Field Instrumentation Studies 

of Earth Tremors and Their 

Geologic Environments in 

Central Utah Coal Mining Areas 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 693 

Field Instrumentation Studies 

of Earth Tremors and Their 

Geologic Environments in 

Central Utah Coal Mining Areas 

By FRANK W. OSTERWALD, JOHN B. BENNETT!, JR., C. RICHARD 

DUNRUD, and JOHN 0. MABERRY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 693 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1971 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director 

Library of Congress catalog-card No. 72-180658 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 35 cents (paper cover) 

Stock Number 2401-1209 
CONTENTS 

Page 

Abstract ---------------------------------------------------------------------------------------- 1 

Introduction ---------------------------------------------------------------------------------- 1 

Acknowledgments ---------------------------------------------------------------- 2 

Instrumentation -------------------------------------------------------------------------- 3 

Methods of seismic interpretation ---------------------------------------- 6 

Gentry Mountain monitoring experiment ------------------------------ 7 

Mining in Gentry Mountain area ---------------------------------- 8 

Page 

Gentry Mountain monitoring experiment-Continued 

Seismic work at Gentry Mountain ---····--·---------------------- 9 

Little Park Wash monitoring experiment ---·-··-----·------------· 10 

Mining at Little Park Wash -------------------------·-····----------- 14 

Seismic work at Little Park Wash -------------·-··-------······ 14 

Su_mmary and conclusions -------------------------------------------------------- 16 

References ------------------------------------------------------------------------------------ 20 

ILLUSTRATIONS 

Page 

FIGURE 1. Map of east-central Utah --------------------------------------------------------------------------------------------------------------------------------------------------····· 2 

2. Schematic diagram of preamplifier circuit -----------······---------------·--·--···--·················----------···-------------------------------------------------- 3 

3. Photographs of preamplifier ------------------------------------------------------------------------------····--------------------------------------------------------------- 4 

4. Graph showing preamplifier current drain plotted against power-supply voltage ------------------------------------------·········· 4 

5. Graph showing response of preamplifier -----------------------------------------------------·······-----------------------------------------------·----········--· 4 

6. Diagram showing field instrumentation ·········--------·------------·-······----------------------·--· ----·-·······-----··--------------·---------------------------- 5 

7. Photograph showing interior of instrumentation van -·-------------------------------·-·--·---·--·-·------·--------------------------------------·----- 6 

8. Schematic diagram of pen-drive amplifier and power supply ------------------------ ------------·-------------------------------------------------- 7 

9. Graph showing response curves for pen-drive amplifier and for pen-drive amplifier plus penmotor ··---·------------------ 7 

10. Graph showing response of low-pass filter -·------·---------------------·--·-----------------------·-·------·----------·--------------·---------------------------- 8 

11-13. Photographs: 

11. Traveltime-curve protractor -------------------------·-----------------·-----------------·---------------···-----·----------·------------------------------------ 8 

12. Intrusive rocks west of Gentry Mountain -------------·-···-------------------------·-·-------·····---------------·-----------·--------------------- 9 

13. Graben and fault near Gentry Mountain ---·--------------------·-···------------------------·--------------------------------------------------- 10 

14. Typical recorded seismograms at Gentry Mountain, Sept. 4, 1967 ------------------------------------------------------------------------------- 11 

15. Geologic map of Gentry Mountain area ---···--·---------------------···-········--·--------------------------------------------------------------·--------------- 12 

16. Typical recorded seismograms at Gentry Mountain, Sept. 8, 1967 ---·--·-------------·--.. -----------------·---------------------------------- 14 

17. Seismogram of tremor at Sunnyside district, Dec. 26, 1963 ........................ ---------------------------------------------------·--------------- 15 

18. Graphs showing number of tremors per day at Gentry Mountain and Sunnyside --·------·-···---------------------------------------- 16 

19. Typical recorded seismogram in Geneva mine, Little Park Wash, Aug. 26, 1968 ··········--·-----------·--------------------------- 17 

20. Typical recorded seismogram at Little Park Wash, Aug. 26, 1968 ---·--···-------·-------·----------·----------·----------·----------------- 17 

21. Geologic map of Little Park Wash ai-ea ------·---·------·---.. -----.. ·-·--.. -----······--·---------·--·----·------·----------·--·---.. --·---·------·------·------- 19 

22. Graphs showing number of tremors per day at Little Park Wash and Sunnyside ------------------------------------------------------ 19 

III 

FIELD INSTRUMENTATION STUDIES OF EARTH TREMORS AND THEIR GEOLOGIC 

ENVIRONMENTS IN CENTRAL UTAH COAL MINING AREAS 

By· FRANK W. 0STERWALD, JOHN B. BENNETT!, JR., C. RICHARD DUNRUD, and JOHN 0. MABERRY 

ABSTRACT 

Temporary field-recording networks were installed at 

Gentry Mountain and Little Park Wash, Utah, during the 

summers of 1967 and 1968 respectively, to study seismic 

activity related to coal mining and geologic conditions. 

Tremors, many of which were small manmade earthquakes, 

were recorded both on chart paper and on magnetic tape; 

instruments were designed or modified to operate for extended periods with minimum maintenance. Hypocenter positions were estimated to be accurate within 750 feet. 

Results at Gentry Mountain indicated that tremors occur 

near mining areas and along large north-trending faults west 

of the mining area. At Little Park Wash they indicated that 

nearly all tremors originated near the south part of the 

Geneva mine. A well-defined belt of faults crossing Little 

Park Wash 5 miles south of the mine was seismically quiet. 

INTRODUCTION 

The U.S. Geological Survey has studied geologic 

features that may be related to dangerous coal mine 

bumps that have occurred in the mines of eastcentral Utah for several years. Bumps, which are 

violent, spontaneous disruptions of coal faces and 

ribs, are a common hazard to lives and property in 

many of these mines. This work originally was 

undertaken at the request of, and in cooperation 

with, the U.S. Bureau of Mines. Since July 1961, 

the work has been carried on by the U.S. Geological 

Survey, but the Bureau of Mines has given continuous informal cooperation in the field. Most of 

the work was done in the Sunnyside district, about 

25 miles east of Price, Utah (fig. 1). An important 

part of this study is a seismic monitoring network, 

operated continuously at Sunnyside since 1963, to 

locate sources of tremors with respect to geologic 

features and to mining. Preliminary studies of data 

from this network indicate that: (1) tremors are 

very common within the mining district; (2) although many tremors occur at considerable distances 

from the mine workings, cyclic variations in numbers of tremors per day seem to be related to variations in mining cycles; (3) many tremors originate 

near faults; and (4) dangerous bumps may occur in 

the mines during times of markedly increased daily 

number of tremors (Dunrud and Osterwald, 1965; 

Osterwald and Dunrud, 1966). Seismic activity was 

much greater at Sunnyside than was anticipated; for 

example, about 50,000 tremors were recorded during 

1967 (Barnes and others, 1969). These findings 

were somewhat unexpected because it was thought 

that the Sunnyside district was aseismic and that 

only a few tremors, directly related to bumps, would 

be recorded. 

