, and can reflect any one of a number of factors. In 

the case of the Westinghouse data these factors probably include source 

coupling, propagation effects, the source radiation pattern, and variation 

of the low velocity alluvium thickness at the seismometer. 

We have attempted to assess the source radiation pattern effect using the 

data from Field Report 8*,Copper Queen Mine, Figures 2.4.3 and 2.4.4, compiled 

in Table 2.4-3 of that report. In Table 3, we show their amplitude readings 

for both first motion and for maximum trace amplitude. Only the vertical 

seismometer is used. Also shown is the theoretical amplitude, V of the m' 

vertical component for a point vertical source in an infinite medium. The Vm 

for such a source is of the form (Love, 1944, p. 304-305). 

where r is slant range 

8 is the angle between the vertical and the 

source-to-receiver direction 

and A is a constant 

The formula given is strictly valid only if the receiver is many wavelengths 

from the source. This requirement is not well met in the present experiment. 

We have set A to fit the observed amplitude at the seismometer on the surface 

directly above the source, receiver 1. The source and receiver locations are 

shown in Figure 6. Values for a l/r variation are also given. Again we normalized to receiver l. 

The results in the Table are not conclusive. However in general, the l/r 

fit is closer than the V fit. The V often greatly underestimates the 

m m 

amplitude. 

The data, on Figure 5 obtained from plot 38 of Field Report 8*, (plot 38 

is reproduced here as Figure 7a) is of interest. These data were obtained 

for a thumper source put in the Copper Queen Mine, 900 feet below the surface. 

* Ibid. 

Arthur D Little, lnc. 
Table 3 

Source Pattern Effects (Co~per Queen Mine) 

a) First Motion Peak (~IPS) 

Receiver 

1 2 3 

Source (I), Timber 

Observed 

Theory, V 

l/r ariap pion 

Source (2), Thumper 

Observed 

Theory, 'm l/r Variation 

Source (I), Timber 

Observed 

Theory 

l/r Variation 

Source (2) Thumper 

Observed 

Theory 

l/r Variation 

b) Maximum Trace Amplitude (p~p~) 

Receiver 

1 2 3 

Arthur D Little, fnc. 
Receivers 

v 

A 

V 

Surface 

Source(1) 

Timber 

Source (2) 

Thumper Scale 

FIGURE 6 SOURCE-RECEIVER LOCATIONS FOR COPPER QUEEN MINE 

WESTINGHOUSE SIGNAL STRENGTH EXPERIMENT 

Arthur D Little, Inc. 
Arthur D Little, Inc. 
Seismometers were at the 7001, 4001, 3001, 2001, and surface levels directly 

above the source. The fall-off of amplitude is slightly greater than l/r. 

Another important observation is that the surface seismometer has a peak frequency of about 50 Hz while the peak frequency on the below-surface seismometer 

(at 200 feet) is about 100 to 125 Hz. 

The amplitude on the surface seismometer is only about 1/3 that of the 

seismometer at the 200' level. The reason for the change in amplitude may 

be either attenuation in the low velocity surface layer or a resonance effect 

on the waves due to the low velocity surface layer. There is some indication 

that the latter is the major factor. Namely, plot 39 of Field Report 8* 

(reproduced as Figure 7b) reveals that an initial %lo0 Hz signal is propagated 

downward through the surface layer from a surface source to the below-surface 

seismometers. However, the initial part of the signals are followed in time 

by %40 Hz energy leaking downward from the resonant surface layer. 

It is felt that further systematic experiment, and theoretical analysis 

of relevant models of source and propagation effects, are required to improve 

estimates of the signal strength and character in various mine situations. 

V. DETECTION RANGES - BASED ON EXPERIMENTAL DATA 

The initial discussion of detection range will be for a single sensor. 

It is based on Figure 5 which gives, estimated signal levels and the detection 

tllresllolds required under two noise conditions. The detection level is set 

to give one false alarm every 100 seconds on a single subarray trace, so at 

this level it will be necessary to detect on perhaps three subarrays to 

safely conclude that a true signal has been received. Consistent relative 

arrival times on the subarrays will be a strong indication of a repeated 

source at a fixed location. 

In Table 4 we give the maximum slant ranges for detection for different 

combinations of source and noise conditions. The values in the Table are 

the best estimates of detection range we can make at this time based on the 

experimental data available. 

Ibid 

Arthur D Little, Inc 
Arthur D Little, Inc 
Table 4 

Maximum Slant Range for Detection (Feet) 

For a Single Sensor--Before Signal-to-Noise Improvement Techniques 

(For Natural Noise Conditions) 

Natural Noise Condition 

Low (75%) High (25%) 

Source Threshold Threshold 

Strong Thumper Signal > 2000. 1400. 

Weak Thumper Signal 1300. 700. 

Strong Timber Signal 

Weak Timber Signal 

Strong Sledge Signal 

Weak Sledge Signal 

At this point we make some speculative estimates of the detection thresholds required under conditions for which the noise data base is weak, namely 

for "maximum" natural noise conditions. By inspection of Figures 1, 2, and 3, 

it appears that the natural noise level rarely rises about 3 times the 25% 

detection threshold of Figure 5. This threshold,denoted as Max., is shown 

on Figure 8. Also shown are the signal level curves. We speculate that S/N 

improvement techniques can give a gain of 10 dB at all three noise levels. 

The figures of 10 dB would be the S/N gain against uncorrelated noise for a 

10 element subarray. Gain obtained by burial could also be significant. In 

high levels of natural noise due to wind or rain the gain by burial could be 

considerably above 10 dB. Since there is presently no data to assess these 

gains we have taken the modest value of 10 dB between the two. On this basis 

we also put curves for the three noise level conditions with 10 dB S/N improvement on Figure 8. For these conditions, the estimated detection ranges are 

given in Table 5. 

Further experimental data must be analyzed before we can make any estimate of the detection ranges in the presence of man-made noise of the type 

and level which might be present during uncontrolled rescue operations. However it is highly probable that heavy man-made noise would make detection 

impossible, using only surface seismometers, if the signaling miner is more 

than tens of feet to a few hundred feet from the seismometer. 

Arthur D Little, Inc. 
I 

Max. Noise 

- 

Max. + SIN 

25% 

25% + SIN lmprovement 

- 

7 5% 

Detection Thresholds 

75% + SIN Improvement 

I 1 I I I I I 

Slant Range (Feet) 

Seismic Signal Amplitude Estimates Plotted Versus Slant Range from Typical Sources; 

Detection Thresholds for Three Natural Noise Conditions With and Without Benefits 

of 10 dB Signal-to-Noise lmprovement 

FIGURE 8 COMPOSITE PLOT FOR ESTIMATING DETECTION RANGES 

Arthur D Little, fnc. 
Table 5 

Maximum Slant Range for Detection (Feet) 

(For Natural Noise Conditions Only) 

Source 

Natural Noise Conditions 

Max. Max. + 25% + 75% + 

Strong Thumper Signal 950 1400 >2000 >2000 

Weak Thumper Signal 425 700 1000 >2000 

Strong Timber Signal 650 1050 >I500 >2000 

Weak Timber Signal 375 550 800 >I500 

Strong Sledge Signal 550 900 1250 >2000 

Weak Sledge Signal 300 450 625 >I400 

(+) Indicates: +10 dB SIN Improvement 

VI. EFFECT OF NOISE LEVELS ON ARRIVAL TIME ESTIMATION ACCURACY - BASED ON EXPERIMENTAL DATA 

The two limits on the accuracy of the location of the miner are the 

accuracy of the velocity model and the accuracy of the reading of the 

arrival time of the P wave. The effects of deficiencies in the velocity 

models are discussed elsewhere. Here we concentrate on errors in arrival 

time measurement due to the presence of seismic background noise. Higher 

signal-to-noise ratios are needed for accurate estimates of arrival times 

than that needed to simply detect a miner-generated signal. Therefore, it 

is assumed that the signal-to-noise ratio is improved by stacking repeated 

signals, if signal repetitions have been received. 

We discuss the errors in arrival time with reference to the schematic 

generalized signal shown as Figure 9. This signal illustrates several 

features of the signal waveforms which can affect the measurement of signal 

arrival time. Several examples of these features are shown in Figures 10a, 

b, and c, which are tracings of actual seismic signals taken from the 

Westinghouse Field Reports* (see Table 6 for identifications). The signal 

in Figure 9 has a frequency of 50 Hz (period, T = 20 ms) which is an average 

frequency for the signals observed by Westinghouse. 

* Ibid 

Arthur D Little, Inc. 
FIGURE 9 SCHEMATIC GENERALIZED SEISMIC SIGNAL 

(Applicable to Mine Data Obtained to Date) 

Arthur D Little, lnc. 
FIGURE 10(a) TRACINGS OF ACTUAL SUMMED SIGNALS 

FROM WESTINGHOUSE FIELD REPORTS 

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First Arrival 

Same 

FIGURE 10(b) TRACINGS OF ACTUAL SUMMED SIGNALS 

FROM WESTINGHOUSE FIELD REPORTS 

Repeat @ 

Vertical 

Ld 

Arthur D Little, lnc 

",w Horizontal 
FIGURE 10(c) TRACINGS OF ACTUAL SUMMED SIGNALS 

FROM WESTINGHOUSE FIELD REPORTS 

Arthur D Little, Inc. 
Table 6 

Legend for Tracings of Actucl 

Summed Signals Shown in Figures 10a, b, & c 

Tracing 

No . -__-_---_---_-_-__---------------------------------------------------------------- 

1. Plot 23 F.R. 6 - 13 ele~ent subarray, 30 blows -. 

.-) 

2. Plot 35 F.R. 4 - 7 ekzents , 50 blows 

I 

3. It f 1 - 1 vertical , It blows I 

, 30 blows I L\ Figure 10 (a) J 

/ 

5. Plot 37 F.R. 7 - Array (subarray?) 2, 30 blows i 

, 

6. Plot 41 " - Array 7, 30 blows 

\ 

7. Plot, 42 " - Not known 30 b1ov.s I 

8. Plot 13 " - Array 5 "blows ,I 

----_---------------------------------------------------------------------------- 

9. Plot 36 " ? Slows 7 

10. Figure 17, F.3. 2, ch. 5, South. 180 bicws 

11. Figcre 22, F.R. 2, ch3, 19 Hex arr3y 31 blows 

12. Figure 24, F.R. 2, 7 ele~ents 100 blows 

13. Plot 15, F.R. 8, ch 5 15 blows 

' Figure 10(b) 

It ch 2 

t 1 ch 7, Horizoctal 

It blows I, 

t t 2 - - -- - - - - - - - - - 7 - 

16. Plot 17 " ch 7, 

17. I' It ch 4, 

30 blows 

11 

18. Plot 55 " ch 6, 25 blows 

19. Plot 57 t 1 ch 3, Arrsy i<, 7CC) ' le7;e1, 29 blcws / 

Figure 10 (c) 

20. Plot 35 comp~rison of sxall 5.rrays 339 single gea~phon2, 

a) sing12 cl;arLnel, b) pa-allel, c) serie5 ccrrectia: 

21. Plot 15, F.R. 9, ch 2 and 3, horizontal ar-d verticzl, 15 blo;,;s - J -------------------------------------------------------------------------------- 

Arthur D Little, lnc. 
We assume that the arrival time is picked by a trained analyst, and we 

discuss the arrival time errors which might arise for different levels of 

noise. The true arrival time of the signal is T 

A* [T~ isthe time of the 

signal at point A and the other times used (T B' TC, T ) are similarly D 

defined.] If the noise level is very low, the analyst will pick the arrival 

time, denoted by AT, within 1 ms of T The first peak B of the signal is A* 

usually small compared to the second peak C. If the noise level is only low 

enough to recognize peak B, then he picks T as the arrival time. This 

B 

gives an error of about 4 ms. However, it would be better to assume that 

TB = TA + ~14. If this is done the error in AT will probably be reduced to 

on the order of 2 ms. 

A much larger error in arrival time can occur in cases when peak D is 

larger than peak C, and the noise level is such that the analyst misses 

peak C, but can pick pe~k D. Examples of signals where peak D is larger 

than peak C are shown in Figure 10 as traces 6, 8, and 13. Peak D may be 

6 dB above peak C. By picking T several cycles of the signal have been D' 

missed and the error in arrival time will be 50 to 100 ms. If T is picked C 

on some subarrays and T on others, very poor locations will result. D 

There are fortunately some telltale indications if the initial few 

cycles of the signal have escaped detection, and T was picked as the arrival 

D 

time by mistake. First if TD is picked on only one or two of seven subarrays, 

these times will show up as large, late residuals on the least squares fit 

for the source location. A second indication is that a very large signal 

may occur on the horizontal seismometers at T An example of this large D' 

horizontal motion is shown on Figure 10, traces 13 and 15 and 21. We believe 

the large late arrivals may be the direct S (shear wave), or a shear wave 

genera~ed when the P wave hits the base of the alluvium layer below the 

receiver. A better understanding than we presently have might allow a better 

possiblity of telling whether the first arrival picked by the analyst is a 

T type late arrival. D 

VII. EFFECT OF ALLUVIUM ON ARRIVAL TIME ESTIMATION ACCURACY 

The surface alluvium has a very low P wave velocity. The velocity can be 

2000 feetlsec. or even less. Suppose at a mine we have 50 feet of alluvium 

under subarray A and no alluvium under subarray B. Let the rock P wave 

velocity be 10,000 feetlsec. Then the traverse time through the alluvium at 

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subarray B will be 5 ms. Thus if a location is made with these arrival 

times with no correction for the presence of the alluvium at A, the 20 ms 

extra delay at A will have the effect of a 20 ms arrival time reading error. 

A example of this delay can be observed directly in Figure 11. In Field 

Report 8*, data is given for a source at 900 feet depth with receivers at 

various depths and on the surface. In our figure the arrival times are plotted versus distance from the source. If the travel time curve is extrapolated 

from the straight line fit to the last 3 underground arrivals, the time predicted for the surface arrival is 16 ms earlier than the observed arrival 

time at the surface. 

This problem of the error in arrival time due to the alluvium can be 

corrected by determining the thickness and velocity of the alluvium at each 

subarray. This can probably best be done by an easily run shallow refraction 

survey using either a timber or perhaps a seismic thumper as a source. Reflection seismic methods, using special equipment, might also be useful. Another 

method which might prove usefu1,which we have used at Penn State,is to use the 

dispersion properties of the Rayleigh waves set up with a sledge source. 

VIII . RECOJ9KENDED PROJECTS - - - - . -- - - - 

In order to improve the performance estimates presented in this Part; 

to better evaluate the utility of signal-to-noise improvement techniques such 

as seismometer burial, bandpass filtering, subarrays , and signal stacking; 

and to develop more effective signaling and detection strategies; the following experimental and theoretical efforts are recommended. 

Perform a series of careful seismic noise and signal strength measurements in Eastern coal mining regions. These measurements should be performed 

by crews well-experienced in seismic and geophysical field work. At each of 

the sites care should be taken to determine the geological/seismic structure 

of the overburden material, so that the experimental results can be compared 

with those predicted by different theoretical models. 

- Seismic noise measurements should be performed in representative Eastern 

mining areas that are "quiet", i. e. not dominated by manmade noise sources ; 

and in areas and under circumstances that are representative of those encountered during mine emergencies or disasters. Noise spectrum levels should be 

obtained up to a frequency of 300 Hz. The spatial coherence properties of 

(4,5) the noise should be studied as a function of seismometer spacing, together 

with the utility of looking at individual seismometer outputs as opposed to 

that from a whole subarray. The impact of the depth and method of seismometer 

* Ibid 

Arthur D Little, lnc 
J Actual Surface Arrival 

16 ms Arrival Time Estimation Error 

t Predicted 

Arrival 

Based on Linear 

Extrapolation 

\ 

13,300 ftlsec Slope 

Fit to Arrival Time 

Points at 400, 300, 200 ft. depths 

800 Distance from Source (feet) 

100 0 + Depth (feet) 

Data from Field Report 8, Plot 38. 

FIGURE 11 EXAMPLE OF TIME DELAY CAUSED BY SURFACE 

WEATHERED ALLUVIUM LAYER 
burial on the received seismic noise should be examined by careful experiments 

at sites with different surface materials. At sites over mines where both 

signal and noise measurements are planned, the effect of seismometer burial 

on both received signal and noise levels should be determined. Lastly, representative manmade sources encountered during mine emergencies should be characterized, together with some of the likely disaster noise sources in the 

mine, such as fires, running water, cracking rocks, and roof falls. 

- Controlled, systematic seismic signal experiments should be performed 

with the thumper, timber, sledge, and perhaps other practical sources, in 

several Eastern coal mines that are representative with respect to depth, 

overburden geology, and surf ace topography. Signal properties, such as 

strength and frequency content, of single source blows or pulses should be 

examined as a function of type of source, entry cross-sectional dimensions, 

position and composition of the impact area in the entry, source and seismometer depths,slant range, near-surface layers, and seismic velocity profile. 

The measurement band should extend up to a frequency of about 300 Hz, to check 

whether useful signal frequency content above 100 EIz may have been masked 

by system noise or lossy surface layers in past measurements. 

Perform supporting theoretical analyses to better understand the signal 

generation and propagation behavior expected for practical miner sources 

in coal mines. Items of particular interest are: the efficiency of seismic 

signal excitation, the effect of the mine entry cavity and the source impact 

point in it, the effects of layering in general and the surface layer in 

particular. Preliminary analysis indicates that it should be possible to 

model the mine entry problem as a point source applied to the surface of a 

cylindrical cavity; and that surface layering effects can be examined using 

(6) Haskell matrix techniques. 

Develop automatic detection procedures that will choose only the most 

"interesting" seismic energy arrivals, or probable miner signals, for detailed examination by a trained analyst. An automatic detection or event screening procedure need not be complex, and in its simplest form could be based 

on the exceedance of a preset threshold on one or more seismometers or subarrays, and set according to the prevailing noise condition. This should 

ease the large data processing burden that otherwise would be imposed on 

analysts under emergency conditions. However, it is not intended to replace 

the trained analyst, for he is the one who will be best qualified to assess 

the likely cause of the received waveform, and to subsequently ascertain its 

Arthur D Little, Inc. 
"arrival time", after any required signal-to-noise ratio enhancement. 

(~t Develop an ability to determine, in a timely manner on site, the thickness and seismic P-wave velocity of the alluvium directly under each of the 

subarrays. This is needed in order to compensate the signal arrival times 

for the likely substantial and different amounts of time the signal has spent 

in this low-velocity, variable-thickness, surface layer to get to each subarray. 

ZX, FSFERENCES 

1. Love, A.E.H., Mathematical Theory of Elasticity, Dover, New York, 

1944. 

2. Frantti, G.E., The Nature of High Frequency Noise Spectra, Geophysics, 

28, 547-562, 1963. 

3. Horton, C.W., Sr., Signal Processing of Underwater Acoustic Waves, 

U.S. Government Printing Office, Washington, D.C., 1969. 

4. Capon, J., Greenfield, R.J., Lacoss, R.T., Design of Seismic Arrays 

for Efficient On-Line Beamforming", Lincoln Laboratory Technical Note, 

196 7-26, 27 June 196 7. 

5. Lacoss, R.T., Capon, J., Greenfield, R.J., "preliminary Design of a 

Long Period Seismic Array for orw way", Lincoln Laboratory Technical 

Note, 1968-4, 24 January 1968. 

6. Haskell, N. A., Crustal Reflection of Plane P and SV Waves, 

Journal of Geophysical Research, Vol. 67, No. 12, pp. 4275, 

pp. 4751-4759, Nov. 1962. 

Arthur D Little, Inc. 
APPENDIX A 

RELATION OF PEAKS OF NOISE ENVELOPE TO RMS LEVELS 

The envelope of narrowband noise is given by the Rayleigh distribution (e. g. Horton, 1969, p. 96) . The results we give below have experimentally been found to fit wideband seismic data, (see Capon et al. 1969). The 

probability density function Is given by: 

2 '2 p(~) =-B exp (-~/20 ) 

0 2 

wlierf R 2s Zhc 2x0 to peak amplitude of the envelope. 

Over one cycle, the mean square (MS) value is 

1 T2 - 

T lo (t) dt = + R~ 

Thus the MS value of. narrowband noise is 

= 1 lrn P (R) R~ dR 2 0- 

The probability of R exceeding R is 

0 

If we take R = 3 RMS 

0 

Arthur D Little, lnc. 
Then the chances of the envelope exceeding 3 RMS on a single trial 

is about one in .000123. We take 3RMS as a reasonable single channel 

detection threshold. We note that for a bandwidth of 75 Hz we get an 

independent sample of R every 1/75 sec. Therefore we go about 100 seconds 

between false alarms on each channel. 

A useful relationship in evaluating Frantti's (1963) method of spectral 

estimation is that 

E [~R]/E [RMS] = 2 1; RP(R) ~R/E [RMS] 

Arthur D Little, lnc 
PART THREE 

ESTIMATES OF MINER LOCATION ACCURACY: 

ERROR ANALYSIS IN SEISMIC LOCATION 

PROCEDURES FOR TRAPPED MINERS 

Arthur ll Little. lnc 
PART THEE 

ESTIMATES OF MINER LOCATION ACCURACY: 

ERROR ANALYSIS IN SEISMIC LOCATION 

PROCEDURES FOR TWPED J'IINERS 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. SUMMARY 

11. INTRODUCTION 

111. METHOD OF CALCULATION AND PRESENTATION 

IV. DISCUSSION OF ERROR MAPS 

A. TIME ERRORS 

B. MODEL ERRORS 

C. MODEL DIFFERENCES 

D. DEPTH KNOWN 

E. CHANGING ARRAY DIMENSIONS 

F. LAYERED MODELS 

G. CALIBRATION OF EARTH MODELS 

REFERENCES 

- Page 

3. iii 

3. iv 

3.1 

3.2 

3.4 

3.6 

3.6 

3.6 

3.6 

3.7 

3.7 

3.8 

3.8 

3.9 

Arthur D Little, li 
PART THREE 

Table No. 

ESTIMATES OF MINER LOCATION ACCURACY: 

ERROR ANALYSIS IN SEISMIC LOCATION 

PROCEDURES FOR TRAPPED MINERS 

LIST OF TABLES 

1 4-Layer Model 

Title 

2 Comparison of Location Errors for Two 

Approximate Models 

Summary of Error Diagrams 

Page 

3.8 . 

Arthur D Little Inc 
PART THREE 

ESTIMATES OF MINER LOCATION ACCURACY: 

ERROR ANALYSIS IN SEISMIC LOCATION 

PROCEDURES FOR TRAPPED MINERS 

LIST OF FIGURES 

A Collection of Location Error Diagrams for the 

24 Computer Run Conditions Described in Table 3. 

Runs 1 Through 24 - Pages 3.13 Through 3.36 

Arthur D Little, Ir 
PART THREE 

ESTIMATES OF MINER LOCATION ACCURACY: 

ERROR ANALYSIS IN SEISMIC LOCATION PROCEDURES FOR TRAPPED MINERS 

Robert S. Crosson 

David C. Peters 

University of Washington 

I. SUMMARY - -- 

A method of error analysis has been applied to the location technique 

of mon-linear least squares iterative inversion in order to evaluate the 

resolving power of several seismic array configurations with various assumed 

earth models and errors and inaccuracies in arrival times. 

The results obtained demonstrate that lateral accuracies of location 

are improved significantly when the depth of the miner is known. Lateral 

location to within 100 feet appears achievable in many instances. If it is 

possible to refine earth models significantly beyond what has normally been 

assumed in this work by the use of on-site data, or if the mine is shallow 

(300 feet or less), accuracies of .about 30 feet 'or so may be attainable. 

Inaccuracies in earth models of about 5% are found to contribute much 

more heavily to these location inaccuracies than errors of a few milliseconds 

in picking arrival times; however, arrival time errors of 15-20 ms or above 

will dominate these model inaccuracies. 

The expected accuracy of location is found to fall off very rapidly 

as the miner moves outside the array. The strength of this effect depends 

markedly upon the geometry of the array configuration and can be reduced by 

careful design. Also, as the size of the array is increased, expected location errors within the array are not altered much, but continue to match the 

error associated with the smaller array over a larger area (assuming that 

all stations can still pick up the miner's signals). 

Better location accuracy, especially with respect to depth control is 

achievable in an earth where the velocity is depth-dependent (increasing with 

depth) than in one which is homogeneous. This is an advantage since the 

Arthur D Little, lnc 
actual earth is clearly closer to the former situation. Models where the 

seismic velocity increases linearly with depth can be found which are excellent approximations to a layered earth for the purposes of location. 

It has to be emphasized that the location accuracies predicted in 

this work are subject to the major ass.umption that the actual behavior of 

the earth can be represented reasonably accurately by the models selected. If 

this is not the case, then location inaccuracies resulting from the use of 

these models may be much larger than those predicted here; new classes of 

models may have to be developed. 

It can be concluded, however, that the location accuracies predicted 

for the non-linear least squares iterative inversion technique make it appear 

promising for use as a miner location algorithm. Alternative and potentially 

better location techniques remain subjects for future investigation. These 

may, for example, include different weighting schemes for the seismometers 

in an array, or allow the possibility of iterating and improving the earth 

model used, as well as the predicted location. 

11. INTRODUCTION 

Procedures for determining the location of impulsive seismic sources 

in the earth have been the object of studies by seismologists for many years. 

Recent expansion of the use of dense networks of detection stations and high 

frequency sensors and recording apparatus, particularly for the study of very 

small earthquakes, has stimulated the development of high-precision location 

techniques. The accuracy and resolving ability with which a given array of 

sensors can locate a seismic source depend on the closeness with which the 

model represents the real earth as well as on the array configuration; errors 

in the input parameters such as arrival times; and the particular algorithm 

used in the calculations. For the standard technique of non-linear least 

square iterative inversion, a method of error analysis has been developed 

which is very useful in evaluating the resolving power of a given station 

configuration with known model and arrival time errors (Peters and Crosson, 

1972). The method is based on a procedure known as prediction analysis 

Arthur D Little, lnc. 
(Wolberg, 1966), and it allows error predictions to be made without actually 

carrying out the inversion calculations. For the seismic location problem 

it is convenient to diagrammatically represent the error structure by mapping 

the errors onto the array geometry by means of contour maps. 

The work reported in this Part is a direct application of the error analysis 

procedure to the problem of locating a trapped miner who is able to communicate seismically with the surface by means of producing small impulsive 

seismic disturbances. Given basic input data such as the arrival times of 

a discrete event at a series of detectors located at the surface, and known 

input in terms of an earth model, the problem is virtually identical to the 

local earthquake problem except for scaling. In the case of the trapped 

miner, source depth may be known quite accurately and the earth model may 

also be known relatively well compared to the typical earthquake investigation. 

The limited objectives of this Part are to evaluate the 

effects on location errors of such factors as model uncertainties, timing 

errors, array geometry, and different classes of models. To carry out such 

evaluations we have calculated standard error maps, contoured in the horizontal 

plane, for three classes of models, three array geometries, and various 

combinations of input parameter errors. The results should be interpreted 

not so much as absolute error predictions but as resolution maps showing the 

relative effects of various assumptions. Caution is required in interpretation because systematic bias in, for example, model assumptions with 

respect to the real earth,may produce systematic errors not accounted for by 

the error analysis. On the other hand, relative resolving power of the 

given configuration is properly indicated. 

Arthur D Little, Inc 
111. METHOD OF CALCULATION AND PRESENTATION 

The method of error prediction is described by Peters and Crosson 

(1972). A velocity model is chosen from which pulse travel times can be 

calculated. The normal equations are formed for the non-linear least 

squares solution for the source at a given location, and the source location 

errors are calculated. The process is repeated for a number of locations 

in an x-y grid and the resultant values are contoured. 

Statistical weighting is used so that data with large relative errors 

do not influence the calculations as strongly as data of higher accuracy. 

Thus, in the least squares method each station in the array is weighted with 

the reciprocal of the square of its associated uncertainty, which is a function of the errors in the model parameters and the derivatives of the travel 

time to that station with respect to these parameters. All velocity models 

used in these cal.culations are laterally homogeneous, velocity varying only 

with the z coordinate. The catalog of resulting contour maps numbered 1 

through 24 is included in this Part. A standard format with four machineplotted maps for each case is presented. The four plots are respectively 

a a representing rms error in x and y coordinates, a representing rms 

x' Y z 

error in z when z is not fixed, and a representing the rms error in all 

tot 

three coordinates. 

a =dX2+a 2 +az 2 

tot Y 

The a's are to be understood as estimated standard errors or one standard 

deviation of a normal distribution, so that the probability is 68% that the 

estimated value lies within a of the true value (and 95% that it lies within 

20 of the true value). The x coordinate is toward the top of each diagram and 

y is toward the right side. Where a contours are not plotted, the depth z 

was assumed known and fixed at 600 feet. All calculations are based on a 

source depth of 600 feet. A scale in feet is indicated on each diagram and 

all error values are in feet. Crosses mark 500 feet from the array center 

in both x and y for each diagramsand squares indicate station locations. 

Contours are labeled with their respective error values and it should be 

pointed out that contour intervals are variable to better illustrate a 

wide range of error characteristics. Thus, care must be exercised in directly 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

Arthur D Little, In 
comparing different diagrams. Contours are plotted in multiples of 10, 25 

or 100 feet. Thus, for example, if the minimum error contour in a plot is 

40 feet, the error never falls to 30 feet, but may be as low as 31 feet at 

+ 

some points. Each diagram is labeled as to the velocity model used and the 

errors incorporated into the calculations. Note that where a 5% model error 

is used it means that 5% error was assumed in all model parameters. For 

example, with a layered model both layer velocities and interface depths 

are included. For the linear velocity model both the surface velocity and 

the velocity gradient are included. An error of p% in the data means they 

are assumed to have been selected from a normal distribution about the 

true value which has a standard deviation of p%. 

+ The minimum total error is shown in each plot. 

Note: Due to an error in scaling for the plotter, the x and y scales 

in Runs 1, 2, 5, 6,.8, 9 and 12 differ by a ratio of 5:4. 

This is of no significance in interpretation. 

Arthur D Little, Inc 
IV. DISCUSSION OF ERROR MAPS 

Run 1 shows the error distribution for a constant velocity model with 

no model error and 1 millisecond time error. It is useful for comparisons 

with other cases utilizing the hexagonal array. Errors increase rapidly 

outside the array margin. Differences in x and y plots result from small 

differences in the symmetry about these two directions. The general features 

of Run 1 are found in all the hexagonal array analyses. 

A. Time Errors 

If there are no model errors, i.e., the model is known exactly, then 

the relative effect of arrival time errors is large. For example, a comparison of Run 9 with 5 millisecond time error and Run 1 with 1 millisecond time 

error shows,as would be expected,an increase in location error by a factor 

of 5. On the other hand, if model error is present, a change from 1 to 5 

millisecond time error has a much smaller net effect, as illustrated by a 

comparison of Runs 10 and 3 for a linear velocity case. The conclusion to 

be drawn is that compared to probable model errors, a few milliseconds of 

arrival time error have a small effect. 

However, once arrival time errors rise to 10 ms and above, they begin 

to dominate model errors. Location inaccuracies again rise roughly linearly 

with arrival time errors once these have risen to 15-20 ms or so (Runs 21-23). 

B. Model Errors 

Model errors exert strong control on the resolution capability of a 

given configuration. Comparison of Runs 1 and 12, where the only differences 

are in error assigned to the constant velocity model, illustrates this feature. 

Similarly, a comparison of Runs 2 and 3 illustrates the same effect for the 

linear velocity model. The total error almost quadruples at the array margin 

when going from no error to 5% model error. 

