Seismic Activity During 

the 1968 Test Pumping at 

the Rocky Mountain Arsena I 

Disposal Well 

By D. B. Hoover and J. A. Dietrich 

GEOLOGICAL SURVEY CIRCULAR 613 

This report concerns work 

done in cooperation with the 

U.S. Army Corps of Engineers 

COLORADO WATER 

RESOURCES LIBRARY 

U.S. GEOLOGICAL SURVEY 

WRD. DENVER 

Washington 1969 
United States Department of the Interior 

STEWART L. UDALL, Secretary 

Geological Survey 

William T. Pecora, Director 

Free on application to the U.S. Geological Survey, Washington, D.C. 20242 
CONTENTS 

Page 

Abstract---------------------------------------------------------

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

Data acquisition system------------------------------------------- 2 

Monitoring operations --------------------------------------------- 2 

Results of test---------------------------------------------------- 3 

Acknowledgments------------------------------------------------- 4 

References cited-------------------------------------------------- 4 

ILLUSTRATIONS 

Figure 1. Location m<lp of seismic stations used during the test 

program showing the time difference for arrivals 

Page 

between stations STK and W1---------------------------- 9 

2. Empirical relationship between magnitude and coda--------- 10 

3. Computer output format for an earthquake occurring 

on July 18, 1968 --------------------------------------- 11 

4. 1968 6-hour seismicity data------------------------------ 12 

5. 1968 10-day average seismicity--------------------------- 14 

6. 1968 Bergen Park 10-day average seismicity--------------- 14 

7. Map of earthquake epicenters for September 19o8 ----------- 15 

8. Map of earthquake epicenters for Oct. 1 to Nov. 4, 1968------ 16 

9. Histogram showing distance of earthquakes from station 

WI--------------------------------------------------- 17 

10. Temperature logs observed in the injection disposal 

well on Sept. 4, 1961, and Nov. 10, 19o8 ------------------ 18 

TABLES 

Page 

Table 1. Time of occurrence of pumping tests----------------------- 2 

2. Hypocenters for some Derby earthquakes occurring 

during 1967 and 1968------------------------------------ 19 

3. Derby earthquakes from Sept. 1 to Nov. 15, 19o8------------- 29 

III 

Seismic Activity During the 1968 Test Pumping at 

~ 

the Rocky Mountain Arsenal Disposal Well 

By D. B. Hoover and J. A. Dietrich 

f. h,_ 

During the 1968 pumping tests at the Rocky Mountain Arsenal 

disposal well, the U.S. Geological Survey was responsible for moniwring earthquakes occurring in the area of the arsenal ami making 

chemical analysis of the fluids removed. Three criteria were established ro suspend the pumping if anomalous earthquake activity 

occurred during the pumping rest. These criteria were based on the 

frequency, magnitude, and location of the local earthquakes. 

The pumping program consisted of four rests which occurred 

between September 3 and October 26, 1968. During periods of 

pumping, earthquake activity remained within acceptable limits 

and no suspensions of the pumping were required. After each of 

rhc two rna jor pumping periods an increase in the frequency of 

small earthquakes occurred. During the first of rheserwo periods 

of high seismic activity the Geological Survey recommended a delay in the stan of the next phase of the pumping until the activity 

subsided. Most of the earthquakes during l9o8 occurred northwest 

uf the arsenal; however, in rhe 212-month period after the start of 

rhe test, a larger percent of the earthquakes occurred on the arsenal than in the previous 8-month period. The rcmperarare in the 

cooled zone ar rhe bonom of the well was I2°F warmer 2 weeks 

after pumping stopped than it was in January 196H. Preliminary 

chemical analyses indicate rhar very linle mixing between was r e 

fluids and connate water has occurred. 

INTRODUCTION 

In September and October 1968 the U.S. Army Corps 

of Engineers made a pumping test of the Rocky Mountain Arsenal disposal well. This well had been used to 

inject about 165 million gallons of waste fluid into 

Precambrian basement rock 12,000 feet below the surface of the Denver basin. Shortly after the start of injection in early 1962 small earthquakes were recorded 

from the vicinity of the arsenal. These earthquakes, 

commonly known as Derby earthquakes, have continued 

although injection was discontinued in 1966. Most investigators agree that the earthquakes have been triggered by the injected fluid and a recommendation has 

been made (Healy and others, 1968) that part of the 

fluid be withdrawn in an attempt to decrease the earthquake activity. The pumping tests were designed to determine if substantial amounts of the fluid could be 

pumped from the disposal well. 

In a memorandum of understanding dated June 5, 

1968, between the U.S. Geological Survey and the Corps 

of Engineers, Omaha District, the Geological Survey 

assumed responsibility for five aspects of the test 

pumping program at the Rocky Mountain Arsenal disposal well. Briefly these five areas of responsibility 

were as follows:· 

l. To establish a seismic monitoring system for use 

during the pum'Jing tests. 

2. To provide liaison with the Colorado School of Mines 

to obtain benefit from related information which 

that institution could provide. 

3. To install a special down-hole instrument package 

60 days prior to the test for use during and after 

pumping. 

4. To monitor the seismic activity and advise the 

Corps of Engineers immediately of any unusual 

seismic activity that might occur during the test 

and recommend suspension of the test if anomalous seismic activity developed. 

5. To provide for fluid sam'Jle collection and selective 

analysis of fluids removed from the reservoir. 

The major emphasis under these areas of responsibility was to provide a seismic monitoring program 

which would assure maximum protective warning 

should any anomalous seismic activity occur in conjunction with the fluid removal. 

The pumping tests were designed to determine if 

large volumes of fluid could be removed from the 

Rocky Mountain Arsenal disposal well and if any change 

in seismic activity would be caused by the fluid removal. The preponderance of opinion was that a test 

program, which would remove only a small part of the 

fluid that had been injected into the reservoir, would 

constitute no additional seismic hazard to Denver. 

However, because the test was to be conducted in a 

largely unknown system, which had previously produced slightly damaging earthquakes, there was noway 
to guarantee the complete safety of the proposed test. 

The monitoring procedures and criteria for suspending the test were designed to provide for the maximum 

safety of the populace of Denver. This report covers 

Geological Survey activities. The results of the pumping test are given in a report to the Corps of Engineers 

(van Poollen, 1969). 

ln the preparatory phases of the program, difficulties were encountered in making the special down-hole 

instrument package operational. These difficulties, 

coupled with the possibility of losing or damaging the 

instrument package during the test, were considered 

sufficient reason to abandon the plan to operate the 

down-hole instrument during the test. The absence of 

the down-hole data in no way affected the ability to 

evaluate the seismic hazards during the pumping 

program. 