As a result of these unexpected findings, two 

seismic monitoring experiments were conducted outside the area of the Sunnyside monitoring network 

by means of a specially designed mobile recording 

laboratory. One experiment was conducted above 

another coal mining area, and one above a prospective coal mining area. These experiments were designed to answer these questions: ( 1) Is the unexpectedly high degree of seismic activity at Sunnyside unique, or does similar activity occur in other 

areas from which Cretaceous coal is mined, and 

(2) does the intensity of seismic ·activity at Sunnyside stem from the mining, or is it related to stress 

accumulations along fault belts near but outside 

the district? Sites for the two experiments were 

selected at Gentry Mountain near Hiawatha, Utah, 

and at Little Park Wash, 15 miles south of Sunnyside (fig. 1). Site selection was based on geologic 

structure, position with respect to mine working, accessibility, and topography suitable for installing 

the networks. 

This report describes the instruments in the 

mobile laboratory and presents some results obtained from the field installations. The geology of 

both sites is described briefly, with emphasis on 

features related to coal mining and to seismic 

activity. Responsibilities for various aspects of the 

work were divided among the authors. Osterwald 

planned and directed experiments at both sites and 

also planned and set design limits for the instrumentation system. Bennetti designed electronic components or modifications of components so that all 

1 
2 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

30' 

15' 

39° 

00' 

111 ° 00' 45' 30' 15' 

FIGURE 1.-Map of east-central Utah showing areas of this report. Mine areas stippled. 

parts of the instrumentation system matched. He 

also assembled, tested, and calibrated the entire 

system and assisted with its field operation. Dunrud 

supplied geologic and mining data for the Gentry 

Mountain experiment and detern1ined epicenters 

and foci of tremors at both sites. Maberry operated 

the instrument van, made playbacks from taperecorded data at both sites, and supplied geologic 

data for the Little Park Wash experiment. All the 

men participated in installing, operating, maintaining, and removing both networks after the seismic 

monitoring experiments were completed. 

ACKNOWLEDGMENTS 

Thanks are due many persons who directly or indirectly supported the investigations. Ira W. Hatch 

and Dean Collard, of the U.S. Forest Service, gave 

permission to use National Forest Land at Gentry 

Mountain and aided in selecting sites for the field 

camp, seismic network, and recording truck. Max 
INSTRUMENTATION 3 

+ 

Cl 15vdc 

+ 

Signa l input 

+ 

60,u~ 

18K 

50 

20 18 K 

Resistor values in ohms. 

Cl through C6-

15501'fd, 50 vdc 

computer grade 

Ql through Q5-

78Dl - l 

NPN Silicon 

h te = approximately . 275 

14.7 K 

50 

14.7K 

Gain variable 5,000 to 30,000 

Input impedance= 1200FL at 10 cps 

Lighting protection-input and output 

22 

Drawn by: J. 0. Maberry 

Signal output 

Checked: J. B. Bcnnetti, Jr., electronics engineer 

FIGURE 2.-Schematic diagram of preamplifier circuit. 

A. Robb provided mining data and times of underground blasting during the Gentry Mountain monitoring. Gary Hansen, U.S. Bureau of Land Management, gave permission to use land and roads 

administered by the Bureau at Little Park Wash. 

R. M. von Storch, Joseph A. Harvey, and John 

Peperakis allowed access to lands and facilities administered by their companies during the monitoring at Little Park Wash. Special thanks are given 

to Friederich-Wilhelm Wellmer of the Mining University of Clausthal, Germany, for assistance in installing the network and for helpful geologic discussions at Gentry Mountain. Jerome Hernandez 

and Barton K. Barnes assisted the authors during 

the installation, operation, and removal of the 

Gentry Mountain network. Ray W. Osterwald voluntarily helped install the Little Park Wash network and maintained the signal wires throughout 

most of the recording period during an emergency 

at the beginning of the study in which additional 

personnel were needed to do the scheduled work. 

Mark Pradovich of Dragerton, Utah, provided logistic support during the work at Little Park Wash. 

INSTRUMENTATION 

Six Electro-Tech EV-17 vertical component seismometers arranged in two crudely L-shaped arrays 

were used in each field network. Total length of 

each network was about 7 miles; as a result, both 

direct and refracted compressional seismic waves 

were recorded on the seismograms. Sites for the 

seismometers were selected so that the instruments 

could be buried in contact with bedrock; each site 

was surveyed to locate its position accurately within 

100 feet. Each seismometer was wrapped in a plastic 

sack, placed on bedrock, and firmly covered with soil 

to insure good coupling. 

Signals from the seismometers were fed into 

transistorized, high-gain, low-frequency preamplifiers specially designed for low drift and low power 

drain (figs. 2, 3). These battery-powered preamplifiers, modified from the design of preamplifiers used 

at Sunnyside (Maberry, 1966, p. 9; Osterwald and 

Dunrud, 1966, p. 101), operate without battery 

changes for long periods of time (fig. 4) under 

widely varying temperatures and were designed to 

transmit signals through as much as 20 miles of 

wire. The preamplifiers boosted electrical signals 

generated by the seismometer coils 7,500 times. The 

input impedance of these preamplifiers could be 

changed easily to match several types of transducers 

by installing suitable damping resistors inside the 

preamplifiers. Frequency response was flat, within 

2 percent between 0.5 cycle per second to 300 cycles 

per second (fig. 5). Devices were incorporated in 

each preamplifier (fig. 2) to prevent high-voltage 

buildups in the signal lines which might result in 

lightning discharges. These devices, specially designed for the purpose, were installed on both the 

input and the output of preamplifiers, because 

earlier experience at Sunny-side indicated that highvoltage buildups between seismometer cases and 

coils frequently caused damage to seismometers and 
4 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

FIGURE 3.-Transistorized preamplifier. Upper, Exterior, 

showing packaging; Lowe1·, Interior, showing construction. 

preamplifiers. If electrical potential in the wires due 

to storms exceeded plus or minus 10 volts, these 

lightning safety devices shorted the potential in both 

wires to a one-point ground at the van. When used 

in a mobile network, each preamplifier, with its 

battery pack, was placed in a military surplus steel 

ammunition box near the seismometer. 

Signals from the preamplifiers were transmitted 

through military surplus twisted-pair telephone 

wires, which were laid on the ground or in brush or 

trees. The wires led directly to recording equipment 

mounted in a military surplus instrument van. Field 

camps were established near the van, because the 

operation of the instruments needed 24-hour supervision. Signals were divided inside the van (fig. 6); 

one part passed through variable attenuators (fig. 

15 .---------.---------.---------.---------, 

(/) 

w 

"' w 

c.. 

::;: 

~10 ...J 

~ 

~ 

z 

;;: 

"' Q 5 ,.._ 

z 

w 

"' "' :::J 

(.) 0 

0 

0 

0 

0 

L---------~-------- ~o ----- ~~4~------~~a· 

POWER-SUPPLY VOLTAGE, IN VOLTS 

Drawn by: T. E. Miller, electroniCS techn ician 

Checked: J. B. Bennetti, Jr., electroniCS engineer 

FIGURE 4.-Transistorized preamplifier current drain plotted 

against power-supply voltage. 