C. Model Differences 

The differences in error structure as a function of changing models are 

not large in most cases. Generally, models with velocity increasing with 

depth, such as a linear velocity or layered model, offer superior resolution 

Arthur D Little, Inc 
compared with a constant velocity halfspace, especially with respect to depth. 

Since the real earth is perhaps closer to the linear or layered models, some 

advantage is gained. The total error diagrams for Runs 1 and 2 illustrate 

the model dependent effect between the constant-velocity and linear-increase 

models, when the models are assumed to be exact. Note that the linear velocity 

increase model yields better resolution within the array proper than the 

uniform halfspace model; however the rate of deterioration of location accuracy 

outside the array is more rapid than for the halfspace. Examination of the 

layered model results of Run 14 shows behavior similar to that of the linear 

model. 

D. Depth Known 

Several cases were calculated to show the resultant increase in resolution when it is assumed the depth is known, as it could well be in the case 

of trapped miners known to be at specific levels. Run 4 compared with Run 3 

shows the fairly marked effect of fixing depth for two otherwise identical 

cases. Resolution within the boundaries of the array becomes very uniform. 

Comparison of cr for these two cases is not really meaningful since cr 

tot tot 

for the z unknown case is dominated by cr . The same kind of improvement z 

is noted for all fixed vs. free depth comparisons such as Runs 14 and 16, 

and Runs 7 and 8. However, this result, as discussed in Section IV-G, 

appears to be invalid if a homogeneous earth model is used, when a variable 

depth allows a better lateral location accuracy to be achieved. 

E. Changing Array Dimensions 

Previous resolution studies suggest that improved control may be 

obtained if an array does not have a high degree of symmetry. The explanation for this phenomenon is that arrival time data from a highly 

symmetrical array may be largely redundant and thus lacking in location 

11 information". Less symmetrical configurations are illustrated in Runs 

11 and 13, both for a linear-velocity model, and in Run 15 for a layeredmodel. In Run 11, a modified "H" array shows significant improvement 

over the highly symmetric hexagonal array used in Run 3. Similarly, the 

11 stretched" hexagonal array used for Run 13 shows slight improvement 

over the hexagonal array of Run 3. Thus array configuration is an 

important factor in the design of the system. 

Arthur D Little, Inc 
2,000 fps 

4,000 

8,000 

12,000 

half-space 

The locations for these events were then computed using two simpler 

"best fit" models. 

(i) Homogeneous half-space, V = 8,500 fps P 

(ii) Linear velocity model, vP = 4,200 + 5002 fps 

The term "best fit" in this context means that these models best 

fitted a travel time curve for the 4-layer model in a least-squares sense 

over distances of interest to this experiment. 

Arthur D Little, Inc 
It can be seen from Table 2 that the linear velocity model provides an excellent fit to the "real" 4-layer earth both inside and outside the hexagonal array; the homogeneous half-space is a much less 

satisfactory approximation for location purposes, deteriorating particularly rapidly at the boundaries of the array. Interestingly, the 

homogeneous half-space model always provides a more accurate lateral 

fix when the depth of the seismic event is allowed to vary from its 

true value rather than when it is fixed. This is only true for the 

linear velocity model when the seismic event falls within the array. 

When the depth is allowed to vary, there is a corresponding inability 

on the part of the approximate models to match the true tfme of occurrence of the seismic event, as shown in Table 2. 

Preliminary conclusions that may be drawn from these results 

are that in practical terms a linear velocity earth model, which is 

computationally much easier to handle, may be used to represent a 

layered earth for location purposes without introducing serious errors; 

secondly, if a homogeneous earth model is used, it may be wiser to 

let the depth vary even if it is known, since errors in arrival times will 

predominantly introduce an error in the computed z coordinate which, if not 

left free to "compensate" for this, will cause larger errors in the x 

and y coordinates.(As the seismic event moves away from the center of 

the array, arrival times become more sensitive to the x and y coordinates; 

hence, this reasoning eventually breaks down, as shown by the results 

obtained for the linear velocity model.) 

V. REFERENCES 

Peters, D.C. and Crosson, R.S. (1972). Application of Prediction 

Analysis to Hypocenter Determination Using a Local Array, Bull. 

Seis. Soc. &., v. 62., pp 775-788 .- 

Wolberg, J.R. (1967). Prediction Analysis, D. Van Nostrand Co. , Inc., Princeton, N. J. 

Arthur I3 Little Inc 
TABLE 2 

COMPARISON OF LOCATION ERRORS FOR TWO APPROXIMATE MODELS 

Arrival Times Generated Using 4-Layer Earth Model-Event 

Locations Computed Using "Best it" Constant Velocity 

Half-Space and Linear Velocity Models with Assumed 

Model Errors of 5% 

Location Array: 7 Seismometer 

Hexagonal Array: 600 ft. side 

Computed Event Location (feet) 

Actual Event Const. Vel. Const. Vel. Lin. Vel. in. el. 

Location (feet) Depth Varied Depth Fixed Depth Varied Depth Fixed 

X 100 

Y 0 

z 600 

t 0 secs 

x 300 

Y 0 

z 600 

t 0 secs 

x 500 

Y 0 

z 600 

t 0 secs 

x 700 

Y 0 

z 600 

t 0 secs 

X 9 00 

Y 0 

z 600 

t 0 secs 

Arthur D Little, In, 
TABLE 3 

SUMMARY OF ERROR DIAGRAPIS 

Run Arrav 

Type 

Hex 

Hex 

Hex 

Hex 

Hex 

Hex 

Hex 

Hex 

Hex 

Hex 

H 

Hex 

Mod Hex 

Hex 

H 

Hex 

Hex 

Hex 

Hex 

H 

Hex 

Hex 

Hex 

Hex 

Station Velocity Parameter Error Depth 

Spacing, Model Fixed? 

- ft. 0 0 

v (%) t (sec.) 

Con 

Lin 

Lin 

Lin 

Con 

L in 

Lin 

Lin 

Con 

Lin 

Lin 

Con 

L in 

2 Lay 

2 Lay 

2 Lay 

2 Lay 

4 Lay 

4 Lay 

Lin 

Lin 

Lin 

Lin 

Lin 

* indicates depth fixed for error computations. 

Arthur D Little Inc 
TABLE 3 (Continued) 

Con -- Constant Velocity Model: V = 12,000 fps P 

Lin -- Linear Velocity Model: V = 5,000 + 18 fps 

P 

2 Lay -- Two-Layer Model: Depth, ft. Velocity, f 

ps 

0-200 6,000 

200 + 10,000 

4 Lay -- Four-Layer Model: 0-10 

10-100 

100-300 

300 + 

Arthur D Little Inc 
NOTE: Vertical and Horizontal 

Scales are Different 

in the Ratio of 5:4 

on Some Runs 

0 min. tot 

= 46.4 

MODEL: Constant Velocity 

v = 12000fps 

0. = 0% 

at = 1 ms 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

Note Large Effect of 

Time Error when 

Model is Known 

RUN 1 

3.13 Arthur D Little Inc 
MODEL: Linear Velocity 

v = 5000 + 182 

0, = 0 

ot = .001 

RUN 2 

ERROR CONTOURS IN FEET 

Linear Velocity 

Gives Much Better 

Depth Control 

(5 min. tot 

= 27.9 

SOURCE DEPTH - 600 FEET 3.14 

Arthur D Little Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 3 

3.15 Arthur D Little Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 4 

3.16 Arthur D Little Inc 
H 

0 500 ft. 

v = 12000 Expanded array 

a, = 0 Compare to 1 ; ototmin. = 25.9 

ot = .001 

ERROR CONTOURS IN FEET RUN 5 

SOURCE DEPTH - 600 FEET 

3.17 Arthur D Little Inc 
Expanded Array 

Compare to 2; ototmin. = 18.7 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 6 

3.18 

Arthur D Little lnc 
v =5000+ 182 

av = 5% 

0, = .OOl 

Double Array Dimensions 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 7 

3.19 

Arthur D Little Inc 
v =5000+18z 

av = 5% 

at = .001 

Depth Fixed 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

Expanded Array 

Compare to 4; ototmin. = 54.0 

RUN 8 

3.20 

Arthur D Little, Inc 
I-----------------I 

0 500 ft. 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

(IXi = 5 x ox (plot 1) 

i 

oto,rnin. = 231.9 

RUN 9 

3.21 

Arthur D Little. Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 10 

3.22 Arthur D Little Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 11 

3.23 

Arthur D Little Inc 
0 

- 

500 ft. 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

Compare to 1,3, 9 

otOtmin. = 136.2 

RUN 12 

3.24 Arthur D Little, Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 13 

3.25 

Arthur D Little Inc 
2 Layer Model 

a, = 5% 

a, = ,001 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 14 

3.26 

Arthur D Little. Inc 
(T 

tot 

2 Layer Model 

0, = 5% 

ot = ,001 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 15 

3.27 

Arthur D Little Inc 
2 Layer Model 

0, = 5% 

0, = .001 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 16 I 

3.28 

Arthur D Little. lnc 
2 Layer Model 

0, = 5% 

ut = .005 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 17 

3.29 

Arthur Il Little Inc 
4 Layer Model 

0" = 5% 

a, = .001 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 18 

3.30 

Arthur D Little. lnc 
4 Layer Model 

o, = 5% 

o, = .005 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 19 

3.31 

Arthur D Little Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 21 

3.33 

Arthur D Little Inc 
v = 5000+ 18z 

0, = 5% 

0, = .015 

ERROR CONTOURS IN FEEi 

SOURCE DEPTH - 600 FEET 

RUN 22 

Arthur D Little Inc 
ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

RUN 23 

Arthur D Little Inc 
RUN 24 

ERROR CONTOURS IN FEET 

SOURCE DEPTH - 600 FEET 

Arthur D Little Inc 
PART FOUR 

ESTIMATES OF MINER LOCATION ACCURACY: 

WESTINGHOUSE LOCATION PROGRAM w~~~~tl 

Arthur D Little Inc 

PART FOUR 

Table No. 

1 

ESTIMATES OF MINER LOCATION ACCURACY: 

WE STINGHOUS E LOCATION PROGRAM "MINER" 

LIST OF TABLES 

Title 

Earth Model 

"L-Fee t Hexagon" Array 

"L-Feet Double-Square" Array 

Error Data From "Minert' Location Program 

4. iii 

Page 

4.3 

4.4 

4.5 

4.8 & 4.9 

Arthur D Little Inc 
PART FOUR 

Figure No. 

1 

2 

3 

4 

5 

ESTIMATES OF MINER LOCATION ACCURACY: 

WESTINGHOUSE LOCATION PROGRAM" MINER" 

LIST OF FIGURES 

Title Page 

Block Diagram of Comparison Test 4.6 

Notation Used in Error Graph 4.7 

"~iner" Location Error 300 Foot Double Square 4.10 

"Miner" Location Error 400 Foot Hexagon 4.11 

"Miner" Location Error 150 Foot ~ouble Square 4.12 

Arthur D Little, Inc 
PART FOUR 

ESTIMATES OF MINER LOCATION ACCURACY: 

WESTINGHOUSE LOCATION PROGRAM tt~~~~~w 

Arthur D. Little, Inc. 

I. INTRODUCTION 

Crosson and Peters treat the errors that result in miner location due to 

errors in the overburden earth model used for computing location. A parallel 

effort by J. Powell of PMSRC is discussed here, where the location method 

used is that of the Westinghouse location program - "Miner". This location 

program was tested by Powell by using arrival times generated from the overburden earth model of Table l* rounded to the nearest millisecond. Location 

computations were then made using 3 geophones at a time. The average location is tabulated for all geophone triplets except when 3 geophones are in 

line. Geophone arrays were as shown in Tables 2 and 3. The manner in which 

the test was done is illustrated in Figure 1. 

I. SUMMARY OF RESULTS 

The arrival time differences, based on the Table 1 earth model, together 

with geophone locations based on the array geometries of Tables 2 and 3, were 

entered into the computer, together with a stated depth of 700 feet and an 

estimated overburden seismic velocity of 10,000 feet per second. These parameter values were processed by the location program - "Miner". Figure 2 

illustrates the interpretation of the plots and data. The tabular data and 

plots of Table 4 and Figures 3, 4, and 5 illustrate the location error results 

obtained. 

These plots indicate that for sources within the array, the errors are 

considerably less than the measured errors obtained during field tests of 

the present location system. The possible reasons for this discrepancy are 

noted in Part Eight (Earth Models). 

*References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

Arthur D Little Inc 
The work summarized here is based on arrival time differences resulting from one particular representation of the earth. Other representations of the earth will yield other results. When hard data has been 

developed on the real seismic properties of coal mine overburdens, much 

more definitive results concerning the location accuracy of program 

"~iner" can be developed. 

It is further noted that the present test of "Miner" did not make 

any use of the overspecification of location that results from the use of 

seven arrival times to vary the model velocity used in computation. 

Figure 5 does illustrate the behavior of errors for an array judged to 

be too small for the known depth of source. For this example the dependence of location error on input velocity is shown. 

Arthur D Little. Inc 
Layer 

Number 

Surf ace 

Table 1 

Earth Model 

Layer 

Thickness 

(ft > 

Layer 

Velocity 

(ft/sec) 

Source 

Arthur D Little Inc 
Table 2 

"L-Feet Hexagon" Array 

Geophone No. 

1 

2 

3 

4 

5 

6 

7 

Arthur D Little, lnc. 
Table 3 

"L-Fee t Double-Sauare" Arrav 

Geo~hone No. 

Arthur D Little Inc. 
FIGURE 1 BLOCK DIAGRAM OF COMPARISON TEST 

Arthur D Little Inc 

- 

Computed Source 

Coordinates 

T T 

Compare Computed 

and lnput 

Source Coordinates 
Input Source Location 

e.g., 707,707 

Computed Location 

e.g., 550,575 

@ Geophone 

Note that: 

1. The origin of the coordinate system is at the center of the array 

2. The origins, I, and C are almost in a straight line 

3. The distance from origin to I exceeds the distance from origin to C, so error is negative. 

FIGURE 2 NOTATION USED IN ERROR GRAPH 

Arthur D Little Inc 
Table 4 

Error Data From "Miner" Location Program 

Assumed Velocity = 10,000 Ft/Sec 

True Depth = Assumed Depth = 700 Ft 

D Refers to Error as Source Moved Along a Diagonal 

X tc Error as Source Moved Along X Axis 

Y to Error as Source Moved Along Y Axis 

a) Errors for 300 Feet Double Square Array 

Source 

Distance (Feet) 

From Array Error (Feet) in Computed Location 

Center D X Y 

b) Errors for 400 Feet Hexagon Array 

Source 

Distance (Feet) 

From Array Error (Feet) in Computed Location 

Center D X Y 

Arthur D Little, lnc 
Table 4 (Continued) 

Error Data From "~iner" Location Program 

X Errors (Feet) for 3 Different Assumed Velocities 

As Source Moved Along X-Axis 

True Velocity Less than 8000 ~t/Sec 

True Depth = Assumed Depth = 700 Ft 

c) Effects of Assumed Velocity on Location Error for 150 Ft 

Double Square Array 

Source 

Distance(Feet) 

From Array Assumed Velocity in Ft/Sec 

Center 10,000 8,000 6,000 

Arthur D Little Inc 
For: 

Diagonal Path 

)( X-Axis Path 

A Y-Axis Path 

t Input Velocity = 10,000 fps 

X 

FIGURE 3 "MINER" LOCATION ERROR 

300 FOOT DOUBLE SQUARE 

I I I I 

- 10 

1 00 200 300 400 500 X 

- Offset from Center (feet) 
E- 

. 

I-' 

I-' 

For: 

Diagonal Path 

X X-Axis Path 

A Y-Axis Path 

Input Velocity = 10,000 fps 

FIGURE 4 "MINER" LOCATION ERROR 

400 FOOT HEXAGON 

PART FIVE 

THE REFERENCE EVENT METHOD OF SEISMIC 

LOCATION FOR MINE RESCUE SYSTEMS 

Arthur D Little. Inc. 
PART FIVE 

List 

List 

I. 

11. 

111. 

IV . 

v. 

VI . 

THE REFERENCE EVENT METHOD OF SEISMIC 

LOCATION FOR MINE RESCUE SYSTEMS 

TABLE OF CONTENTS 

of Tables 

of Figures 

SUMMARY 

INTRODUCTION 

THEORY 

VELA UNIFORM EXPERIENCE 

FIELD METHODS FOR MINE RESCUE 

FIELD EXFERIMENT 

VI I. CONCLUS IONS 

VIII. REFERENCES 

Page 

4.iii 

4. iv 

5.1 

5.2 

5.2 

5.5 

5.6 

5.12 

5.15 

5.17 

Arthur D Little, Inc. 
PART FIVE 

Table No. 

THE REFERENCE EVENT ZETHOD OF SEISMIC 

LOCATION FOR MINE RESCUE SYSTEMS 

LIST OF TABLES 

Title 

Seismic Location Methods 

5, iii 

Page 

5.13 6 5.14 

Arthur D Little Inc 

PART FIVE 

- THE REFERE-T MFTHOD OF S EISMIC 

LOCATION FOR MINE RESCUE SYSTEMS 

\dm. C. Dean 

TELEDYNE GEOTECH 

Alexandria Laboratories 

I* Srnfi¶ARY 

The location of trapped miners from their seismic signals will be inaccurate if we assume the P-wave propagation velocity is a constant. Pwave velocities are anythingbut constant in regions about mines, so some 

calibration is necessary to obtain more accurate seismic locations. 

The reference event method compares the time arrivals of signals generated 

by the miners with those previously recorded from a reference or calibration event in the vicinity of the miners. This method locates the miners' 

position relative to the calibration source. Hence, the location of the 

miners is absolute if the reference event position is known absolutely, 

usually from surveys and mine maps. 

Advantages resulting from the system,besides greater accuracy,are 

locations independent of the velocity model assumed, the same solution from 

the full array and from any subset of four or more seismometers in the array 

(three if the miners' depth is known), fewer seismometers required, and no 

complex conlputers required for analysis. 

VELA Uniform experience shows that the accuracy of locations of teleseismic explosions and earthquakes is improved by an order of magnitude 

over locations computed from average travel time curves. 

Each calibration event is applicable only over a limited range. We 

recommend a field test of the method at a mine to measure its location 

accuracy, the range of effectiveness for each calibration event, the number 

of seismometers needed, and the number of reference events required per mine. 

From these experiments we could decide whether the reference event 

method was vseful and, if so, what form a practical rescue system would 

take. 

Arthur D Little. Inc 
11. INTRODUCTION 

To date the seismic location system for locating miners trapped underground has been applied assuming a uniform isotropic earth. The use of 

this assumption leads to errors of one to several hundred feet in the seis- 

* mic locations (Westinghouse 1972). Under favorable conditions we should 

expect time reading errors on the order of one tenth of a cycle of the 

dominant signal period. Kith the 80 Hz to 100 Hz signals, the 1 to 2 millisecond time reading errors could account for mislocations on the order of 

10 to 20 feet, assuming no errors in the earth model. Thus the errors 

experienced by Westinghouse can only be accounted for by the inappropriate 

velocity model of the geologic region around the mine. 

If seismic locations to within less than a few hundred feet are to be 

attained, then one of two approaches must be followed. Either the geologic 

structure defining the velocity about the mine must be determined by a 

refraction survey or some othermeans, or reference events must be used 

to calibrate the P-wave travel times to pre-set seismometer locations. 

The purpose of this work is to develop the reference event theory and discuss its application for the mine res.cue systems; refraction surveys and 

more sophisticated velocity models are Jiscussed elsewhere in this report. 

111. THEORY 

The concept of the relative event approach is fairly simple. Since 

accounting for the variations in the velocity of propagation is necessary 

for accurate seismic locations, why not measure the signal delays from 

source to seismometers directly with a test event? Repeated sources from 

the same location will reproduce the same propagation delays. F1oreover, 

sources only slightly displaced from the reference event location will nearly 

reproduce the same propagation delays. To compute tlre change in location of 

the new (unknown) event from that of the reference event, we can use any 

velocity model we wish since most of the path (and hence, most of the propagation delay) from source to seismometer almost duplicates that from the 

reference event. Thus by computing the small displacement accurately from 

the known test event, we can determine accurately the location of the 

unknown event . 

* Westinghouse Contract H0210063 with Bureau of Mines. 

Arthur D Little, lnc. 
In earthquake seismology the standard location method (Geiger 1910) 

minimizes the sum of the squares of the residuals between measured P-wave 

arrivals, t and the calculated arrivals, Fi, based upon some velocity i' 

model 

The calculated time, Fi, for a P-wave to travel from some particular 

th 

event to the i- seismometer is a function of the event coordinates, u, 

- th (actuaUyu, = xo, u2 yo, u = z and u = t ) and the i- seismometer 3 0' 4 0 

coordinates x i, yi, z as well as well as the P-wave velocity between the two. i' 

F. is a non-linear function of the space and time coordinates of the 1 

seismometers and events. This is true even if the velocity is assumed to 

be uniform. Hence, the equations are easier to solve in a least squares 

sense if we expand F in a Taylor's series and neglect the higher order i 

terms. 

The approximation is good when the new location, u, is in the vicinity 

of u* for which F(u*) is presumably known. 

Now the equation (1) can be written as 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

Arthur D Little Inc 
arrivals, t -F * = e . i i i 

The least squares solution of these equations is 

For the development of the method and its associated errors see Flinn (1965). 

To apply the Geiger method we merely have to choose coordinates of an 

arbitrarv event location, uk = (xo*, Yo*, zo*, to*), and perform the matrix 

multiplication iteratively until the solved-for-displacement vector, 6, goes 

to zero. 

In the usual case the least squares solution still leaves us with 

residuals ( Ei R2 ) which are too large. Moreover the resulting location i 

estimates from any of tlie n-1 or n-2 subsets of the seismometer netirork can 

be quite different than the location estimate of the full n-seismometer 

network. Consequently, weak sources and strong sources with identical 1.0- 

cations aleapt to be located apart fro111 each other. 

Arthur D Little lnc. 
The situation is quite different if the first location estimate, (u* = 

x *, yo*, z0*, to*) is from a calibration source in the vicinity of the un0 

known. In this case several advantages result: 

1. The least square residuals are small. 

2. The accuracy of the method is relatively independent of the velocity 

model we assume in the vicinity of the source. 

3. Any subset of four or more seismometers in the network give a location as accurate as the full network. As a result weak event locations are 

frequently as accurate as those of strong events. 

4. Fewer seismometers are needed in the network to yield accurate 

locations. 

5. The waveforms at a particular seismometer from the calibration event 

and the unknown event often are quite similar to each other. Thus relative 

timing between the events is much easier since it is not limited to first 

motions but can make use of large dominant features later in the P-wave 

train. 

6. Utilizing the reference event method a computer can identify which 

of n seismometers have had reading.errors and by how much, as long as no 

more than a third of the seismometer readings are in error. 

IV. VELA UNIFORM EXPERIENCE 

For several years the VELA Uniform program has made use of the reference event method for locating teleseismic earthquakes and underground 

explosions. In a study using various networks from 4 to 13 stations,Chiburis 

1968,compared the accuracy of teleseismic locations both with and without 

travel time corrections for 17 underground explosions at the Nevada Test 

Site. The stations ranged from 2000 to 9000 kilometers from the epicenter. 

Chiburis compardboth the travel time residuals, which is the method we have 

described in the previous section, and travel time anomalies, which calibrates 

the difference in arrival times between pairs of seismometers using reference 

events. The accuracies of the travel time anomaly method and the travel 

time residual method are essentially the same. There are operational advantages to travel time anomalies, since the method is independent of the time 

origin of either the reference event or unknown event. 

Arthur D Little Inc 
Figure 1 shows the location error in kilometers for 17 NTS explosions 

versus the number of recording stations both with and without travel time 

corrections. These results imply that the location accuracy is independent 

of the number of stations. 

Figure 2 shows the location errors for NTS explosions versus the azimuth 

of the network. The network azimuth is measured as the widest angle drawn 

from the epicenter to all pairs of stations. Location accuracy improves as 

network azimuth increases both with and without travel time corrections. 

Similar data for Asian explosions and earthquakes in Figure 3 show the same 

trends. These experiments show that the reference event method improves 

locations by an order of magnitude over the uncalibrated least squares locations. 

We can make an estimate of the ultimate accuracy attainable for relative 

locations of teleseismic earthquakes from the spectral considerations. For 

wide-aperture networks the timing accuracies of signal arrivals are approximately 0.1 seconL with the signal spectra peaked near 1.0 Hz. 

From the thing error and velocity we have 

dt = 0.1 seconds, expect2d timing inaccuracy. 

v = 15 kmlsec, apparent (average) 

P-wave velocity at earth's surface. 

du = v dt = 1.5 km, expected location error. 

Thus the 1-to 2-kilometer relative location accuracy achieved by the 

wide-aperture VELA networks as indicated in Figure 3 approaches the asymptotic 

limit of location accuracy we can expect. 

V. FIELD METHODS FClR MINE RESCUE -- 

We consider here three ways in which the influence of the earth may be 

accounted for in computing the location of trapped miners seismically: 1) 

the uniform velocity approach; 2) the refraction survey approach; and 3) 

the reference event approach. Each method may be applicable in different 

circumstances. 

The first approach involves little sophistication in attempting to 

improve the seismic location accuracy. Upon detecting seismic signals from 

trapped miners, the approximate location of their source is computed assuming 

a uniform, isotropic earth. Then if the seismic array does not surround the 

Arthur D Little Inc 
- I 

7 A Key: 

A Without Corrections 

With Corrections 

- 

A 

- 

- 

A 

- 

A A 

A 

A 

- A A 

A A 

r 

7 

7 

- . 

- 

. . 

- .. 

0. 8 

- . . 

- . 

* 1111AIA111 

Number of Stations 

FIGURE 1 LOCATION ERROR VERSUS NUMBER OF RECORDING STATIONS 

Arthur D Little Inc 
A Without Corrections 

With Corrections 

- A Key: 

- 

- 

- 

- 

- 

- 

- 

- 

- a 

- at " 

- 

a 

- a 

I I I I .,I I . 

Azimuth Aperture, Degrees 

FIGURE 2 LOCATION ERROR VERSUS AZIMUTH APERTURE 

Arthur D Little, lnc. 
than 6000 km 

I I I I 1 I I 1 I 1 I 

0 10 20 30 40 50 60 70 80 90 100 

Az Window Degrees 

FIGURE 3 LOCATION ERROR VERSUS NETWORK AZIMUTH APERTURE 

Arthur D Little Inc 
miners' position, or if the dimensions of the seismic array are too large, 

the seismometers may be redeployed in a smaller array surrounding the miners. 

Subsequent signals from the miners may then provide a more accurate location 

estimate. However, we would not place any confidence in the seismic location for positioning a drilling rig for a life-support hole. Rather the 

drilling rig location would be based only upon mine maps and companion surveys on the surface of the ground. Seismic locations would indicate approximate locations of trapped miners. In this way seismic location errors as 

large as 200 feet or more may be acceptable. 

Advantages of this approach are that it is simple and that it requires 

no precalibration of the mine. 

Disadvantages of this approach are that rescue operations may have to 

depend upon a more accurate seismic location and that there may not be time 

nor subsequent signals from the trapped miners to make redeployment of the 

seismometers practical. 

The second approach is to calibrate the geology surrounding the mine 

with a refraction survey. Then the uniform isotropic earth assumption is 

discarded forsmore realistic model. Powell (1972) illustrated the magnitude of location errors arising when a uniform velocity was used instead 

of the true structure in a few three-layer models. In optimum cases we 

may improve the location accuracy by an order of magnitude, but perhaps 

somewhat less in practice. The reason is that, although the refraction survey may describe the first order variations in the seismic velocities about 

the mine, it may not be detailed enough to measure the secondary features 

(velocity anomalies, faults, fractures, etc.) in the vicinity of the seismometers. These secordaryvariations in geology may cause the test array of 

seismometers to behave differently than the array deployed in an emergency. 

There are trade-offs to be considered in this situation, in terms of 

the complexity of the velocity model envisaged and the extent and analysis 

of the refraction survey required. The size of the uncertainties remaining 

in coal mining environments will have to be resolved by experiment. If the 

refraction survey is carrled out at the mine following a disaster rather 

than in a gre-zzlibrzLicn exercise, the importance of having trained, experienced personnel to perform it cannot be underestimated. For the interpretation of the data, they will require at least a general knowledge of the 

Arthur D Little, Inc. 
geological structure of the region. In principle, it is also possible to 

improve the location accuracy by iterating the velocity model as a result 

of a preliminary location; the improvements obtainable with this approach 

remain to be determined. 

Advantages of approaches relying on calibrated geology are that a 

reduction of the expected seismic location errors by factors of 2 to 5 

may provide sufficient accuracy for positioning a drilling rig in the most 

favorable circumstances or at least allow a miner to be located to within 

a dimension of a pillar. IIowever, several actual or potential disadvantages 

still remain. The locations may still be inaccurate but the inaccuracies 

unknown. The proper velocity model may be applied inaccurately, perhaps 

due to the lack of trained personnel, during an actual emergency. Finally, 

the emplacement of seismometers during the refraction survey may be sufficiently 

different from those used during the location procedure, that the velocity 

model may not apply well enough to the location array. 

The third approach is the reference event method which requires a 

seismic array permanently installed (or seismometer positions chosen in 

advance of disasters) and pre-di~aster calibration of the mine with seismic 

signals from different parts of the mine. 

Advantages of this approach include improved location accuracy by at 

least an order of magnitude over uniform velocity models, elimination of 

the need of refraction surveys, and no fancy data processing techniques. 

Disadvantages of the method include the need for precalibration of 

the mine, permanently installed seismometers (or permanently assigned seismometer locations), and perhaps more calibration signals than we might 

wish, especially as the mine dimensions increase. 

The density of calibration signals required, the number and placement 

of seismometers, and the costs of the method are questions to be resolved 

by experiment. 

Several designs of the seismic location system utilizing the reference 

event approzch are possible. One is to install seismometers, cables and 

recording instruments permanently around the mine. Fire drills (test seismic signals) are taken periodically from different parts of the mine as 

Arthur D Little Inc 
the mine dimensions expand. These recordings, clearly labeled as to source 

location, can be reproduced on clear plastic overlays for easy comparison 

with signals recorded during an emergencv. In this way good seismometer 

locations would be assured (buried for improved signal-to-noise ratio) and 

the eq-uipment would demonstrate its reliability as calibration (reference) 

events were recorded about the mine. Signals could be read and approximate locat-ions determined by analysts without the need for a computer. With 

or without a computer, mine personnel could acquire trainin9 in operatin& 

the system as calibration data were collected. 

A second design would be to locate test seismic sources (small explosives or weight drops) throughout the mine which can be triggered from the 

surface. IJhen a seismometer array has been deployed during an emergency, 

and an approximate location of trapped miners determined from their signals 

assuming a uniform velocity model, then test seismic sources would be set 

off in that section of the mine. The signals from the miners and those 

from several test sources would be compared. Then the relative location of 

the trapped miners would be determined from the test signals which most 

closely matched those generated by the miners. 

The characteristics of the three types of systems, utilizing the uniform 

velocitv, the refraction survey, and the reference event methods, are summarized in Table 1. 

VI. FIELD EXPETIbENT - 

The reference event method should be tested bv a controlled experiment 

at a mine. The Westinghouse data taken to date do not provide data from a 

multitude of close to widely spaced sources received by a fixed seismometer 

arrav. The objectives of such an experiment will be (1) to demonstrate whether 

the relative event method, which has been so successful for locating teleseismic earthquakes, can also be applied to seismic sources in mines, and 

(2) to determine the calibration range of applicability of the reference events. 