By agreement with the Corps of Engineers, provision was made for a temporary halt of the pumping 

tests on the recommendation of Geological Survey personnel in Denver should any anomalous seismic activity become evident. Resumption of testing could be decided at the local level, or, if conditions warranted it, 

the decision would be referred to joint conference between the Geological Survey and the Corps of Engineers. A recommendation to terminate the test would 

be subject to approval of the Director of the Geological 

Survey and District Engineer, Omaha District, Corps 

of Engineers. 

On the basis of t<he previous earthquake activity in 

the Derby area in 1968, the Geological Survey established three criteria to be used for calling a temporary halt in the pumping program at the field level. 

These criteria were reported to the Corps of Engineers on August 12, 1968. The first criterion was 

based on the local seismicity .lf the frequency of Derby 

earthquakes exceeded 10 in any consecutive 6-hour 

period during pumping, the pump would be shut down. 

The second criterion would require an immediate halt 

to pumping if an earthquake of magnitude 3.0 or greater 

should occur. Lastly, any earthquake occur ring within 

a 1.5 mile radius of the well would be cons.idered anomalous and again a temporary but immediate halt 

would be ordered. 

The time intervals during which the pump was operating and the total quantity of fluid removed in each 

test is given in table l. Details on these tests and the 

prior cleanout operations are discussed by van 

Poollen (1969). 

Table 1.-Time of occurrence of pumping tests 

Test 

No. Time of test 

1--- 0600 Sept. 3-0600 Sept. 4 

2--- 2300 Sept. 4-2300 Sept. 5 

3--- 2310 Sept. 7-1800 Sept. 13 

0915 Oct 21-2230 Oct. 26 

Fluid removed 

(gallons) 

5 '8 3 8 

17,950 

1l!2 '513 

200,919 

2 

DATA ACQUISITION SYSTEM 

Figure I gives the locations of the seismometers 

in use dOring the test program. Twenty-one seismometers in 17 locations were used. Fourteen locations 

were on the arsenal arranged in an offcenter cross. 

Three additional stations were on the west side of the 

South Platte River to provide a network of stations 

surrounding the epicentral zone. Two of the locations, 

sites S46 and E35, contained both horizontal and vertica 1 seismometers to provide data on three components of ground motion; other recording I o cations 

provided data only on vertical motion. The seismometers used were Hall-Sears type HS-1 0 having a 2 

Hz natural frequency. 

Data from each seismometer on the arsenal were 

transmitted over wire line to a central recording site 

in building 1706 on the arsenal. Here, all the signals 

were electronically amplified and recorded photographically on a CEC 5-119 oscillographic recorder. 

Paper speed of the 5-119 at l mm per sec (millimeter 

per second) provided sufficient information to monitor 

all channels and catalog local earthquakes. Thirteen 

of the 18 channels were also recorded on a modlfied 

Ampex model 300 tape transport running at 0. 3 ips 

(inches per second). Data recorded on the magnetic 

tape provided sufficient time resolution for accurate 

location of the events. 

The three seismometers west of the South P 1 at t e 

River and one of the seismometers from the arsenal 

array were telemetered over telephone lines to the Denver Federal Center. At the Federal Center, data from 

the three off-arsenal sites were recorded on an applied magnetics tape transport running at 0. 3 ips to 

provide added information at high timer e solution. 

Because of the need for a visible on-line monitoring system during the pump test, a two-channel Geo 

Technical Corp. helicorder system was installed in 

building 25 at the Federal Center. Stations STK and 

W l were recorded :m this visible system during the 

test to provide approximate mclgnitudes and locations 

as each earthquake o c c u r red. A helicorder paper 

speed of 1 mm per sec provided about 0.1 sec time 

resolution. This visible m::mitoring system was installed on June 27, 1968. 

The system can detect Derby earthquakes in the vi-· 

cinity of the arsenal of Richter magnitude approximately -1.0 or larger. The smaller events, however, 

are generally not locatable because of the energy attenuation across the array and reliable arrival times 

are not recorded at the more distant stations. 

MONITORING OPERATIONS 

Because of the criteria established for temporary 

halt of the test, it was necessary to provide an immediate indication of the number and magnitudes of 

Derby earthquakes and to determine their approximate 
locations. The visible monitor provided by the helicorder system in building 2.=, at the F edc rill Center was 

the source of basic on-line inf,>r·mation. Uuringpumping operations a 24-hour watc ii was made· and the 

record was examined by trained l'hservers c1·ery 5 

minutes. As each Derby earrhquakc o,·curred, the observers recorded the arrival time Jt , ach of the two 

stations STK and W1, the location ghc.·n by the time 

difference !STK -lW1, and the approximn:c· magnitude. 

The identification of a Uerb\· cart nquaKe was not 

difficult because they have a characteristic Jppearance 

unlike most other disturbances on record. Some booms 

might occasionally be mistaken for earthquakes, but 

the time difference between stations S 1 K and i\ I usually served to distinguish questionable ,. v ~' n t s. ThL· 

timing of the individual events was tabu l J ted anJ 

graphed as each occurred to provide the stati::;ric ntecessary to implement the first criterion for temporary 

halt of the test. 

The duration of the coda, or tim•;:: that the ground 

was disturbed during each earthquake, was tabulated 

and related directly to the magnitude, The high sensitivity of the system and its limited dynamic range 

precluded the use of amplitudes co determine the m'lgnitude from body waves over any wide range. To resolve this difficulty an experimentally determined relationship was used to relate the coda on the helicorder 

to Richter magnitude determined by the Color ado 

School of Mines at its Bergen Park Observatory. 

This method has been found to work well in the magnitude range of events recorded at Bergen Park. It is 

recognized that serious problems exist in extrapolating this relationsl1ip to the very small magnitude 

event::;, and the magnitudes in the range below zero 

should be considered approximate only. The experim:=ntally determined relationship is illustrated in figure 2. 

Approximate epicenters were obtained by measuring 

the time difference between stations STK and WI and 

plotting the epicenter using the appropriate scale (fig. 

1). These two stations are on the long axis of the active zone and most of the earthquakes occur between 

them. Seismic events occurring at the same time at 

both stations are located on the line midway between 

the two stations; events o:::curring early at WI would 

be closer to the W·-"ll. Earthquakes whose arrival time 

was 0. 75 second or more early at station WI were considered anomalous and accurate locations were determined as rapidly as possible from the magnetic-tape 

recording system. 

Precise hypocenter locations were obtained by reproducing the earthquakes recorded on magnetic tape 

onto an expanded time base photogra]hic record and 

timing each arrival to 0.01 sec. The arrival times for 

each event were then introduced into a computer program developed by J. P. Eaton, and a least squares fit 

obtained to the data. Average time residuals were less 

than +0.01 sec and most residuals were within +0.03 

3 

sec. A typical output from this program is shown in 

figure 3. This event occurred at 20 hours, 24 minutes, 

~.3=J sec GMT on July 18, 1968. 