7c) and then through specially designed pen-drive 

amplifiers (fig. 7a; fig. 8) to a 6-channel, electricwriting paper recorder (fig. 7b), and the other part 

passed through FM oscillators (fig. 7d) to a specially 

modified magnetic tape recorder (fig. 7e). The tape 

recorder, which had 14 channels for data, used linch magnetic tape and was operated at a tape 

speed of 1.5 inches per second. Frequency response 

of the pen-drive amplifiers is shown on figure 9. 

Time marks were placed on paper records each 

minute by a chronograph (fig. 7!) consisting of a 

relay circuit closed by a 1-rpm (revolutions per 

minute) synchronous timing motor. The time marks 

0 

1-

Q 

w 

~ 0.6 ...J 

..:: 

::2' 

Cl: 

0 

z_ 0.4 

z 

~ <;) 

0.2 

I. Frequency response with 15 vdc power, 7,500 gain . 

2. Response is constant, but clipping occurs at the 

following loads and output voltages: 

Load (ohms) Clipping voltage (peak to peak) 

1000 4.2 1500 

2200 

3300 and more 

5.0 

6.7 

8.3 

Drawn by: J. 0 . Maberry 

Chec ked : J. B. Ben netti, Jr., electron ics engineer 

~----~----~2~,~~2o ~--~ ---- o ____ oo --...J 

FREQUENCY, IN CYCLES PER SECOND 

FIGURE 5.-Frequency response of preamplifier. 
INSTRUMENTATION 5 

Battery-powered 

preamplifer 

1-7 miles 

Seismometer 

(buried on bedrock) 

'""'" 1nvany '"' I 

t-------l~ FM-record 

electronics Magnetic-tape 

recorder 

FM-playback electronics 

Oscillograph 

FIGURE 6.-Block diagram of field instrumentation. 

provided a visual index so that tremors recorded on 

the magnetic tape could be located rapidly, as described briefly below. Radio time signal tones broadcast by the National Bureau of Standards radio 

station WWV were automatically recorded on paper 

records by means of a manually closed relay circuit 

(fig. 7 g). The operator of the equipment referred 

the marks to Greenwich Mean Time by scaling the 

distance on the paper record from each time signal 

mark to the nearest minute mark recorded by the 

chronograph. 

Recordings of tremors selected from the paper 

records by inspection were played back from the 

magnetic tape usfng specially designed transistorized playback and filter units (fig. 7, h) and a lightbeam oscillograph (fig. 7, i). Direct-writing lightsensitive paper that required no liquid processing 

was used. Frequency response of the tape 

system was flat from 0 to 200 cps (cycles per 

second); however, a filter (fig. 7, k) was usually inserted during data playback to prevent extraneous 

60-cps noise from entering the oscillograph (fig. 

10). Frequency response of the galvanometers in 

the oscillograph was flat from 0 to 100 cps. Voice 

and International Morse code time announcements 

from WWV were recorded continuously on one tape 

channel. Signals from this tape channel passed from 

the playback unit through an amplifier-filter unit 

(fig. 7, j) to headphones to enable an operator 

audibly to locate time signals on the tapes. 

Electric power for the recording laboratory was 

provided by a 15 kilovolt-ampere gasoline-powered 

motor-generator unit mounted in a trailer. Voltage 

was maintained automatically at a constant level. 

Frequency, monitored by a meter on the unit, was 

adjusted manually by use of a throttle and was 
6 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

-, 

FIGURE 7.-Field seismic instrumentation installed in van. 

a, pen-drive amplifiers for paper recorders; b, paper recorder; c, attenuators; d, FM oscillators; e, magnetic tape 

recorder; /,chronograph; g, WWV radio receiver; h, tape 

playback and filter sections; i, oscillograph; j, audiodetector 

for WWV; k, low-pass filters; l, oscilloscope for visual 

monitoring of any channel. 

maintained by a governor control. Usually the frequency was maintained at 59 to 61 cps. All components in the recording system were designed for 

long-term, but not necessarily continuous, operation. 

Nearly continuous operation could have been maintained for the 2-week periods if various mechanical 

cooling-system failures had not occurred in the 

motor-generator unit. 

METHODS OF SEISMIC INTERPRETATION 

Hypocenters (map positions and focal depths) of 

tremors recorded by both temporary networks were 

determined using methods developed in the operation of the Sunnyside network. Seismic wave traveltime curves were plotted in color on clear mylar to 

make a protractor to be laid over a map of the area, 

using information obtained from three seismic refraction profiles in the Sunnyside district (Tibbets 

and others, 1966). The curves were drawn in different colors for easy reference by the operator. Because available geologic information indicated that 

seismic velocities in the Gentry Mountain and Little 

Park Wash area were about the same as at Sunnyside, this protractor was used without modification 

in both experiments. 

To locate a tremor hypocenter, the operator measured from the seismogram the arrival time of the 

compressional wave and shear wave at each seismometer. A graph was then constructed to determine the origin time of a tremor, by plotting the 

difference in arrival times between compressional 

and shear waves at each seismometer against lapse 

of time, on the assumption that both waves were 

generated simultaneously at the tremor source. 

Travel times of the waves to each seismometer were 

determined by measuring the arrival time of the 

compressional wave at each seismometer and subtracting from it the graphically determined origin 

time. 

Compressional wave traveltimes for a selected 

tremor were fitted to traveltime curves on the 

protractor by a method of repeated trials using successive approximations and gradually reduced errors 

to obtain the best solution. The hypocenter was 

located at one of the intersections of two families 

of irregularly elliptical curves when a best fit was 

achieved (fig. 11). 

The traveltime curves on the protractor show in 

three dimensions the distance that direct and refracted compressional waves will travel radially 

from a source, in 0.1-second intervals for tremor 

sources ranging from 0 to 10,000 feet deep. When 

the oscillograph was operated at a speed of about 

2 inches per second, timing lines were placed on 

the oscillograms every 0.1 and 0.01 second so that 

milliseconds could be interpolated if necessary. Interpolation between the curves on the protractor, 

coupled with the accuracy of oscillogram timing, 

yielded hypocenters accurate to within 750 feet horizontally and vertically of their true locations at 

both Gentry Mountain and Little Park Wash. Hypocenters of tremors for which no magnetic tape 

record was available, however, were accurate only 

to within 2,500 feet of their true locations, because 

arrival times of compressional waves were measured 

only on the paper records. 
GENTRY MOUNTAIN MONITORING EXPERIMENT 7 

QI Q2 Q3 Q4 Q5 

8.2 8.06 

0.5A. 12.8vdc 50vdc 

>OO~ 250K 1210 

lw 

CD 170I'fd 1701'fd ~~ 15v 15v + p 

2 60 + 82 

!50 3.9K !'fd 60.4K 1200 3.3K - !'fd K - 50v lOW 

50v !) --=1 

!801'fd 3001'fd 

50v 50v 

15K + -

{, 220K 1300 47K 47 30K 150 20K 150 30K 1500 Output to 

chart recorder 

NE-51 

IR203 

BISI 

IR203 

BIS! 

lOW 

2600 + l'fd 

15v -

25 

100W 

300 + 

jbe T 

IN2046 

+ 50vdc 

450ma 

0 

CD Channel I of 6 channels 

f2\ Emitter resistor 1 V is 2-70Q £L and 

1-100"'- lOW in series. 

Ql, Q2-2N2219 

Q3, Q4-2Nl480 

Q5 -2Nl208 

Resistances in ohms. 