The field experiment should comprise from 10 to 15 well-placed seismometers. These sensors should be buried below the weathering layer in drill 

holes if necessary. Every effort should be made to attain good signal sensitivity on single sensors so array summations are not necessary. Different 

Arthur D Little Inc 
TABLE 1 

SEISMIC LOCATION METHODS 

1. Uniform Velocity Method 

Features : 

Advantages: 

Installation - after disgster is reported 

Precalibrat ion - none 

Location Accuracy - several hundred feet 

Drill Locations By - mine maps for precise placement, 

seismic locations indicate 

section of mine. 

Simple 

No precalibration 

No capital outlay prior to disaster 

Minimum training of mine personnel required 

Disadvantages: Seismic locations can indicate only general area of miner 

Deployment of extra seismonleters after first signals 

detected may be desirable 

2. Refraction Survey Nethod 

Features : Installation - after disaster is reported 

Calibration - refraction survey to model 

velocity structure around mine 

Location Accuracy - will vary on complexity of 

geology and thoroughness of 

refraction survey; probably to 

within 100 feet 

Drill Location By - mine maps for precise placement, 

seismic locations narrow search. 

Advantages: More accurate locations than uniform velocity model 

Disadvantages: Location accuracy may be unknown 

Velocity model may be incorrectly applied in an emergency 

Calibration required 

3. Reference Event Method 

Features : Installation - predisaster; permanent 

Precalibration - tests made throughout mine as 

mine dimensions expand 

Location ,4ccuracy - 10 to 50 feet with high confidence 

Drill Locations By - mine maps and seismic locations 

jointly 

Arthur D Little Inc 
TABLE 1 - Continued 

Advantages : 

3. Reference Event Method - Continued 

Accurate locations 

No refraction survevs required 

Data processing required fairly simple 

System in place when emergency arises 

Mine personnel familiar with system from mine 

Calibration tests 

Disadvantages : Predisaster mine installation, tests, and costs 

Necessary system tests required as mine dimensions expand 

Some mine personnel must be trained on system 

Arthur D Little, Inc. 
types of sources should be used (e.g., timber on mine floor, sledge on roof 

bolts) at each source location so the method can be demonstrated with reference and unknown events of the same and different types. Minimum source 

displacements mav be on the order of 25 to 50 feet. Maximum source displacements should be 1000 feet or more if possible. Different sections of 

the mine should be tested including ones for which the seismometer array 

0 surrounds the event location (360 aperture) and ones for smaller apertures. 

One value of having a sufficient number of seismometers is that partial 

arrays (but morethan 3 or 4 sensors) with varying apertures can be compared 

with the full array. 

Costs of running seismic exploration crews within the United States 

average between $30,000 and $50,000 per month including costs for dynamite 

and drilling shot holes. Although we propose to use 10 to 15 sensors all 

in bore hols,the holes will not be deep (average depth 50 feet) so drillir,g 

costs for the mine tests should not exceed those of a normal exploration 

crew. The cables, sensors, and instruments required would be available 

or easily obtainable by an exploration crew. Hence, a geophysical service 

company should be able to conduct a field test of the relative event method 

for $1,000 to $2,000 per day and complete it within two to four weeks. 

As a result of this experiment we should be able to indicate: 

1) whether the reference event method works in mines, 

2) over what range a reference event is applicable, 

3) the source location accuracy of the method, 

4) the number of reference events needed per mine, 

5) the minimum number and placement of sensors required in 

a workable field system, 

6) the analysis procedures to be followed, and 

7) an estimate of the capital and operational (emergency, 

calibration, and testing) costs in a practical field system. 

VII. CONCLUSIONS 

1. We have considered two alternative seismic approaches to improve 

the accuracy of seismic locations for miners trapped underground over methods 

which assume a uniform P-wave velocity in the earth. The first approach uses 

seismic measurements, such as a refraction survey, to calibrate the velocity 

Arthur D Little Inc 
structure about the mine. The second approach calibrates the source-toseismometer traelpaths with reference events at known locations in the 

mine. 

2. The method yielding the most accurate seismic locations is the 

reference event method. When the displacement between the unknown and 

reference events is small, the location accuracy will be limited only by 

the timing accuracv of the signals. 

3. The reference event method provides absolute rather than merely 

relative locatim accuracy since calibrations are tied to surveyed (nonseismic) locations. Methods based upon purely seismic measurements may 

provide accurate relative locations (small least squares error) but still 

contain absolute biases (lateral shifts between true and calculated locations). 

4. The reference event method has the disadvantages of requiring 

calibration events, permanently installed seismometers or prelocated calibration sources triggered from above ground, and several reference events 

per mine for complete calibration. 

5. A field installation utilizing the method has several operational 

advantages. As well as accuracy, these include readiness in the event of 

a disaster, fire-drill testing of the system bv calibration events, 

familiarity with the svstem on the part of mine personnel, and no complex 

computers or analysis required. 

6. We recommend field tests to verify the method. Key questions to 

be answered include the range of effectiveness of each reference event 

and the number of reference events required to completely calibrate a mine. 

7. A field test could be conducted at a mine over a period of two to 

four weeks for costs not exceeding those incurred by Westinghouse in previous seismic experiments at a mine. Total costs should be in the $25,000 

to $50,000 range, or less. 

Arthur D Little, lnc. 
VIII. REFERENCES 

Chiburis, E. F., "Precision Location of Underground Nuclear Explosions 

Using Teleseismic Networks and Pre-determined Travel-Time Anomalies," 

Seismic Data Lab., (Teledyne) Report No. 214, 1 March 1968, (Report 

available from Defense Documentation Center, Alexandria, Virginia). 

Flinn, E. A., "confidence Regions and Error Determinations for Seismic 

Event Location," Reviews of Geophysics, Vol. 3, No. 1, February 

1965. 

Geiger, L., Herdbestimmung bei Erdbeben aus den Ankunftzeiten, K. Gessell. 

Wiss. Goett., 4, 331-349, 1910. 

Powell, James, "A Theoretic Examination of Mine Calibration," memo to 

Arthur D. Little, Inc.,Sept. 1972. 

Westinghouse Report, "Coal Mine Rescue and Survival system': Section 11, 

"seismic Communications and Location System," draft; Chapter 2.7, 

pgs. 11-55 to 11-82; note especially Table 2-12, pg. 11-68; July 1972. 

Arthur I2 Little. Inc 
PART SIX 

FIELD UTILIZATION OF SEISMIC SYSTEMS 

Arthur D Little Inc. 
PART SIX 

FIELD UTILIZATION OF SEISMIC SYSTEMS 

TABLE OF CONTENTS 

I. SUMMARY 

11. INTRODUCTION 

111. REQUIREMENTS 

IV . OPERATIONAL PERSONNEL 

V. SUPPORTIVE R AND D 

Page 

6.1 

6.2 

6.3 

6.5 

6.6 

Arthur D Little, Inc. 
PART SIX 

FIELD UTILIZATION OF SEISMIC SYSTEMS 

Frank Pilotte 

VELA Seismological Center 

Alexandria, Virginia 

I. SUMMARY 

Proper design characteristics for a seismic system to locate miners during a mine disaster are considered in terms of a total system concept. Field 

hardware, processing equipment, operating personnel, deployment, training, 

and supportive R and D are necessary elements of the total system. Each of 

these elements is discussed and an indication given as to the requirements 

necessitated by each one. 

Hardware must be portable, rugged, and fieldworthy. Processing equipment 

must be simple to operate, expandable for future processing improvements, and 

ruggedized for field use. A small well-trained team must be available for quick 

response in times of emergency. Alternative deployment procedures are necessary 

to allow for a variety of situations including both ground and air delivery. 

Supportive R and D is used to support training and upgrading of the system. 

Arthur D Little Inc 
11. INTRODUCTION 

Elere we discuss a set of design characteristics that would result in 

an improved seismic system for miner location following a mine accident. 

The system, when implemented as proposed, will be an adaptable multipurpose seismological array packaged in hand-portable sized containers for 

use under severe field conditions. The system will be capable of monitoring 

up to 12 individual sensors, recording on magnetic tape, providing visual 

displays, and accomplishing some data processing and analysis. 

In selecting individual items, great emphasis should be placed on the 

use of equipment which has been design tested and proven under operational 

field conditions. Special design modifications should be used only as required to meet special needs of remote and severe field operations; for example, 

the use of modular-type moisture-proof-container packaging for seismometers and 

field amplifiers. 

In order to specify the design of this equipment, it is necessary to 

assume the following : 

1. Optimum location accuracy requires calibrated and timed signals. 

2. Power may not be obtainable at the various remote locations where 

the system will be deployed. 

3. Measurements will be made under field conditions where electronic 

test and repair facilities are not readily available. 

4. Emergency conditions will exist at the ti~e ofdeployment and 

quick response is absolutely essential. 

5. Personnel making the measurements must be able to evaluate the 

data within a short length of time. 

6. The system should be expandable to meet future requirements of 

improved analysis. 

7. Maximum use of off-the-shelf components. 

To operate under these assumptions, the system should have the following 

features : 

o The basic system should contain an accurate calibrating device. The 

calibrator should apply an impulse of known polarity to verify seismometer polarity, and sine waves of known amplitude at any desired 

frequency to the seismometer calibration coil to obtain a frequency 

response at a known gain. 

Arthur D Little Inc. 
o The sensing system should be a vertical seismometer-amplifier 

combination capable of direct burial. The seismic signals 

would be fed to a recording and processing system powered by 

the same source powering the amplifier. 

o Monitoring and field analysis will require a playback unit 

capable of producing the data at either .5mm/ms or l.Omrn/ms 

on a paper strip recorder. A monitoring oscilloscope should 

also be provided. 

o The tape recorder should be able to record up to 12 channels 

of data plus time and compensation channels. A time code 

should be encoded on the tape. Additional design provisions 

should be made for inserting operational amplifiers, modules, 

attenuators, and filters as desired. 

o The whole system should be as compact and lightweight as 

possible, and sufficiently rugged to withstand transport under 

the worst field conditions. Simplicity, mobility, ruggedness, 

and ease of setup and operation are prime design goals. 

111. REQUIREMENTS 

To minimize the interference of nearby cultural (man-made) and weatherinduced noise, seismic surveys usually employ either seismometer burial or small 

array techniques. In the mine disaster case, the rescue team will often be 

hampered by the absence of favorable surface geology at the points where the 

particular deployment must be made. Of the two possible techniques, seismometer burial appears to be the simpler solution. A seismometer capable of 

operating at shallow depth will enable the rescue team to pick any desired point 

for measurement and then drill (possibly with a hand auger) until reaching some 

suitable foundation materials. Even at the shallow depths reached by hand 

drilling, the seismometer should have a considerably reduced response (compared 

to a surface site) to locally induced cultural noise (seismic and acoustic). 

In addition, if relatively solid foundation material can be reached, some signal 

attenuation may be avoided. 

In many situations, the simplest, most direct method to determine a location 

will be for the operator analyst to read relative signal arrivals from the individual array elements. Being able to record such signals from each element of 

the array on an identical, selectable time basis will greatly improve the operat~r'~ 

Arthur D Little lnc 
response time and the precision of the location. The sought-after objective 

is the ability to record under any field conditions with a completely independent portable system capable of highly accurate, dependable results. 

It is proposed that both the seismometer and amplifier be packaged in 

the same case. This will result in a single, easily transportable instrument 

package that can be placed in a constant environment away from molestation. 

The time encoder should be a highly accurate digital device capable oi 

providing several different frequency standards in order to broaden the overall 

capability of the system. Of particular importance is a 100-kz signal on the 

compensation trace. This frequency is then used as a reference to obtain an 

accurate time-based playout in high speed visual reproductions. 

A properly equipped field analysis and processing center is essential if 

rapid response and adaptability are to be provided to what will surely be a 

fluid situation. During the course of a location attempt, it will frequently he 

necessary to make judgments regarding seismometer emplacement and coupling, 

noise characteristics in the area, transmission quality, and signal reception. 

Thus, it may be necessary to vary bandpass filters and apply other processing 

techniques. For this reason, inclusion of a playback unit in addition to a 

monitoring oscilloscope is necessary. 

The package for the filters, attenuators, and operational amplifiers should 

be designed with plug-in cards to provide for rapid changes in the data circuits. 

Power will be provided by public power facilities when available; however, 

battery backup should be provided to maintain system operation if the primary 

power source fails or if a primary source is not used. The battery pack should 

have sufficient capacity to maintain operation for at least twelve hours. A 

battery charger should be included to recharge a fully discharged battery bank 

within two hours. 

All interconnecting cables should be prefabricated. Connections should be 

waterproof and should be designed so that improper connections cannot be made. 

System cabling should be designed for maximum portability. 

Sufficient accessory items like hand tools, test equipment, and spare parts 

should be carried to and from the field by operating personnel. The accessory 

kit would possibly include its own power supply so that the operation of this 

equipment would not use power from the principal source. 

Arthur D Little. Inc. 
A well-coordinated field exercise is impossible without reliable 

communications. This factor is paramount where time is a critical factor 

during an emergency. To meet this need, special radio communications can 

be provided as part of the total system to assure efficient operation of 

the crew. 

Major attributes of a field system which have to be emphasized are 

ruggedness, simplicity, portability, and reliability. While there need not 

be a one-to--one correspondence, useful guidelines for the criteria to be 

placed on a field system can be obtained fro111 Military Specifications for 

field equipment. The cost of a field system is likely to be on the order of 

$100,000. 

The crew required to operate the seismic detection and location equipment 

must be considered a part of the total system. As much care and attention 

must be given to the selection and training of the team as to the design and 

construction of the equipment. 

IV. OPERATIONAL PERSONNEL 

To successfully perform under emergency conditions, the seismic detection 

and location equipment (SDLE) must be manned by a team trained and experienced 

with its deployment and use. As a minimum requirement, a three-man cadre 

trained to work together who are completely familiar with all phases of the 

equipment and its operation should be available to deploy the SDLE in the event 

of an emergency. Additional men needed to expedite the setup and calibration 

of the equipment could be provided by the mine company involved in the disaster. 

The three-man cadre would consist of the following: 

0 An operator/analyst (team chief) 

0 An electronic technician(second in command) 

0 A field technician 

The team chief should be a geophysical engineer or someone with an equivalent background whose responsibility includes interfacing with the disaster/ 

rescuer coordinators (mining and/or Government officials), deploying the SDLE, 

and making final processing and location decisions. He should be a mature 

individual who is thoroughly familiar with mining operations and practices. The 

overall success of the mission will depend on his ability to preserve the integrity 

of the whole team and to direct its operation in a confused situation. 

Arthur D Little Inc 
The electronic technician should be qualified and trained to set up and 

operate the entire field system. He must be able to troubleshoot and repair 

most system electrical and mechanical malfunctions or failures. In the 

absence of the team chief, he will substitute as data analyst. 

The field technician should be experienced in geophysical field work and 

capable of directing the efforts of temporary field workers acquired on site. 

He must be familiar with the use of hand portable and light drilling equipment. 

His principal responsibility will be to install the seismometers, lay cables, 

and assist in setting up the analysis center. 

Training and practical experience in the use of the seismic equipment are 

the keys to successful field operations under emergency conditions. Selected 

personnel should be trained to operate as a team and, as such, be deployed on 

I I operational" missions several times a year. As many of the pressures associated 

with a real disaster as possible should be simulated during these training excercises. 

V. DEPLOYMENT OF SYSTEM 

Transportation from the staging area to the field presents special problems. 

Emergencies may occur at any time and in the most remote areas. Several 

different contingency plans are necessary to meet the demand for rapid deployment. For use near the staging areas, a suitable four-wheel-drive truck should 

be available. The truck should be outfitted with appropriate racks and accessory 

gear such that the field equipment could be installed within one-half hour and 

dispatched to the field. In addition, the field equipment should be so packaged 

that it could also be hand portable or cart portable for air movement by either 

commercial or private aircraft. Consideration should be given to the use of 

contract or military helicopter for direct delivery to the field site. On 

delivery to the field, a truck might be made available or the packing crates used 

to form the analysis center enclosure. 

VI. SUPPORTIVE R AND D 

Field R and D should serve two purposes. Each R and D field trip could 

start as a training exercise to improve the performance of the team and to 

expose areas of weakness or deficiency in the operating procedures. The second 

objective would be to test a new ~rocedure or possibly gather data to evaluate 

some point of theory. Certain ideas suggested elsewhere in this report need 

clarification and evaluation. For example, more data are needed to estimate the 

calibration range and absolute location accuracy associated with the reference event 

technique, signal attenuation through various media, calibrated noise measurement 

for optimization of signal passband, and efficiency of signal generators. 

6.6 Arthur D Little, Inc. 
PART SEVEN 

THEORETICAL SEISMIC SIGNAL SOURCE 

AND TRANSMISSION CHARACTERISTICS 

Arthur D Little, Inc 
PART SEVEN 

THEORETICAL SEISMIC SIGNAL SOURCE 

AND TRANSMISSION CHARACTERISTICS 

TABLE OF CONTENTS 

Page 

List of Tables 

List of Figures 

I. SUMMARY 

11. INTRODUCTION 

111. SOURCE STRENGTH AND SOURCE SPECTRUM 

IV . NATURE OF THE MINER'S SOURCE 

V. SIGNAL ATTENUATION 

A. GEOMETRICAL SPREADING . 

B. ENERGY DISSIPATION 

C . EIJERGY PARTITION 

VI . DISTORTION OF SEISMIC WAVE FRONT FOR AN IMPACT IN 

A MINE OPENING 

VII. THEORETICAL ESTIMATION OF THE SIGNAL LEVEL AS A 

FUNCTION OF RANGE 

VIII. DEVELOPMENT OF LOW-FREQUENCY SEISMIC SOURCE FOR THE 

DETECTION OF SURVIVING MINERS 

I:<. FUTURE INVESTIGATIONS 

X. REFERENCES 

APPENDIX A - USE OF A COUPLER IN THE CONVERSION OF 

IMPACT ENERGY INTO SEISMIC ENERGY 

APPENDIX B - QUADRATURE WEIGHTING METHOD FOR MINER 

LOCATION ARRAYS 

Arthur D Little, Inc. 
PART SEVEN 

Table No. 

THEORETICAL SEISMIC SIGNAL SOURCE 

AND TRANSMISSION CHARACTERISTICS 

LIST OF TABLES 

Title 

Average Values of Q 

Q's for Typical Weathering Layers 

Average Values of Attenuation Coefficient,a 

7. iii 

Page 

7.13 

7.14 

7.14 

Arthur D Little. Inc. 
PART SEVEN 

THEORETICAL SEISMIC SIGNAL SOURCE 

AND TPWISMISSION CHARACTERISTICS 

Figure No. 

1 

2 

3 

LIST OF FIGURES 

Title Page 

The Force Function. and the Fourier Transform 7.6 

Source Impact Spectrum Assumed by Westinghouse 7.8 

Attenuation Coefficient Versus Frequency with 

a Low-Frequency Cut-off 7.13 

Four Incident Plane Waves are Shown Approaching 

a Plane Interface. Any One of These Produces 

Four Outgoing Waves, P, S, P', Sf. The Angles 

of Emergence for Shear Waves are a and a', and 

for Compressional IeJaves, 6 and 6'. The Upper 

Medium is Unprimed. (After Nafe, 1957). 7.16 

Fraction of Incident Energy Carried Away in 

Refracted (P, S) and Reflected (P' , St) Waves 7.18 

Radiation Patterns of a Simple Force in (a) 

An Infinite Medium and (b) A Mine Opening 7.19 

Plane Views for Mine Tunnel 7.20 

Distorted Wave Fronts of a Vertical Section A-A' 7.21 

Distorted Wave Fronts of a Vertical Section E-B' 7.22 

Distorted Wave Fronts of a Vertical Section B-B' 

for an Impact on Rib 7.23 

Models for Estimating Signal Levels on the Surface 7.24 

Estimated Peak-to-Peak Vertical Particle Velocity 

for the First P-SJave Arrival (Based on Theoretical 

Considerations) 7.26 

Permanent Installation of a Pendulum 

Attenuation of High Frequencies Through Weathering Layers as Deduced from Plots 28 and 39 of 

Report 8, Copper Queen 7.28 

Arthur D Little, lnc. 
PART SEVEN 

THEORETICAL SEISMIC SIGNAL SOURCE 

AND TRANSMISSION CHARACTERISTICS 

LIST OF FIGURES 

(Continued) 

Figure No. Title 

15 Examples of Low Frequency Sources 

16 Repeated Low-Frequency Signals As Received 

on the Surface 

Page 

7.29 

Arthur D Little Inc 
PART SEVEN 

THEORETICAL SEISMIC SIGNAL SOURCE AND TRANSMISSION CHARACTERISTICS 

John T. Kuo 

Columbia University 

I. SUMMARY 

The miner's seismic source strength can be approximately estimated on the 

basis of a single force acting in an infinite medium. Because of the uncertainty involved in estimating the amount of conversion from mechanical energy to 

seismic energy, the source strength thus estimated may be in error by as much 

as a half-order of magnitude. Calculations of wave transmission must take into 

account geometrical spreading, dissipation of energy by internal friction, and 

energy partition due to reflection and refraction of waves impinging on interfaces in the layered earth. 

Theoretically derived peak-to-peak particle velocities in microinches per 

second (PIPS) are given for two models ; viz: (i) 50-feet thick and (ii) 100- 

feet thick 4000 ft/sec layers with Q = 20, overlying a half-space of 10,000 ft/ 

sec material with Q = 5O;for the cases .of a hammer blow and a timber impact, 

at the frequencies of 50 Hz and 100 Hz. Comparison of the theoretically derived 

peak-to-peak particle velocity with experimental data taken at the Copper Queen 

Mine indicates that the theoretical particle velocity may be overestimated. 

A discussion of the distortion of seismic wavefronts by mine tunnels 

indicates that it is unfavorable to use a seismic source impact on the floor 

of the tunnel, since deceptive delays in arrival time are liable to occur at 

the surface. 

A program of parallel theoretical and experimental work is required to 

clarify uncertainties still associated with the nature and strength of the 

miner's seismic source signal which cannot be resolved within the approximations 

of this work. Its major components include theoretical investigations of the 

(1) Wave diffraction and scattering of an impact source 

on a face of a cylindrical cavity. 

(2) Impact of an elastic object on an elastic medium. 

Arthur D Little Inc. 
Experimental measurements of the signal spectrum under carefully controlled 

conditions are also necessary in order that the frequency spectrum of the source 

be determined accurately; it is virtually impossible to determine the source 

strength near or at the source since the problem of the efficiency of conversion 

of mechanical to seismic energy is extremely difficult to handle. 

For the initial detection of a surviving miner in a disaster struck mine, 

a "low-frequency" source of considerable strength is desired. It is proposed 

that experimental efforts be devoted to the development and test of such a source, 

in conjunction with the concept of a coupler to enhance the conversion of mechanical 

energy into seismic energy. 

11. INTRODUCTION 

The thrust of this work is confined to the surface seismic detection and 

location of trapped miners in a -- coal mine. It is imperative that the procedure 

of locating trapped miners be as unsophisticated to operate as is feasible; the 

final system should ideally be as close to a "push button" type as possible. 

The investigation of the problem of the detection and location of a trapped 

miner starts from the following initial conditions : 

(i) A relatively weak but high-frequency seismic source 

(ii) Seismic-wave transmission in .an inhomogeneous medium generally 

capped by an extremely lossy weathering layer of variable thickness. 

(iii) Relatively high background noise in the frequency band of the 

signal. 

(iv) Limitations in the resolution of currently employed seismic 

methods in both the time and frequency domain. 

The following analysis is designed to shed light on items (i) and (ii). 

The results obtained in this investigation of seismic sources are consistent with being able to detect miners at ranges up to on the order of 1000 feet, 

and to measure arrival times to within a few milliseconds. Hence under the most 

favorable signal-to-noise and geological conditions, it is conceivable (see 

Appendix B) that the location of a miner to within 30 feet should be achieved 

by seismic means, and a reasonable expectation in a range of situations would 

be location accuracies to within 100 feet. 

111. SOURCE STRENGTH AND SOURCE SPECTRUM 

It is reasonably certain that the miner detection and location system has 

to depend predominantly upon the compressional wave, certainly for location 

purposes, as neither shear waves nor surface waves offer the necessary resolving power. Suppose that a hammer blow (or a timber impact) on the roof, rib 

Arthur D Little, Inc. 
or floor in a given mine can be approximated by a single force in an infinite 

medium. Such an approximation is only good for estimating the order of magnitude of the source strength. More precise estimates demand a rigorous theoretical treatment of the problem. Neglecting the distortion of the wave front, due 

to a system of cavities, which will be discussed in a later section, the radial 

component of the particle displacement for near-field, as shown by White (1965), 

is given by 

u = G cos 4 1 r 2 I r 2 11 r [T g(t- v) + - g (t- 7) + +I g (t- )I (I)* r 4npr rV r 

where G is the magnitude of the force, p is the density of the medium, V is the 

compressional wave velocity, and is the angle between the source and 

the point of observation with respect to the vertical. 

Fortunately, for the present application of Equation (1) to the seismic 

detection and location of a miner, the distance from the source to the observation point is generally large, in the order of at least several wavelengths, e.g., 

a frequency of 75 Hz and a velocity of 8000 ft/sec corresponds to a wavelength of 

106 feet, whereas the observation point is typically located at least 400 feet 

away from the source. From that point of view, the first term in the right-hand 

side of Equation (1) is predominant, as the second and third terms decay very 

rapidly at large distances. However, the efficiency of the conversion of the 

mechanical energy into seismic energy at the immediate point of impact is extremely 

difficult to estimate accurately, as all appreciable amount of energy is dissipated 

at the point of impact due to fracture and plastic deformation of the rock. 

For a crude estimate of the particle displacement at an observation point 

located sufficiently far away from the source, Equation (1) may be written as 

which is also used by Westinghouse (see Westinghouse Final Report (1971) ,+volume 

11, p. 78-83). It is possible to extrapolate the particle displacement back to 

the source in a half-theoretical and half-empirical fashion to obtain values for 

the source strength and frequency characteris tics. 

* References to Figures, Tables, and Equations apply to those in this Part unless 

otherwise noted. 

Westinghouse Contract H0101262 with Bureau of Mines. 

Arthur D Little. lnc 
Introducing the dissipation of energy by internal friction, Equation (la) 

may then be written as 

where a is the dissipation coefficient. The radial component of the particle 

velocity can then be obtained by differentiating Equation (lb), neglecting the 

2 

terms higher than l/r . - 

There is a factor of two increase in the displacement if the detection of the motion 

is made on the surf ace of a half-space. In addition, the vertical displacement 

usually detected is a component of the radial particle displacement so that equation (2) should be multiplied by a factor of 2 cos@- 

Instead of letting the force be of the form 

as used by Westinghouse, a closer representation of the real source, 

as recorded through the Westinghouse seismic system, may be given by 

-at g(t) = e sin bt. 

Arthur D Little, Inc 
The force function g(t) has the form shown in Figure 1. The integral of the 

force from a hammer blow or a timber impact is equal to an approximation of an 

impact of very short duration for the case of an inelastic collision, I, such 

that 

where M is the mass of the impact object and v is the impact velocity. 

Substituting g(t) from Equation (4) into (5) and solving for G, we have 

The Fourier Transform of Equation (4) thus gives the spectrum for the impact 

(a hammer or timber upon the roof, rib or floor) as follows 

03 

-at -iwt 

e sin bt e dt 

b Assuming that a = - where n is either an integer or a non-integer, n 

equations (6) and (7) become, respectively 

and 

nu where R = - be 

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FIGURE 1 THE FORCE FUNCTION AND THE FOURIER TRANSFORM 

Arthur D Little, Inc 
It follows that 

The maximum value of I G(iw ( thus occurs at 

w= bn for w>o 

n 

2 

n with a corresponding value, I G(iw) 1 = -i~;. 

At w = 0, we have r) 

The ratio of I~(iw) lw=bJy& 

is thus 

Experimental results are needed to determine the spectrum for various sources 

under various rock types. 

Arthur DLittleInc 
The spectrum of the hammer blow or timber impact has the form of 

Figure 1; thus as n approaches one, the spectrum approaches that assumed 

by Westinghouse, as depicted in Figure 2 below; 

FIGURE 2 SOURCE IMPACT SPECTRUM ASSUMED BY WESTINGHOUSE 

i .e., flat from DC to the corner frequency w . C 

Therefore the radial component of the particle velocity of Equation (2) 

becomes 

and 

for a # b 

(t- $) ]e-ar 

b for a = - 

n 

Arthur D Little, Inc. 
For a multilayered model, the radial component of the particle velocity, 

by virtue of equation (12), becomes 

n 

-Car 

2 22 1 n n 

u = Mv(a +b ) cos 4 

r x Tn(i) (14) 4nb2pv, 2R 1 n 

where V is the compressional wave velocity of the medium in which the source 1 

is located, and T is the transmission coefficient through the multilayered n 

medium. 

IV. NATURE OF THE MINER'S SOURCE 

Consider the impact of an elastic rod of length, R, upon a rigid halfspace. At the impact, t = t v = v and o = v 6 where t is the time, 

0' 0' 0 0 

v is the velocity of the impact, a is the stress, E is young's modulus of 

0 0 

the rod, and p is the density. 

Later, for t > t if the contact duration is sufficiently long, we have 

0' 

o 

asv=- and c v~ 

6 

Arthur D Little Inc 
Therefore the stress exerted on the rigid medium is 

and we have 

Hence the stress on the rigid medium is 

The behavior of equation (19) may be summarized as follows: 

Arthur D Little, Inc. 
R 2R (4) att +-<t<t +- 

0 C 0 C 

Therefore, if the impact duration is sufficiently long, the longitudinal 

vibration of the rod is of importance to the stress on the impact medium. It 

is anticipated that for the case of the impact of an elastic object such as a 

timber on an elastic medium, the stress should be a function of E 1' E2' 

p1 , and p2 , and furthermore, the initial impact stress might be a function of El, E2, pl, and p2, as well as of Vd This might explain why a timber 

impact, in addition to its heavier mass, generates lower frequency as well as 

larger signals than a hammer blow. 

Arthur D Little Inc 
V. SIGNAL ATTENUATION 

Attenuation of seismic waves is attributed principally to 

(1) geometrical spreading 

(2) energy dissipation 

(3) energy partition due to reflection and transmission 

at the interfaces of a layered medium. 

A. Geometrical Spreading 

According to equation (la), in the far-field the particle displacement 

is simply inversely proportional to the first power of the distance between 

the source and the observation point. 

B. Energy Dissipation 

-1 The dissipation function Q for compressional waves propagated in 

common rocks may be given by (Futterman, 1963) 

where a is the attenuation coefficient. 

For small dissipation such that - 4naV << 1, 

W 

equation (20) may be approximated by 

-1 

so that the attenuation coefficient in terms of Q is 

where f is the frequency in Hz. 

*This expression differs by a factor of 2 from that given in the Westinghouse 

Final Report (1971), Section 11, p. D-16. 

Arthur D Little Inc. 
Therefore, the attenuation coefficient is a function of w as shown in 

Figure 3. Basic physical considerations indicate that the attenuation should 

disappear at some low frequency cut-off wo , which has accordingly been included in Figure 3, although reliable estimates of its values are not yet available. 

a' 

FIGURE 3 ATTENUA-TION COEFFICIENT VERSUS FREQUENCY 

WITH A LOW-FREQUENCY CUT-OFF 

Valuable information on the value of Q for Eastern Coal Province, Southern 

Appalachian field, Interior Coal Province, and Rocky Mountain coal regions is 

given by Wes tinghouse (~inal Report 11, p . D16-18) .* Average values of Q for 

various rock types are approximately given in (without specifying the frequency 

range) Table 1. 