RJ:;SULTS Or TEST 

The detailed seismicity observed in the Derby area 

for the period January 1 to November 15, 1968, was 

compiled in figure 4. The diagram shows the number 

of earthquakes observed in each one-quarter-day 

interval throughout the year. The period of greatest 

activity was the last quarter of July 15,1968, when 22 

ea nhquakes were observed. This relatively large 

number of events includes the magnitude 3. 3 event at 

1 S33 GMT and its aftershock sequence. This is the 

largest Derby earthquake in 1968. The next two largest earthquakes were a magnitude 2. 9 event which occurred at 1904 GMT July 27 andamagnitude 3.2 event 

recorded at 1429 GMT on November 2. No large number of aftershocks were noted after these twu later 

events. !\orm'llly Derby earthquakes of magnitude 3.0 

or less do not have a noticeable aftershock sequence. 

Prior to pumping, the next highest peak on the seismicity plot occurred on May 6 when nine events occurred in o ho.1rs. Because of this and the otherwise 

gem.'rally low level of activity during the year, it was 

decided that l (J events in a 6-hour period would constiwrc anomalous activity and justify a temporary halt 

in operations. 

;\fter the start of the pumping test more than I 0 

earthquakes were' recorded in only one 6-hourperiod. 

On November 14, in .'i hours, 14 small earthquakes occurred, none of which were larger than magnitude I .4. 

These events occurred 18 days after the termination 

of the test and during an interval of r c l at i v e quiescence. 

Because the average level of activity is not readily 

seen on the detailed plot of figure 4, a running 10-day 

average seismicity plot was prepared I fig .. 'i). This 

diagram 3hows th= n'1mher of earthquakes ir any 1 0-day 

interval, starting on January I, 1968, and pL>r~cd at the 

start of the interval (that is, Januaryl-lOwas plotted 

on January I). A 1 0-day interval was chosen since this 

was the time span from the start of the pump t(CSt to 

termination of the first three cycles ofpumping. It was 

felt that this might show more clearly any anomalous 

activity that might be associated with the purrc1ing. A 

smnother function was obtained, and the acri\·i ty occurring on July 15, although still very definite, ' ·sn't 

represent such a marked anomaly. The two hi.=~·~ s t 

levels of activity occurred on Septem her:.::::. and 

October 28 when .57 and 42 events respectively w c r c· 

recorded in the 10 days following those dates. ! ~esc· 

occurred 19 days and 7 days after the start of rtlc' two 

major pumping cycles. 

The second major phase of the test was sch=duled w 

start in late September at about the time that the seismic activity was rising to its highest level. The Ceological Survey concludc=d that there was a significant 
chance of having to invoke one of the stop criteria if 

pum;::>ing was resumed during this particularly active 

period; therefore, on September 20 a postponement of 

pumping for a period of at least 15 days or until the 

seismicity reach2d lower I eve Is was requested. On 

October 17 the Corps of Engineers was informed that 

the activity was again normal and pumping could b·e 

resumed. 

It was recognized that after June 27, when the visible monitor system wets installed, there was some 

bias present in the data. This bias was due to the presence of a duplicate monitoring s y s t em, which was 

watched by many more persons than had been involved 

in the earlier data acquisition process. Some additional small earthquakes were undoubtedly identified 

because of the intensive and repeated examination of 

the records. To determine if this bias was significant, 

the smaller earthquakes in the sequence were re jeered 

and only the larger events were considered. This was 

done using the data on Derby earthquakes provided by 

the Colorado School of Mines Bergen Park Observatory where the lower limit of sensitivity for Derby 

shocks is about magnitude 1.0. This also provided an 

independent estimate of the seismicity pattern that 

was completely independent of any bias that might be 

present in our instrumentation and analysis system. 

The 1 0-day running average obtained using only the 

Bergen Park Observatory data is shown in figure 6. 

Although fewer events were recorded at Bergen Park 

(a maximum of seven in any I 0-day period), the two 

seismicity plots correlate remarkably well. We believe that the bias in the later part of our seismicity 

d.:lta is certainly less than 10 events and probably less 

than 5 events per 10-day period. 

Table 2 lists all of the Derby earthquakes for which 

reliable hypocenter locations have been obtained by 

means of the computer program. Only part of the earthquakes prior to April I, 1968, have been located and 

the list for this p·eriod is incomplete. Most events occurring after April I, 1968, that were large eno•Jgh to 

provide good signal strength across the array have 

been located and are listed. 

From these data, maps showing the epic~nter locations of the September to November 1968 earthquakes 

were prepared (figs. 7 and 8). These data show that 

most of the events occurred in the vicinity of the flood 

plain of the South Platte River northwest of the we II, 

but a few also occurred at the arsenal and w·~st of the 

river. The epicentral zone is similar to the zone described by Healy and others (1966). There is, however, 

an indication that the majority of earthquakes occurred 

a few \ilomders to the northwest of the major center 

obtained in late 1965 and early 1966. This northwestward migration has also been observed by Major and 

Simon ( 1968). 

To compare the pattern of activity prior to the pump 

test with that during and immedlately after, data fro:n 

table 2 w'ls used to prepare the histograms in figure 9. 

In these histograms the numher of events in a given 

4 

distance interval are plotted against the epicentral distance from station WI. This is approximately the distance from the well and was used for convenience since 

it is a statistic obtained from the co:n;Juter program. 

The distribution of events since September 3, 1968, 

is broader than that for events that were located during the preceding year and a half. Since early September, earthquakes have occurred both closer to the well 

(some have been east of the well) and more farther 

northwest of the well than in the previous IS-month 

period. 

The complete seismicity data from September 1 to 

November 15, 1968, is included in table 3. This table 

contains the information obtained during the tesc from 

the visible monitor in building 25. At no time during 

pumping operations was it necessary to invoke any of 

the criteria established for a temporary halt. During 

nonpumping intervals, a few earthquakes occurred that 

appeared to be ano:n e~lously close to the well. These 

events were precisely located from the array data 

but no,le o:::curred so close to the well that termination 

of the test w:1s recommended. The magnitude 3 event 

on November 2 and the 14 events on November 14 o:::-

curred after termination of the test. 

The thermal history of the well has been of interest 

because of the possibility that a thermal stress triggering mechanism may be contributing to instability 

in the region. The thermal regime is also of interest 

for correcting fluid densities in the well bore and for 

understanding changes in transmissibility in the fluid 

reservoir due to changes in temperature. The fluid 

tem,•erature also places practical limitations on the 

rate of fluid removal by limiting the amount of pressure reductio:~ so as nclt to initiate boiling in the fluid 

column. In January 1968, a temperature log was run 

in the well by the Geological Survey in which a 25°C 

temperature decrease was foJnd in the lower 160 :.'eet 

of hole. Total depth at that time was 12,000 feet. This 

temperature inversion was also confirmed in work by 

Ball Bros. Research Corp. in June 1968. This relatively 

large temperature inversion is due to the injection of 

165 mmion gallons of cold waste fluid into the reservoir during operations from January i 962 to February 

1966. Because the test pumping program was drawing 

hot fluids fro:n the reservoir into the chilled region 

immediately aro:.md the well1we were interested in determining the amount of wetrming at the bottom. On 

November 10, 1968, 2 weeks after the test was terminated, a temperature log was run by Schlumherger 

Well Service Co:npany. This log is shown in figure 10, 

along with the log originally run in September 1961, 

2 days after the lower liner was cemented. The most 

recent log agrees within the measuring accuracy with 

the log ob:ained in January 1968, except in the region 

of the temperature inversion. The bottom of the hole, 

11,991 feet, w:1s found to have warmed up l2°F; most 

of this wets a result of the pumping. 