Current in milliamperes 

Gain= 10 

Frequency response: 

1-1000 cps. 

Drawn by: J . 0. Maberry 

Checked : J. B. Bennetti, Jr., electronics engineer 

FIGURE B.-Schematic diagram of pen-drive amplifier and power supply. 

1.5 ~------,---1------.,---1--------, 

>-

t:: 

z 

~ 

0 

f- 1.0 -

0 

w 

N 

_J 

<( 

::. 

a:: 

~05 

~ 

~ 

0.. 

f-

~ 

0 

I 

20 40 60 

FREQUENCY, IN CYCLES PER SECOND 

Drawn by: .J. 0. Maberry 

Checked : J. B. Benn etti , Jr. , electronJCS engineer 

FIGURE 9.-Frequency response curves for pen-drive amplifier 

and for pen-drive amplifier plus penmotor. 

GENTRY MOUNTAIN MONITORING EXPERIMENT 

The vicinity of Gentry Mountain, 37 miles west of 

Sunnyside and 16 miles southwest of Price, Utah 

(fig. 1), was selected for the first seismic monitoring 

experiment because of its geologic similarities to the 

Sunnyside district, its geographic position near the 

coal mining district near Hiawatha, Utah, in the 

Wasatch Plateau coal field, and its gently sloping 

upland topography. 

The upland surface of Gentry Mountain is underlain by limestones and calcareous claystones of the 

Flagstaff Limestone (Paleocene and Eocene?). Noncoking bituminous coals in the Blackhawk Formation (Upper Cretaceous), crop out about 1,700 feet 

below the surface of Gentry Mountain in the cliffs 

to the east and along canyon walls of branches to 

Huntington Creek Canyon (fig. 1) to the west of 

the summit. These coals were deposited in a regressive sequence of marine, brackish-water, and 

nonmarine sediments similar to but stratigraphically 

below the sequence at Sunnyside, Utah (Clark, 1928, 

p. 15-16; Spieker, 1931, p. 26-27, 37-39; Young, 

1955). Large, generally northwest-trending sandstone-filled channels in coal, known as "washouts" or 

"wants" by miners, occur at Hiawatha (Spieker, 
8 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

>-

t::: 

z 

:::l 

0 

.... 

0 

u.J 

LOt-----

:;as 

< 

:I; 

0 "' z 

...: 

:::l 

"-

.... 

:::l 

0 

~----~25~--------~ ~--~~------ loo 

FREQUENCY, IN CYCLES PER SECOND 

Drawn by: J . 0 . Maberry 

Checked : J . 8 . Bennett i, Jr., electron iCS eRg1neer 

FIGURE 10.-Frequency response of optional low-pass filter for 

tape recorder. 

1931, p. 63-64). Thick persistent beds of sandstone 

underlie the coals in both districts; at Gentry 

Mountain the sandstone beds form large, east-facing 

faceted cliffs which have many reentrants at the 

base of the Wasatch Plateau (Spieker, 1931, p. 7-8). 

Light-colored fine-grained igneous rocks were intruded along faults cutting rocks probably as young 

as Eocene (Flagstaff Limestone) , both as dikes and 

as irregular masses west of Gentry Mountain (fig. 

12). East of Hiawatha, dark-brown fine-grained 

micaceous igneous rocks were emplaced in Mancos 

Shale (Upper Cretaceous) as irregular masses along 

small faults. 

Conspicuous north-trending faults cut the western 

part of the Gentry Mountain area and divide it into 

a series of ridges and valleys (known locally as 

"hollows") (fig. 13) that corresponds to a series of 

horsts and grabens. These faults displace a stripped 

surface upon the Flagstaff Limestone by as much as 

several hundred feet. The stripped surface, presumably of late Tertiary or early Quaternary age, 

has a soil mantle as much as several feet thick. The 

soil locally contains residual limestone nodules, and 

it is found along the floors of hollows as well as on 

tops of ridges. Soil is thicker along the flanks of 

some ridges than on the tops. The soil probably is 

older than the major faulting. 

Small stream courses are entrenched in some of 

the hollows, particularly near their confluence with 

large canyons. Large canyons tributary to Huntington Creek Canyon (such as Tie Fork Canyon shown 

in figs. 12 and 15) have cut across the hollows and 

ridges and apparently are the result of rapid erosion 

along modern master streams. 

MINING IN GENTRY MOUNTAIN AREA 

Room-and-pillar mines were opened at the outcrops of the coal beds near the towns of Wattis, 

Hiawatha, and Mohrland (fig. 1) between 1909 and 

1917 (Spieker, 1931, p. 2-3). Some sections of the 

mines at Hiawatha and Wattis were mined during 

the present study. In general, raises and slopes were 

driven up and down the very gentle westward and 

southwestward dips beneath Gentry Mountain. Entries were driven from the raises and slopes nearly 

parallel to the strike in both directions. Rooms were 

turned at intervals from the entries. Because of 

the very gentle dips and varying strike, mining produced a complicated pattern of workings wherein 

large unmined blocks of coal are surrounded by 

areas containing numerous pillars. 

Extraction in previously mined areas is not complete. Large parts of Gentry Mountain are underlain by old mine workings that contain numerous 

small unextracted pillars which probably are highly 

stressed. Mining in the area is limited on the west 

by the easternmost of the north-trending high-angle 

faults (known locally as the Bear Canyon fault) because information from exploratory workings indicates that large inflows of water could be expected 

if mine workings were extended through the fault 

(M.A. Robb, oral commun., 1966). Large dangerous 

bumps have occurred in the mines (John Peperakis, 

oral commun., 1961), but serious mining problems 

have been avoided by abandoning mine sections 

prone to bumps. 

FIGURE 11.-Traveltime-curve protractor used to locate tremor 

hypocenters. Each curve in a family of irregularly elliptical curves represents the traveltimes of compressional 

waves originating at different depths from the central area 

of the family of curves. When the predetermined correct 

traveltime curve intersects the map position of each seismometer, the hypocenter of the tremor is found at the 

center of the family of curves. Curves are of different 

colors for easy reference by the operator. 
GENTRY MOUNTAIN MONITORING EXPERIMENT 9 

FIGURE 12.-Intrusive rocks west of Gentry Mountain, in northwest wall of Tie Fork Canyon. Left, Light-colored dikes in 

north-trending faults cutting Castlegate Sandstone (Cretaceous); Right, Light-colored intrusive mass in north-trending 

faults cutting strata from Castlegate Sandstone (Cretaceous), at bottom of picture, to North Horn Formation (Cretaceous 

and Paleocene) on skyline along northwest wall of Tie Fork Canyon. Fault is the east side of a graben forming Wild 

Cattle Hollow. 

SUSMIC WORK AT G•:NTRY MOUNTAIN 

Seismic activity at Gentry Mountain was monitored between August 28 and September 10, 1967. 

Recording was not continuous during this period 

because of several mechanical failures and because 

cattle frequently broke the signal wires. Actual recording time is estimated to be about 75 percent of 

the total time. 

Seismometers were arranged in two elongated 

triangular arrays in the western part of the Hiawatha mining area (fig. 15); part of the southern 

array was adjacent to the active mining sections of 

the King mine No. 2. Geologists conducting this 

study lengthened the westward-trending legs of both 

arrays to cross some of the north-trending horsts 

and grabens (McCadden and Gentry Hollows) in the 

hope that epicenters and focal depths of tremors 

originating along the faults might be accurately 

determined. 