TABLE 1 

AVERAGE VALUES OF Q 

Rock Type Q 

Cap rock 50 

Do lomi t e 200 

Limes tone 120 

llarls tone, sand- 50 

stone, shale and 

siltstone 

* Ibid. 

7.13 

Arthur D Little Inc 
Since the coal region is generally covered by weathering layers and soils, 

the following are values of Q for soils for compressional waves in the frequency 

range of interest (Table 2): 

TABLE 2 

Q's FOR TYPICAL WEATHERING LAYERS 

Frequency ? Sou~ce Format ion Range 

Pottsville sand- 100-900 Hz 7 

stone 

Pierre shale 

Collins 

and Lee 

(1956) 

McDonal 

et al. 

(1958) 

The average values of a are approximately (Table 3): 

TABLE 3 

AVERAGE VALUES OF ATTENUATION COEFFICIENT, a 

Rock Type Compressional Q Frequency a 

wave velocity 

ft /sec 

Hz nepers / f t 

Dolomite 

Limes tone 

Sands ton? 

Weathering zone 

C. Energy Partition 

The fraction of the energy incident in a plane wave upon a plane interface, 

separating two semi-infinite media, that is carried away in each of the reflected 

and refracted waves, can be directly calculated on a computer. Among various 

authors, e.g., Costain et al. (1963), McCamy et al. (1962)*, etc., Nafe (1957) 

has expressed the Knott equations (1899) in common coordinate system for the 

four separate problems of incident P (or SV) waves from either side of the interface in a symmetrical form, which is convenient for numerical calculation. 

*There is an error in sign in McCamy et al.'s (1962) paper. 

Consequently, their results are incorrect. 

Arthur D Little, lnc. 
Referring to Figure 4, if the incident waves are assumed to have unit 

amplitude, the sixteen equations for the amplitudes may be expressed as the 

matrix product : 

where 

tana 

1 

-2 tana 

114 

I -1 t ana 

tana' 

-1 

-2p'tana' 

N = 

t ana ' 

-tan6 -1 1 

-pq -2~ tana 

2 where IJ ' and IJ are rigidities, and q and q' are equal to (tan a -1) and 

2 (tan a' -I), respectively. 

The notation of (P,s') or (P' ,P) refers to the outgoing wave by the 

first letter, and the incident wave by the second letter. 

Arthur D Little. Inc 
FIGURE 4 FOUR INCIDENT PLANE WAVES ARE SHOWN APPROACHING A 

PLANE INTERFACE. ANY ONE OF THESE PRODUCES FOUR 

OUTGOING WAVES, P, S, P', S'. THE ANGLES OF EMERGENCE 

FOR SHEAR WAVES ARE o AND o ; AND FOR COMPRESSIONAL 

WAVES, 6 AND 6 '. THE UPPER MEDIUM IS UNPRIMED. (After 

Nafe, 1957). 

Arthur D Little, Inc, 
The cases for the velocity ratios of 1:2, 1:2.5, and 1:3, and the densities 

2.3 and 2.8, which are directly applicable to the present requirements of a 

weathering zone in contact with sandstone or limestone, are shown in Figure 5 

0 for the range of incident angles from 0 to 60 . 

The present results can be easily applied to the case of plane waves in a 

multilayered medium used to represent the geological structure of a coal mine 

region. A similar analysis was performed by Haskell (1962) in treating crustal 

reflection of P and S waves in a layered medium. However, the problem of calculating reflection and transmission coefficients for a point source located in a 

layered medium requires further investigation. 

\TI. DISTORTION OF SEISMIC WAVE FRONT FOR AN IMPACT SOURCE IN A YINE OPENING 

Evidently, the assumption of a simple force in an infinite medium for a 

hammer blow (or a timber strike) on either the roof or the ribs of a mine 

opening is not adequate. The radiation pattern generated by a simple force in 

an infinite medium is spherical, whereas that of a simple force impacted on a 

cavity has a distorted spherical shape. Figures 6a and 6b give a comparison of 

these two wave front patterns. 

Because of the general complexity of a mine section including a grid of 

tunnels, it is virtually impossible to represent the wave front generated by 

a source under actual mine conditions. Fortunately, the wave length we are 

dealing with is generally large in comparison with at least the cross-section 

of an opening. Unless the impact is on the floor, the approximate spherical 

wave front of the impact on either the roof or the rib would not be significantly distorted as it impinges on the surface, as shown in Figure 6b. 

It must be cautioned, however, that when the impact is on the floor the 

wave front is severely distorted. The degree of its distortion naturally 

depends upon the dimensions of the opening as shown in Figure 7; for a floor 

impact the first arrival of P waves on the surface should be expected to have 

a considerable time delay. Figures 8, 9 and 10 represent the wave distortion 

in sections A-A' and B-B' for a three-dimensional representation of a long 

tunnel with impact on the roof, the rib and the floor. 

Arthur D Little Inc 
i' in degrees i' in degrees 

0 10 20 30 40 50 60 0 10 20 30 40 50 60 

FIGURE 5 FRACTION OF INCIDENT ENERGY CARRIED AWAY IN 

REFRACTED (P, S) AND REFLECTED (P', S') WAVES 

Arthur D Little. Inc 

i' in degrees 

E (S1,P') 

- 0.8 

I 

I 

g- o-6 

P ' 

* 

I S' 

-0.4 

0)-- - \ 

-0.2 0 

i' in degrees 

/- - 

I 

0 10 20 30 40 50 60 0 10 20 30 40 50 60 

7 

E(P1,P') 

- 

I 

I 

cn 

0 

w 

- C 

- * W c P' + 

c I a, 

0 

U 

c - - 

.c 

0 

\ C 

\ 0 .- \ C, 

U 

2 

LL 
(a) A simple force in an infinite medium 

(b) A simple force in a mine opening 

FIGURE 6 RADIATION PATTERNS OF A SIMPLE FORCE IN (a) AN INFINITE 

MEDIUM AND (b) A MINE OPENING 

Arthur D Little, Inc 
Plane View 

FIGURE 7 P L A N E V I E W S F O R MINE TUNNEL 

Arthur D Little, Inc. 
FIGURE 8 DISTORTED WAVE FRONTS OF A VERTICAL SECTION A-A' 
FIGURE 9 DISTORTED WAVE FRONTS OF A VERTICAL SECTION B-B' 

7.22 Arthur D Little, lnc. 
FIGURE 10 DISTORTED WAVE FRONTS OF A VERTICAL 

SECTION B-B' FOR AN IMPACT ON RIB 

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VII. THEORETICAL ESTIIQITION OF THE SIGNAL LEVEL AS A FUNCTION OF RANGE 

Neglecting the effect of noise on the signal, the particle velocity may 

be approximately calculated by Equation 13. The remaining problem is then to 

estimate the efficiency of energy conversion from mechanical impact to seismicwave transmission, which naturally depends on the dimension, elastic properties 

and the velocity of the impact body, and the stress thereby induced in the impact 

medium. Such an estimation, without controlled experimental data, involves 

a high degree of uncertainty. We will assume a 70% effective elastic collision 

as a hammer strikes the rock in a mine opening. 

As a specific example, we use the models of Figure 11, which are close to the 

geological model at Imperial Mine (Westinghouse Final Report 11,"Figure 3.1-3, 

p. 92) Surface 

Weathered Layer 501, 4000 fps, Q = 20 

Surface 

Weathered Layer loo', 4000 fps, Q = 20 

10,000 fps, Q = 50 1 450' 

FIGURE 11 MODELS FOR ESTIMATING SIGNAL 

* Ibid. LEVELS ON THE SURFACE 

Arthur D Little, Inc. 
and the values of 

M = a 10-lb - sledge hammer; a 40-lb timber 

v = 16.1 ft/sec for hammer; 11.5 ft/sec for timber 

p = 2.67 gm/cm3 for 10,000 ft/sec half-space 

Taking into account all the factors of the geometrical spreading, energy 

dissipation, and energy partition at the interface as described in the preceding 

section, the vertical component of the peak-to-peak particle velocity on the 

surface of.the model is given in Figure 12 for the cases of 50 Hz and 100 Hz * 

as a function of slant range for a hammer blow and a timber impact. The up- and 

-down-link experimental data for the frequency range of 70 to 83 Hz (Table 2.5.3-1, 

Westinghouse Field Report 8)' at Copper Queen is also plotted in the Figure. 

The rates of decay for the theoretically calculated and the experimental data 

agree rather closely. The theoretical magnitude of the peak-to-peak particle 

velocity seems somewhat overestimated for a hammer blow, as the source used 

at Copper Queen is a thumper for uplink and a timber for downlink. This is an 

unfair comparison, as the geological models vary between the theoretical situation and that of Copper Queen, since the geology at Copper Queen is complicated 

by faults and irregular distribution of alluvial materials. Nevertheless, it 

does provide evidence of the applicability of such a crude approximation in 

theoretical calculations. 

VIII.. DEVELOPTENT OF LOW-FREQUENCY SEISTlIC SOURCE FOR THE DETECTION OF SURVIVING 

IIINERS 

Present seismic detection methods are handicapped because only very weak 

signals can be generated by a trapped miner with available tools such as a sledge 

hammer or a timber. The detectability of a trapped miner should be greatly 

enhanced if a suitable low-frequency source can be developed. Since the option 

of what a miner may be able to carry is rather limited, it appears not altogether 

unreasonable to consider a permanent installation of a mechanical source generator 

of the simplest kind. An electrically or electronically driven transducer is 

ruled out because of its requirement for either sophistication or power. It 

seems that heavy-weight simple pendulums can be installed in strategic locations 

in an actual mine section. As the signal strength for an impact source is directly proportional to the mass of the impact body, a "lead" sphere type of simple 

pendulum may be appropriate. Such installations cost relatively little. The 

support of the pendulum can be anchored either to the roof or to the rib as 

* A relatively large value of n has been assumed, so that the source signal strength 

(see Figure 1) is noticeably higher at lOOHz than 50Hz. 

* Westinghouse Contract H0210063 with Bureau of Mines. 

Arthur D Lttle. Jnc 
FIGURE 12 ESTIMATED PEAK-TO-PEAK VERTICAL PARTICLE 

VELOCITY FOR THE FIRST P-WAVE ARRIVAL 

(BASED ON THEORETICAL CONSIDERATIONS) 

Arthur D LittleInc. 
the following diagram (Figure 13) i1 ~lus ' trates. 

Roof Anchored 

Point of Impact 

Rib 

Anchored 

of Impact 

FIGURE 13 PERMANENT INSTALLATION OF A PENDULUM 

The signal can be generated repeatedly without great effort on the part of 

a trapped miner. Furthermore, the particle velocity is also directly proportional to the impact velocity. If the impact of a timber is comparable 

to that of a hammer blow, the magnitude of the particle velocity due to the 

impact of a lead sphere would be about an order of magnitude higher than that 

due to a 10-lb sledge hammer blow. If the impact is made on a floor filled 

with soft earth material or in a coal seam, a coupler may be installed at the 

point of impact to enhance the conversion of mechanical energy into seismic 

energy without much energy loss in permanent deformation of the medium. Experimental results of impact on sand and sand-silt clay show a great deal of promise 

for eliminating energy loss from plastic deformation and heat generation (Appendix 

A and Mereu et al. (1963) ) . For the initial detection of surviving miners in a disaster-struck mine, 

a positive, immediately identifiable signal of ~es/no would be of great value 

for subsequent operation. Since the high frequency components of a signal attenuate rapidly in earth materials, particularly in weathering layers such as alluvium 

and soil, as is clearly demonstrated in Figure 14, a "low-frequency" source is 

preferred, i.e., with a peak frequency in the neighborhood of 10 Hz. A hammer 

Arthur D Little Inc 
Level 900 700 500 300 100 Surface 

Uplink - 900 Level to Surface 

0 100 300 500 700 900 Level 

Surface 

Downlink - Surface to 900 Level 

FIGURE 14 ATTENUATION OF HIGH FREQUENCIES THROUGH 

WEATHERING LAYERS AS DEDUCED FROM PLOTS 

38 AND 39 OF REPORT 8, COPPER QUEEN 

Arthur D Little Inc. 
or a lead sphere with a spring mount as shown in Figure 15 promises to generate 

lower frequencies of this order. Future efforts toward developing a low-f requency 

source could be very worthwhile. 

Coal Seam 

/ Spring Mounting \ 

Hemispherical 

Coupler 

FIGURE 15 EXAMPLES OF LOW FREQUENCY SOURCES 

Arthur D Little. Inc 
energy of repeated sources. If the signals are sufficiently strong, their 

envelopes could themselves offer direct visual identification of the presence 

of surviving miners . Once surviving miners have been successfully detected, 

a down-link signal can be sent to tell survivors to use a high-frequency source 

with a shorter range of transmission for the purpose of accurate location. 

IX. FUTURE INVESTIGATIONS 

(1) Wave diffraction and scattering of an impact source on a face of 

a cylindrical cavity. 

(2) The impact of an elastic object on an elastic medium. 

(3) Spectrum of the source, sufficiently far from the source to 

determine ~(iw) as a function of frequency. This information 

should be of great value for more accurate determination of 

the source strength, as it is virtually impossible to 

determine the source strength near or at the source because 

the conversion of mechanical energy to seismic energy remains 

a difficult problem. 

Arthur D Little, lnc 
REFEFENCES - 

Collins, F., and C. C. Lee (1956). Geophysics 21, 16-39. 

Costain, J. K., K. L. Cook, and S. T. Algermissen (1963). Bull. Seism. 

SOC. Am. 53, 1039-1074. 

Futterman, W. I. (1962). J. Geophys. Res. 67, 5279-5291. 

McCamy, K., R. Meyer, and T. J. Smith (1962). Bull. Seism. Soc. Am. 52, 

923-956. 

McDonal, F. J., F. A. Angona, R. L. Mills, R. L. Sengbush, R. G. Van Nostrand, 

and J. E. White (1958). Geophysics 23, 421-439. 

Mereu, R. F., R. J. Uffen, and A. E. Beck (1963). Geophysics 28, 531-546. 

Nafe, J. E. (1957). Bull. Seism. Soc. Am. 47, 205-219. 

White, J. E. (1965). Seismic Waves: Radiation, Transmission and 

Attenuation, McGraw Hill, New York 302 pp. 

Knott, C. G. (1899). Phil Mag. 48, 64-97 

Coal Mine Rescue and Survival System, Vol. 11, ~ommunications/~ocation 

Subsystem, Westinghouse Final Report, Bu Mines Contract H0101262, Sept., 1971. 

Haskell, N.A. (1962) , J. Geophysics Res. 67, 4751-4759. 

Westinghouse Field Report No. 8, Copper Queen Mine, Bisbee, Arizona, 

January 19 72, Contract H0210063. 

Arthur D Little Inc 
APPENDIX A 

USE OF A COUPLER IN THE CONVERSION OF 

IMPACT ENERGY INTO SEISMIC ENERGY 

Mereu -- et a1 (1963) presented an interesting paper on the efficient 

transfer of impact energy into seismic energy in soil-covered areas by 

means of a falling weight-coupler system. This concept is equally 

applicable to the present problem of impact on a coal seam or on a floor 

generally covered with rock debris or soils. Through their theoretical 

and experimental model studies on sand and clay-silt sand, the authors 

concluded that for compressional waves: 

(I) A coupler such as a plastic steel hemisphere embedded 

in the medium at the impact point can increase the 

amplitude of the seismic output by reducing plastic 

deformation at the point of impact, i.e., 

where A is the amplitude of the seismic signal, M the 

mass of the coupler, and V the maximum velocity of 

C 

the coupler. 

(2) The seismic energy is not proportional to the source 

energy. 

Arthur D Little Inc 
APPENDIX B 

QUADRATURE WEIGHTING METHOD FOR MINER LOCATION ARRAYS* 

In principle it is possible to cope with the problem of bias in location 

estimation by using a different station weighting procedure than that adopted in 

Part Three. The stations in each quadrant are considered in separate groups. 

When an approximate location has been determined, the residues for each station 

in a group are computed, and obviously "abnormal" stations are rejected. Subsequently, an average residue is calculated as 

where N is the number of stations in the group. 

It is assumed that residue values follow a Gaussian distribution about this mean 

value, to which a weighting factor of unity is assigned. Finally a weighted residue is computed for each station by using a weighting factor which corresponds 

to the position of the original residue on the Gaussian distribution. 

Appropriate quadrants for the miner location problem might be as 

follows (?igure El) . 

I 

x-y Plane 

FIGURE B1 QUADRANT GEOMETRY 

*This method has been in common use at the Lamont Geological Observatory for 

earthquake focus relocations (Kuo et al.). 

Arthur D Little Inc 
PART EIGHT 

EARTH MODELS 

Arthur D Little. lnc 
PART EIGHT 

EARTH MODELS 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. INTRODUCTION 

11. COAL MINE GEOLOGY 

111. BASIC SEISMIC DATA REQUIRED 

IV . AN INTERIM EARTH MODEL 

V, CONCLUSIONS 

VI . REFERENCES 

APPENDIX A - SEISMIC SURVEY OVER THE CLARION 4A COAL SEAM 

Page 

8. iii 

8. iv 

8.1 

8.1 

8.6 

8.8 

8.7 

8.10 

8.11 

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Table No. 

PART EIGHT 

EARTH MODELS 

LIST OF TABLES 

Title 

Interim Earth Model 

Page 

8.9 

Arthur D Lttle, lnc 
PART EIGHT 

EARTH MODELS 

LIST OF FIGURES 

Figure No. Title 

1 Compressional Velocities for Typical Overburden Materials 

2 Stratigraphic Cross Section From Steubenville 

to Toronto Using the Brush Creek Coal as the 

Datum 

A1 Seismic Velocity Profile 

A2 Seismic Velocity Profile 

A3 Seismic Velocity Profile 

A4 Seismic Velocity Profile 

Page 

Arthur D Little Inc. 
PART EIGHT 

EARTH MODELS 

Arthur D. Little, Inc. 

I. INTRODUCTION 

The question of earth models has repeatedly arisen in our work. An 

accurate representation of the seismic properties is required for three 

reasons : 

1. To be able to determine from a set of received arrival times, the 

location of a seismic source in the earth, and secondly the degree of 

accuracy required in the model used for calculating source location 

from the set of arrival time differences. 

2. To be able to determine the expected arrival times at an array of 

geoph~nes produced in response to a hypothetical source in the 

earth. 

3. To be able to estimate received signal strengths more accurately. 

The work reported here on earth models is based on information from several consultants and from others who expressed an interest in the problem and 

supplied information to us. 

11. COAL MINE GEOLOGY 

On one of our earlier assignments for the Bureau of Mines, Earth Science 

Research Inc. of Cambridge, Massachusetts prepared for us a short description of 

the lithology to be expected at coal mine sites. This description follows, together with the ranges of compressional seismic velocities (~igure I*) associated 

with typical materials comprising the layered structure of a coal mine area. 

Coal is primarily associated with fresh water sediments including sandstones, 

shales, and clays, and occasionally may be metamorphased to varying degrees. 

In the Appalachian Basin the coal beds occur within cyclical sequences of 

non-marine shales, sands tones, conglomerates, limes tones, and clays. The beds 

range in thickness from a few inches to 60 feet, averaging between 2 feet and 

10 feet. They have generally broad areal extent, occasionally up to 5,000 

square miles, and have an overall tabular or lens-like shape. Within a particular 

lens, local changes in thickness are normal. 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

Arthur D Little Inc 
Material Compressional Velocity (mlsec) 

0 2000 4000 6000 8000 

Weathered Surface Material 

Gravel, Rubble, Sand (Dry) 

Gravel, Rubble, Sand (Wet) 

Clay 

Sandstones 

Shales 

Limestones 

FIGURE 1 COMPRESSIONAL VELOCITIES FOR 

TYPICAL OVERBURDEN MATERIALS 

Arthur D Little. Inc 
Coal beds typically contain thin bands of clay, shale, fine grained 

or nodular pyrite, marcasite, and siderite. Graphite is also prevalent 

with the content depending on the degree of metamorphism. In the steeply 

folded rocks of the anthracite region in northern Pennsylvania, which have 

undergone dynamic metamorphism, the graphite content is above average. 

Cyclothems are cyclical sequence deposits which repeat in succession 

throughout the geologic column of a coal basin. When ideally developed, 

a typical cyclothem, starting with the oldest beds, is as follows: 

1. Fine grained micaceous sandstone and siltstone grading into 

conglomerate varying from thin to massive bedded, in which 

occasional plants are found. 

2. Grey sandy shale which often contains ironstone concretions. 

3. Fresh water limestone occurring as nodules or discontinuous 

beds. 

4. An underclay, medium or light grey in color and somewhat 

calcareous. 

5. Coal seam. 

6. Grey shale with pyritic nodules and ironstone concretions 

towards the base. Fossils are rare. 

7. Marine limestone. 

8. Black laminated shale with large concretions and often 

fossiliferous. 

9. Marine limestone with fossils. 

10. Grey sandy shale or shaly sandstone often grading into 

conglomerates. The shales may have fossils and sometimes 

ironstone concretions. 

Part or all of this sequence may be repeated many times in the coal series. 

Arthur D Little Inc 
J. Powell of the U.S. Bureau of Mines has conducted an investigation of coal 

mine geology for this present investigation. Utilizing data obtained from 

References (I), (2), and (3) and information supplied by Mr. George Smith, a 

geologist with U.S. Steel, Powell concludes: 

Geologic strata are usually horizontal, a slope of 100 feet per mile 

would be unusually large. 

Although the strata are horizontal, they often pinch out or grade into 

different rock types. 

The outstanding example of this pinch-out would be sand and gravel 

deposits laid down in stream beds. In cross section, a bed may be 

tens of feet thick in one spot and have disappeared completely a few 

hundred feet away as shown in Figure 2. 

Geologic cross sections keep their general characteristics for distances of several miles. For example, if most of the overburden at 

point A is limestone, most of the overburden at a point 2 miles east of 

A will probably be limestone. 

Geologic sections can change. considerably over a distance of ten miles. 

To continue the above example, the overburden at a point 10 miles east 

of A could well be shale. 

Items 4 and 5 above indicate that for many mines (i . e. , those which 

could be contained within a square a few miles on a side) there exists 

much common geology. 

In Pennsylvania and northern West Virginia, there is little faulting. 

As one goes south faulting becomes more common. In western Kentucky 

faults with vertical displacements of tens of feet are not unusual. 

Coal is one of the most persistent beds; that is, in general a coal 

bed will continue for greater distances than other rock beds. 

Arthur D Little, Inc 
Arthur D Little Inc 
From these data and descriptions some general comments can be made. 

Seismic compressional velocities in the regions of the earth through which 

a miner's signal must travel, from the mine tunnel area to the surface, will 

range from that of limestone (as high as 14,000 feet per second) to that of 

the weathered layer (as low as 500 feet per second). It will generally be 

true that the higher velocities will be encountered at the greater depths 

and the lower velocities near the surface. The extreme range of compressional velocities encountered suggests that accurate knowledge of the 

velocity profile in the region under which the miner is trapped may be 

required in order to perform accurate location calculations based on arrival 

time differences. 

111. BASIC SEISMIC DATA REQUIRED 

If the arrival times are perfectly obtained, then the accuracy of the 

location is dependent on the accuracy of the model used to represent the 

earth in the computation of location. Elsewhere in this Volume, Crosson 

and Peters, and Powell, treat the effect of model errors on location errors. 

These analyses compare hypothetical laterally homogeneous, horizontally 

layered earths represented by similarly layered models or continuous models 

where the seismic velocity increases linearly with depth, and homogeneous 

half-spaces. These two studies show that the location errors that can be 

assigned to model errors of this class are much less than the errors experienced with the present seismic location system. This suggests several 

possibilities : 

1. Horizontally layered earth models may be inadequate to 

represent the real earth. 

2. Gross timing errors may have been introduced by the system 

instrumentation and/or by operator misinterpretation of the 

seismic recordings. 

3. The depth of the weathered layers under the receiving geophones may not be properly taken into account with the 

present sys tern. 

4. Source cavity-produced errors may be present and unaccounted 

for. 

5. Survey errors may have been large. 

Arthur D Little Inc 
We are concerned here only with the possible inadequacies of the earth 

models used to date. It is not possible to say at present what effects gross 

model errors have, because the seismic properties of the real earth over coal 

mines are not adequately known. This lack of knowledge emphasizes the need 

for comprehensive seismic surveys at a few eastern coal mine sites.* These 

comprehensive tests would reveal what properties of the real earth need to 

be included in the model, in order to make the model errors small enough to 

reach the desired location accuracy. The survey tests are outlined elsewhere 

in this report but would include: 

Surface refraction surveys configured to yield layer data to 

at least the working depth of the mine. 

High resolution vertical reflection surveys to substantiate the 

refraction survey and/or identify spatially varying layer properties. 

Core holes with geological logging. 

Core hole to core hole velocity measurements to substantiate 

larger velocity properties. 

Arrival time plots from mine located impulsive sources as an 

additional confirmation of seismic properties. 

Precise measurement of weathered layered thickness at seismometer positions. 

One of the objectives of this comprehensive seismic survey is to establish 

if a surface seismic survey can provide adequate detail for the preparation of 

a sufficiently accurate earth model for location computation purposes. Our 

discussions with persons experienced in surface refraction surveys (4) indicates 

that a careful refraction survey done by an experienced survey team can identify 

well defined layer boundaries to within a few feet to depths near a thousand 

feet, and that seismic velocities can be measured to within a few percent. 

The work of Crosson and Peters indicates the degree of location accuracy that 

would result for models of this accuracy. In addition to undertaking conventional refraction surveys, it may be desirable to consider the technique of 

Donath and KUO(~) as discussed below. 

The method of refraction surveys for determining the seismic velocity 

structure of the earth, which is based on fitting straight lines through sets 

of points on a distance versus arrival time plot, is geared to the specification 

of plane layered models of the earth. It will not pick up features such as 

varying layer thicknesses or fractures. However, it is possible to interpret 

refraction survey data in a more sophisticated manner to reflect, if appropriate, 

* See Appendix A. 

Arthur D Little. Im 
the underlying region? 

IV. A?? INTERIM EARTH MODEL 

Based on available information, and recognizing the uncertainty of important data, Powell has developed a seismic earth model which can be expected to 

be typical of eastern soft coal regions. The model is not intended to be one 

for use in the location of miners at a mine disaster, but is rather one 

which can be used to determine the behavior of arrival times for hypothetical 

source locations in an earth that has the structure of the model. From such 

sets of arrival times the accuracy of various location earth models can be 

established, and a grasp of how accurately the location earth model must approach 

the real earth can be obtained. As such we consider this model to be an interim 

one, which can be used for theoretical analyses of location earth model performance, and can be varied to determine the sensitivity of alternative location 

earth models. The model, which is composed of laterally homogeneous horizontal 

layers, is described in Table 1. Crosson and Peters, in Part Three of this Volume, 

use earth models based on this interim model, but simplified to cases of 2 and 

4 layers and the case of a continuous velocity variation. 

Arthur D Little, Inc 
TABLE 1 

INTERIM EARTH TIODEL 

Layer 

number 

Surface 

Layer Layer 

thickness velocity 

(ft) (f t /see) 

V. CONCLUSIONS 

A comprehensive seismic survey at a number of coal mine sites is recommended as a means of obtaining data to the accuracy necessary for further miner 

location, earth model development, including a comparison of alternative models. 

An interim seismic velocity earth model is suggested on the basis of general 

geological properties of soft coal regions. This model is based on laterally 

homogeneous horizontal layers, which may be inadequate to properly describe a 

real mine environment. Its accuracv can onlv be determined when all potential 

sources of error in arrival time measurements have been accounted for. 

Arthur D Little Inc 
Arthur D Little, Inc 
APPENDIX A 

SEISMIC SURVEY OVER THE CLARION 4A COAL SEAM 

Since the completion of the work upon which this report is based, we 

have obtained seismic velocity profiles through the good offices of Mr. 

Dennis Rubin of American Electric Power Service Corporation. These profiles were taken for AEP by Weston Geophysical Engineers, Inc. of Weston, 

llassachusetts. These profiles were taken in the Meigs County area of Ohio 

over the Clarion 4A coal seam. Elevations and distances on these profiles 

are scaled with major divisions equal to 100 feet. Velocities are in feet 

per second. The profiles are shown in Figures Al, A2, A3, and A4. 

These data provide part of the needed base for developing good earth 

models as noted in this Part. The nature of these data also emphasize the 

need for further data, to greater depths and higher accuracy over other 

coal seams. 

Arthur D Little Inc 
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Arthur I2 Little Inc 
Feet 

Source: American Electric Power Service Corp. and Weston Geophysical Engineers, Inc. 

FIGURE A4 SEISMIC VELOCITY PROFILE 
PART NINE 

SEISMIC NOISE CHARACTERISTICS 

Arthur D Little, Inc 
PART NINE 

SEISMIC NOISE CHARACTERISTICS 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. SUMMARY 

11. INTRODUCTION 

A. SO'B SEISllIC ELEMENTALS 

B. THE REPRESENTATION OF A SEISMIC WAVE 

C. ELEMENTARY ARRAY PROCESSING 

D. SIGNAL REPRESENTATION 

111. BASE SEISMIC NOISE LEVEL 

A. STATISTICAL CLASS 

B. DATA ANALYSIS AND ESTIMATION OF BASE NOISE LEVELS 

OF MOTION BETWEEN 10-100 HZ 

IV . COMMON NOISE SOURCES 

A. ACOUSTIC: PISTON AIRCRAFT 

8. WIND AND RAIN 

FIXED LOCAL DISTURBANCES 

D. MOVING SOURCES AT A DISTANCE 

E . INTRA-MINE SOURCES 

V. HIGH FREQUENCY LOW LEVEL SEISMIC NOISE 

VI . OPTIIIUII ARRAY PROCESSING 

VII . NARROWB,AI!TD DETECTION 

VIII. REFERENCES 

Page 

9. iii 

9.iv 

9.1 

9.2 

9.2 

9.4 

9.5 

9.5 

9.10 

9.10 

Arthur D Little, Inc. 
PART NINE 

Table No. 

SEISMIC NOISE CWCTERISTICS 

LIST OF TABLES 

Title 

1 Table of Seismic Velocities for Common 

Materials 

2 Separation Guidelines for Dealing with 

Man-Made Noise Sources 

9. iii 

Page 

9.3 

9.22 

Arthur D Little, Inc 
PART NINE 

SEISMIC NOISE CHARACTERISTICS 

LIST OF FIGURES 

Figure No. Title 

1 Representation of an Impulse 

2 K Plane Response for Equally Weighted 7- 

Seismometer Hexagonal Array with Seismometer 

Spacing d 

3 Spatial and Bandpass Frequency Filtering 

4 Location of the Miner's Signal in (w,k) Plane 

5 Siesmic Base Levels for a Single Surface 

Seismometer 

6 Westinghouse Data for Seismic Noise Level 

at 23 Ft. Depth During a High Surface 

Noise Condition (Bruceton) 

7 Estimated Seismic Base Noise Passed by 

Shallow Buried Arrays 

8 Air-Coupled Surface Waves in Layered Media 

9 Signal and Noise Zones Excited by Distant 

Sources in Layered Media 

10 A Representation of a Single Fixed Noise 

Source 

11 The Problem of High Frequency, Low Level 

Measurements 

Page 

9.6 

Arthur D Little. Inc. 
PART NINE 

SEISMIC NOISE CHARACTERISTICS 

Francis Crowley 

Air Force Cambridge Research Laboratories 

I. SUMMARY 

Elementary concepts of seismic wave properties are reviewed to establish a 

framework for discussing seismic noise and its suppression. A liberal number of 

references is included for those who wish to pursue the topic in detail. A base 

motion noise level is established for a single surface seismometer. It is argued 

that simple array processing and seismometer burial should regularly permit us to 

approach this base noise level which is found in areas free of conspicuous man-made 

seismic noise sources. 