Preliminary analysis of the fluids pumped from the 

well indicated that very little mixing of the injected 
waste fluid with connate water had occurred (R. L. 

Wershaw, written commun., 1968). These conclusions 

were based ;Jrincipally o,1 radium and lithium analyses. 

Complete results will be reported when the an.:tlyses 

are finished. 

ACKNOWLEDGMENTS 

We wish to acknowledge the cooperation and assistance of the Colorado School o<' Mines throughout this 

investigation. Particular thanks go to Maurice Major 

and Ruth Simon for making a~1aila'1le som2· of their 

Be:cgen Park data arJd for much fruitful discussion. 

We extend our appreciation to the Corps of Engineers 

for financial support during the past years and during 

the test program. The valuable assistance of J amt~S 

Zeltinger and Lou Gustafson, Corps of Engineers representatives on site during the test, W'!S greatly appreciated. These two individuals were of particular 

service to as in the fluid 3am;:>ling program during 

their long vigils at the well site. We extend our appreciation for helpful advice and additional equipment 

to our Survey colleagues in Menlo Park, Calif., specifically J. P. Eato,l, W. H. Jackson, and John Roller. 

5 

We would like to acknowledge the assist an:: e of 

Rhoda Robinson, Penny Miller, A. C. Austin, Don 

Peterson, R. F. Schoenfeld, Dolores W~lson, and Tom 

Davison, who conscientiously spent many hours, often 

late at night, peering at the slowly revol~vlng recording drum. To these people goes much credit for the 

success of the operations during the test program. 

REFERENCES CITED 

Healy, J. H., and others, 1966, Geophysical and geological investigations relating to earthquakes in the 

Denver area, Colorado: U.S. Geol. Survey open-file 

report. 

1968, The Denver earthqJakes: Science, v. 

--y()T, no. 3848. 

Major, Maurice, and )imon, Ruth, 1968, A seismic 

study of the Den·;er [Derby] earthquakes: Colorado 

School of Mines Quart., v. 63, no. 1. 

van Poo1 len, 1-1. K., 1969, RockyMountainArsenalwell 

pumping tests, 1968: U.S. ArmyC:orpsofEngineers, 

Omaha District. 

FIGURES l-10 AND TABLES 2, 3 
esrK_ 

';<.Q2__",,/":;(/ ________ . ---::: ---,1 -........ ~osec I 

/ 

• 't::, • • • • el W3 WI Nl N2 E35 E6 I 

J eEz 1 

,~~y~ / : ~ , ," eEl 1 

( , i esl : 

I I 

J 

" I 

' J 

. DERBY,] 

LJ 

ROCKY MOUNTAIN 

:I 

~ 1 I ~, 

I 

ARSENAL 

L_- --------------

I 0 lmi 

-I 0 lkm -=--::-.-=-

.546 

EXPLANATION 

ARSENAL WELL 

• 

RECORDING SITE 

SINGLE COMPONENT 

• 

RECORDING SITE 

THREE COMPONENT 

1------+--

APPROXIMATE FAULT TRACE 

8 TIME SCALE WI- STK 

Figure 1. Location map of seismic stations used during the test program 

showing the time difference for arrivals between stations STK and Wl. 

9 
4. 

3. 

w 

Q 

=> 

2. 

1-- ,.... 

0 z 

(!) 

<( 

~ I. 

0. 

-I. 

2 5 10 20 50 100 200 

CODA LENGTH, mm (RECORDING SPEED I mm PER SEC ) 

Figure 2. Empirical relationship between magnitude and coda. 
KREC=12 INST= 3 ZRES= 5.00 

N4 680718 2024 o.o 7.84 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 1\12 680718 2024 o.o 7.83 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

W3 680718 ;>024 o.o 7.21 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

E35 680718 2024 o.o 7.96 o.o o.o 10.12 o.o o.o o.o o.o o.o o.o o.o o.o 

E1 680718 2024 o.o 7.96 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

S46 680718 2024 o.o 8.32 o.o o.o 10.74 o.o o.o o.o o.o o.o o.o o.o o.o 

E2 6807111 2024 o.o 7.89 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

S2 680718 2024 o.o 8. 11 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o W1 680718 2024 o.o 7.48 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

STK2 680718 2024 o.o 6.92 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

WILL 680718 2024 o.o 6.62 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

KING 680718 2024 o.o 7.08 o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o o.o 

CODES (MODE LPC INST LOSW LHY KOUT KAZ)=( 0 0 3 3 0) ORGS= 5.35 AV RESTO= -o.oo PMAG= -9.99 

DATE ORIGIN LAT LONG DEPTH AAF SOP SDX SDY soz SDT KS TA XMAG I I KR EC VH 

680718 2024 5.35 39. 52.60 104. 55.07 4.9 0.02 0.03 0.1 0.2 0.2 77.77 12 -9.99 5 12 o.oo 

STATION DELTA AZI AN IN OS ABE TP TS KESID PMAG RSPMG XMAG RSXMG RMK w G 

N4 9.4 97. 83.2 2.49 o.o -0.01 9.99 -9.99 -9.99 -9.99 1. 00 1.00 

N2 9.2 104. 82.9 2.48 o.o o.o1 -Y.99 -9.99 -9.99 -9.99 1.00 1.00 

W3 5. 1 116. 65.9 1.116 o.o 0.06 9.Y9 -9.Y9 9.99 -9.99 1.00 1.00 

E35 10.1 103. 84.5 2.61 4. 77 -0.01 -9.99 -9.99 -9.99 -9.99 1.00 1.00 

E1 10.0 113. 84.4 2.61 o.o o.oo Y.99 -9.99 9.99 -9.99 1. 00 1.00 

546 12.2 130. 87.0 2.97 5.39 -0.01 -9.YY -9.99 -9.99 -9.99 1.00 1.00 

E2 9.7 107. 83.8 2.54 o.o -o.o2 -9.Y9 -9.99 -9.99 -9.99 1.00 1.00 

S2 11.0 122. 85.9 2.76 o.o -o.o2 -9.99 -9.99 -9.99 -9.99 1.00 1.00 

W1 7.1 109. 76.4 2.13 o.o 0.01 -9.Y9 -9.99 -9.99 -9.99 1.00 1.00 

STK2 3.5 305. 51.4 1.57 o.o o.o1 -9.99 -9.99 -9.99 -9.99 1.00 1.00 

WILL 1.0 64. 16.7 1.27 o.o -0.03 -9.99 -9.99 -9.99 -9.99 1.00 1.00 

KING 4.7 26. 62.5 1. 73 o.o o.o1 -9.Y9 -9~99 -9.99 -9.99 1.00 1.00 

Figure 3. Computer output format for an earthquake occurring on July 18, 1968. 
10-

8-

6-

>-

<t 

0 

4-

2 ~,II J, !1~1 U ,IJ U 1,1(11,1,, ,~;~d:~~ j 

0: 

w 

CL 

en 20- w 

:X: 

<t 

:::> 

0 

I 

r0: 

<t 

w 

IJ.._ 

0 

0: 

w 

(IJ 

:2 

:::> 

z 10-

8-

6-

4-

Figure 4. 1968 6-hour seismicity data. 