During the time the Gentry Mountain network 

was operated, 109 seismic tremors were recorded; 37 

tremors were large enough to measure and to determine positions of hypocenters. Most of these were 

of local origin; their sources were within the area 

of the network. A few distant earthquakes were 

recorded, and the response of the mobile system was 

calibrated roughly by comparing the amplitudes of 

these earthquake records with amplitudes of the 

same earthquakes on records from the Sunnyside 

network on which magnitudes could be determined. 

Recorded were at least two sonic booms from aircraft that were felt and heard by project personnel. 
10 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

FIGURE 13.-Graben and fault near Gentry Mountain. 

Upper, View south along crest of Gentry Mountain showing graben of McCadden (left distance) and Gentry (right 

foreground) Hollows; Lower, Bear Canyon fault cutting 

Flagstaff Limestone (Paleocene and Eocene?) near east 

margin of McCadden Hollow. Outcrop is along steep northeast wall of Huntington Creek Canyon that has resulted 

from late-stage rapid erosion along modern drainage 

systems. U, upthrown side ; D, downthrown side. 

Richter magnitudes of the seismic waves generated 

by these sonic booms were estimated to be between 

1.0 and 1.8, compared with seismograms of earthquakes of similar magnitudes. 

Two general types of tremors were recorded at 

Gentry Mountain. One type consisted of numerous 

small shallow-focus tremors originating within or 

near the mining areas and producing seismograms 

similar to those of most tremors recorded at Sunnyside (figs. 14, 17). Tremors of the second type produced seismograms with longer wave trains in which 

wave groups were separated (fig. 16) and originating at slightly greater depths than those of the first 

type. 

Although tremors of the first type originated in 

or near mining areas, they were more frequent on 

days when no mining was done (fig. 18A), in contrast to similar tremors at Sunnyside which are 

more numerous during times of active coal mining. 

The tremors were not caused by blasting in the 

mines, because nearly all occurred at times when no 

blasting was being done (M. A. Robb, written 

commun., 1967). Tremors from a few blasts were 

recorded, but these were of small amplitude and 

were detected by only one seismometer near the 

actively mined sections. The cyclic pattern of these 

tremors differs from that of similar tremors at 

Sunnyside (fig. 18A, B), probably because of differences in geologic structure and mining practices 

at the two localities. Tremors of the first type probably result from the redistribution of stresses as a 

result of mining. The sharp rise in daily number 

of tremors during mining in the northern part of 

the Sunnyside district as compared to the drop in 

daily number of tremors during mining at Gentry 

Mountain (fig. 18A) may be due to different mining 

procedures at Gentry Mountain. Most of the mining 

beneath Gentry Mountain is development work, in 

which pillars are left standing, whereas most at 

Sunnyside is production work in which as many 

pillars as possible are completely removed. Stress 

probably is relieved much more slowly during development work because support is removed slowly. 

The differences in the number of tremors in the 

northern and southern parts of the Sunnyside district (fig. 18B) may be the result of differences in 

fault patterns in the two parts of the district 

(Barnes and others, 1969, p. 3). 

Recorded at Gentry Mountain, tremors of the 

second type, which originated along the major 

north-trending faults bounding the west side of 

Gentry Mountain, were much less frequent than 

those of the first type and showed no apparent correlation with mining. These tremors probably result 

from release of stress concentrated along the faults. 

Some of this stress concentration may be due to 

readjustments made in response to mining, but some 

may be due to release of natural stress. Existence 

of natural stress in the area is probable, because 

small earthquakes are reported commonly along 

similar north-trending faults a few miles to the 

west of Gentry Mountain (for example, see U.S. 

Coast and Geodetic Survey, 1968, p. 5). 

LIITLE PARK WASH MONITORING EXPERIMENT 

The area of Little Park Wash is an intermittent 

stream valley east of and nearly parallel to the westfacing Book Cliffs about 13 miles south of Sunnyside, Utah. It was selected for the second monitoring 

experiment because of access afforded by an oc-
LITTLE PARK WASH MONITORING EXPERIMENT 11 

Seismometer station 1 

~1111 f~lllllfiHII rnJJ 11 11 H111*1TH Sei smometer station 2 

111111 ! i l-1111 Jtl r I1 H 111111111 ~ II~ l f II Sei smometer station 3 

\ - 1-= ·- 1- - - I= 

-=- - -- - - -- 1=:: 

-

1.-: \ - .. 

~ ~ 

nr I -~ 

1·- -

- I 

1-

Setsmometer station 4 

f-0" 

Seismometer station 5 

I I I [ -1 ;I I I I I I I I I I, I ! I I I I I I I ! I I I ~1 -1 I I I 1-J I_ I2202 GMT 2205 GMT 

Seismometer station 6 0 1 MINUTE \ _ ______ __ __] 

FIGURE 14.-A. Seismogram showing first type of tremor 1·ecorded at Gentry Mountain, Sept. 4, 1967; Richter magnitude, 1.4; 

epicenter shown on figure 15 by letter A. B. Seismogram showing first type of tremor recorded at Gentry Mountain, 

Sept. 4, 1967; Richter magnitude, 1.9; epicenter shown on figure 15 by letter B. 

casionally maintained road which crosses a conspicuous belt of west-northwest-trending faultsand because it overlies a large block of unmined coal 

about 15 miles by 5 miles in map dimensions adjacent 

to the Sunnyside district, where future mining is 

planned. Some tremors recorded by the Sunnyside 

monitoring network probably originated along this 

fault belt, even though it was impossible to determine their epicenters accurately because of their 

distance outside the network. Local mine officials 

shared the authors' opinion that movements were 

occurring along faults in the belt, as indicated by 

the active rockfalls from the face of the Book Cliffs 

(J. B. McKean, oral commun., 1968). Whether or 

not tremors occur in an area of coal deposits before 

mining begins is of considerable scientific and economic interest in predicting future mining conditions and in determining whether natural stresses 

cause the numerous tremors that occur in the Sunnyside district. 

Little Park Wash is an intermittent stream that 

flows generally southward an unusually short dis-
12 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

T 

15 

s. 
LITTLE PARK WASH MONITORING EXPE~JMENT 13 

0 

EXPLANATION 

[EJ . 

. 

. 

. 

Flagstaff Limestone 

[~~~] North Horn and Price River Formations, 

Castlegate Sandstone, and Blackhawk 

Formation 

Dashed line indicates approximate position 

of coal 

Mancos Shale 

Contact 

u 

D 

Fault 

Dashed where approximately located. U, 

upthrown side; D, downthrown side 

•1 

Seismometer station 

• 

Recording van and camp 

Tremor epicenter 

Number ·indicates Richter magnitude; 

letter indicates tremor shown onfigures 

14.16 

Generalized outline of 

mine workings 

SCALE 1:62 500 

}i 

til 

::J 

0 

w 

u 

<( 

1-

w 

0:: 

u 

2 MILES 

0 2 Kl LOM ETERS 

FIGURE 15.-Map of Gentry Mountain area, showing generalized geology, temporary seismometer locations, tremor 

epicenters, and generalized mine workings. Seismograms 

for hypocenters A and B shown on figure 14 ; for C, 

on figure 16 . Geology by C. R. Dunrud and F. W. Osterwald, 1967, modified in part from Spieker (1931). Base 

from U.S. Geological Survey, Hiawatha and Scofield 15-

minute quadrangle maps, 1:62,500, 1923. 

tance behind the main escarpment of the Book Cliffs 

(fig. 1). A broad alluvial flat entrenched as much 

as 15 feet by the present stream extends along the 

upper course of Little Park Wash. Meanders in the 

lower course are entrenched as much as 250 feet 

into the Bluecastle Sandstone Member of the Price 

II 

I 

River Formatioi and into the Castlegate Sandstone. 