The sensitivity of the base seismic level to a number of common disturbances 

is presented. Solutions that promise to hold the "effective" seismic noise at a 

site near the base level are given for acoustic, meteorological and fixed local 

surface sources. Guidelines are suggested for controlling other local man-made 

sources, e.g. vehicular traffic, by keeping them at sufficiently large distances 

away from the seismometers to keep noise at permissible levels. These guidelines 

are speculative and conservative. They should be the subject of future study. 

The ability to process against general local activity, drilling, and intramine sources is limited. Certainly no dramatic gain is to be expected. When 

strong man-made and/or intramine noise sources are not controllable, detection may 

well be impossible to achieve, unless the seismometer can be moved close enough 

to the suspected miner position, i.e. via very deep holes, to compensate for the 

likely vast differences in strength of the miner signal and the uncontrollable 

man-made noise sources. However, many'intramine sources, e.g., falling water, 

rock bursts, explosions, etc. , may well preclude the existence of a hale miner in 

their vicinity, and therefore any need to attempt detection of a miner at such 

locations. 

The following recommendations are made to enhance the detection and location 

of a miner signaling seismically. They are: 

1. Seismometer burial in slim holes. 

2. Narrow band detection, using multiple narrow band filters to cover 

the likely signal band. 

3. Broadband recording and analysis for time-of-arrival estimation. 

Arthur D Little. Inc 
11. INTRODUCTION 

A. Some Seismic Elementals 

The bulk of seismic noise is the aggregate of propagating seismic waves. 

Being waves,each coherent elemental contribution can be represented as 

u = U(kR - at). (I>* 

Here the motion, u, appears to have constant phase when an observer moves at 

a velocity c =w/k. The angular frequency o is 2n times the number of cycles of a 

periodic element sensed by a stationary observer per unit time, while k, the wave 

number, is 2n times the number of cycles observed at an instant over a unit distance. 

The amplitude of the wave is determined by the source and path attributes. 

In the far field and for small source dimensions, u attentuates as 1/R in its 

body phases!l)~ody waves are the only waves that exist in a homogeneous, isotropic, 

elastic body of infinite extent at small motion levels!2)They are of two kinds, a 

P wave whose particle motion is directed along the propagation path and an S wave 

whose motion is normal to this path. Typical parameters of body waves are given 

in Table 1. +- The p wave displ-acement u due to a localized force F (t) observed in the far 

field in a medium of velocity V and density p is given by: P 

. . + +- 

The velocity of motion at a point u is a complete replica of F(t) delayed in 

time by the propagation delay, R/V . Far field particle velocity ratios of soil 

P 

to rock for a common F(t) and distance are then 

fiS PR V S = soil 

- = -*% 100 ; where 

G P 

R S ps R = rock 

Looking ahead to our discussion of seismic noise levels, we should expect motion 

levels in soils to be substantially larger than those in rock, when the distributions of sources and source strengths are roughly equivalent. 

An alteration of seismic body waves always occurs at a boundary. The waves 

are converted in kind; boundary phases develop. Techniques for computing the transmissivity of layered media have been the aim of much theoretical work (3,4). 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

9.2 Arthur D Little, Inc 
TABLE 1 

TABLE OF SEISMIC VELOCITIES FOR COMMON MATERIALS 

Material 

IGNEOUS AT SHALLOW DEPTH 

GRANITE 

DIORITE 

GNEISS 

SEDIMENTARY ROCKS 

LIMESTONE 

MARBLE 

CHALK 

SLATE 

UNCONSOLIDATED SEDIMENTS 

WETCLAY 

SAND (TIGHT) 

SAND (LOOSE) 

SOIL 

ALLUVIAL CLAY 

ALLUVIAL SAND 

TALUS 

WEATHERED LAYER 

* SHIMA ** WATKINS 

(37) (38) 

4,920 - 5,413 375 - 1,150 *** 

1,970 - 6,073 1,150 - 1,340 *** 

655 - (min. meas.) 

*** GEOLOGICAL SOC. OF AMER, MEMOIR 97 

(39) 

Arthur D Little Inc 
-1 We speak of waves observed on the earth's surface that attenuate as R in the 

far field as body waves, and those that attenuate as R -'I2 as surface waves, each 

also having different phase velocities. Between these two lie the so-called leaky 

modes. For horizontally stratified media, leaky mode behavior should dominate 

the miner's signal(3). Normal or locked mode transmission should govern an area's 

noise attributes when excited by distant surface sources (4,361 

Much of the analysis of seismic wave transmission to date achieves mathematical 

success only when applied to the complexities met on a small scale near the earth's 

surface. Computational tools are only now becoming generally available to deal with 

these complexities (27) in a more general fashion. 

For a regularly layered area and large distances from the source,surface 

waves exhibit the following properties: 

(1) An attenuation with distance as 116 

(2) An attenuation from the s~rface in terms of k 

(3) A highly selective enhancement of the motion in k,w space 

(4) A phase velocity dependence on k, o (Dispersion) 

For this case, u, is not a delayed version of F(t). Indeed path attributes 

heavily mask the true history of the source. Schematically we can view the earth 

as a highly complicated filter that delays and colors the source. 

In summary the earth is a linear, passive, time invariant, realizable filter 

with the following properties: 

(1) Adding inputs, adds outputs 

(2) Measurements between the source and receiver are coherent 

(in the absence of noise) 

(3) Filtering is mult i-dimensional in k , w . (4) Reciprocity exists between the source and receiver. 

(5) When the collective source attribute is gaussian, the output is 

gaussian. 

B. The Representation of a Seismic Wave 

We define G(a ), the spectral estimate of our motion measured at a stationary 

point as 

G(w) = F.T. {u(t) -u(t+nAt) ) time average (4) 

In like manner G(k) is 

space average (5) 

Arthur D Little Inc. 
TABLE 1 

TABLE OF SEISMIC VELOCITIES FOR COMMON MATERIALS 

IGNEOUS AT SHALLOW DEPTH 

GRANITE 

DIORITE 

GNEISS 

SEDIMENTARY ROCKS 

LIMESTONE 

MARBLE 

CHALK 

SLATE 

UNCONSOLIDATED SEDIMENTS 

WETCLAY 

SAND (TIGHT) 

SAND (LOOSE) 

SOIL 

ALLUVIAL CLAY 

ALLUVIAL SAND 

TALUS 

WEATHERED LAYER 

* SHIMA ** WATKINS 

(37) (38) 

4,920 - 5,413 

1,970 - 6,073 

655 - (min. meas.) 

*** GEOLOGICAL SOC. OF AMER, MEMOIR 97 

(39) 

Arthur D Little Inc 
-1 We speak of waves observed on the earth's surface that attenuate as R in the 

far field as body waves, and those that attenuate as R -112 as surface waves, each 

also having different phase velocities. Between these two lie the so-called leaky 

modes. For horizontally stratified media, leaky mode behavior should dominate 

the miner's signal(3). Normal or locked mode transmission should govern an area's 

noise attributes when excited by distant surface sources (4,361 

Much of the analysis of seismic wave transmission to date achieves mathematical 

success only when applied to the complexities met on a small scale near the earth's 

surface. Computational tools are only now becoming generally available to deal with 

these complexities (27) in a more general fashion. 

For a regularly layered area and large distances from the source,surface 

waves exhibit the following properties : 

(1) An attenuation with distance as l/& 

(2) An attenuation from the s~rface in terms of k 

(3) A highly selective enhancement of the motion in k,~ space 

(4) A phase velocity dependence on k, w. (~ispersion) 

For this case, u, is not a delayed version of F(t) . Indeed path attributes 

heavily mask the true history of the source. Schematically we can view the earth 

as a highly complicated filter that delays and colors the source. 

In summary the earth is a linear, passive, time invariant, realizable filter 

with the following properties : 

(1) Adding inputs, adds outputs 

(2) Measurements between the source and receiver are coherent 

(in the absence of noise) 

(3) Filtering is multi-dimensional in k, w. 

(4) Reciprocity exists between the source and receiver. 

(5) When the collective source attribute is gaussian, the output is 

gaussian. 

B. The Representation of a Seismic Wave 

We define G(o ), the spectral estimate of our motion measured at a stationary 

point as 

G(w) = F.T. {u(t) -u(t+nAt) ) 

In like manner G(k) is 

time average (4) 

space average (5) 

Arthur D Little. Inc. 
and G(k, w) = F.T.{u(x,t) *u(x+nhx, t+nht) 1 

spatio-temporal average 

(F.T. = the - Fourier - ~ransform) 

(---- = complex conjugate) 

Let us now represent the attributes of an impulse in a non-dispersive medium 

for these various representations. The impulse is 

u = 6 (kx-wt). 

The representations are shown in Figure 1. 

C. Elementary Array Processing 

Arrays are space filters. Their response H(k) is determined by their arrangement in space. For a uniform distribution of seismometers about a point, seismometer summing has the effect of low pass filtering. Hankel transforms apply in 

this simple case(30). The response of a seven element, hexagonal array is given 

(6) in Figure 2 . 

If we now combine frequency and spatial filtering we can pass or reject certain regions in w, k (Figure 3). For a general discussion of arrays in detection, 

see Part Ten. 

D. Signal Representation 

The presumed features of the miner's signal are: 

(1) High apparent velocity, c = w/k large 

(2) Repetitive coherent wavelets 

a) F(t) Impulsive: the frequency of the maximum 

particle ~elocit~(~).y to the reciprocal of the 

half period of the contact time . 

b; Path invariant 

(3) Proportionately large vertical component 

(P wave and flat layering) 

(4) A lowering of peak frequency with distance due to 

1) Internal layering (32) 

2) Inelastic response, especially in surface alluvium 

(5) Quarter wave leaky resonance of upper layer can enhance the signal 

(3) wavelet at discrete frequencies 

(8) (6) The signal appears coherent only over a small area at the surface . 

9.5 Arthur D Little. Inc 
G (k) = 1 

FIGURE 1 REPRESENTATION OF AN IMPULSE 

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FIGURE 2 K PLANE RESPONSE FOR EQUALLY WEIGHTED 7-SEISMOMETER 

HEXAGONAL ARRAY WITH SEISMOMETER SPACING d 

3.7 Arthur D Little, lnc 
Reject (Temporal) 

Reject (Temporal) 

I I 

FIGURE 3 SPATIAL AND BANDPASS FREQUENCY FILTERING 

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The approximate location of the miner's signal in the U, k plane is 

shown in Figure 4. 

FIGURE 4 LOCATION OF THE MINER'S SIGNAL IN (w,k) PLANE 

Arthur D Little Inc 
111. BASE SEISMIC NOISE LEVEL 

A. Statistical Class 

(18) In the main, seismic sources have been found to be random and independent . In the absence of a conspicuous source, limit-in-the-mean theorems apply so that the 

motion level at a point has gaussian attributes. For the case at hand, there is 

little to suggest either experimentally or conceptually that motions cannot be effectively treated as gaussian variates. As such all the probability information of 

the motion of a point is given by its covariance or its Fourier transform spectra 

(mean = 0). The treatment of seismic noise fields for detection is a natural 

extension of the treatment of random scalar processes. The subject is well developed. For our immediate purposes,spatial sampling allows us to preferentially accept 

elementary wave components in the signal region. The effectiveness of arrays fundamentally rests on our proper recognition of the propagation attributes of the noise 

and signal in the w , k plane. 

B. Data Analysis and Estimation of Base Noise Levels of Motion Between 10-100 Hz 

Seismic noise above 10 Hz is not a well developed topic, and the bulk of the 

open literature that does exist requires some interpretation before being compared 

to periodograms or spectra. 

Approximately 20 years ago Wilson conducted a careful experiment in England 

to discern the origins and nature of microseisms over the band 4-100 Hz. In his 

experiments he found ground particle velocity rms noise levels as low as 0.2 pips in 

chalk areas and as high as 1 pips in clay soil areas, over the 4-100 Hz passband, 

in the presence of system noise of 0.1 pips. These levels represent the rms noise 

levels remaining after sources such as vehicular traffic , machinery, aircraft, windvegation, rain etc., were removed. 

More recently Frantti reported surface measurements in the band 10-100 Hz. 

His results are presented in a series of reports (11,12,13). Given in Figure 5 are 

the smoothed results of his 1965 report. Here we have taken the liberty to modify 

his original plots by restoring the measurements to the peak-to-peak value in a 

113 octave band by multiplying his spectral value by 113 octave. This multiplication is consistent with spectral units. Results are given in terms of the 

upper and lower quartiles and the median, as found at some 90 locations. He selected sample data "during time periods that appeared to be free from obvious, local 

anomalous sources of noise near the site at the time of recording1'. As such his 

levels should also approximate "base seismic levels. " 

Arthur D Little Inc 
- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

Brandner et al 

- 

- 

- 

- 

Westinghouse 

(Down Hole) 

(Bruceton, Pa.) 

- 

- 

- 

- 

- 

; I I I I I 1111 I I I r I 1111 I I I rrr~i 

10 1 00 

Frequency (HZ) 

FIGURE 5 SEISMIC BASE LEVELS FOR A 

SINGLE SURFACE SEISMOMETER 

Arthur D Little Inc 
Both ÿ rant ti's (1962)and ~ilson's data show a strong trend towards clustering 

the small levels in areas with a surface geology of rock. Both noted a significant increase of level with wind. The upper quartile levels of Figure 5 (after 

Frantti) are taken to be more suggestive of the base level for alluvial areas. 

Rock areas in turn are more nearly represented by the lower quartile levels. 

Also given in Figure 5 are Westinghouse spectra taken at the USBM experiment- 

(8) i- a1 mine at Bruceton, Pa. Again we have converted the data to the peak-to-peak 

value to be found in 1/3 octave bands, by summing the spectra over 113 octave and 

converting to a peak-to-peak estimate by multiplying the rms value by 1.7. These 

Westinghouse values fall between w rant ti's median and lower quartile values in the 

range 10-100 Hz. Above 100 Hz we have only this Westinghouse data*. For this region 

 rantt ti's estimates are extrapolated beyond 100 Hz using the slope of the Westinghouse data taken at Bruceton mine above 100 Hz. This portion of the spectra above 

100 Hz must be considered quite speculative. 

Also shown in Figure 5 are data taken by Bradner et al!16)and Goforth (17) 

The Bradner values are taken near the ocean. Using Frantti's regional distribut ion (I3) of seismic levels Bradner's results appear low, the explanation probably 

lying in the care used by Bradner in installing the seismometers. By contrast 

the Goforth data are well represented by the Frantti data. As with Wilson, Goforth 

has presented a base value. The upper value can be associated with a local anomaly 

caused by geothermal activity known to exist in the area. Having established a 

base seismic level and its variation under various conditions for a single surface 

sensor, a judgement must now be made as to how this seismic energy is distributed in 

the LJJ , k plane, in order to determine the base level that would be passed by a 

small array. 

Very few investigators have considered the structure of high frequency seismic 

noise fields. Aki 'I8) in an extraordinarily comprehensive paper on seismic noise 

has derived the essential tools for treating the problem. In this work he considered the spatial attributes of an isotropic seismic noise field. These concepts were 

tested by surface observations. Using only a pair of seismometers and negligible 

computational hardware, Aki constructed a reasonable picture of the noise at his 

recording site. He found much of the noise to occur as fundamental mode surface 

waves. In turn Akamatu (I9) conscious of the work of Wilson and Aki, concentrated 

Westinghouse Contract H0210063 with Bureau of Mines. 

* 

The "seismic" noise levels reported by Westinghouse prior to the Bruceton mine 

experiment are not used to estimate the distributions in seismic base level noise, 

because the lower bounds of that noise data were masked by system noise. 

Arthur D Little, Inc 
on the distribution of seismic waves with velocity. She found the bulk of the 

noise confined to velocities much less than 3,000 ft./sec. Guided by these two 

works and the work of Phillips(20) on small shallow buried arrays, the conclusion 

is that a small array will have little effect on baseband noise in shallow rock 

areas. In contrast, for alluvial areas direct summing of a small aperture seismometer array will diminish the base level by 6 db or more at the frequencies of 

interest. 

Westinghouse noise data taken at the Bruceton mine can be used to suggest the 

impact of seismometer burial on base noise. Given in Figure 6 are the motion levels 

at a 23 ft. depth during a surface high noise condition. The reported value at this 

depth falls below quiet surface levels by 2-12 db. Also shown are the corresponding. 

high surface noise levels, and the average surface noise levels at that site. 

Therefore a combination of shallow burial and the use of arrays might be reasonably expected to attenuate base seismic levels by 10 db in low velocity alluvial 

areas. In shallow hard rock areas, the attenuation will be substantially smaller 

if our experience in the 1-10 Hz band remains valid. Consequently the base seismic 

noise level in the miner's signal band, after burial and array summing, should be 

reasonably close to values in Frantti 's lower quartile . Futhermore , variation 

about the median should be significantly reduced below the original "untreated" 

surface noise dispersion. 

Estimated base noise peak-to-peak levels, as seen by 113 octave passbands 

have been plotted in Figure 7 for shallow buried arrays. Figure 7 indicates that 

the upper quartile-to-median noise levels, after burial and arrays, should fall to 

levels between median-to-lower quartile levels of Figure 6 for a single surface 

seismometer, over the frequency range approximately bounded by 40 to 120 Hz. 

This is the band where most of the miner generated signal energy has been found 

to date. Figure 7 also reveals the flattening of the Figure 6 noise spectrum 

over the 10-100 Hz range, and the mo2e rapid roll-off above 100 Hz,expected with 

shallow buried arrays. 

The values shown are sensitive to bandwidth. As given, they are directly 

applicable only to narrow band signal detection. The curves are readily adjusted 

to larger bandwidths in their flat areas by multiplyipg the value shown by 

where n is the number of third octave bands in the desired larger bandwidth. 

Arthur I3 Little, Inc 
- 

- 

Down Hole 

I 

100 

Frequency (Hz) 

FIGURE 6 WESTINGHOUSE DATA FOR SEISMIC NOISE LEVEL 

AT 23 FT. DEPTH DURING A HIGH SURFACE NOISE 

CONDITION (BRUCETON) 

Arthur D Little Inc. 
7 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- Upper 

Quartile 

- 

Median 

- 

- 

- 

- 

- 

- 

- Lower 

- Quartile 

7 

t I I I I I I Ill I I I I IIIII I I I1 IIII, 

Frequency (Hz) 

FIGURE 7 ESTIMATED SEISMIC BASE NOISE PASSED BY SHALLOW BURIED ARRAYS 

Arthur D Little, Inc 
At low frequencies, seismic spectral levels appear to be flat with 

velocity. At higher frequencies, spectra tend to be flat with acceleration. 

Since, at very high frequencies, the base level becoiiies exceedingly small, 

and system noise is approximately flat with velocity, (8) we can therefore 

expect that any measuring system will eventually become system-noise-limited, 

if this spectral trend continues in the base seismic noise. 

The Figures 6 and 7 plots represent our best estimates based on the 

limited noise data available to date in the 10-100 Hz frequency band of 

interest. As such, they should still be considered speculative base levels 

requiring verification, particularly for the Eastern coal mining regions. 

IV. COMMON NOISE SOURCES 

Having established a base seismic noise through our system, the impact 

of conspicuous noise sources must now be assessed. Three common sources of 

seismic surface noise are acoustic, wind (rain), and fixed local machinery. 

Each source will be considered in turn with a method of dealing with it to 

maintain an overall seismic noise value near our base level. 

A. Acoustic: Piston Aircraft 

According to Wilson, low flying aircraft are capable of increasing the 

seismic base level when they close to within about 10,000 ft. In this case, 

the ground disturbance sensed by the seismometer should take the form of an 

air coupled seismic surface wave, assuming that the seismometer is sufficiently buried to protect it from the direct air wave. Such disturbances 

occur when the horizontal phase velocity of the air wave matches that of 

the seismic surface wave in the ground. In this situation, large motions 

result (Crowley) (33) but the structure of the disturbance is such that 

simple array processing should be quite effective. As shown in Figure 8, 

such behavior occurs at the intersections of the v line with the Rayleigh a 

wave curves (1) and (2). 

The sensitivity of a site to air-coupled disturbances is best determined 

by firing a small explosion on the surface. Once the wave number, k, of the 

air-coupled term is known, an omnidirectional array can be constructed to 

suppress it by something near 20 db. As aircraft approach closer to the 

sensor at low levels, at a distance of say 5,000 ft., the air-coupled wave 

pole in (w, k) will start to migrate towards the signal zone. Also, the 

array will cease to suppress the disturbance. At a distance of say 1,500 ft., 

the disturbance will probably start to saturate any system working at a base 

seismic level in a uniformly layered area with an alluvial surface geology. 

Arthur D Little, Inc. 
Locked Modes Region 

- va = Velocity of Sound in Air 

(horizontal component) 

d = seismometer separation 

k 

Lea kin!, m.muuVQ 

Locked Modes Region 

va = Velocity of Sound in Air 

(horizontal component) 

or 7-element array 

4 Path of Pole Migration for c > va 

(1) Fundamental mode Rayleigh wave 

(2) Higher order mode Rayleigh wave 

FIGURE 8 AIR-COUPLED SURFACE WAVES IN LAYERED MEDIA 

Arthur D Little Inc 
Other sources of acoustic noise, such as diesel generators, can be dealt with 

by combinations of seismometer burial and coherent processing as discussed in 

Section C below. 

B. Wind and Rain 

A single surface seismometer is severely affected by wind and rain. As 

noted by Wilson, Frantti and Westinghouse our base noise level can be exceeded by 

two orders of magnitude during a meteorological disturbance. Surface arrays when 

summed in this condition suppress this type of noise by no better than d'%-' . 

This processing gain is trivial in light of the desired base level. In contrast 

to array processing, burial appears to be extremely effective. Westinghouse reported a 6 db attenuation by burying to only 0.5 ft. and an attenuation between 

20-40 db was achieved by 20 ft. of burial. Modest burial of a single sensor, or 

shallow burial of a small subarray, should hold most meteorological disturbances 

to permissible noise levels. 

C. Fixed Local Disturbances 

Wilson noted pumps disturbed his base level at a distance of less than 

10,000 ft. Such disturbances are quite capable of degrading our signal zone 

as depicted in Figure 9. Normal array processing can be effective only for 

that portion of the noise exterior to the signal zone. An alternative approach 

for rejecting these disturbances is offered based on the fact that the noise 

source area is coherent with the disturbance sensed by the subarray. The problem 

is schematically represented in Figure 10. 

Since the earth is a linear filter, a measurement in the neighborhood of the 

source will be completely coherent with n' (t), i.e., the unpredictability of the 1 

motion n (t) is a source attribute, not a transmission attribute. Hence a 1 

measurement at p of n (t) can remove the n' (t) contribution sensed at the 1 1 1 

subarray location p Following Levinson 2' a predictive filter can be constructed between two points even with a minicomputer. The key to the success of this 

coherent processing is that the dynamic range of the measuring system be sufficient 

to obtain an adequate representation of n (t). 1 

For the bulk of static sources, e.g., machinery, the resulting disturbance 

is narrow band. In this case a short prediction operator is adequate. Processing 

gains of 20 db should be readily attainable. 

D. Moving Sources at a Distance 

Moving seismic sources, e.g., vehicle traffic, man walking, drilling etc., 

disturb our signal band in the manner of Figure 9. Neither shallow burial nor 

arrays offer much hope of a dramatic processing gain. For this case the only 

Arthur D Little, Inc. 
Ray leigh Waves Lowest vs in area 

(locked modes) 

Lowest Velocity for Propagation 

Fundamental Rayleigh Mode 

Nonpropagating Disturbances 

(moving or time dependent loads: near field) 

FIGURE 9 SIGNAL AND NOISE ZONES EXCITED BY 

DISTANT SOURCES IN LAYERED MEDIA 

Arthur D Little Inc 
nb (t) Base Noise 

Linear Transmission 

P, (Source) 

I 

s(t) Signal 

hF = Predictive Operator 1+2 

n1 it) >> nb(t) near P, 

Note: From reciprocity the noise source and observation point can be exchanged. Such exchanges would 

provide a basis for evaluating inelastic effects at the miner's source. 

FIGURE 10 A REPRESENTATION OF A SINGLE FIXED NOISE SOURCE 

Arthur D Little. Inc 
way to ensure a S/N gain is to move the detector closer to the source and away 

from the noise. As a rule of thumb the noise of a surface noise source gives rise 

to a signal below the surface that is twice that of a point buried source. Hence 

for a detectable signal (3 = S /S ) in the far field for a common path material 

m n 

we have: 

6 (</R,) / in/^,) = 3, (8) 

i.e., a concentrated noise source at the surface, F ,must be removed a distance 

n 

equal to 6 detector distances in order to detect a miner source, F of the same m' 

strength, all else being equal. 

For the purpose of this discussion we have ignored the possibility of a signal separation in frequency due to the source character, the losses normally met 

in the surface layer caused by internal reflections, and inelasticity. Our conclusion should be on the conservative side for a deeply buried detector. Clearly, 

as the detector enters the near field of the sourcs a large enhancement in the 

-3 miner's signal occurs since wave losses in this region vary as R . E. Intra-mine Sources 

Intra-mine disturbances will produce signals in the miner's signal zone; hence 

an array processor will tend to pass them. The impact of "hard" noise sources such 

as these and seismic disturbances caused by deep drilling are difficult to assess. 

For a comparable source strength, these sources should be removed from the array 

at least three (3) times the distance of the miner in order not to interfere with 

detection. In the event that these noise sources are substantially closer, the 

base noise levels suggested here cannot be maintained. Table 2 is suggested as a 

guide for controlling noise sources to hold seismic levels near the base values 

of Figure 7. 

Arthur I3 Little Inc 
TABLE 2 

SEPARATION GUIDELINES FOR DEALING WITH MAN-MADE NOISE SOURCES* 

Type 

Light Vehicular 

Piston Aircraft 

Lone Trees and 

Telephone Poles 

(heavy wind condition) 

Drilling 

Man Walking 

Machinery (heavy) 

Intra-Mine Sources 

(miner equivalent) 

Distance Detector 

10,000 ft. 

5,000 ft. 

20,000 ft. 

5,000 ft. 

400 ft. 

150 ft 

7,500 ft. 

5,000 ft. 

1,000 ft. 

500 ft. 

10,000 ft. 

2,000 ft. 

3,000 ft. 

3,000 ft. 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Burried Array 

Single Phone 

Coherent Processing 

Single Phone 

Buried Array 

* The detector scheme and noise source-detector separation distances shown are those which should be sufficient to keep the 

disturbance of the associated noise source within the "base" 

noise levels discussed in Chapter I11 of this Part. These 

guidelines should be considered both speculative and conservative. 

Arthur D Little, Inc 
V. HIGH FREQUENCY LOW LEVEL SEISMIC NOISE 

The measurement of high frequency low level seismic disturbances will probably 

always be eventually limited by system noise due to the inherent properties of a 

seismometer (25) , its coupling to the ground(7), and the lossy character of the 

ground(2). The problem is depicted in Figure 11. 

(1) The free period of the seismometer, f (4-20 Hz), depending on 

a 

choice of seismometer. 

(2) The cutoff frequency of the seismometer due to 

ground coupling (100-300 Hz). 

(3) The cutoff frequency due to the seismometer coil inductance (10-70 x f ) 

a 

(4) Parasitic responses of the sesimometer (50-100 x f ) 

a 

Here it is assumed that the seismometer is buried at least to a depth sufficient 

to suppress direct forces on its case by other than earth motion, i.e., rain drops, 

wind loading, acoustic. A depth of burial in the range of a few feet should suffice. 

For the problem at hand the need to treat ever higher frequencies is eventually 

limited by the expected performance/cost ratio of the system. It is well known that 

the impact of horizontal layers on highly incident seismic waves is basically that 

of a low-pass filter. This loss and losses due to inelastic properties of a real 

earth serve to force us to consider "low frequency" signals even for impulsive 

sources at distances of say 1000 ft. Also as we are forced to consider frequencies 

substantially higher than 100 Hz, uniform, hard coupling of the seismometers to 

the earth becomes ever more difficult. In addition, data rates rise, and the 

useful dynamic range of any measuring sys tem is invariably bandwidth-limited . 

Comparing the reduced expectations for signals suggested by the present observations and the penalties incurred, it is recommended that the upper frequency of 

a miner's rescue system be no more than 250 Hz. 

VI. OPTIMUM ARRAY PROCESSING 

The value of optimum array processing in a general sense cannot be now assessed. However several factors mitigate against normal optimum processing. 

(1) The computational burden exceeds the limited capacity 

of a field-deployable system. 

(2) The time required to determine the covariance matrix estimates of the 

noise field appear excessive. 

(3) The nature of the noise field being of man-made origin should exhibit 

strong non-stationary properties. 

(4) The signal character over the sub-array is not well known in advance. 

Arthur D Little. lnc 
Thermal Noise 

Frequency 

fa = Free period of seismometer fa 2, (4-20)Hz depending on choice 

of seismometer 

fb = Cutoff frequency due to ground coupling, 100-300 Hz 

f, = Cutoff due to coil inductance, 2, 50 x fa 

dl ,d2 = Parasitic responses of seismometer, 2. (40-50) x fa 

FIGURE 11 THE PROBLEM OF HIGH FREQUENCY, LOW LEVEL MEASUREMENTS 

Arthur D Little Inc. 
VII. NARROWBAND DETECTION 

As stated by Greenfield in Part Ten, bandpass filtering can improve the 

signal to noise ratio when the major energies of signal and noise are separated 

in frequency. Since the response of a layered earth is sensitive to the depth of 

the source, we can anticipate on seismic grounds that the spectral content of the 

miner's signal(3) will differ markedly from the noise level spectra caused by surface sources (36). For example the Westinghouse data from the Geneva mine (Field 

Rept. 2) exhibit a signal to noise (SIN) ratio variation as a function of frequency 

which shows maxima near 45 and 150 Hz. Furthermore, the ratio is quite variable 

over the system passband; i.e., there is a large separation of signal and noise in 

frequency. 

Based on the above result, some form of narrow band envelope detection should 

be explored as a potentially valuable technique. As envisioned in this technique, 

data from each subarray would conceptually be filtered through something like 113 

octave bands. Each elementary band would then be normalized, rectified, and low 

passed with a filter having a time constant somewhat shorter than the duration 

of the miner's signal. The resulting levels would then be passed to a variable 

density, area or event, display to generate exceedence patterns. The statistics 

for this kind of narrow band signal envelope detection processing are well known. (35) 

For the miner detection problem, coincidence of threshold exceedences can 

be looked for between subarrays, Furthermore, the repetitive characteristic of 

the miner's signal can serve as the final basis for rejecting false alarms. It 

is recommended that the potential of narrow band filtering and envelope detection 

be considered using the existing data base. Clearly, its value should be compared 

with other detection schemes that are simple, well known, and easily automated. 

Arthur D Little. lnc. 
VIII . REFERENCES 

White, J.E., Seismic Waves, Radiation, Transmission and Attenuation, 

John Wiley and Sons, 1958. 

Love, A.E., A Treatise on the Mathematical Theory of Elasticity, 

Cambridge, University Press, 1927. 

Phinney, R.A., Theoretical Calculation of the Spectrum of First Arrivals in 

a Layered Elastic Media, Princeton University Report, June 1965 (Department of Geology). 

Gilbert, F., Propagation of Transient Leaking Modes in a Stratified Elastic 

Wave Guide, Rev. in Geophys 2 No. 1, Feb. 1964. 

Brackett , R., Finite Dimensional Linear Sys tern, John Wiley and Sons, 1970. 