12 
OCTOBER NOVEMBER 

Figure 4.--Continued. 

13 
60-

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Q 

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Ill 

::!< 10 ::> 

z 

1968 DERBY SEISMICITY 

Figure 5. 1968 10-day average seismicity. 

~ a: 4. 

~ 

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z 

1968 DERBY SEISMICITY BERGEN PARK DATA 

Figure 6. 1968 Bergen Park 10-day average seismicity. 
0 0 

~------------------

0 

0 0 

ROCKY MOUNTAIN 

ARSENAL 

---===='-ilo ___ lmi 

1•--==0,.__.1 km 

\ 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

EXPLANATION 

ARSENAL WELL 

0 

EARTHQUAKE EPICENTER 

SEPTEMBER 1968 

Figure 7. Map of earthquake epicenters for September 1968. 

15 
0 

------------------\ 

ROCKY MOUNTAIN 

ARSENAL 

---="----""o ___ lmi 

-.L-==:::0'--_1 km 

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EXPLANATION 

ARSENAL WELL 

0 

EARTHQUAKE EPICENTERS 

OCT.- NOV. 1968 

Figure 8. Map of earthquake epicenters for October 1 to November 4, 1968. 

16 
CJ) 

w 

~ 

<X 

:::> 

0 

:c 

Ia: 

<X 15 

w 

lL 

0 10 

a:: 

w 5 CD 

~ 

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z 

15 

APRIL- DEC. 1967 

JAN. -AUG. 1968 

SEPT.-NOV. 1968 

mc»mmmmmmmmmm 

....:oo.....:f\in~ldc.rir-.:a>m I I I 1 I I I I I. I I I. -=oo-=C\if'()vl.('ju:>r-..:mm 

EAST I WEST 

DISTANCE RANGE 

FROM STATION WI, km 

Figure 9. Histogram showing distance of earthquakes from station Wl. 

17 
0 

0 

0 

)( 

ILL 

I 

1--

a... 

w 

2 

4 

6 

8 

0 10 

12 

~NOV. 10> 1968 

SEPT. 4> 1961 ~ 

100 200 300 

TEMPERATURE , DEGREES F 

Figure 10. Temperature logs observed in the injection disposal 

well on September 4, 1961 and November 10, 1968. 

18 
Table 2.-Hypocenters for some Derby earthquakes occurring during 1967 and 1968 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

67 01 01 09 17 06 39 52.18 104 54.29 5.3 5.8 

67 01 02 20 02 09 51.22 52.90 3.7 3.6 

67 01 03 12 59 38 53.18 55.52 5.0 8.1 

67 01 05 04 30 41 51.55 54.48 5.7 5.9 

67 01 10 05 07 48 51.85 52.85 4.8 3.7 

67 01 12 22 36 54 52.02 50.76 5.4 1.3 

67 01 13 01 15 18 51.71 55.00 4.0 6.6 

67 01 .13 15 33 27 52.88 51.66 6.9 3.4 

- 67 01 14 08 19 22 51.94 53.67 6.8 4.8 '!:) 

67 01 15 02 09 24 51.74 56.11 5.0 8.2 

67 01 17 21 24 46 50.89 50.94 3.0 0.8 

67 01 18 10 40 57 51.90 55.15 3.3 6.9 

67 01 18 16 47 54 51.86 53.78 4.6 5.0 

67 01 20 11 19 07 51.51 53.35 5.9 4.3 

67 01 20 17 12 14 52.59 54.42 2.6 6.2 

67 01 21 16 26 47 50.75 50.71 3.1 1.2 

67 01 22 10 44 33 52.38 53.19 7.0 4.4 

67 01 24 20 06 45 51.12 51.50 5.4 1.7 

67 01 24 20 09 34 51.04 51.47 2.9 1.7 

67 01 25 09 30 25 51.01 54.86 6.4 6.5 

67 01 25 04 20 22 51.61 54.29 7.6 5.6 
Table 2. -Hypocenters for SOJJ,le Derby earthguakes occurring during 1967 and 1968--Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) W1 (kilometers) 

h m s 

67 01 25 12 23 05 39 51.95 104 51.53 ·5. 9 2.0 

67 01 29 23 34 25 51.83 54.88 7.2 6.5 

67 02 02 01 53 38 52.60 52.95 6.5 4.3 

67 02 03 05 27 59 52.31 55.51 5.8 7.5 

67 02 03 05 34 13 52.44 52.75 6.1 3.9 

67 02 03 05 37 05 52.83 54.22 6.9 6.1 

67 02 03 05 39 30 52.17 52.74 6.1 3.7 

67 02 03 05 42 40 52.41 52.67 6.8 3.8 

67 02 03 05 43 22 51.19 51.59 6.3 1.8 

tv 67 02 03 06 13 22 51.78 52.58 6.4 3.3 :::> 

67 02 03 06 31 41 51.56 52.29 4.6 2.8 

67 02 05 19 53 12 51.70 50.64 5.7 0.7 

67 04 10 22 12 01 52.31 53.35 4.5 4.6 

67 04 10 22 51 26 53.31 54.83 5.0 7.3 

67 04 11 18 20 30 52.58 53.80 4.7 5.4 

67 04 11 18 20 38 53.07 54.94 5.4 7.2 

67 04 11 18 56 13 53.07 54.77 9.0 7. 0 

67 04 13 21 53 10 52.50 53.49 5.8 4.7 

67 04 14 06 47 14 52.30 53.64 6.1 5.0 

67 04 14 07 12 58 51.82 54.11 5.4 5.4 

67 04 14 20 25 01 52.08 54.10 5.1 5.5 

67 04 14 12 54 50 52.38 53.55 5.6 4.9 

67 04 14 20 27 08 52.09 53.93 5.3 5.3 
Table 2.-Hypocenters for some Derby earthquakes occurring during 1967 and 1968-Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

67 04 14 21 36 01 39 52.50 104 54.04 5.7 5.7 

67 04 14 23 16 24 52.92 53.61 4.3 5.4 

67 04 15 00 15 38 51.96 53.99 5.1 5.3 

67 04 15 00 55 58 53.00 53.82 4.0 5.8 

67 04 15 09 18 24 53.19 54.21 4.5 6.4 

67 04 15 09 19 49 53.52 54.34 4.7 6.9 

67 04 15 13 08 34 53.12 54.39 5.0 6.6 

67 04 15 22 35 29 52.44 53.61 5.9 5.0 

67 04 16 00 20 40 53.10 54.08 4.4 6.2 

N 67 04 16 11 29 23 52.81 54.19 5.5 6.1 ...... 