Near the Pric~ River the wash is entrenched into 

the Blackhawk Formation. The wash is a major 

tributary to the Price River, which is superimposed 

upon the present regional structure and topography. 

Little Park Wash, however, soon will be captured by 

westward-trending watercourses down the face of 

the Book Cliffs. At one point near the recording 

van and camp (fig. 21) the bed of the wash is less 

than a fourth of a mile from the face of the cliffs. 

In sec. 26, T. 16 S., R. 14 E., one of the major 

tr-ibutaries to Little Park Wash already has been 

captured. Because they cause rapid erosion, 

ephemeral streams on the Mancos Shale and along 

the face of the cliffs are forming a new westwardand southwestward-flowing drainage pattern which 

is destroying the older superimposed drainage 

pattern. 

Most of the land surface in the Little Park Wash 

area was formed on the Bluecastle Sandstone Member of the Price River Formation (Upper Cretaceous), the Castlegate Sandstone (Upper Cretaceous) , and the calcareous mudstones, siltstones, 

and sandstones of the North Horn Formation (Upper Cretaceous and Paleocene). Locally, residual 

sandy soil has formed on the surface, and many 

watercourses are filled with alluvium. A steep, 

maturely dissected upland ridge of alternating layers of reddish cliff-forming sandstones and nonresistant calcareous mudstones of the Colton Formation (Eocene) trends northward roughly parallel to 

and 1 to 3 miles east of Little Park Wash. Locally, 

sandstones of the North Horn Formation and sandstones and limestones of the Flagstaff Limestone 

(Paleocene and Eocene?) form benches 25-100 feet 

above the alluvium-covered floor of Little Park 

Wash. 

Structure in the Little Park Wash area is simple. 

Rocks near Little Park Wash dip eastward from 

5o to 10°. They are cut by a few steeply dipping 

east- and southeast-trending normal faults and have 

as much as 275 feet of stratigraphic separation, although the amount of separation lessens to the east 

as the faults pass upward into the Colton Formation. The rocks are also cut by a swarm of westnorthwest-trending faults that is part of a major 

fault belt, as much as 4 miles wide, which was 

traced northwestward about 28 miles from the confluence of Range Creek and the Green River (fig. 

1). Structure sections through this fault belt suggest that it is the collapsed crest of a faulted 

anticline. 

Bituminous coking coal in the Blackhawk Forma-
14 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

Seismometer station 2 

Seismometer station 3 

Seismometer station 4 

0 1 MINUTE 

FIGURE 16.-Seismogram showing second type of tremor recorded at Gentry Mountain, Sept. 8, 1967; Richter magnitude, 1.9; epicenter shown on figure 15 by letter C. 

tion (Upper Cretaceous) underlies Little Park Wash 

between 100 to 850 feet below the surface, in the 

area of figure 21. Below the coal is a persistent 

cliff-forming sandstone unit about 130 feet thick; 

above the coal is a 100- to 200-foot-thick sequence 

of siltstone and shale beds, containing lenses of 

thin-bedded sandstone, which is overlain by the 

Castlegate Sandstone. The coal and its associated 

rocks are part of a regressive sequence of marine, 

brackish-water, and nonmarine rocks which were 

formed during a generally eastward withdrawal of 

the Cretaceous sea (Spieker, 1949). 

MINING AT LITTLE PARK WASH 

The Geneva (Horse Canyon) coal mine, from 

which much of the coal mined in the Sunnyside 

district is produced, is a few miles north of the 

Little Park Wash area (fig. 21). Coal is mined in 

the Geneva mine by driving multiple entries nearly 

parallel to the strike of coalbed outcrops in Horse 

Canyon; slopes are driven downdip at intervals 

along these entries. Other multiple entries are 

driven nearly parallel to the strike at intervals along 

the slopes. Coal beneath large westward-projecting 

points of the Book Cliffs that are isolated by deep 

canyons is mined from raises driven updip. All 

mining is by room-and-pillar methods, in which 

rooms are driven updip from various entries, and 

pillars are extracted during the retreat. A pair of 

exploratory entries were driven southeastward from 

the Geneva mine into a large block of unmined coal 

beneath the northern part of the Little Park Wash 

area; otherwise, no mining has been done in the 

area of the monitoring experiment. 

Coal extraction within the Geneva mine has not 

been complete, partly because of difficulty in controlling the roof when some pillars are removed and 

partly because some large blocks of coal are lost 

through damage from bumps. Large bumps have 

occurred in the mine (Dunrud and Osterwald, 1965, 

p. 177, 180-181). Many earth tremors, some of 

them related in space or time to bumps, were recorded in and near the Geneva mine by the Sunnyside seismic monitoring network ( Osterwald and 

Dunrud, 1966, p. 103-104). 

The Book Cliffs mine also was located a few miles 

north of the Little Park Wash area and about 1 mile 

south of the Geneva mine portal (fig. 1). The mine, 

which was owned by the Book Cliffs Coal Co., was 

opened about 1945 as a source of industrial coal. 

Multiple entries were driven at small angles to the 

strike, and diagonal raises were driven at angles of 

about 30° to these entries. Areas between diagonal 

raises were opened by rooms and crosscuts driven 

nearly parallel to the strike and dip. Square pillars 

that resulted from opening the rooms and crosscuts 

were removed in final stages of mining. The mine 

was small, occupying only the area beneath two 

prominent westward projections of the Book Cliffs, 

but mining was profitable because the coal was as 

much as 22 feet thick. As pillars were removed, 

spectacular subsidence cracks appeared in the Book 

Cliffs, and many loose rocks fell from the cliffs. The 

mine was abandoned in 1967. 