Spieker, L., Seismometer Array and Data Processing System, Final Report 

AFTAC Project V~/077, Texas Instruments Inc., Dec. 1961. 

Kitsunezaki, C., Field-Experimental Study of Shear Waves and Related Problems, Contributions, Geophysical Institute, Kyoto University, No. 11, 

1971. 

Coal Mine Rescue and Survival System, F.Y. 1972 Annual Report* 

Westinghouse Electric Corp., ~altimore, Md., Contract H0210063. 

Crowley, F., et al., An Analysis of the Vibration Environment at ~orthrop's 

Norwood Test Facility with Application to Gyro Testing, Environmental 

Research Paper 325, AFCRL 70-0355 

Sax, R., Stationary of Seismic Noise, Geophysics Vol. 23, No. 4, Aug. 1968. 

Frantti, G. et al., The Spectrum of Seismic Noise, Bull. Seismic Soc. Am. 

Vol. 52 ill, Jan. 1962. 

Frantti, G., The Nature of High Frequency Earth Noise Spectra, Geophysics, 

Vol. 28, No. 4, Aug. 1963. 

Frantti, G., Investigation of Short Period Seismic Noise in Major Physiographic Environments of the Continental United States, Institute of Science 

and Technology, University of Michigan, AFCRL-65-406, Jan. 1965. 

Wilson, C., The Origins and Nature of Microseisms in the Frequency Range 

4 to 100 c/s, Proc. Roy. Soc. 217, 1953. 

Brune, J., and Oliver, J., The Seismic Noise of the ~arth's Surface, 

Bull. Seis. Soc. Am. Vol. 49, October, 1959. 

Bradner, et al., Study of Earth Noise on Land and Sea Bottom, University 

of California, San Diego, Institute of Geophysics and Planetary Physics, 

S & P, 1964. 

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Goforth, T. , Douze, E. , Sorrells , G. , Seismic Noise Measurements in a 

Geothermal rea, Geophysical Prospecting vol. 20, No. 1, March 1972 

Aki , K., Space and Time Spectra of Stationary Stochastic Waves with Special 

Reference to Micro-tremors, Bull. Res. Inst. Vol. 35, June 1957. 

Akamatu, K., On Microseisms in the Frequency Range from 1 c/s to 200 c/s. 

Bull. Res. Inst. Vol. 39, 1961. 

Phillips, G, and Changsheng, Wo, Study of Seismic Signals and Noise by Means 

of Buried Arrays, AFCRL-66-578, June 1966. 

Robinson, E., Statistical Communication and Detection with Special Reference 

to Digital Data Processing of Radar and Seismic Signals, Charles Griffin and 

Co. Ltd. 1967, London. 

Bradford, J., et al., Weather-Seismic-Noise Correlation Study, United Electrodynamics Mc. , July, 1964, AFCRL 64-607. 

Bendat, J., and Piersol, A,, Measurement and Analysis of Random Data, John 

Wiley and Sons, 1958. 

Armstrong, B. , Acoustic Emission Prior to Rock Bursts and Earthquakes, Bull. 

Seis. So. Am. Vol. 59, No. 3, June 1969. 

Byrne, C., Instrument Noise in Seismometers, Bull. Seis.So. Am. Vol. 51, No. 1 

1961 

Sage and Melsa, Sys tem Identification, Academic Press, 1971, New York. 

Zienkiewicz and Cheung, The Finite Element Method in Structural and Continuum 

Mechanics, McGraw Hill, 196 8. 

Bennet, W., Spectra of Quantized Signals, Bell Systems Tech. Journal 27(3), 

1948. 

Stratonovich, R., Topics in the Theory of Random Noise, Gordon and Breach, 

1963, New York. 

Sneddon, Fourier Transforms, McGraw Hill, 1951. 

Robinson, E., Seismic Arrays for the Detection of Nuclear Explosions, 

Mass. Inst. Tech. June, 1964, AFCRL 64-885. 

Landers, T., and Claerbout, J., Effects of Thin Soft Layers on Body Waves, 

Bull. Seis. Soc. Am. Vol. 59, No. 5, 1969. 

Crowley, F., On the Application of Air Coupled Seismic Waves, Environmental 

Research Paper 302, AFCRL 69-0312, July, 1969. 

Backers, G., and Gilbert, F., Constructing P-Velocity Models to Fit Restricted 

Sets of Travel Time Data, Bull. Seis. Soc. Am. Vol. 59, No. 3, June 1969. 

Davenport, W., and Root, W., Random Signals and Noise, McGraw Hill, 1958. 

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36. Spencer, T., et al., Theoretical Studies Related to the Determination of Seismic 

Energy Source Depth, California Research Corporation, La Habra, California, 

July 1964, Contract AF19(604)-8344, Flnal Report. 

37. Shima, E., et al., S Wave Velocities of Subsoil Layers in Tokyo, Bull. Earth 

G. Inst. 46, 1968. 

38. Watkins, J., et al., Dependence of In-situ Compressional Wave Velocity on 

Porosity in Unsaturated Rocks. Geophysics, Vol. 37, No. 1, Feb. 1972. 

39. Clark, S., Handbook of Physical Constants, Geological Soc. of Amer. Memoir 

97, 1966. 

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PART TEN 

SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

Arthur D Little Inc 
PART TEN 

SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

TABLE OF CONTENTS 

List of Tables 

List of Figures 

I. SUMMARY 

11. BRIEFDESCRIPTION OFTECHNIQUES 

A. LINEAR PHASE FILTERING OF MULTICOIPONENT 

DATA 

B. REMODE 

C. DELAYED SUM 

D. WEIGHTED DELAY AND SUM 

E. MULTICHANNEL MAXIMUM LIKELIHOOD ARRAY 

PROCESSING 

F. MULTICHANNEL WEINER FILTERING 

G. SINGLE CHANNEL BANDPASS FILTERING 

H. SINGLE CHANNEL PREDICTION ERROR FILTERING 

I. MULTICHANNEL PREDICTION ERROR FILTERING 

J . MATCHED FILTERING 

K. DESIGN OF SUBARRAY CONFIGURATION 

L. BURIAL OF SENSORS 

111. SIGNAL PROCESSING FOR DETECTION OF A MINER 

A. SIGNAL-TO-NOISE IMPROVEMENT ON THE INDIVIDUAL 

SENSOR LEVEL 

B. SIGNAL PROCESSING AT THE SUBARRAY TERMINAL LEVEL 

Page 

10. iv 

10.v 

10.1 

10.2 

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PART TEN 

SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

TABLE OF CONTENTS 

(Continued) 

C. DETECTION PROCESSING ON THE FULL ARRAY LEVEL 

IV. SIGNAL PROCESSING EFFECTS RELATED TO LOCATION 

V. REFERENCES 

10. iii 

- Page 

10.10 

10.11 

10.15 

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PART TEN 

Table No. 

1 

SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

LIST OF TABLES 

Title 

Comparison of Arrival Times 

Page 

10.13 

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Figure No. 

PART TEN 

SIGNAL-TO-NOISE RATIO IMPROVE'hlENT TECHNIQUES 

LIST OF FIGURES 

Title 

Effect of Direct Summing on Waveform 

Comparison of a Seismic Signal Before and 

After Passin& Through the Westinghouse 

Matched Filter 

Page 

10.12 

Arthur D Little, lnc 
PART TEN 

SIGNAL-TO-NOISE RATIO IMPROVEMENT TECHNIQUES 

Roy Greenfield 

Pennsylvania State University 

I. SUMMARY 

During the detection phase, several procedures can be used to improve the 

signal-to-noise ratio (SIN) . 

6 Subarrays of up to 10 seismometers should be used. The apparent 

failure to obtain improvement in SIN in the Westinghouse subarrav 

work is probably due to excessive noise in the electronics. The 

spacings needed for sensors in the subarray must still be established. 

The sensors should be buried. Even burial to a few feet will probably 

give appreciable reduction of noise. A deeper burial will probably 

further reduce the noise; and, if the seismometers can be put below 

the weathered layer, the signal level will probably be increased. 

The reduction in noise by burial will be especially effective during 

high noise periods due to wind or rain. 

Before attempting detection, the waveforms should be bandpass filtered. 

The bandpass should go from 25 Hz to an upper frequency of 100 to 

200 Hz. Further measurements with a low noise system must be done 

before the signal-to-noise ratio can be determined for the 100 to 

200 Hz range. Any narrow band noise should be removed by notch 

filters . 

If noise levels differ among seismometers of a subarray, weights 

inversely proportional to the noise power should be applied to the 

seismometers. 

6 Automatic methods of screening data for possible signal arrivals 

should be developed, but the final determination that the signal on 

a subarray output appears to be from a miner should be made by an 

analyst. Detection of "signal" on several subarrays should be 

required for positive identification. 

In the location phase, after detection: 

If repeated signals are received, they should be coherently added 

(stacked) to give as good a SIN as possible for use in determining 

signal arrival times, to be used in location computations. The miner 

should, if possible, repeat the signal 25 to 50 times. 

Arthur I2 Little. lnc 
It is probably not worth the increase in system complexity to implement 

such complex signal processing methods as mult i-channel maximum likelihood 

filtering, linear particle filtering, or prediction error filtering. These 

will probably not give much signal- to-noise improvement. Matched filtering 

does not compress the body wave signals in time, and thus will not improve 

system performance any more than any suitable bandpass filter. 

11. BRIEF DESCRIPTION OF TECHNIQUES 

A. Linear Phase Filtering of Multicomponent Data [ 1 ] 

The vertical component of a seismometer is added to a time shifted version 

of the horizontal component. With proper time shift this processing can accentuate a linearly polarized P wave arrival while suppressing eliptically polarized 

Rayleigh surface wave noise. 

B. Remode [2] [3] [41 

A nonlinear method to accentuate linearly polarized portions of single 

sensor 3-component seismic data. 

C. Delayed Sum 

The output of each of a group of seismometers is delayed so that signals 

traveling at a selected horizontal phase velocityare added coherently. Note 

that the presently used system of subarray addition is a special case of delayed 

sum with zero delay between channels. Noise which is uncorrelated is reduced 

by a factor of 1/N in power where N is the number of seismometers. Coherent 

noise with phase velocities different from the direction at which the subarray 

is aimed is also reduced; the amount of reduction depends on the subarray 

pattern. 

D. Weighted Delay and Sum 

This processing is similar to delayed sum processing, but amplitude weighting of the channels is designed to maximize the suppression of coherent noise. 

The weights for this processing can be adaptively designed [ 51 to optimize 

suppression of a time varying noise field. The method is also useful if the 

noise level is unequal among channels. 

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Arthur DLittl Inc. 
E. Multichannel Maximum Likelihood Array Processing [6 ] [ 7 ] 

The seismometer outputs are first time aligned for the horizontal phase 

velocity of the signal. Then an individual filter is applied to each channel. 

This processing is designed to operate where the signal is the same on each 

channel. Filter design requires extensive digital computation, and the 

filtering aperation itself is costly in computer time. This form of processing 

can give large S/N improvement when a wideband signal is to be examined and 

coherent noise is present. 

F. Multichannel Weiner Filtering [8 ] 

This form of processing is similar to multichannel Maximum Likelihood 

Processing; however, the filters are designed for a signal modeled as a stationary multidimensional random process. 

G. Single Channel Bandpass Filtering 

Bandpass filtering can improve S/N if the major energies of the signal and 

noise are separated in frequency or if the signal is of narrower band than the 

noise. 

He Single Channel Prediction Error Filtering [9 ] 

A filter is designed based on the noise to predict the noise ahead in time. 

The predicted noise is subtracted from the seismometer output, reducing the 

noise at the output of the filter. At the commencement of the signal the filter 

does not attenuate the signal, so the S/N ratio can be improved. This type of 

filter works best when the noise is fairly narrow band, so the filter can do 

a good job of noise prediction. 

I. Multichannel Prediction Error Filtering [ 10 ] 

The noise on each channel is predicted by applying filters to the noise on 

all the channels. This noise is subtracted from each channel and a trace produced 

for each channel. When the noise field is coherent between the channels, this 

procedure can give better noise reduction than the single channel prediction error 

filter. 

J. Matched Filtering [ 11 ] [ 121 

If the signal waveform is known, a matched filter can compress in time a 

dispersed waveform by removing the dispersion effect, and thus give an improveprovement of S/N equal to the time bandwidth product. The matched filter is 

implemented by convolving the signal with a filter whose response is that of 

the known waveform. In addition,the application of a matched filter acts as 

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a bandpass filter, and thus gives an additional S/N improvement by rejecting 

out-of - signal-band noise. 

K. Design of Subarray Configuration [13] [14] 

A configuration of seismometers has a frequency dependent array response 

pattern. In areas of coherent noise the placement of sensors can be such as to 

put a low part of the beam response at the horizontal phase velocity of the noise. 

Spacing of the sensors far enough apart so the noise appears incoherent leads 

to a 1/ reduction in noise amplitude, where N is the number of seismometers 

in the subarray. 

L. Burial of Sensors [15] [16] [17 1 

If noise is composed of Rayleigh waves the noise amplitude falls off with 

depth; burial of sensors can lead to a decrease in noise amplitude. If noise 

is due to transient surface loading near the seismometer and has a certain correlatior, 

distance, then the noise level will also fall off with depth. 

111. SIGNAL PROCESSING FOR DETECTION OF A MINER 

Detection of a trapped miner by seismic means requires that the presence of 

a signal is identified in the presence of ambient background noise, and that this 

signal may be identified as the efforts of the miner. In this detection section 

we first consider what can be done on the subarray and individual sensor to improve SIN, then discuss how to use the subarray outputs to detect the miner's 

presence. 

A. Signal-to-Noise Improvement on the Individual Sensor Level 

Filtering methods which could be considered for application to a single 

skismometer output include Remode, Linear Phase Filtering of Multicomponent 

Data, Bandpass Filtering, Single Channel Weiner Filtering, Single Channel 

Prediction Error Filtering, and Matched Filtering. We now cemment on the 

usefulness of these various methods. 

1. Remode - This type of processing will not be useful for several reasons. 

First it must be designed and applied digitally. For application to 50 sensors 

at a sampling rate of 500 to 1000 samples per second the conlputation load would 

be far too large and not practical. Secondly the filter is designed on the 

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in-phase property of the P wave on the horizontal and vertical seismometers. 

From Westinghouse data, it appears that the arriving P wave is almost completely 

linearly polarized, but in the vertical direction, i.e., no horizontal (see 

Plot 49, Westinghouse Field Report No. 8).* Because of this, the Remode filter 

design would not work for P waves. However, it might work on part of the later 

arrivals. The reason for the vertical polarization is believed to be caused by 

the ray being bent toward the vertical as it traverses the low velocity material 

normally near the surface. Thirdly, it has not been established that the ambient noise is elliptically polarized as for a Rayleigh wave. Fourthly, implementation requires addition of horizontal sensors to each channel. 

2. Linear Phase Filtering of Multicomponent Data - This type of filter 

might improve the SIN ratio, by subtracting a properly phase-shifted version 

of the horizontal from the vertical record. This could remove some of the 

elliptically polarized noise from the vertical. It is rather hard to estimate, 

without implementing the filtering on actual data, how well it will work. However, if the noise is predominantly Rayleigh wave from one direction, this 

method could work where Remode does not. This type of filtering could be done 

with analog equipment. Again, it would be required to have horizontal as well 

as vertical sensors. 

3. Bandpass Filtering - Most of the signal energy is below approximately 

200 Hz, and for many of the signals, it is below 100 Hz. (See Figures 2-11, 

2-12, 2-13 of the Westinghouse Fy '72 Report.)* Westinghouse data suggests 

that significant seismic noise energy may exist out to frequencies of 500 

Hz or more (see Figures 2-7, 2-8, 2-9). However, its contamination by 

electronic system noise lowered our confidence that the data really shows 

the presence of high frequency seismic noise. If the high frequency noise 

shown by Westinghouse is indeed seismic noise, bandpass filtering can 

increase the signal-to-noise ratio. Judging from these figures, the noise 

could be reduced by 3 to 6 db by low-pass filtering below 100-200 Hz with 

no significant loss of signal power. If signal detection is done by an analyst 

looking at clear records, he will do some bandpass filtering by eye so the lowpass filtering will not gain much. However, if detection is done by automatic 

threshold detection or by looking at a very compressed time scale visicorder 

record, it is imsortant to remove the high frequency noise. The optimum cutoff 

* Westinghouse Contract H0210063 with Bureau of Mines. 

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frequency will depend on noise spectra and an estimation of the signal spectra 

expected from the undetected signal. In any given situation a combination of 

theory and experimental data will allow us to estimate the signal spectra. In 

general*longer travel paths will lower the average frequency of the signal. It 

is clear from the Westinghouse results that at some mines narrow band noise sources 

are present. In such circumstances a notch (or narrow band rejection) filter 

should be used. Such filters can probably best be implemented with analog 

equipment. 

4. Matched Filtering - Matched Filtering can give an improvement in SIN by 

compressing the energy of a dispersed waveform in time or by simply acting as 

a bandpass filter. Work was done by Westinghouse to evaluate matched filter 

performance. The filter clearly gives a significant S/N improvement. (see 

Figures 5 and 6,Appendix E of Westinghouse Report.)* However, the time-bandwidth 

product of the signal is not great and the matched filter does not seem to cornpress the signal in time. Therefore, it appears that the signal-to-noise improvement obtained by the matched filter is a result only of its bandpass filter 

characteristics. (The filter used does seem to be a reasonable bandpass filter 

to use.) It does not appear to predict the signal shape well enough to design 

a true matched filter, and it does not appear that the signal is dispersed sufficiently to warrant the attempt. 

5. Single Channel Prediction Error Filtering - This type of filtering is 

most useful when the noise is fairly narrow banded. Then it is able to predict 

the noise ahead fairly well and subtract it from the trace. The spectral data 

show that the noise is wideband and thus it would not be expected that prediction error filtering could make a large s/N improvement. When tried by Westinghouse the Prediction Error filter provided essentially no improvement (see 

Westinghouse Fy '72 Report, Appendix E, page 29). * 

6. Burial of Sensors - Large S/N improvement may be possible by burying the 

sensors. Very little information seems to be available in the literature for the 

frequency range of 30 to 200 Hz. (I also spoke to several people in exploration 

seismology and was told that because of time and costs, they do not normally bury 

geophones.) At the much lower frequencies of 1 to 5 Hz burial of a few hundred 

feet can give noise reductions of 20 to 40 db. (Seriff, A.J., et. al., Seismic 

Noise in Deep Boreholes, Contract No. AF 19 628-2785, Shell ~evelopment Co., 

Houston, Texas, June 21, 1965.) 

* Ibid. 

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The noise reduction is greater on windy days. Since the surface noise 

level is high on windy days, even greater S/N gain can be obtained under this 

condition. 

The amount of S/N gain obtainable by burial under various noise conditions 

cannot be estimated because we presently have no data on the spatial coherence 

or the depth variation. The theoretical discussion in the Westinghouse Report, 

Appendix C, discusses some of the possible reasons for the decrease in noise 

level. It is unfortunate that the experimental program discussed in Appendix C 

was terminated before data could be analyzed. Before any estimate can be made 

of S/N improvement, data must be analyzed to get empirical noise reductions and 

to get the spatial structure of the noise field. If the Westinghouse data is 

available, examination may allow some estimates of S/N improvements as a function 

of depth of burial. The only available results are from Section 11-4.4 of the 

Westinghouse Report. Here noise reduction of 19 db at 30 Hz; 44 db at 100 Hz; 

and 55 db at 250 Hz were obtained for a seismometer in a 23-foot borehole relative 

to a surface seismometer. The data is from the USBM Safety Research Mine, and is 

for data taken during a hard rain (see Figure 2.4-4, Westinghouse Report).* 

addition there are indications (see Part Two, IV) that below a surface alluvium 

layer the signal may be of considerably higher amplitude than at the surface. 

It is also indicated that the energy spectra is shifted to higher frequencies 

for a seismometer below the alluvium. So it is clear that effects on the signal 

as well as noise reduction resulting from burial should be studied. The 

experimental and theoretical approach should be combined. 

The range of depths which should be studied in the program should extend 

to as great a depth as it might be feasible to implant seismometers after a mine 

accident. If it is feasbile to lower or pre-place seismometers in the coal 

seams, the signals and noise levels in seams should be studied. 

I will not at present make a complete discussion of the signal effects of 

burial. However, there are some conditions under which the signal may also be 

reduced in strength with burial which should not be overlooked. For example, a 

sinusoidal P-wave, vertically incident upon a perfectly reflecting interface in 

a lossless medium can produce a vertical standing wave pattern whose amplitude 

is given by A cos [2nfz/Vp], whre z is depth. For f=100 Hz, and V =2000 ft/sec, 

P 

the first null of this standing wave pattern will occur at z=5 ft. 

* Ibid. 

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B. Signal Processing at the Subarray Terminal Level 

1. Delayed Sum Processing - This type of processing can give gains of 1/N in 

power (N is number of sensors in the subarray) for 'random' noise, and a gain 

depending on the beam pattern for coherent noise. Signal loss, because of 

differences in signal shape must be considered also. 

Let us assume that the traces are time aligned so the signals of interest 

add. The delayed sum output is 

where fi (t) is the individual sensor output. If the noise of total power,Pin, is 

composed of a coherent fraction C (in power) then the fraction of noise power 

which is incoherent is (1-C). (We caution that the coherent portion of noise 

depends on the sensor spacing. For example all noise will appear coherent if 

sensors are close together, and all noise will appear incoherent if the sensors 

are moved far enough apart.) If the beam response of the subarray reduces the 

coherent noise power by a factor of G then the noise on the output is 

If the subarray is large enough the noise reduction will always go to 1/N in 

power. Failure to obtain 1/N gain is only an indication that the noise is 

coherent to some extent. The Westinghouse experience with subarray summing 

is not representative of the improvements that can be achieved with this technique. 

Measurement of the noise spatial coherency [ 131 between sensors as a function of separation can be used to decide the necessary separation between sensors to get close to 1/N noise reduction, larger coherence distances demanding 

larger separations. The data taken to date above coal mines is insufficient 

to form a basis upon which I can make a recommendation of subarray element 

spacing, because the subarray design nust reflect the noise field encountered 

there. 

There is another consideration if the distance over which the noise is 

coherent forces us to a large diameter subarray. If the array is not small 

* References to Figures, Table, and Equations apply to those in this Part unless 

otherwise noted. 

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compared to the signal horizontal wavelength, signal amplitude decreases and 

distortion will occur unless the subarray is steered toward the signal. Let 

us assume that we form the sum with no time delays for a signal of 10,000 ft/ 

sec horizontal phase velocity, and frequency of 100 Hz. Typically an array with 

seismometers within a circle of diameter d will have less than 3 db signal reduction if < 0.25. Thus d could be as great as 25 ft. for less than 3 db v 

n signal loss. In the detection mode, we do not know the direction and horizontal phase velocity of the signal. If it were necessary to go to a larger 

subarray diameter, or if the horizontal phase velocity were less than 10,000 

ft/sec, it might be necessary to form a few delayed sum beams, perhaps 5 at 

each subarray, in order to prevent excessive signal loss. This type of processing can be implemented with analog equipment. 

2. Weighted Delay and Sum - If the noise is unequal and uncorrelated on the 

seismometers of a subarray, then unequal weight will give a greater noise reduction than equal weighting. This type of weighting is called Brennen combining. 

If the noise is in the main coherent and coming from a small number of fixed 

sources,unequal weightings of the seismometers can be used to shape the subarray 

beam to reject the coherent noise. This type of processing can probably be implemented with analog equipment. [I81 

3. Subarray Configuration - If the noise is in the main propagating at a 

single velocity, such as the Rayleigh wave velocity, proper construction of the 

subarray geometry may produce an important noise reduction. Namely, the diameter 

of the array can be chosen to give a near null at the Rayleigh wave velocity. 

This has been well discussed in the Westinghouse Report. We note that in practice it may be inconvenient to first set up sensors to determine noise properties, 

then redeploy the sensors to give a better subarray beam pattern. 

4. Methods of Multichannel Filtering - It was suggested in Appendix E of 

the Westinghouse Report that complex signal processing methods might be useful. 

Such methods include Multichannel Maximum Likelihood, Multichannel Weiner, and 

Multichannel Prediction Error Filtering. I will not go into detail; however, I 

do not feel these methods would be appropriate for subarray or full array application. These methods require for S/N improvement that the noise be highly 

coherent and time stationary, that the signal be highly coherent between sensors, 

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and that the gains on the various channels be carefully matched. It is probable 

that some or all these conditions will be violated. These methods require a 

very large computing facility for the sampling rate under question. 

5. Repetition of Source Blows - Summation of repeated source blows will always 

reduce the noise power by 1/~. This was borne out in westinghouse's work. They 

also showed that when the traces could be properly time aligned no significant 

signal loss occurred. It was also shown that if the traces could not be properly 

aligned some signal loss occurred, so the S/N gain was not as great as N in power. 

(See Figure I1 2-15, Westinghouse Report.) 

In the detection mode if the miner's signal has not been identified on any 

channel, it will not be possible to time align successive signals for S/N 

improvement. Thus the measurement of S/N gain will not be available when needed 

most. However,if a signal is seen at intervals on a single subarray output the 

method can be used to determine if the signal is on other subarray outputs. This 

could be useful to verify that the signal on the best channel is in fact due 

to a signaling miner and not to some unimportant signal source, such as a banging 

door, near the one subarray. 

C. Detection Processing on the Full Array Level 

We start with the signal outputs from the separate subarrays. I do not think 

that any sort of multichannel filtering will be useful for combining the subarray 

outputs. It will be found, I'm sure, that the noise is incoherent between subarrays. Even simple delay and sum processing will not be practical. There 

could be as much as 200 ms. delay between subarray arrival times. This delay 

is not known before detection. To coherently sum sensors with 100 Hz energy they 

must be properly aligned to within 1 m sec. or better. Thus there are 200 possible relative delays between each pair of subarray outputs. It is clear that 

delay and sum would impose an impossible computational load. 

In the detection mode the array processor must handle a great deal of data. 

If the processing is done digitally a sampling rate on the order of 1000 samples/ 

sec per subarray is needed. Thus 7000 samples per sec are coming in. Thus it 

is probable that the signal processing for detection must be fairly simple. The 

most reasonable way to detect the miner is to use a criteria that a signal be 

detected on several subarrays within some time window representing the estimated 

travel time differences between the subarrays. This will be useful if the S/N 

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is not much greater on one of the subarrays than on the others. By use of this 

'coincidence detection' ,a detection can be made at a lower signal threshold for 

a fixed 'false alarm' rate than would be possible for a sirigle subarray. 

The threshold that should be used for a detection on each subarray signal 

should be set at 3 times the RMS noise level on that channel. If the noise 

level is not time stationary, the level should be set by, for example, setting 

the threshold at 3 times the RMS noise level over the last 30 seconds. (Geotech 

and Lincoln Laboratories have done extensive work on detection criteria for 

nuclear detection.) 

As possible signals are detected, the data for these detections should, of 

course,be saved for use in the location process. 

IV. SIGNAL PROCESSING EFFECTS RELATED TO LOCATION 

After a miner has been dete~ted~portions ofthe data containing signals 

can be reprocessed to improve arrival time estimates. The summing up of repeated 

source blows is useful for improving signal to noise. 

The summing up of the seismometers of a subarray improves SIN. However, if 

direct sum with no delays is used,then some slight signal distortion can occur 

since the signals are added with slight misalignment. A simple sketch of this 

effect is given in Figure 1. This summing will in general make the first break 

somewhat less sharp and will distort the waveform slightly. The arrival time 

reading error which could result might be on the order of 2 ms. It is difficult 

to say if the noise reduction would compensate for this. The magnitude of the 

signal distortion will increase as the size of the subarrays are increased. One 

means of alleviating this effect would be to put in a delay line for each seismometer after the approximate location is found. This would align the traces in 

the subarray sum. 

The matched filter proposed in Appendix E*has some advantage. The S/N ratio 

is improved. However, as stated previously this is due to the bandpass filtering 

effect whereby the filter removes high frequency noise. The matched filter does 

not get SIN improvement by compressing a dispersed wave train. Filtering by the 

filter constructed in Figure 3 of the Westinghouse Fy '72 Report, Appendix E, 

changes the signal waveform. Here the signal distortion is not great, as shown 

* Westinghouse Fy '72 Report, Contract 

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Wave Direction- 

+ 10'- 

Geophones @ @ 8 

1 2 3 

Time ,-t 

FIGURE 1 EFFECT OF DIRECT SUMMING ON WAVEFORM 

Arthur D Little, Inc. 
in Figure 2. Howeveq an example taken from [ll] shows how a slightly different 

matched filter can change the output waveform and reverse polarization. One 

set of Westinghouse data was available to determine how time picks on the unfiltered data compared to the picks made on matched filtered data. In Appendix 

E arrival times were picked on match filtered data, (Appendix E, Table 1). 

The analvst's time picks on this data, before matched filtering, were found 

on the input to the computer location program in Field Report No. 4.* For both 

setsof time picks we calculated the arrival times relative to channel 6. 

(Only four channels were picke.d in Appendix E.) Table 1 shows the comparison. 

Channel 

Number 

1 

Difference 

TABLE 1 - COMPARISON OF ARRIVAL TIMES 

- A-T - A-T 

Matched Filter Signal Field Report 4 

16.25 m. sec. 12.8 m. sec. +3.4 m. sec. 

10-30 m. sec. 9.7 m. sec. 1.6 m. sec. 

14.25 m. sec. 16.3 m. sec. -2.1 m. sec. 

Thus we feel that the time picks from the matched filter output may be 

in error on the order of 2 m. sec. This is to be contrasted to the RMS scatter 

of time picks on the matched filtered data of from 1.00 to 0.71 m. sec. (ms) 

given in Westinghouse, Appendix E. 

In general, except in very high signal to noise situations where first 

breaks can be seen, an error of 1 or 2 ms will probably have to be tolerated. 

However, if a half cycle is missed, this will introduce approximately a 10-15 

ms error. Data processing should probably concentrate on methods to avoid 

this missing of a half cycle. In particular it may be helpful to determine the 

polarization to be expected at each site when we have a rough fix on the source 

location. 

* Westinghouse Contract H0210063. 

Arthur D Little. lnc 
Channel 7 

Channel 6 

Channel 5 

Channel 2 

Channel 1 

(From Figures 5 & 6 of Appendix E of Westinghouse Report) 

- Raw Trace 

-- Matched Filtered Trace 

FIGURE 2 COMPARISON OF A SEISMIC SIGNAL 

BEFORE AND AFTER PASSING THROUGH 

THE WESTINGHOUSE MATCHED FILTER 

10.14 

Arthur D Little, Inc. 
V . REFERENCES 

1. Mercado, E.J., Linear Phase Filtering of Multi Component Seismic 

Data, 33, 926, 1968 

2. C.B. Archambeau, E.A. Flinn, and D.G. Lambert, "Detection, Analysis, 

and Interpretation of Teleseismic Signals 1. Compressional Phases From 

the Salmon vent ," J. Geophys . Res. , Vol. 71, pp. 3483-3501, July, 

1966. 

3. C. Mims and R. Sax, "Rectilinear Motion Detection (RE-MODE)", Teledyne, 

Inc., Alexandria, Va., Seismic Data Lab Report 118, March 1965. 

4. C.B. Archambeau and E.A. Flinn, "Automated Analysis of Seismic Radiation for Source Characteristics ," proceedings of the IEEE, Vol. 53, pp. 

1876-1884, Dec. 1965. 

5. Lacoss , R.T., Adaptive Combining of Wideband Array Data for Optimal Reception, IEEE Geoscience Electronics, GE-6, 78-86, 1968. 