67 04 16 14 07 46 53.69 54.48 4.4 7.3 

67 04 17 08 44 02 52.58 53.89 4.9 5.5 

67 04 18 13 43 14 53.09 53.76 4.4 5.8 

67 04 20 12 14 17 52.94 53.76 4.6 5.7 

67 04 20 14 04 03 52.31 53.29 6.8 4.5 

67 04 20 23 31 15 52.92 54.50 4.8 6.6 

67 04 21 12 03 28 52.77 53.59 5.1 5.3 

67 04 22 02 40 16 52.24 54.47 4.6 6.1 

67 04 29 08 31 27 52.01 53.71 5.1 4.9 

67 04 29 09 29 44 52.94 53.51 4.2 5.3 

67 04 29 16 00 44 52.31 54.80 5.2 6.6 

67 04 30 03 02 01 52.17 54.02 5.6 5.4 
Table 2. -Hypocenters for some Derby earthquakes occurring during 1967 and 1968--Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

67 05 02 16 29 39 39 52.21 104 53.78 5.1 5.1 

67 05 03 11 20 09 51.51 50.52 5.9 0.3 

67 05 03 11 53 57 52.03 53.61 4.8 4.8 

67 05 03 13 27 59 52.06 54.06 6.3 5.4 

67 05 05 21 21 28 52.06 52.43 6.4 3.2 

67 09 09 14 48 55 52.47 53.85 4.5 5.4 

67 09 09 14 56 12 52.44 54.40 6.6 6.1 

67 09 09 15 13 25 52.22 53.55 5.4 4.8 

67 09 09 15 39 49 51.98 54.41 4.9 5.9 

N 

67 09 09 15 51 15 52.57 54.95 4.2 6.9 N 

67 09 09 16 01 28 52.93 55.33 4.1 7.7 

67 09 09 16 16 43 52.51 53.09 7.7 4.1 

67 09 09 16 16 47 52.27 53.88 5.5 5.3 

67 09 09 16 30 06 52.87 54.78 3.2 6.9 

67 09 09 17 15 45 53.30 56.30 5.0 9.2 

67 09 09 17 26 05 52.92 54.61 3.1 6. 7 

67 09 09 17 33 10 52.53 55.05 4.6 7.0 

67 09 09 17 35 44 52.84 54.77 3.9 6.8 

67 09 09 17 48 21 53.41 57.20 6.1 10.5 

67 09 09 19 43 56 52.71 54.22 3.4 6.0 

67 09 09 19 47 06 52.82 54.86 3.4 7.0 

67 09 09 19 53 16 52.26 54.86 3.8 6.6 

67 09 09 20 12 37 52.68 55.00 4.9 7.0 
Table 2.-Hypocenters for some Derby earthquakes occurring during 1967 and 1968-Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

67 09 09 20 53 50 39 52.83 104 54.46 3.2 6.4 

67 09 09 20 57 03 51.93 53.97 3.7 5.3 

67 09 09 21 07 50 52.83 54.37 3.0 6.3 

67 11 14 10 07 49 52.38 53.27 6.5 4.6 

67 11 14 10 41 37 52.02 53.30 6.7 4.4 

67 11 15 07 10 09 52.23 53.16 6.3 4.3 

67 11 15 07 10 14 51.68 52.10 4.7 2.5 

67 11 27 05 09 23 53.17 55.35 6.5 7.9 

67 12 11 06 50 47 52.16 53.57 7.0 3.8 

N 67 12 11 12 30 43.6 51.65 53.77 4.8 3.8 w 

67 12 11 12 30 43.7 51.59 53.59 4.7 3.5 

67 12 20 06 17 36 53.43 52.90 3.1 5.2 

68 02 03 06 53 33 53.64 55.23 4.9 8.1 

68 02 05 07 45 35 52.24 53.36 7.0 4.6 

68 02 10 08 43 43 52.82 53.71 7.1 5.5 

68 02 10 12 44 45 52.57 53.88 6.7 5.5 

68 02 13 03 39 20 51.86 50.80 5.8 1.1 

68 02 13 08 25 01 51.98 54.08 6.5 2.9 

68 02 18 06 11 57 52.25 54.41 6.2 6.0 

68 02 18 23 30 46 52.30 54.25 5.6 5.8 

68 02 24 14 06 50 52.69 53.54 4.0 5.2 
Table 2. -Hypocenters for some Derby earthquakes occurring during 1967 and 1968-Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

68 04 06 04 00 08 39 50.86 104 53.04 6.8 3.9 

68 04 06 22 58 54 52.91 55.07 5.5 7.3 

68 04 07 12 26 52 52.74 54.69 5.2 6.4 

68 OS 16 02 57 38 52.39 53.00 5.1 3.9 

68 OS 19 14 57 16 52.32 52.91 7.1 3.8 

68 OS 19 15 02 12 52.39 52.81 7.5 3.9 

68 OS 23 10 56 44 52.48 54.94 6.2 6.6 

68 OS 26 09 12 56 52.39 55.23 5.9 7.2 

68 OS 29 23 32 25 52.24 52.77 6.6 3.8 tv 

.... 68 06 04 18 58 14 52.47 53.20 6.9 4.5 

68 06 OS 11 51 43 52.29 53.75 7.3 5.1 

68 06 10 OS 23 21 51.96 53.37 5.0 3.4 

68 06 11 03 54 56 52.78 52.24 6.7 6.1 

68 06 11 03 55 10 52.57 54.05 6.3 5.7 

68 06 14 11 so 08 53.59 53.99 2.7 6.6 

68 06 21 16 00 46 52.03 52.59 6.1 3.4 

68 06 23 07 46 11 51.48 54.55 5.2 6.0 

68 06 23 17 25 26 52.72 53.70 4.5 4.3 

68 06 25 07 32 06 52.56 53.45 4.1 4.9 

68 06 27 08 46 54 52.23 53.37 6.2 4.6 

68 06 28 09 24 25 52.21 53.40 6.2 4.6 
Table 2.-Hypocenters for some Derby earthquakes occurring during 1967 and 19 6 8 -Con t in u e d 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