SEISMIC WORK AT LITTLE PARK WASH 

Seismic activity along Little Park Wash was 

studied from August 17 to August 30, 1968. Two 

elongated triangular seismometer arrays that 

trended roughly north-northwest were arranged so 

that the northernmost seismometer was more than 

7 miles from the southern (fig. 21). The northern-
LITTLE PARK WASH MONITORING EXPERIMENT 15 

-r- ---1--

F- --~---+ 

)--

----t---- 1-- 1-

f~ --t--- - ·--

-- 1+-· --- 1--- ---

i--'h--- c--- .· . .:. --~------- ·- ---+-----c 1--

- ----· 

~-=:...c-!8~1-- ~------=- - 1---t ·- t~=~- __ -- <--" f-- t- - -+-- t-- l---\--- ·-c.;::...-:::-. r---=--~~-+ --- . t- - +---+-- 1-+- +- ~-- -+- -+--. 1---- +- -- ~=1-- + --'1--- + r- -+- -+-----\-- \-"'-- ~-1='-F A 

\="-=---\- ··-\-· -+--+- + - · -~ 't- +·cc-..cW·,'; -H- ~:-.--\-- -\ ~r-----\------1---+--·c -\-----\· ·l \----1- ---\-----\-- ----\·c-·t---i-·--+ \---·+ ,. '~' 

/.· 439 GMT+ 13.6 seconds . ¥1'/: .J 1 JJ 1441 GMT+ 13.6 s~cond!;\ /--+ /'-- -f--+--1----f-- ~ tl F:::·F--i----1- +-+-+ -f--+-- .. · -+---+---l--+-+.,+--+--R 

-1--+---f-- +¥--'---!---- --~-~--- f--+--f i 

_,...-::{,- -+---+--t --- t--:::h:-1 

j- -.- j--· - i---- --- -->---+---

. -+---'-- ·-----

1-· --

·--· ·--

--- ~-- -!- - +-~-~-~=-+-~~ .c .. --- t- Cc_:_ 

'------+-- +-- ----\-- +---- -+------+------ ~- c-- +---

--tc ___ \. -~t--t:- \--- =f' ::F --+-- +--·-+- -\----+ -\---+. l; -+ +-~-- +---~\ 

0 MINUTE 

FIGURE 17 .-Seismogram of large local tremor recorded in northern part of Sunnyside district, Dec. 26, 1963 ; Richter 

magnitude, 3.7. 

most seismometer was about a half mile north of 

the southern boundary of the Geneva mine. This 

distance between the two seismometer arrays was 

considered necessary to insure a distinction between 

compressional seismic waves that were refracted 

along a layer of Paleozoic carbonate rocks (Tibbetts 

and others, 1966) and compressional waves that 

traveled directly from their sources. Consequently, 

focal depths of the tremors could be determined 

accurately. 

Recording on chart paper was almost continuous 

during the monitoring period except for short times 

when the motor-generator was shut down for 

servicing, and it was estimated to be effective more 

than 90 percent of the total time. Recording on 

magnetic tape was lost for about 36 hours during 

the first part of the recording period because some 

personnel were unfamiliar with operation of the 

tape deck. High winds produced excessive "tree 

noise" during the first few days of recording. "Tree 

noise" is caused by wind moving trees, which in 

turn locally move the ground. After a few trees 

near the seismometers were removed, records became very clear. 

About 70 tremors were recorded by the network 

along Little Park Wash. Nearly all of these tremors 

large enough to measure (Richter magnitudes ranging from 1.5 to 2.8) originated in or near the 

southern part of the Geneva mine at depths of as 

much as 3,000 feet below the mine level and within 

7,000 feet laterally of the active mining area (fig. 

21) . Most were restricted to a block bounded on 

two sides by eastward-trending faults. Nearly all 

the tremors too small to measure were recorded 

only by the seismometers closest to the Geneva mine, 

which indicates that these small tremors also originated in or near the southern part of the Geneva 

mine (fig. 19). A few tremors of small amplitude 

and long wave train were recorded (fig. 20); their 

epicenters were southwest of the network and probably were within the San Rafael Swell (fig. 1). 

Some of the tremors within or under the Geneva 

mine were sufficiently large to be recorded also by 

the Sunnyside network; therefore, amplitudes could 

be compared between the two networks. 

The occurrence pattern of tremors recorded at 

Little Park Wash corresponds generally with the 

occurrence pattern of those recorded at Sunnyside. 

The pattern particularly corresponds to the mining 

work cycle in the Geneva mine (fig. 22A), although 

individual peaks and troughs during the latter part 

of the recording period do not precisely coincide. 

This lack of coincidence is not clearly understood, 

but it is probably the result of the response of the 
16 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

(f) 

0:: 

0 

~ 

w 

0:: 

fLJ.. 

0 

0:: 

10 

/ ;: 

30 31 I 2 3 

August I 

A 

y_ X 

4 5 6 

September 

~200,--,--,-~--~~--~~--~~--~~~~~ 

~ 

::J 

z 100 

10 

August September 

FIGURE 18.-Semilogarithmic plot of recorded tremors per 

day at Gentry Mountain (A) and at Sunnyside (B) for the 

period August 30 to September 10, 1967. H, Horse Canyon 

seismometer (southern part of Sunnyside district); B, 

Bear Canyon seismometer (northern part of Sunnyside 

disti·ict). X, day the mines were worked. Broken curve indicates day of poor data because of equipment failures. 

Horse Canyon seismometer to stress readjustments 

along faults in the abandoned Columbia mine (fig. 

1). Differences were expected in the occurrence pattern curves from the seismometers of the network 

at Little Park Wash and that at the Bear Canyon 

locality of the Sunnyside district. These differences, 

which are similar to those noted previously by 

Barnes and others ( 1969, p. 3), probably arise because geologic features and mining practices are 

different in the northern (Bear Canyon) and 

southern (Horse Canyon) parts of the Sunnyside 

district. 

Seismograms are affected by the source mechanism at the focus of tremors, by the paths of seismic waves through the earth, and by geologic features along the paths of waves (Simon, 1968, p. 1). 

Similar seismograms, therefore, if recorded on similar instruments, suggest similar tremor origins and 

similar paths of the resulting waves. Most tremors 

recorded at Little Park Wash yielded seismograms 

similar to many of those recorded at Sunnyside, as 

well as to those of the first type recorded at Gentry 

Mountain (figs. 14, 16, 17, 19, 20). These similarities indicate that all these tremors were of similar 

origin and were caused by shallow stress readjustments to mining activity. They were small manmade 

earthquakes. 

SUMMARY AND CONCLUSIONS 

Earth tremors that originate in coal mining areas 

are related to geologic features and to active coal 

mining. Because of the cyclic pattern of occurrence 

of such tremors, special components and techniques 

are needed to permit nearly continuous seismic monitoring under difficult field conditions for a· period 

of at least 2 weeks, or for a period long enough to 

include at least one cycle of repetition. Results from 

seismic monitoring experiments at Gentry Mountain 

and Little Park Wash, Utah, indicate that the seismic activity recorded by a fixed network in the 

Sunnyside district, Utah, is not unique because similar kinds and similar numbers of tremors occur in 

and around at least one other active coal mining 

area. Shallow-focus tremors at Gentry Mountain 

occur in and around active mining areas, as do 

similar tremors at Sunnyside. A large block of 

unmined coal adjacent to the Sunnyside district in 

the Little Park Wash area was seismically quiet 

during the monitoring period. These facts indicate 

that large stress concentrations may be caused by 

removal of coal. As shown by the distribution of 

hypocenters, stress readjustment may extend 

thousands of feet below, and as much as 2 miles 

distant from, active mining areas. 

Faults are convenient loci for stress concentrations resulting from mining in nearby areas. Although some tremors originated along faults outside 

active mining areas at Gentry Mountain, very few 

tremors occurred in similar environments at Little 

Park Wash. Natural stress may have more influence on the generation of some tremors at Gentry 

Mountain because of the major faults that form the 

eastern margin of the Wasatch fault zone. These 

faults are sources of many earthquakes. 
LITTLE PARK WASH MONITORING EXPERIMENT 

Seismometer 

station 1 

I 

I 

I 

i 

I 

I 

Seismometer , 

station 2 i 

I 

Seismometer 

station 4 

Seismometer 

station 5 

Seismometer 

station 6 

I 

I I 

(J 

I I 

, I 

I 

l 

I 

I 

I 

I ! 