6. J. Capon, R.J. Greenfield and R.T. Lacoss, "~ong-Period Signal Processing results for the Large Aperture Seismic Array," Geophysics, Vol. 34, 

pp. 305-329, June 1969. 

7. J. Capon, R.J. Greenfield, R.J. Kolker, and R.T. Lacoss, "Short-Period 

Signal Processing Results for the Large Aperture Seismic Array", Geophysics, Vol. 33, pp. 452-472, June 1968. 

8. Backus, M.M., J.P. Burg, R. Baldwin, and E. Bryan, Wideband Extraction 

of Martle P Waves from Ambient Noise, Geophysics, 29, 672-699, 1964. 

9. Wiener, N., "Extrapolation, Interpolation, and Smoothing of Stationary 

Time Series", MIT Press, Cambridge, Massachusetts , 1949. 

10. Clairbout , J .F. , Detection of P Waves from Weak Sources at Great Distances, Geophysics, 29, 19 7 , 1964. 

11. Capon, J., R.J. Greenfield, and R.T. Lacoss, Long Period Signal Processing Results for the Large . &~erture Seismic Array, Geophysics, 34, 305- 

329, 1969. 

12. Alexander, S.S., and D.B. Rabenstine, Detection of Surface Waves from 

Small Event at Teleseismic Distances, Seismic Data Lab, Report 175. 

13. J. Capon, R.J. Greenfield, and R.T. Lacoss, "~esign of Seismic Arrays 

for Efficient On Line Beamf orming , " Lincoln Laboratory Technical Note, 

1967-26, 27 June 1967. 

Arthur D Little. Inc 
Arthur D Little, lnc 
PART ELEVEN 

SEISMIC DETECTION/LOCATION INSTRUMENTATION 

Arthur D Little, lnc. 
PART ELEVEN 

SEISMIC DETECTION/LOCATION INSTRUPENTATION 

TABLE OF CONTENTS 

List of Figures 

I. INTRODUCTION 

11. WESTINGHOUSE SURFACE SYSTEM 

A. SEISMIC DETECTION SUBSYSTZM 

B. SIGNAL CONDITIONING SUBSYSTEM 

C. SIGNAL PROCESSING SUBSYSTEM 

D. LOCATION PROCESSING SUBSYSTEM 

111. SYSTEM MODIFICATION 

IV. SYSTEM SPECIFICATIONS 

V. SUGGESTED SYSTEM CONFIGURATION 

A. SEISMIC DETECTION SUBSYSTEM 

B. SEISMIC SIGNAL PROCESSING AND LOCATION SUBSYSTEK 

VI . DEPLOYMENT 

- Page 

11. iii 

Arthur D Little. In 
PART ELEVEN 

SEISMIC DETECTION/LOCATION INSTRUMENTATION 

TABLE OF FIGURES 

Figure No. Title 

1 Present Seismic System (Floor Plan) 

2 Equipment Layout (Present System) 

3 Block Diagram (Present System) 

4 Suggested Seismic Detection Subsystem 

5 Suggested Trailer Van Signal Processing and 

Location Subsystem 

- 'Page 

11.3 

11.4 

11.5 

11.10 

Arthur D Little, Inc. 
PART ELEVEN 

SEISMIC DETECTION/LOCATION INSTRUMENTATION 

Arthur D. Little, Inc. 

I. INTRODUCTION 

The instrumentation specification in the National Academy of Engineering 

(NAE) report of March, 1970, set forth some rather general guidelines that the 

seismic surface system should follow. The fact that there was no comparable 

equipment in existence at that time, and the need to produce a system from 

presently available equipment, was spelled out in that document. 

The features that the system should include were listed, and included: 

Quick and simple deployment 

Portability 

Battery-powered operation 

All-weather operation 

Computational simplicity and speed 

High reliability and long shelf-life 

Dual service for location and communication 

Adaptability to widely varying seismic velocities, 

topography, and geologic structures 

Minimum maintenance 

Capability of continuous operation for extended 

periods, and 

Reasonable cost 

Since that report, there has been a substantial amount of field work 

addressing the trapped miner detection and location problem carried out by 

Westinghouse Corporation under contract with the Bureau of Mines. Two complete 

surface systems have been designed, built, and field tested and substantial 

documentation has been produced on the mine environment and background noise 

using these systems. These systems, built from off-the-shelf equipment, have 

been designed with maximum flexibility in mind in order to explore what configuration a field unit should have. 

Arthur D Little. Inc 
This Bart reviews the Westinghouse surface system, reviews the 

general system specifications in light of present experience, and describes 

in some detail a recommended system configuration that attempts to meet all 

the requirements of a truly fieldable system. 

11. WESTINGHOUSE SURFACE SYSTEM 

-I- Two complete surface systems were built by Westinghouse on contract with 

the Bureau of Mines. Since the fabrication of these systems, a substantial 

amount of field experience has been gained with these units in actual test 

measurements at a number of working mines in the United States. Improvements 

and modifications have been made to the original system as field experience 

has dictated. 

The present system is housed in a portable van that can be transported 

either by a companion 4 x 4 truck to which it is normally attached or via plane 

(e.g., a C-47). The instrumentation is self-contained except for primary power 

and telephone service. Geophones and cables for the array are stored inside 

compartments for easy accessibility. The power signal and telephone connections 

to the van are made via clearly marked terminal jacks. For field deployment, 

the system comes with a second truck to transport a portable 6" drill, spare fuel, 

and a primary power generator. 

The van floor plan showing storage room and equipment layout is shown in 

Figure 1.* The instrumentation and computer system are centrally placed to balance 

the van for ease of loading and transport. Figure 2 shows the present equipment 

layout and jackfield location. The use of multiple jackfields, allows for maximum 

patching flexibility but does require the operator to be careful in setting up 

the patching arrangement. The use of commercial equipments throughout tends to 

provide more gain controls than may be required on a field system. 

A block diagram of the complete system is shown in Figure 3. The system 

can be subdivided into four subsystems: 

1. Seismic detection; 

2. Signal conditioning; 

3. Signal processing; and 

4. Location processing. 

Contract H0101262 with Bureau of Mines. 

* References to Figures, Tables, and Equations apply to those in this Part 

unless otherwise noted. 

11.2 

Arthur D Little, Inc 
Teletype 

Terminal 

FIGURE 1 PRESENT SEISMIC SYSTEM (Floor Plan) 

Arthur D Little. lnc. 
ll. 4 

Arthur D Little, Inc 
Arthur D Little. Inc 
visual display and/or processing. Processing of the data can be achieved by 

either varying the filter bandwidth with the Krohn-Hite filter bank, or by 

processing the signal in the CSPI data processing system for gain enhancement. 

The CSPI system using the Varian Data 620 i computer can perform fast Fourier 

transforms on incoming signals or noise, and play out power density spectra 

on the x-y plotter. On repetitive seismic signals, the computer is programmed 

to do signal stacking giving a gain enhancement and signal-to-noise improvement 

over background noise. In the signal stacking mode the oscilloscope trigger 

circuit is used to detect the signal arrival on one channel and trigger the 

sampling gate of the computer for the other channels. Two channels at a time 

are treated in this way. Each channel can be displayed on the x-y recorder for 

comparative analysis of first arrival times. 

D. Location Processing Subsystem 

The present location processing subsystem as shown in Figure 3 is not located 

on-site with the other system. The crew chief now uses the telephone to send 

Arthur D Little, Inc 
first arrival time data, estimated on-site by viewing all seven channels on 

the play out of the x-y recorder or the Visicorder. A resident location program called MINER is used in a remote time-share computer to compute the estimated 

signal source location based on array arrival time data. 

111. SYSTEM MODIFICATION 

The Westinghouse system described above has provided a substantial insight 

into the system and fieldability problems that are encountered in deploying such 

a unit and making practical field measurements. Some major modifications were 

incorporated into the Westinghouse system as deficiencies in system performance 

were identified. The preamplifiers and the high gain amplifiers were replaced 

along with the tape recorder. 

Present modifications now in process call for an increase in memory capacity 

of the CSPI processing system. The present capacity of 8,000 16-bit binary words 

will be expanded to 20,000. This will reduce signal processing Yime substantially 

and reduce corrective maintenance time. The number of input channels to the computer will be increased from two to eight to reduce the analysis time. 

In the signal detection subsystem, current plans call for a change in the 

present parallel geophone arrangement to a series connection and a new transformer 

in the preamp to match the new geophone connection. This will improve the 

sensitivity of the subarray. 

A high speed paper tape reader will be used with the computer expanded memory 

to increase the operating efficiency. Additional amplifiers and filters will be 

added to interface the tape recorder to the computer. 

In summation, the above modifications are designed to expand processing 

capacity, reduce processing time, and improve system sensitivity. 

IV. SYSTEM SPECIFICATIONS 

The specifications listed above in Section 1, as spelled out in the NAE report, 

are still a valid set of specifications. However, in view of the experience 

gained in the interim period, a more detailed set can now be made covering the 

seismic surface instrumentation. 

Quick and simple deployment can be specified in relation to deployment by 

any common means of transport. This is related to the availability of the transportation, and requires a somewhat differe~~t packaging concept than used up to now. 

It relates to portability; where the packages could be hand loaded onto a 

Arthur D Little. lnc 
need for detection and/or location. 

The system must be adaptable to the condition expected. For example, there 

may be occasions when power is not available or telephone communication nonexistent. The system configuration must be tailored to operate under almost any 

condition. 

Minimum maintenance and reliable operation is a must if the system is on 

stand-by at all times. Small portable units incorporating solid state design 

where possible should meet this criterion. Continuous operation for extended 

periods of time is feasible with small rechargeable battery operated units. 

The concept of small portable units could reduce overall program costs, 

since specialized equipment may not be necessary. 

Arthur D Little, Inc 
V. SUGGESTED SYSTEM CONFIGURATION 

The need for a truly portable hand carried system has been established 

in many cases during the extensive field work*in the past two years. Contrasted with this is the requirement of computer equipment to perform signal 

processing to enhance signal-to-noise in high noise environments. Thus, the 

suggested system described in this section will attempt to meet these conflicting requirements in addition to all the others stated above. 

Our approach to the system configuration is to recognize the fact that 

there are a wide span of field requirements that must be met. These range 

from the need for possible simple detection processes in remote quiet areas 

to a complex detection/location problem in high noise environments with 

relatively easy accessibility. In one case, a simple hand carried system 

with hard copy play out may be all that is necessary, where in the latter case 

a full system with a sophisticated computer system may be required. We have, 

therefore, taken a modular approach, with each subsystem capable of add-on 

to meet the existing requirements. 

In each of the portable package designs described below, we have considered 

only equipment that is now available. Little or no major R&D work is required to 

produce the field package described below, only good equipment layout and packaging design are required. Figure 4 shows the overall block diagram of the suggested 

seismic detection subsystem. A description of this subsystem and the signal processand location subsystem will be covered in the following sections. 

A. Seismic Detection Subsystem 

The seismic detection subsystem consists of the array element geophones, 

the associated cables, and a hand carried array control unit. 

We recommend geophones that can be placed in boreholes , or on the surface 

if hard rock overburden is encountered. The phones could be of the marine-type, 

since they are more sensitive than the ones now used. Tests conducted with the 

Westinghouse system indicated a 6-8 db discrimination to local noise sources with 

a geophone buried one foot in the ground. The phones should be completely sealed 

against water since they will frequently be in water. 

A hand auger can be used to make the boreholes for easy implantation. A 

much better coupling could be established to the surrounding earth if dirt were 

tamped back over the phones, or if some form of integral bellows arrangement 

could be used to expand the phone casing to the borehole walls. 

Integral with each geophone should be a preamp with 70 db of gain, and a calibration coil that induces a known motion to the phone sensing elements. * Westinghouse Contracts H0101262 and H0210062 with Bureau of Mines. 

11.9 Arthur D Little Inc. 
FIGURE 4 

I I 

TIME I I I HI GAIN I CALIBRATION 

CLOCK I AMPS CIRCUITS AND 

I I JACK FIELD CONTROL I 

SUGGESTED SEISMIC DETECTION SUBSYSTEM 

BATTERY 

. 

JACK FIELD 

VISICORDER , 

H 

----- - 

MOBILE 

RADIO 

8 CHANNEL 

MULTIPLEXER 

UNIT -- - - - -IL 

--- 

a 

TEL TRANSCEIVER INTERFACE 

I 

7 

LOW PASS 

FILTERS 

REPRODUCE -TO TRAILER 

TAPE 

RECORD/ 

VAN 

I 

I 

I 
The calibration circuit is necessary to establish the proper operation of each 

phone in the array, and to reference the relative delay in the system between 

channels. Should a delay exist, for example, in the tape recorder subsystem 

as was the case in the Westinghouse system, the delay can be recognized and 

measured. First-motion picks on seismic signal records could then be 

adjusted to allow for instrumentation delays. 

Should multiple geophones be used for each element array, we recommend 

they be wired in series for the output signal to achieve greater sensitivity 

than the present arrangement, and that each calibration coil be connected 

individually to ensure the proper operation of every phone in the array. 

In configuring this system, we considered the use of digital vs. analog 

geophones. The use of digital geophones has many advantages in field applications. Digital systems are more immune to noise interference than analog 

systems, and once in digital format, waveforms can be processed in a more convenient manner. An additional advantage is the ability to obtain a greater 

dynamic range of up to 90 db by utilizing digital formats, geophones, and recorders. The maximum dynamic range of current analog systems is approximately 45 db. 

The use of the system for miner detection would require only the array 

and a portable scope and Visicoder system. Since the signals on the scope 

and the Visicoder are analog, we see no reason to complicate the front end of 

the system with A/D and D/A circuits. The need for a large dynamic range in the 

system has not been demonstrated in the Westinghouse field work. Therefore, with 

a proper gain setting, a 40 db dynamic range seems adequate for all expected conditions. Considering all the advantages of both systems, we have concluded that 

for this application, the use of the analog format in the array system is preferable to digital. 

The cable connecting each geophone to the control unit should be a three 

twisted pair cable with a separate external shield. A balanced transformer should 

be used at the geophone output interface and the control unit input circuit interface. The ground return can be the geophone housing connected to the external 

cable shield and the control unit case. The third pair of wires are used to 

power the geophone preamp from the control unit battery supply. 

The array control unit should be a hand carried aluminum watertight case 

approximately 2 x 3 x 1 feet and weighing under 75 pounds. Key elements in this 

unit are: 

a. system time clock, 

b. main amplifier and gain adjust unit, 

c. control status panel, and 

d. battery unit 

11.11 Arthur D Little, Inc. 
volts peak-to-peak under varying input signal levels. AGC can be used effectively since arrival times are of importance and not absolute signal levels. 

The control status panel consists of the calibration circuitry, switch 

control, and output signal switches to display individual channels for oscilloscope viewing, or all channels for magnetic tape recording. Output BNC and/or 

multipin connectors will be used to connect to companion units such as the 

portable oscilloscope and magnetic tape recording systems shown in block diagram 

form in Figure 4. 

The hard copy play out unit shown in Figure 4 can be a portable unit equivalent to a Visicoder unit capable of reproducing all seven channels plus the 

timing track. This will allow first cut estimation of arrival times on each 

channel, and with the control status panel and array unit, constitute a cornplete austere field system. Integral with the Visicoder unit would be a 

switchable low pass filter unit for each channel. Suggested cutoff frequencies 

are 200 Hz and 500 Hz. A filter roll off of 24 db per octave is recommended. 

Arthur D Little, Inc. 
* 

A key field unit in this system is the 8 channel MUX and a telephone interface unit shown in Figure 4. This unit is designed to interface directly with 

the array control unit and works with the standard level output on each channel. 

Each channel consists of an input buffer stage coupled to a VCO with a 

center frequency assigned to allow seven signal channels plus a time channel 

to be sent over a standard telephone line. The output of each VCO is then combined and buffered to a common output circuit designed to reflect to the telephone system an off-hook telephone set. A standard telephone set is also incorporated in this unit to permit communication between the field crew and/or 

the data processing center. Should telephone lines be available, the array subsystem, array control unit, oscilloscope, and the 8 channel MUX unit could constitute the entire field system. Data processing could then be performed at 

any point in the United States (Boulder, Pittsburgh, etc.) . 

The interface to the telephone line can be a short patch or may be in some 

cases up to several miles of 20 gauge cable. This cable may in many cases interface on a hard wire basis with the trailer van described later. 

An alternative to the telephone hard wire connection could be another hand 

carried package housing a mobile radio transceiver. This could provide radio 

transmission of the data to some more accessible location at which point the 

data could be interfaced with the telephone network or to the trailer van. 

B. Seismic Signal Processing and Location Subsystem 

The trailer van subsystem is configured as shown in-Figure 5. Major components are the minicomputer and associated A/D converter and disk pack, variable 

filter banks such as the Krohn-Hite, an x-y plotter such as a Calcomp, Visicorder 

or equivalent for hard copy play out, and a monitoring unit with a memory type 

oscilloscope. 

In addition to the equipment above, an eight channel discriminatory bank 

and a mobile radio transceiver would be required to interface with the field 

units. Telephone equipment with signaling capability would be required should 

the communication link be hard wired. 

A more powerful minicomputer, in the PDP-11, class and associated disk pack 

has the following advantages over the present system: 

1. It appears likely that computer programs already in existence for 

signal processing, and system organization and control may be 

available to the Bureau of Mines. 

2. The disk pack arrangement with digital format is more efficient in 

interfacing a computer in the signal processing mode. Access time 

is significantly less, programs are available on data search, and 

Arthur D Little Inc. 
Arthur D Little, Inc 
reproduction costs are also competitive. 

3. Location programs such as "MINER" could be incorporated in 

this system thus eliminating the need for an additional 

time-share facility. 

VI . DEPLOYMENT 

The suggested configuration described above solves the critical requirements of portability, rapid deployment, and cost. It is flexible in configuration to satisfy a wide range of needs and is of comparatively low cost for 

initial purchase and maintenance. 

We visualize a possible deployment of this system in phases: on notification of a disaster, the initial deployment would be of the array subsystem, 

the array control unit, and the scope. These three units are sufficient to 

perform the initial function of miner detection. They can be hand carried 

on a commercial airliner or even in a passenger car. They are reasonable in 

cost so that a number of these could be placed in strategic locations throughout the United States. We expect that such a subsystem could be deployed and 

begin the miner detection process in several hours. Several variations in 

this scenario can be made. If telephone lines are known to be available and 

working, it is conceivable that as a fourth unit only the 8 channel MUX need 

be deployed and real-time data collection and processing could be performed 

at Pittsburgh, for example. On the other hand, a full blown system may be 

more convenient on-site, in which case the trailer van and additional subsystem units could be deployed as soon as possible. The important characteristic of the portable system described in this section is the ability to 

begin the detection process in a minimum of time, and to deploy the larger 

and more cumbersome comprehensive location system later when it is needed. 

In many cases, the van may not even be necessary. 

In summary, the suggested system represents a truly portable self-contained 

system that is self-calibrated, tested, and usable under a wide variety of 

conditions. It is modular in growth to match every type of disaster condition, 

and is reasonable in cost. All system units and circuits described are offthe-shelf items that can be integrated and packaged to satisfy the abovedescribed sys tem requirements. 

Arthur D Little Jnc 
PART TWELVE 

BRIEFING CHARTS 

Arthur D Little, Inc. 
PART TWELVE 

BRIEFING CHARTS 

TABLE OF CONTENTS 

I. INTRODUCTION 

11. PROGRAM BRIEFING FOR SEISMIC CONSULTANTS 

A. OPENING REMARKS 

B. INTRODUCTION TO COAL MINE DISASTERS 

C. OVERVIEW AND STATUS OF SEISMIC LOCATION PROGPUM 

D. FORMULATION OF THE MINER SEISMIC LOCATION PROBLEM 

E. DESIRED END PRODUCT AND SCHEDULE OF PRESENT EFFORT 

F. IDENTIFICATION AND DISCUSSION OF MAJOR TASKS 

AND TASK ASSIGNMENTS 

111. ORAL PRESENTATION OF STUDY RESULTS TO PITTSBURGH 

MINING SAFETY AND RESEAECH CENTER 

A. OVERVIEW AND SUMMARY OF PRINCIPAL FINDINGS 

B. PROBLEM FORHULATION AND TASKS 

C. DETECTION OF AN ISOLATED MINER 

D. LOCATION OF AN ISOLATED MINER 

E. SEISMIC SYSTEM FIELDABILITY AND 1NSTRUMENTA.TION 

F. CONCLUDING REMARKS 

Page 

12.1 

Arthur D Little, Ir 
PART TWELVE 

BRIEFING CHARTS 

I. INTRODUCTION 

In this Part, we have included copies of the flip charts and overhead 

projector viewgraphs used in the two briefings we conducted as part of 

this seismic detection and location task. The first one was an overview 

and problem definition briefing given to the seismic consultants on 

September 7, 1972. The second was a formal oral presentation of study 

results to technical staff members of the Pittsburgh Mining and Safety 

Research Center on November 21, 1972. 

Arthur D Little. Inc 
11. PROGRAM BRIEFING 

FOR 

SEISMIC LOCATION OF ISOLATED MINERS 

Arthur D. Little, Inc. 

In order to provide the seismic consultants with a clear and concise: 

a) definition of the seismic miner location problem; 

b) summary of the relevant background information regardi ng the Bureau's sei smi c 1 ocation program to 

date; and 

c) i denti fi cati on and assi gnment of speci fi c tasks ; 

we prepared and gave the consultants a comprehensive briefing. This 

briefing consisted of a flip chart presentation, complemented by the 

use of film, slides, and viewgraphs, and culminated in an interactive 

discussion of the problem, specific tasks, and consul tants ' indi vidua1 areas of interest and corresponding assignments. In short, the 

seismic briefing was organized into the six parts listed below, and 

summarized in this Part by reproductions of the briefing visual aids. 

A. OPENING REMARKS - ADL 

B. INTRODUCTION TO COAL MINE DISASTERS - BUMINES 

C. OVERVIEW AND STATUS OF SEISMIC - BUMINES 

LOCATION PROGRAM 

D. FORMULATION OF THE MINER SEISMIC - ADL 

LOCATION PROBLEM 

E. DESIREDENDPRODUCTANDSCHEDULE -ADL 

OF PRESENT EFFORT 

F. IDENTIFICATION AND DISCUSSION OF - ADL/PARTICIPANTS 

MAJOR TASKS AND TASK ASSIGNMENTS 

Arthur D Little Inc. 
A. OPENING REMARKS 

ARTHUR D. LITTLE, INC. - R. LAGACE 

Arthur D Little. Inc. 
OBJECTIVE 

DETECTION AND LOCATION 

OF MINER 

BY SEISMIC MEANS 

PRESENT EFFORT 

DETERMINE: 

8 HOW AND HOW WELL OUR OBJECTIVE 

CAN BE ACHIEVED 

Arthur D Little Inc 
IN PART1 CULAR: 

IDENTIFY WHAT CAN BE DONE AND HOW WELL -- BY SEISMIC MEANS -- TO: 

8 DETECT A MINER 

8 LOCATE A MINER TO WITHIN A SECTION 

8 LOCATE A MINER TO WITHIN AN ENTRY WIDTH 

Arthur D Little. Inc 
B. INTRODUCTION TO COAL MINE DISASTERS 

U.S . BUREAU OF MINES - H. PARKINSON, PMSRC 

This part of the briefing included: 

1. Viewing of the Bureau film: SAFETY PRACTICES IN LOW COAL 

MINES, with special narration by H. Parkinson. 

2. Viewing color slides of the U.S. Steel Mine site used for 

the demonstration of the Coal Mine Rescue and Survival 

Sys tem . 

3. Discussion of Coal Mine Layouts, Activities, and Disasters 

with the Aid of Actual Mine Maps, and the Visuals included in this section. 

Arthur D Little. Inc 
.- 

SIXETCH OF 

M/tVERS UTIL /ZING 

Arthur D Little, Inc 
Arthur I2 Little Inc 
C. OVERVIEW AND STATUS OF 

SEISMIC LOCATION PROGRAM 

U.S. BUREAU OF MINES - J.POWELL, PMSRC 

Arthur D Little. Inc. 
OUTLINE 

WHERE ARE WE NOW? 

0 HISTORY 

0 PHILOSOPHY AND RATIONALE 

0 SYSTEM SET-UP 

0 EXPERIMENTS AND INVESTIGATIONS 

0 RESULTS 

Arthur D Little Inc 
NAE RECOMMENDATIONS 

- AND 

REQUI REMENTS 

REQUIRED: 50 FT. ACCURACY 

To BE 25 FT. ACCURACY ATTAINABLE 

(2 millisec. timing error at 10,000 fps velocity 

5 20 ft. error) 

Arthur D Little Inc. 
SYSTEM (LOCATING) 

t 

ARRIVAL TIME 

DIFFERENCES 

b 

* 

REMOTE ACCESS TTY . 

REMOTE COMPUTER 

LOCATION 

i 

Arthur D Little. Inc 
SYSTEM 

RECORD UNIT. NORMAL MODE 

SUBARRAY 

t_ One of seven I/P channels '4 

PREAMP 

0 INPUT 

Q 

TRANSFORMER 

 TI ) COMPUTER '--{=] 

FILTER G' 

Arthur D Little, Inc 
SUB ARRAY S UBARRAY 

b 

b 

SUBARRAY 

, #4 

b 

Arthur D Little Inc 

, 

SUB ARRAY 

SUBARRAY 

#5 

SUBARRAY 

:#6-- 
* 

7 

-20 FT. 

P 

PREAMP 

SINGLE OUTPUT 

7 GEOPHONE OUTPUT 

Arthur D Little Inc 
HISTORY - (A) 

Arthur D Little. lnc 

NAE RECOMMENDATIONS 

AN D 

REQUI REMENTS * 

A 

. 

v 

BUILD SYSTEM i 

RESULTS 
HISTORY - (8) 

I PAUSE : ANALYSES I 

I 

( VERIFICATION TEST I 

( STILL NOT ADEQUATE I 

C - 

8 J 1 

ABANDON CHANGE 

REQUI REMENTS IMPROVE 

4 * 

Arthur D Little, Inc 
PHILOSOPHY : VARIETY IN 

@ MINE TYPES 

@ GEOGRAPHIC AREAS 

(ASSUMED SYSTEM WOULD USUALLY WORK) 

RESULTS : FAILED NAE REQUIREMENTS 

Arthur D Lttle, Inc 
PAUSE - ANALYSES 

E.G., 

8 THEORETI C EXAMINATION OF SOURCES 

8 EXAMINATION OF PRE-AMP DESIGN 

8 COMPLETE LIST IN SEISMIC APPENDIX 

(Wes ti nghouse FY 1972 Report) 

Arthur D Little inc. 
VERIFICATION TEST 

SIX (6) WEEKS AT EXPERIMENTAL MINE 

(50 FT . OVERBURDEN) , BRUCETON , PENNSYLVANIA 

- Not Always a Realistic Test 

Arthur D Little Inc 
WHAT NEXT? 

0 ABANDON - E . G. , RELY ON E .M. METHODS 

0 CHANGE REQUIREMENTS - E .G., ONLY NEED TO 

KNOW SECTION 

0 IMPROVE - Y 0 U 

CHOICE WILL BE MADE WITH YOUR HELP 

Arthur D Little Inc 
D. FORMULATION OF THE MINER 

SEISMIC LOCATION PROBLEM 

P.RTHUR D. LITTLE, INC. - M. ROETTER 

Arthur D Little, Inc 
CONSTRAINTS AND GIVENS 

INDUCED BY: 

0 MINE 

0 MINERS 

0 SEISMIC SYSTEM 

0 OVERALL RESCUE EFFORT 

Arthur D Little Inc 
E5.i LOCATION ESTI MATION 

L Yes 

I LOCATION DECLARED 1 

Arthur D Little, Inc 
DETECTION OF MINER 

r 1 

SI GNAL ENHANCEMENT < 1 A MO DI FY S I GNAL 

- 

v ENHANCEMENT 

DETECTION RULE < I 4 

No MOD1 FY 

DETECTION 

RULE 

Yes 

Yes 

No I 

MODIFY ARRAY \. ' 

MOVE ARRAY 

MINER GENERATED 

S I GNAL 

LOCALIZATION 

PROCEDURE 

I FAILURE TO DETECT I 

I 

Arthur D Little. Inc 

) *( SEISMIC ARRAY 
PARAMETER ESTIMATION 

0 POSITIVE DETECTION 

No 4 

) RECEIVER ATTRIBUTES 

POSSIBILITIES 

PARAMETER ESTIMATION 

CONFIDENCE IN 

POSSIBILITIES 

Yes 

Arthur D Little. lnc 
MINER LOCALIZATION 

S I GNAL 

DECLARED 

Arthur D Little, Inc. 
SEISMIC LOCATION SYSTEM: 

GENERAL GROUND RULES 

0 HARDWARE : FIELD SUITABLE AND RAPIDLY DEPLOYABLE 

0 SYSTEM CONSTRAINED TO PRESENT STATE-OF-THE-ART 

TECHNIQUES AND HARDWARE 

0 SYSTEM OPERATION FROM SURFACE 

@ SYSTEM SELF-CONTAINED IN ITS OPERATION 

AND CALIBRATION 

@ SYSTEM CAPABLE OF PRODUCING TIMELY 

LOCATION ESTIMATES 

0 SYSTEM OPERATION COMPATIBLE WITH AND 

COMPLEMENTARY TO OVERALL RESCUE EFFORT 

Arthur D Little. Inc 
KEEPING IN MIND THE 

IMPACT OF 

INVESTMENTS IN 

0 EQUIPMENT 

0 TRAINING 

0 SITE CALIBRATION-PREPARATION 

- ON 

PERFORMANCE 

- AN D 

COST 

Arthur D Little Inc 
SEISMIC LOCATION SYSTEM: 

SPECI FIC GROUND RULES 

THE MINER AND HIS MESSAGE 

1 ) The miner has uncertainty as to his true location. 

2) The miner 's location is fixed. 

3) The depth of the miner is known relatively well (0) 

4) Gross location of miner for starting miner detection/ 

location process is given. 

5) Only one miner (true signal source) is signal ling. 

6) The miner has an expectation/certi tude of a 

seismic search. 

7) The mi ner i s a 1 imi ted/non-i deal performer. 

8) The miner has imperfect knowledge of time. 

9) The miner is unimpaired. 

10) The miner's source element must be readily 

avai 1 able and reasonable . 

11) The source impact area is an undeveloped, 

but probable feature. 

Arthur D Little. In( 
THE MESSAGE TRANSMISS ION PATH 

AND NOISE ENVIRONMENT 

1) The seismic path is initially unknown. 

2) The seismic path is 1 inear and time-invariant. 

3) Identification of the earth seismic path must 

proceed from the surface. 

4) The surface will most likely be sloped. 

5) The seismic noise during a rescue operation 

is the sum of: 

a) signal induced noise (path scatter) 

b) rescue sources 

c) basic background 

d) a1 tered mine sources 

e) message noise 

f) system noise 

Arthur D Little, Inc 
THE MESSAGE DETECTION/LOCATION 

ACTIVITY ON THE SURFACE 

1) The surface team will have a mine map and limited 

mi ne geological data. 

2) The surface team has imperfect knowledge of when 

s i gnal s are transmi tted. 

3) The surface team has imperfect knowledge of when 

only noise is present. 

4) Use of arrays and burial of seismometers are not 

mutual ly exclusive options. 

5) Burial to 50 Ft. is an upper bound for the 

seismometer plant in alluvium. 

6) Measurement will not be constrained to the 

vertical component. 

7) The surface team knows the performance of the 

measuring sys tem. 