68 06 28 09 29 44 39 52.49 104 53.68 7.5 5.2 

68 06 28 09 46 20 52.47 53.68 7.6 5.1 

68 07 01 18 11 09 53.18 54.54 3.4 6.8 

68 07 04 14 32 02 51.51 53.52 5.2 4.5 

68 07 05 07 26 48 52.78 54.70 5.6 6.7 

68 07 05 08 22 12 52.72 54.99 6.2 7.1 

68 07 05 12 47 06 52.55 54.75 5.3 6.6 

68 07 05 17 34 28 52.58 53.69 7.0 5.3 

''"' 68 07 11 08 22 05 52.63 54.69 5.9 6.6 :Jl 

68 07 13 08 13 45 52.59 53.66 6.7 5.2 

68 07 15 18 33 13 51.74 52.83 6.6 3.6 

68 07 15 18 44 39 52.42 52.43 7.7 3.5 

68 07 17 -23 47 52 52.06 54.06 6.4 5.4 

68 07 18 00 14 33 51.46 53.32 5.4 4.2 

68 07 18 20 24 05 52.60 55.08 4.9 7.1 

68 07 27 19 04 54 52.91 54.71 5.8 6.8 

68 08 01 14 29 26 52.19 52.73 6.6 3.7 

68 08 07 06 49 41 52.76 55.26 6.0 7.8 

68 08 10 06 06 56 52.81 54.82 5.7 6.9 

68 08 11 OS 35 56 52.79 55.07 5.2 7.2 
Table 2. -Hypocenters for some Derby earthquakes occurring during 1967 and 1968-Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) Wl (kilometers) 

h m s 

68 08 14 01 53 24 39 52.73 104 53.19 5.9 4.8 

68 08 14 02 03 26 52.75 55.08 6.2 7.2 

68 08 25 08 36 40 52.99 55.30 4.8 7.6 

68 08 29 04 27 11 52.72 55.12 6.1 7.2 

68 08 31 13 58 43 52.44 53.45 6.8 4.8 

68 08 31 15 49 09 52.87 53.81 6.6 5.6 

68 08 31 20 04 57 52.67 53.42 4.5 5.0 

68 08 31 22 03 03 52.87 53.16 3.5 4.9 

68 09 01 01 24 46 52.55 53.73 4.0 5.3 

"-' 68 09 02 01 26 22 52.47 55.04 4.1 7.0 0'-

68 09 02 02 29 24 52.13 56.85 5.8 9.4 

68 09 02 15 09 23 52.87 54.20 4.0 6.1 

68 09 04 21 45 30 51.91 53.49 6.6 {1.6 

68 09 06 00 29 36 52.60 54.44 3.7 6.2 

68 09 06 06 53 40 51.84 52.12 6.0 2.7 

68 09 06 06 53 49 51.41 52.44 6.7 3.0 

68 09 07 23 so 48 52.19 53.17 6.6 4.3 

68 09 08 03 46 09 51.36 52.17 6.7 2.6 

68 09 10 19 14 47 53.32 54.24 3.3 6 .. G 

68 09 12 OS 02 25 53.56 54.45 5.0 7.1 

68 09 13 04 26 36 52.52 54.65 5.8 6.5 

68 09 13 04 26 57 52.88 53.96 7.4 5.8 
Table 2. -_Hypocenters for some Derby earthquakes occurring during 1967 and 1968-Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers) '1-.rl (kilometers) h m s 

68 09 16 23 38 31 39 52.67 104 54.66 5.5 6.6 

68 09 19 15 48 35 51.92 50.73 5.2 1.1 

68 09 23 00 35 40 52.80 53.79 7.0 5.6 

68 09 23 01 10 28 52.50 53.92 7.0 5.5 

68 09 23 02 36 53 52.44 53.77 7.0 5.2 

68 09 23 12 22 48 51.92 54.20 4.8 5.6 

68 09 23 14 44 56 51.42 54.00 5.1 5.2 

68 09 24 14 51 27 53.41 54.61 5.9 7.1 

68 09 24 14 52 18 53.63 54.30 5.7 9.7 •J '"

68 09 25 02 12 00 53.45 54.14 4.8 6.6 

68 09 25 08 48 02 52.94 56.03 6.7 8.4 

68 09 26 12 26 11 52.02 53.95 5.6 5.3 

68 09 27 20 47 01 52.11 55.08 5.6 6.9 

68 09 28 03 43 54 51.69 53.45 5.7 4.4 

68 09 28 05 48 36 51.56 53.76 5.8 4.9 

68 09 28 13 46 26 51.76 53.59 5.8 4.7 

68 09 28 16 53 32 52.48 54.72 5.6 6.5 

68 09 29 00 38 34 52.97 53.71 4.3 5.6 

68 09 29 22 22 47 52.90 55.05 5.9 7.3 

68 09 29 22 23 01 52.10 54.72 4.4 6.4 

68 10 06 19 51 35 52.96 55.14 5.4 7.4 
Table 2 .-Hypocenters for some Derby earthquakes occurring during 1967 and 1968 -Continued 

Depth Distance from 

Date Origin Time Latitude Longitude (kilometers} vn. (kilometers) h m s 

68 10 09 02 11 33 39 52.01 104 52.76 6.9 3.6 

68 10 09 06 08 41 52.76 54.66 5.4 6.7 

68 10 11 16 19 22 52.54 53.43 6.4 4.9 

68 10 13 03 47 22 52.53 55.09 5.0 7.1 

68 10 13 13 00 39 52.48 53.55 7.2 5.0 

68 10 13 13 01 14 52.74 53.50 7.0 5.1 

68 10 14 03 10 42 52.40 53.20 7.t 4.5 tv 

00 68 10 13 10 48 13 52.42 53.08 6.5 4.3 

68 10 17 13 24 21 52.24 53.01 6.6 4.1 

68 10 14 05 01 12 51.13 49.75 4.8 1.0 

68 10 30 18 41 05 52.79 53.44 4.3 5.1 

68 10 30 18 45 20 52.49 53.65 1/6 5.1 

68 10 30 18 27 07 52.61 54.85 5.6 6.8 

68 10 30 18 36 35 52.59 54.78 5.1 6.7 

68 11 02 14 29 02 51.70 53.65 6.0 4.7 

68 11 03 19 28 56 52.56 55.07 6.7 6.7 

68 11 02 21 47 13 51.83 52.80 5.8 3.6 
Table 3. -Derby earthquakes from Sept. 1 to Nov. 1 5 ' 1968 

.:lt(Wl-STK) 