I 

_1 1 

, I 

i 

I 

I 

I 

I i I ! I i 

! ! 

I 

I I 

I 

i 

I I i 

i l i i 

! I I 

i ! i 

i : I ! 

[ ! ! 

i 

I 

I ! i i ! I ! I 

I i ! I I : 

I ! I l ! 

I ! ! ! 

i I ! 

I ! 

1-1 

i 

I 

I ~ 

I 

! 

I I 

i I I 

I I 

I I 

n I ! i 

I I i I i I I 

I I I ! l I i I 

i I 

I ! I I 

I 

I I I 

I I i I ! I 

I 

I I I i I 

I 

I ! I I I I I ! 

2400 0001 GMT 

0 1 MINUTE 

L____j 

FIGURE 19.-Seismogram of tremor in southern part 

of Geneva mine, recorded at Little Park Wash, 

Aug. 26, 1968; Richter magnitude, 2.0; hypocenter 

is marked D on figure 21. 

Seismometer 

station A 

I 

I 

I 

I 

I 

I 

I 

I 

I 

! 

I 

I 

I 

I 

I 

i 

! 

Seismometer !--! -----+-1---f.---1--J.I 

station C I 

Seismometer 

station E 

I 

I 

I 

I 

~ 

I i I i l 

I I i 

I 

! i I 

1 1 1 1 r I I ' 

I i I l 

I 

I 

I ' 

I 

! 

I I 

2230 GMT 

0 1 MINUTE 

L____j 

FIGURE 20.-Seismogram of tremor recorded at 

Little Park Wash, Aug. 26, 1968, from source 

south and west of network; Richter magnitude 

unknown. 

17 
18 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 
LITTLE PARK WASH. MONITORING EXPERIMENT 19 

!{ 

EXPLANATION 

Colton Formation 

EJ 

Flagstaff Limestone and North Horn Formation 

Price River Formation 

Castlegate Sandstone and Blackhawk Formation 

Dashed li'TU! indicates approximate position of coal 

Mancos Shale 

Contact 

u 

D 

Fault 

Dashed where approximately located. U, upthrown 

side; D, downthrown side 

~~.a 

Seismometer station 

~ 

Recording van and camp 

() 2.0D el.9 () 2.2 

Sea level to 2,000- 4,000-

2,000 feet 4,000 feet 6,000 feet 

Tremor hypocenters 

Showing altitude above sea level. Numbers indicate 

Richter magnitude; letter indicates tremor shown on figure 19 

Generalized outline of workings of Geneva mine 

SCALE I :62 500 

0 2 MILES 

0 2 Kl LOM ETERS 

>-

a:: 

<( 

!= 

a:: 

w 

ftn 

::l 

0 

w 

u 

<( 

fw 

a:: 

u 

FIGURE 21.-Map of Little Park Wash area, showing gen-

. eralized geology, temporary seismometer stations, tremor 

epicenters, and generalized mine workings. Geology by 

J. 0. Maberry and F. W. Osterwald, 1968. Base from U.S. 

Geological Survey, Woodside, 15-minute quadrangle map, 

1:62,500, 1948. 

100 

A 

10 

en 

a:: 0 

0 

:2: ;X X X X X X X X X 

w 

a:: 

fu.. August 

0 

a:: 

w 200 CD 

:2: 

~ 100 B 

H 

--- No data --

10 

X X X X X X X X 

17 23 24 29 

August 

FIGURE 22.-Semilogarithm,ic plot of recorded tremors per 

day at Little Park Wash (A) and at Sunnyside (B) for 

the period August 17-30, 1968. H, Horse Canyon seismometer (southern part of Sunnyside district); B, Bear 

Canyon seismometer (northern part of Sunnyside district). 

X, day the mines were worked. 

Cyclic repetition of shallow-focus tremors recorded at Little Park Wash shows a general relation to mining work cycles, as do similar tremors 

recorded in the southern part of the Sunnyside mining district. Similar ~.-yclic repetition of tremors at 

Gentry Mountain does not coincide with mining 

workweeks, however, possibly because the mines 

there are engaged primarily in development work 

and both stress accumulation and stress release are 

slower at Gentry Mountain than in the Sunnyside 

district. Rapid release of stress as pillars are removed in the Sunnyside district accompanies actual 

mining work cycles, as indicated by the daily correlations between tremors and work cycles. The 

stress-relief effectiveness of pillar removal and the 

resulting collapse of mine roofs were shown vividly 

by final operations of the Book Cliffs Mine. 
20 EARTH TREMORS, CENTRAL UTAH COAL MINING AREAS 

REFERENCES CITED 

Barnes, B. K., Dunrud, C. R., and Hernandez, Jerome, 1969, 

Seismic activity in the Sunnyside mining district, Utah, 

during 1967 : U.S. Geol. Survey open-file report, 26 p. 

Clark, F. R., 1928, Economic geology of the Castlegate, Wellington, and Sunnyside quadrangles, Carbon County, 

Utah: U.S. Geol. Survey Bull. 793, 165 p. 

Dunrud, C. R., and Osterwald, F. W., 1965, Seismic study of 

coal mine bumps, Carbon and Emery Counties, Utah: 

Am. Inst. Mining Metall. and Petroleum Engineers 

Trans., v. 232, no. 2, p. 174-182. 

Maberry, J. 0., 1966, Instrumentation installations for the 

study of coal mine bumps at Sunnyside, Utah: U.S. 

Geol. Survey open-file report, 12 p., 5 figs. 

Osterwald, F. W., and Dunrud, C. R., 1966, Instrumentation 

study of coal mine bumps, Sunnyside district, Utah: 

Utah Geol. and Mineralog. Survey Bull. 80, p. 97-110. 

Simon, Ruth B., 1968, Earthquake interpretations: Colorado 

School of Mines; Golden, Colo. [85 p.]. 

Spieker, E. M., 1931, The Wasatch Plateau coal field, Utah: 

U.S. Geol. Survey Bull. 819, 210 p. 

--- 1949, Sedimentary facies and associated diastrophism 

in the Upper Cretaceous of central and eastern Utah, in 

Longwell, C. R., chm., Sedimentary facies in geologic 

history [symposium] : Geol. Soc. America Mem. 39, p. 

55-81. 

Tibbetts, B. L., Dunrud, C. R., and Osterwald, F. W., 1966, 

Seismic-refraction measurements at Sunnyside, Utah, in 

Geological Survey research 1966: U.S. Geological Survey 

Prof. Paper 550-D, p. D132-D137. 

U.S. Coast and Geodetic Survey, 1968, Preliminary determinations of epicenters: Monthly Listing, November, 8 p. 

Young, R. G., 1955, Sedimentary facies and intertonguing in 

the Upper Cretaceous of the Book Cliffs, Utah-Colorado: 

Geol. Soc. America Bull., v. 66, no. 2, p. 177-201. 

'¢r U, S. GOVERNMENT PRINTING OFFICE: 1971 0- 441-234