8) Deep pre-planted sensors may be avai lable 

at some mines. 

9) The search aspects of the problem wi 11 be 

tab1 ed. 

Arthur D Little Inc. 
E. DESIRED END PRODUCT 

AND SCHEDULE OF 

PRESENT EFFORT 

ARTHUR D. LITTLE, INC. - R. LAGACE 

Arthur D Little Inc 
DESIRED STUDY OUTPUTS 

0 "BEST" ESTIMATES (Based on Present Data) OF: 

THE PROBABILITY OF DETECTION 

and 

THE ACCURACY OF LOCATION 

OF A MINER TRAPPED IN REAL EARTH. 

0 HOW THESE ESTIMATES CHANGE WITH: 

SYSTEM COMPLEXITY AND COST 

8 WHAT IS STILL NEEDED IN TERMS OF: 

BASIC DATA 

ANALYSES 

EXPERI MENTS 

TO IMPROVE AND/OR VERIFY THESE ESTIMATES 

Arthur D Little In( 
0 

Lateral Range from Miner in Feet 

Conditions : 

System Configuration - Miners Source and Message - Detection MethodMINER DETECTION 

(SAMPLE CONCEPTUAL SKETCH) 

Arthur D Little Inc. 
Parameter Measurement - Error 

Decreasing SIN 

Conditions: 

System Configuration - 

Location Method - 

Miner Depth - Miner's Source and Message - 

Overburden Transmission Characteristic - 

Noise Environment - 

MINER LOCATION 

(SAMPLE CONCEPTUAL SKETCH) 

Arthur D Little, Inc 
System Complexity - Cost $ 

PERFORMANCE VERSUS 

SYSTEM COMPLEXITY-COST 

(SAMPLE CONCEPTUAL SKETCH) 

Arthur D Little. Inc 
F. IDENTIFICATION AND DISCUSSION OF MAJOR TASKS 

AND TASK ASSIGNMENTS 

ARTHUR D. LITTLE, INC. - R. LAGACE 

WITH PART1 CIPATION BY CONSULTANTS, 

AND BUREAU OF MINES 

STAFF AND ADL STAFF 

CONSULTANTS : 

FRANK CROWLEY - WESTON OBSERVATORY AND AFCRL 

WILLIAM DEAN - TELEDYNE GEOTECH 

JOHN KUO - COLUMBIA UNIVERSITY 

ENDERS ROBINSON* - INDEPENDENT 

BUREAU OF MINES : 

HOWARD PARKINSON - PMSRC 

JAMES POWELL - PMSRC 

ARTHUR D. LITTLE. INC. 

JOHN GINTY 

ROBERT LAGACE 

MARTYN ROETTER 

RICHARD SPENCER 

CONSULTANTS : (Who Had to Receive Individual Briefings) 

ROBERT CROSSON 

DAVID PETERS - UNIVERSITY OF WASHINGTON 

ROY GREENFIELD - PENNSYLVANIA STATE UNIVERSITY 

FRANK PI LOTTE - VELA SEISMOLOGICAL CENTER 

* Could not participate as originally intended because of scheduling 

conflicts with prior cornrni tments. 

Arthur D Little Inc 
TASKS 

OUTPUTS s INPUTS 

SOURCES 

Fn of: Type 

: Man 

: Impact Area 

: Tunnel 

w 

EZ: 

e 

5 

5 

0 

n 

W 

H 

LL - - 

! I 

A 

- 

W 

m 

4: 

H 

E 

4: 

> 

9 

5 

DETECTION 

a Strength 

a Directional and 

Coherence Charac ., 

a Pulse Shape 

a Rep. Rate 

TRANS. MEDIUM. a Attenuation 

CH ARAC . Fn of: Layers 

-,Thick, 

Angle, etc.) 

NOISE 

Fn of: Sources 

- Si g. Induced 

- Rescue Sources 

- Basic Bgrd. 

- A1 tered Mine 

- Message 

- System 

SENSORS 

Fn of: Depth 

: Coupling 

SIGNAL PROCESSING 

DATA PROCESS1 NG 

AND COMPUTATION 

LOCATION 

g Directional 

Charac. 

a Earth Model 

(Detai 1 ed) 

a Noise Weighting 

of Parameters 

a Array Geometry 

and Location 

a Location 

A1 gori thms 

a Mine Maps 

PARAMETER ESTIMATION 

x ) 

FIELD 

UTILIZATION 

x 1 a Signal Modification 

- Freq . Response 

- Time Domain 

- Spatial Coh. 

a Spectrum Levels :i a Time Charac. 

i .e. Stationari ty 

Impul si venes 

a Spatial Coherence 

a Sensitivity 

a Array Gain/ 

Di rectional i ty 

a Dynamic Range 

a Pol arization 

a Candidate 

a Detection Methods 

+ Sensitivity + Array Gain/ 

Di rectional i ty + Dynami c Range + Polarization 

a Candidate 

a Estimation Methods 
ADL Direction and 

Integration of Results 

Initial Briefings 

WGL 

BUMINES 

Consultants 

Assignment to Consultants 

Data Gathering and Analysis 

Preliminary Results Meeting 

Sharpening Focus of Effort 

and Resolution of Issues 

Presentation of Findings 

Consolidation of Findings 

Oral Report to BUM1 NES 

Preparation of Written Report 

Written Report to BUMINES 

August 15 

I September 15 October 15 

I I 

November 15 

I 

December 15 

PROGRAM SCHEDULE 
111, ORAL PRESENTATION 

OF 

STUDYRESULTS 

- TO 

PITTSBURGH MINING SAFETY AND RESEARCH CENTER 

NOVEMBER 21, 1972 

SEISMIC LOCATION OF ISOLATED MINERS 

Arthur D. Little, Inc. 

(Copies of Flip Charts and Viewgraphs) 

Arthur D Little, Inc 
A. OVERVIEW 

AND 

SUMMARY 

PRINCIPAL 

FINDINGS 

ROBERT L. LAGACE 

Arthur D Little Inc 
OBJECTIVE OF STUDY 

WHAT CAN BE DONE 

AND 

HOW WELL 

- BY SEISMIC MEANS 

- TO : 

- DETECT A, MINER 

- LOCATE A MINER 

TO WITHIN: A SECTION 

: AN ENTRY WIDTH 

Arthur D Little. lnc 
SEISMIC LOCATION SYSTEM: 

GENERAL GROUND RULES 

0 Hardware : Fie1 d Sui tab1 e and 

Rapi dly Deployable 

0 System Constrained to Present State-of-Art 

Techniques and Hardware 

0 System Operation From Surface 

0 System Self-Contained in its Operation and 

Cal i brati on 

0 System Capable of Producing Timely Location 

Estimates 

0 System Operation Compatible with and Complementary to Overall Rescue Effort 

0 Signal Sources Readi ly Avail able and Reasonable - - No Special , Carried Devices 

0 No Wide-Area Search - - Likely Areas Given 

0 Team Wil 1 Have Benefit of Mine Maps 

Arthur D Little, Inc 
DESI RED STUDY OUTPUTS 

@ "BEST" ESTIMATES (Based on Present Data) OF: 

THE PROBABILITY OF DETECTION 

and 

THE ACCURACY OF LOCATION 

OF A MINER TRAPPED IN REAL EARTH. 

@ HOW THESE ESTIMATES CHANGE WITH: 

SYSTEM COMPLEXITY AND COST 

8 WHAT IS STILL NEEDED IN TERMS OF: 

BASIC DATA 

ANALYSES 

EXPERIMENTS 

TO IMPROVE AND/OR VERIFY THESE ESTIMATES 

Arthur D Little, Inc 
DETECTION OF A MINER 

RANGES 

ON THE ORDER OF 

1000 FEET 

CAN BE ACHIEVED 

SUBJECT TO THE CONTROL OF 

MANMADE NOISE SOURCES* 

This Should A1 low More 

Than Adequate Coverage 

of Typical Mine Sections 

* Namely, surface operations and activity over and in the vicinity of the 

detection area must be severely restricted and possibly prohibited. 

12.46 Arthur D Little, Inc 
LOCATION OF A MINER 

TO WITHIN A SECTION 

LOCATION ACCURACIES 

TO WITHIN 

100 FEET 

TO DEPTHS OF 1000 FEET 

APPEAR ATTAINABLE 

SUBJECT TO: 

- CONTROL OF MANMADE NOISE SOURCES* 

- AN ADEQUATE SEISMIC REPRESENTATION OF'THE EARTH 

* Namely, surface operations and activity over and in the vicinity of the 

location area must be severely restricted and possibly prohibited. 

Signal-to-noise ratios in excess of that for detection will also be 

requi red. 

12.47 Arthur D Little Inc 
LOCATION OF A MINER 

TO WITHIN AN ENTRY WIDTH 

APPEARS TO BE AN UNREALISTIC GOAL 

HOWEVER: UNDER VERY FAVORABLE CIRCUMSTANCES* 

ACCURACIES OF ABOUT 30 FEET APPEAR 

ATTAINABLE 

With the Aid of An Accurate Mine Map - 

This Should Allow Identification 

Of the Entry in Which the Miner is 

Located 

* For manrnade noise, same comments as for previous chart. An even more 

accurate representation of the earth, or a shallower depth (300 feet 

or less), will also be necessary. 

12.48 

Arthur D Little, Inc. 
EXPECTED IMPACT OF 

INVESTMENTS ON 

PERFORMANCE AND COST 

I MPACT Improving 

OF ON+ Overall 

1 Performance 

Truly Fi el dab1 e 

Hardware HIGH 

Trai ned Experienced 

Fie1 d Crews HIGH 

Site Pre-Cal i bration 

Pre~arati on HIGH 

Improved Sei smi c 

Earth Models HIGH 

Conventional S/N 

Enhancement Methods HIGH 

Sophisticated S/N 

Enhancement Methods LOW 

Control 1 i ng Si te 

Manmade Noise HIGH 

Increasing 

Overall 

Cost 

LOW 

MODERATE 

HIGH 

LOW 

LOW 

HIGH 

LOW 

Arthur D Little Inc 
TO IMPROVE AND/OR VERIFY 

PERFORMANCE ESTIMATES 

NEED 

BETTER QUANTITATIVE 

CHARACTERIZATION OF: 

0 SEISMIC SIGNALS FROM SOURCES 

AVAILABLE TO MINERS 

0 SEISMIC NOISE IN COAL MINE REGIONS 

0 SEISMIC PROPAGATION ATTRIBUTES OF 

COAL MINE OVERBURDENS 

Arthur D Little. lnc 
B. PROBLEM 

FORMULATION 

AND 

TASKS 

ROBERT L. LAGACE 

Arthur D Little Inc 
FORMULATION OF PRGBLEN 

1 

CONSTRAINTS AND GIVENS 

I 

DETECTION TECHNIQUE 

No b 

No 

PARAMETER EST1 MAliON C 

J, Yes 

1 1 

LOCATION ESTIVATION 

,L Yes . I LOCATION DECLARED I 

Arthur D Little Inc. 
TASKS 

4 

I NFUTS 

SCURCES I --- 

-- 

Fn of: Type 

: Man 

: Impact Area 

: 'Tunnel 

------- 

c; - TRANS. MEDIUM. ----- 

LL: I -- CiIARAC. 

X Fn --- of: Layers 

b-4 TO Thick, 

Angle, etc.) L" ------ - I NijISE 

--- ---- 

. 

Fn of: Sotrrces ---- 

P - jig. Tr~duced N I - ~3scue ~ources Cn (a - Basic Bsrd. 

- Piessage 

- Sys tern 

Fn of: Depth 

: Coupling 

m 

u 

DETECTION 

H 

CIL 

Q; 

=- 

-/ 5 - 5' 

u 

ct 

c 

cr 

0 

T 

PARAMETER ESTIMATION LOCATION 

9 Directional 

Charac. 

SIGNAL PROCESSING 

DATA PROCESS1 NG 

AND CO~~PUTA~K ------- 

-------------- 

r Strength 

r Directional and 

Coherence Charac.-. 

a Pulse Shape 

- 

FIELD 

UTILIZATION 

a Rep. Rate -- - 

9 Attenuation s Earth Model 

a Signal Modification-. (Detai 1 ed) 

- Freq. Response 

- Tin:? Dornain 

- Spatial Coh. - -- 

e Spectrum Levels a Noise Weighting 

e lime Charac. of Parameters 

i.e. Stationarity 

1rnpul si venessL 

r Candidate 

a Detection Methods ---- 

---- 

5 

r Spatial Coherence 

r Sensitivity 

a Array Gain/ 

Di recti onal i ty 

r Dynamic Range 

a Pol ari zati on 

r Candidate 

e Estimation Methods ---- 

- -- 

a Location 

A1 gori thms 

r Mine Maps 

+ Sensi ti vi ty + Array Gain/ 

Directional i ty 

+ Dynamic Range + Polarization 

a Array Geometry 

and Location 
C. DETECTION 

OF AN 

ISOLATED 

MINER 

ROBERT L . LAGACE 

Arthur D Little, In( 
DETECTION OF A MINER 

CONS I DERATIONS FOR 

ESTIMATING DETECTION RANGES 

0 SIGNAL STRENGTH 

- Source 

- Transmission Loss 

0 NOISE LEVELS 

- Natural Background 

- Manmade Sources 

0 SIGNAL-TO-NOISE 

ENHANCEMENT METHODS 

0 RANGE ESTIMATION 

- Detection Criteria 

Arthur D Little Inc 
Arthur D Little, Inc. 
0.1 I I 1 I I I 1 

200 400 600 800 1000 1200 1400 

Slant Range I Feet) 

Arthur D Little, Inc 
NATURAL SEISMIC NOISE LEVELS: BASED ON FRANTTI 

DATA WHEN NO MAN-MADE NOISE IS PRESENT 

Histogram of Number of Occurrences of Noise RMS Levels 0 

1 

- Natural No~se Levels Exceeded 7596 and 25"; 3 & 4 O f--O 

of the Time are Indicated 

For Frequency = 50 Hz & 

*o 

- 

- 

- 

9 

1 o-~ 1 o-~ 1 o-~ 1 o-~ 

Noise RMS IPS~JWestinghouse data for individual mines are included for comparison, and maximum and minimum noise levels are shown 

as open circles connected by lines. Ignore the vertical axis in relation to these data. Arrows pointing to the left indicate 

that system noise limited noise estimates for low noise periods. The Westinghouse data are taken from the Westinghouse 

Report Table 2-4. The order of the mines, going from the top of the figure to the bottom data points, corresponds to the 

field report numbers for the mines. 

I I 

- 

- 

9 

i I I I 

-4 6 81 2 4 681 2 4 

0 2 596 

1 2 4 6 81 2 

.* 

I I I 

J. 

I I I I *I. I, 
Arthur D Little. Inc. 

v 

- 

dD - 

a 

I - 

I w 

v 

x a, 

% E 0 '- 

x Iu 

a, 

a, 

% E 0 '- 

x IWu- Wu- 

- 0 - 0 a, Q) 

> &? > o\0 a, LO m 

--I CU --I fi 
ESTIMATED PEAK-TO-PEAK VERTICAL PARTICLE 

VELOCITY FOR THE FIRST P-WAVE ARRIVAL 

(BASED ON THEORETICAL CONSIDERATIONS) 

Arthur D Little, Inc 

SIGNAL-TO-NOISE IMPROVEMENT 

METHODS 

FOR DETECTION 

Most Useful 

0 BANDPASS FILTERING 

0 BURIAL OF SENSORS 

0 SUBARRAYS 

- Size Adjust 

- Delayed or Direct Sum 

- Weighted Sum 

FOR ARRIVAL TIME ESTIMATION 

Most Useful 

0 SAME AS ABOVE 

0 SUMMING (STACKING) OF 

REPEATED SIGNALS 

FOR DETECTION AND ARRIVAL TIME ESTIMATION 

Least Useful 

0 REMODE 

0 LINEAR PHASE FILTERING OF MULTICOMPONENT DATA 

0 MATCHED FILTERING 

0 MULTI-CHANNEL MAXIMUM LIKELIHOOD ARRAY PROCESSING 

0 MULTICHANNEL WIENER FILTERING 

0 SINGLE AND MULTICHANNEL PREDICTION ERROR FILTERING 

Arthur D Little, Inc. 
MAXIMUM SLANT RANGES (In Feet) FOR DETECTION-UNDER 

NATURAL NOISE CONDITIONS** 

* WIO - SIN I = Without 10dBSignal-to-Noise lmprovement 

W - SIN I = With 10dBSignal-to-Noise lmprovement 

Source 

Strong 

Thumper 

Strong 

Timber 

Sledge 

Weak 

Timber 

Sledge 

** No obvious manmade noise sources 

Low Noise 

W/O-SIN I * 

>2000 

>2000 

> 1 500 

1100 

900 

High Noise 

W-SIN I 

>2000 

>2000 

>2000 

>I500 

>I400 

Very High Noise 

WIO-SIN I 

1 400 

W/O SIN I 

950 

W-SIN I 

>2000 

W-SIN I 

1 400 

1050 

900 

550 

450 

1050 

900 

550 

450 

>I500 

1250 

650 

550 

r 

800 

625 

375 

300 
SEPARATION GUIUELINES FOR DEALING Wl'l'lI MAN-MAUL NOISE SOURCES* 

Type 

Light Vehicular 

Piston Aircraft 

Lone Trees and 

Telephone Poles 

(heavy wind condition) 

Drilling 

Man Walking 

biachinery (heavy) 

Intra-Mine Sources 

(miner equivalent) 

Distance 

10,000 ft. 

5,000 ft. 

20,000 ft. 

5,000 ft. 

400 ft. 

150 ft 

7,500 ft. 

5,000 ft. 

1,000 ft. 

500 ft. 

10,000 ft. 

2,000 ft. 

3,000 ft. 

3,000 ft. 

Detector 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Buried Array 

Single Phone 

Coherent. Processing 

Single Phone 

Buried Array 

* The detector scheme and noise source-detector separation distances shown are those which should be sufficient tlo keep tile 

disturbance of the associated noise source within the "base" 

noise levels discussed in Part Nine. These guidelines should 

be considered both speculative and cofiservative. 

Arthur D Little Inc 
D. LOCATION 

OF AN 

ISOLATED 

MINER 

ARRIVAL TIME ESTIMATES 

AN D 

LOCATION ACCURACIES USING SURFACE ARRAYS AND EARTH MODELS 

MARTYN F. ROETTER 

LOCATION ACCURACI ES USING REFERENCE EVENT METHOD 

RICHARD H . SPENCER 

Arthur D Little Inc 
MINER LOCATION 

CONSIDERATIONS IN THE ESTIMATION 

OF 

LOCATION ACCURACIES 

ARRIVAL TIME ESTIMATES 

0 Enhancement of Arrival Time 

Accuracies 

TREATMENT OF THE EARTH 

0 Model Representation Based on 

- General Geol ogi cal Know1 edge 

- Refraction Survey Data 

0 "Black Box" Approach with Travel 

Times Based on Reference Events 

Arthur D Little, Inc 
1. ARRIVAL TIME ESTIMATES 

MARTYN F. ROETTER 

Arthur D Little. lnc. 
Arthur D Little, Inc. 
ACCURACY OF ARRIVAL TIMES 

SIGNAL ASSUMED TO LIE IN RANGE 50-100 HZ 

# % 1 ms . ACCURACY I F PEAK OF FIRST ARRIVAL RECOGNIZED 

# Q 5-10 ms. ACCURACY IF PEAK OF A LATER ARRIVAL CHOSEN 

# % 50 ms. ACCURACY IF SEVERAL CYCLES OF SIGNAL MISSED 

Arthur D Little. lnc 
-4 lo' I+- Vp = 5000 fps 
2. LOCATION ACCURACIES 

USING 

SURFACE ARRAYS 

AND 

EARTH MODELS 

MARTYN F. ROETTER 

Arthur D Little Inc 
0 The Thickness of the Upper Weathered Layer 

Can Vary Significantly From One Geophone 

Subarray to Another 

Arthur D Little Inc 
ACCURACY OF EARTH MODELS 

ASSUMPTION: The Earth Can Be Represented 

by a Set of Lateral ly Homogeneous , Hori zontal Layers 

With Different Seismic Velocities. 

THEN : Ref racti on Surveys A1 1 ow The 

Thi cknesses and Vel oci ties of 

These Layers to be Determined 

to Within About 5%. 

The Errors May be Somewhat Less 

for the Upper and Lower Layers, 

and Greater for the Middle 

Layers. 

Arthur D Little Inc 
ACHIEVABLE LOCATION ACCURACY*- I 

0 LATERAL LOCATION ACCURACIES TO 

WITHIN ABOUT 100 FEET APPEAR 

ACHIEVABLE IN MANY SITUATIONS 

0 UNDER VERY FAVORABLE CIRCUMSTANCES, 

ACCURACIES AROUND 30 FEET MAY BE 

ATTAINABLE 

* Based on the Crosson and Peters error analysis applied to the location 

technique of non-linear least squares i terati ve inversion. 

12.74 

Arthur D Little Inc 
ACHIEVABLE LOCATION ACCURACY *- I I 

0 KNOWLEDGE OF DEPTH IMPROVES LATERAL 

LOCATION ACCURACIES WHEN THE SEISMIC 

VELOCITY IS DEPTH DEPENDENT 

0 EARTH MODEL ERRORS OF 5% ARE MORE 

SERIOUS SOURCES OF INACCURACY THAN 

ARRIVAL TIME ERRORS OF 1-5 ms. 

BUT 

0 ARRIVAL TIME ERRORS OF 15-20 ms. 

DOMINATE EARTH MODEL ERRORS OF 5% 

* Ibid 

Arthur D Little Inc 
ACHIEVABLE LOCATION ACCURACY*- I I I 

0 LOCATION ACCURACY INSIDE AN ARRAY 

IS NOT A STRONG FUNCTION OF THE 

ARRAY 'S SIZE OR CONFIGURATION 

0 LOCATION ACCURACY FALLS OFF RAPIDLY 

OUTSIDE THE ARRAY 

- THE RATE IS SIGNIFICANTLY DEPENDENT 

UPON THE ARRAY GEOMETRY 

* Ibid 

Arthur D Little Inc 
ACHIEVABLE LOCATION ACCURACY*- IV 

0 BETTER LOCATION ACCURACY, ESPECIALLY 

WITH RESPECT TO DEPTH, IS ATTAINABLE 

IN AN EARTH WHERE THE VELOCITY IS 

DEPTH DEPENDENT, RATHER THAN CONSTANT 

0 LINEAR VELOCITY MODELS (V = A + BZ) 

ARE EXCELLENT APPROXIMATIONS TO A 

HORIZONTALLY LAYERED EARTH 

* Ibid 

Arthur D Little. lnc 
CONCLUSIONS ON LOCATION ACCURACY 

THESE CONCLUSIONS ARE SUBJECT TO THE 

FOLLOWING CONDITIONS: 

- ARRIVAL TIMES CAN BE MEASURED TO 

WITHIN 1-5 ms. 

- MODELS OF THE EARTH CAN BE APPLIED 

WHICH ARE "ACCURATE" TO WITHIN 5% 

Arthur D Little. In( 
EARTH MODEL ACCURACY 

MODEL "ACCURACY" IS A FUNCTION OF THE: 

1 . SEISMIC SURVEY DATA AND ANALYSIS 

2. VALIDITY OF THE REPRESENTATION OF 

THE COMPLEX STRUCTURE OF THE 

ACTUAL EARTH BY A SIMPLE MODEL FOR 

TRAVEL TI ME COMPUTATIONS 

Arthur D Little Inc 
+ 14 Hex 

15 H 

+ 16 Hex 

17 Hex 

+ 18 Hex 

+ 19 Hex 

+ 20 H 

21 Hex 

22 Hex 

+ 23 Hex 

24 Hex 

2 Lay 

2 Lay 

2 Lay 

2 Lay 

4 Lay 

4 Lay 

L in 

L in 

Lin 

Lin 

Lin 

t Ibid 

* indicates depth fixed for error computations. 

I. 

Arrows indicate the error diagrams shown in the presentation. 

They can be found in Part Three. 

Arthur D Little, Inc 
FURTHER RESOLUTION 

OF THE QUESTION OF 

ACHIEVABLE 

LOCAT ION ACCURACY 

MAJOR PROGRAM COMPONENTS : 

0 COMPREHENSIVE SEISMIC SURVEY 

OF REPRESENTATIVE MINE SITE(S) 

BY EXPERIENCED PERSONNEL 

0 CONTROLLED (STRONG SOURCE) LOCATION 

EXPERIMENTS USING : 

1 . Actual Measured earth velocity 

profile 

2. Simple Model Approximations to 

1. 

Arthur D Little Inc 
For: 

Diagonal Path 

)( X-Axis Path 

A Y-Axis Path 

Input Velocity = 10,000 fps 

- Offset from Center (feet) 

"MINER" LOCATION ERROR 

300 FOOT DOUBLE SQUARE 
Arthur D Little Inc 

3. LOCATION ACCURACIES 

USING 

REFERENCE EVENT METHOD 

RICHARD H . SPENCER 

Arthur D Little. Inc 
Receiving Array 

a 

Arthur Il Little Irx 
Arthur D Little Inc 
REFERENCE EVENT 

EXPERIMENT 

OBJECTIVE: TO DETERMINE ACCURACY AND NUMBER OF 

CALIBRATION EVENTS REQUI RED 

r 10-1 5 Geophones 

r Two or More Sources (~imber, Hammer, Explosives) 

r Source Locations - 25' to 50' Grid Running Over 1,000 ft. 

- Accurately Known Locations 

- Time Mark Desired 

r Aperture Control 

r Must Try in Several Mines 

TO BE DONE BY SKILLED GEOPHYSICAL SERVICE COMPANY 

DETAILED TEST PLAN TO BE DEVELOPED 

Arthur D Little. Inc 
E.. SEISMIC SYSTEM 

FIELDABILITY 

AND 

INSTRUMENTATION 

RICHARD H. SPENCER 

Arthur I3 Little. Inc. 
FIELDABILITY 

GIVEN: 

. LOCATION REQUIRES CALIBRATED SIGNALS 

. POWER MAY NOT BE AVAILABLE 

. TEST AND REPAIR FACILITIES NOT READILY AVAILABLE 

. QUICK RESPONSE UNDER EMERGENCY CONDITIONS REQUIRED 

. OPERATING PERSONNEL MUST BE EXPERIENCED - MUST 

KNOW EQUIPMENT AND ITS CAPABILITIES 

HARDWARE : 

VERTICAL SEISMOMETER - AMPLIFIER ABLE TO BE BURIED 

12-CHANNEL TAPE RECORDER 

ACCURATE, RECOVERABLE TIME CODES ON TAPE 

CONTINUOUS TIME REFERENCE ON TAPE 

SEISMOMETER CALIBRATION DEVICE 

VARIABLE FILTERING - GAIN 

COMPACT LIGHT WEIGHT RUGGED Pl0DULAR SH''lPLE 

PROVEN HARDWARE 

SELECTABLE TIME BASE DISPLAYS 

PROCESSING CENTER 

BATTERY OPERATION 

WATER PROOF NON-AMBIGUOUS CABLING 

TOOLS 

RADIO COMMUNICATION FOR CREW 

PERSONNEL: 

. 3-MAN CREW (MINIMUM) 

OPERATOR/ANALYST - TEST CHIEF-GEOPHYSICAL ENGINEER 

ELECTRICAL TECHNICIAN 

FIELD TECHNICIAN 

ON SITE ADDITIONS 

DEPLOYMENT: . MODULAR PACKING 

. PORTABLE PROCESSING CENTER 

Arthur I3 Little. Inc 
INSTRUMENTATION 

KEY ITEMS 

1 . RAPID DEPLOYMENT OF DETECTION SUBSYSTEM 

2. SELF-CALIBRATING SYSTEM - FRONT END AND 

FINAL OUTPUT - BOTH SENSITIVITY AND 

TIME 

3. PERFORMANCE LIMITED ONLY BY SEISMIC NOISE 

- Geophone/Preamp Unit 

- Burial of Geophones 

4. DISC PACK FOR COMPUTER 

- Fast Programming 

- Extends Capabi 1 i ties 

5. DISPLAYS 

- Real Time 

- Processed 

Arthur D Little Inc 
Arthur D Littie Inc 
BLOCK DIAGRAM INSTRUMENTATION 

Geophones a Calibrator 

& Preamps Amplifiers 0 Visicorder 

Telephone n l nterface 1 Modem 1 

Telephone 

Line 

Arthur D Little Inc 
Arthur D Little. Inc 
F. CONCLUDING REMARKS 

ROBERT L. LAGACE 

Arthur D Little Inc. 
NO 

REQUIREMENTS? 

Arthur D Little Inc 
- 

BIBLIOG2APH1C DATA 

SHEET 

9. Performing Organization Kame and Address 

Little (Arthur D.), Inc. 

25 Acorn Park 

Cambridge, Massachusetts 

02140 

7. Author(s) 

1 Robert L. Lagace, et al. 

10. Pcoject,/Task/Work Unit No. I 

1. No. 

ADL-C-73912-VOL. 11 

8. Performing Organization Rept. 

No. 

11. Contract/Grant No. 1 USBM-H0122026 

4. Title and Subt1:ie 

SURVEY OF ELSCTROMAGNETIG AND SEISMIC NOISE RELATED TO MINE 

RESCUE COWUNICATIONS . VOL . 11. Seismic Detection and 

Locaticri of Isolated Mners. 

12. Sponsoring Organization Name and Address 

U.S. Department of the Interior, Bureau of Mines, 

Pittsburgh Mining and Safety Research Center, 

480C Forbes Avenue 

Pittsburgh, Pennsylvania 15213 

--'Y. Report Date (Preparation) 

January, 19 74 

6. I 

2. 

13. Type of Report 8: Period 

Covered FIN&. 

Aug. 1971 - Dec. 1973 

3.\Pecipient's Accession No. 

115. Supplementary Notes I 

I Initiated under the Coal Mine Health and Safety Research Program. I 

16.Absrracts Volume I1 of this report presents the findings of a short intensive assessment' 

performed during the fall of 1972 by a task team composed of ADL staff and seven special 

seismic consultents, to provide the U.S. Bureau of Mines with independent technical 

judgments regarding the potentials and limitations of seismic methods and systems for: I 

(1) detecting the presence of isolated signaling coal miners, (2) locating such miners 

to within the confines of a 600-by-600 foot mine section, and (3) further locating these 

miners to within a 15-foot entry width, The results of this assessment were obtained by 

I addresszng the following major subject areas treated in this volume: the detection of 

seismic signals and the estimation of their arrival times, the location of the origin of I 1 seismic signals, seismic signal source and propagation characteristics, earth models, I 

seismic no:-se characteristics signal-to-npisp r tio ipprovement teghnigues coal m$ne (operational and emergency envhonments, selsrmc getectlon and locatlon lnstl'umentatlon I l and its effective utilization during mine rescue operations. Experimental seismic data 

gathered by others during a series of mine field tests prior to this task and other 

relevant seismic data were 

17. Key Bords and Document Analysis. utilized for the assessment reported in this volume. 

escrlptors 

Mines-Coal Seismic Noise 

Coal Mines Seismic Wave Propagation 

Rescue Operat ions -Mines Seismic Signal Sources 

Miner Locat ion Seismic Instrumentation 

Seismic Locat ion Through-the-Earth Communications-Seismic 

Seismic Detection 

117b. ~dentifiers/'Open-Ended Terms 

1 

18. Availability Statement r 19. Security Class (This 21. NO. of Pages 

Report) 

UNCLASSIFIED 374 

20. Security Class (This 

L 

22. Price 

Page 

UNCLASSIFIED J FSRhl t\iTiS-35 (REV. 3-72) 

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