Date Time GMT ~seconds) Magnitude 

September 2 0125 .4 0.0 

0228 .8 1.6 

0749 -.1 -0.3 

1509 . 5 o.o 

September 3 2208 -.7 -0.5 

September 4 0016 -.4 -1.0 

0115 .4 -0.1 

0346 .4 0.3 

0456 .3 -0.2 

1900 .3 -0.1 

2145 -.2 1.4 

September 5 0546 .4 -0.4 

2349 .1 -0.3 

September 6 0029 . 2 0.3 

0211 .4 -0.4 

0653 -.7 0.3 

0653 -.7 -0.1 

2325 noisy trace -0.6 

September 7 1604 0.0 -0.5 

2350 .5 0.5 

September 8 0346 -.5 0.1 

0358 . 5 -0.5 

September 10 1914 .3 -0.1 

2009 .2 0.3 

September 12 0503 .4 2.0 

1658 0.0 -0.6 

September 13 0207 noisy trace -0.5 

0355 . 5 -0.7 

0426 -.5 0.5 

0426 .7 0.7 

0720 .1 -0.2 

1424 .1 -0.5 

29 
Table 3. -Derby earthquakes from Sept. 1 to Nov. 15' 1968-Continued 

.:lt (Wl-S'I'K) 

Date Time GMT (seconds) Magnitude 

September 14 0947 .1 -0.3 

2328 -.4 -0.7 

September 16 2257 .3 -0.2 

2338 . 5 0.3 

September 17 0005 noisy trace -0.3 

0614 .1 -0.3 

September 19 0452 .3 -0.5 

1548 -1.6 0.5 

September 20 1003 noisy trace -0.7 

September 21 2016 . 5 -0.7 

September 22 0720 .5 -0.7 

1523 .8 -0.2 

September 23 0035 -.1 0.2 

0109 0.0 0.7 

0111 -.4 -0.5 

0112 -.1 -0.4 

0112 -.4 -1.0 

0112 -.6 0.0 

0236 .1 0.3 

0826 0.0 -0.3 

1222 0.0 0.1 

1444 -.3 0.2 

September 24 1451 . 7 2.3 

1452 .2 1.0 

1506 .4 1.7 

September 25 0212 . 5 1.6 

0848 .4 0.8 

1244 0.0 0.0 

September 26 0104 -.2 -0.2 

0113 -.2 -0.7 

0211 0.0 -0.3 

1226 .1 0.5 

30 
Table 3. -Derby earthquakes from Sept. 1 to Nov. 15, 1968-Continued 

Llt(Wl-STK) 

Date Time GMT (seconds) Magnitude 

Stiptember 27 2047 0.0 1.0 

2306 .1 -0.3 

September 28 0343 -.1 0.4 

0548 -.1 0.2 

0815 0.0 -0.1 

1151 noisy trace -0.3 

1346 0.0 1.8 

1645 0.0 0.0 

1645 .3 -0.3 

1646 .2 -0.5 

1653 .3 0.5 

1817 -.2 -0.2 

2223 . 2 -0.7 

2223 .2 -0.3 

2227 0.0 -0.5 

2228 -.4 -0.6 

2229 noisy trace -1.0 

September 29 0038 -.1 1.8 

0039 -.1 0.8 

0039 -.1 1.6 

0113 0.0 -1.0 

0120 0.0 -0.1 

0607 . 2 0.2 

0608 1.6 0.1 

1122 noisy trace -0.1 

2019 .1 -0.2 

2027 noisy trace -0.2 

2222 .7 1.0 

2223 ,4 1.8 

September 30 1420 .1 -1.0 

1420 noisy trace -0.3 

31 
Table 3. -Derby earthquakes from Sept. 1 to Nov. 15' 1968-Continued 

Date Time GMT 

~t(Wl-STK) 

(seconds) Magnitude 

October 1 0715 -.4 -0.3 

0716 . 7 0.2 

0726 STK bad -0.5 

0848 .8 -0.3 

1721 -.7 -1.0 

October 2 0141 -.5 0.8 

1901 -.5 .1 

October 5 1255 -.3 -.1 

1945 .7 .2 

October 6 0607 .6 . 7 

0659 .6 .2 

1951 . 7 1.8 

October 8 0405 . 5 1.7 

0638 .4 -.6 

0825 -.1 -.1 

0847 . 4 -1.0 

1458 -.1 -.1 

1645 -.5 .6 

October 9 0210 -.4 1.3 

0320 .3 -.7 

0321 .3 -.3 

0520 .5 -.1 

0520 • 6 -.7 

0608 .4 .3 

October 11 1618 -.1 .2 

October 13 0346 . 6 -.7 

0536 noisy trace 0.0 

1047 -.2 -.3 

1048 .3 -.7 

1049 .1 -.3 

1114 .4 -.3 

1300 -.1 1.4 

1300 -.2 1.3 

1301 0.0 -.3 

32 
Table 3. -Derby earthquakes from se·pt. 1 to Nov. 1 5 ' 1968-Continued 

Date Time GMT 

.lt(Wl-STK) 

{seconds) Magnitude 

October 14 0310 -.3 2.0 

0500 -1.5 .5 

October 15 2214 -.1 . 6 

October 17 1323 -.1 . 7 

October 19 0359 .5 -0.1 

October 20 0236 .5 -.2 

0416 -.5 -.3 

0416 -.5 -.6 

0906 -.5 .1 

October 21 0524 -.4 -.7 

1814 1.8 .3 

October 23 0405 1.1 2.0 

October 25 0628 1.0 -1.0 ( 

October 26 0916 -.6 -.2 

1345 .3 -1.0 

1537 0.0 -.4 

2359 .2 -1.0 

October 28 1317 .1 .6 

2115 .2 -1.0 

2215 0.0 .3 

October 29 2258 . 5 -.2 

2258 . 2 .1 

2259 . 7 -.1 

2259 .6 -.1 

2300 . 6 -.6 

October 30 1826 noisy trace . 7 

1835 .5 1.8 

1838 .1 -.7 

1838 .2 -.1 

1844 -.3 . 6 

1846 0.0 -.1 

1846 .3 -1.0 

1846 0.0 .9 

33 
Table 3. -Derby earthquakes from Sept. 1 to Nov. 15' 1968-Continued 

Date Time GMT 

At(Wl-STK) 

(secondsJ Magnitude 

November 1 0303 noisy trace .4 

0504 -.4 -.4 

0515 .5 -.7 

1426 . 6 -.1 

November 2 0523 .5 -.3 

1428 -.6 3.1 

1432 -.5 -1.0 

2146 -.4 -.6 

November 3 1827 .4 .3 

1828 .5 -1.0 

November 4 0006 .2 -1.0 

0825 -.2 -.7 

0834 . 5 .5 

1150 .1 -.5 

1431 .6 -.7 

November 5 0418 0.0 -.2 

0423 0.0 -.4 

1730 -.1 .9 

1950 .2 1.7 

November 6 0002 -.6 .9 

0020 0.0 .2 

0031 noisy trace -.7 

0346 -.2 -.4 

0452 .4 -.7 

0507 . 7 -.1 

November 7 0447 . 6 -.1 

November 8 0424 . 6 -.1 

November 10 0949 -.3 -.8 

1341 -.2 -.1 

November 11 0008 .4 1.4 

0338 -1.3 -.8 

November 12 0526 .3 .8 

34 
Table 3.--Derby earthquakes from 

Date Time GMT 

Sept. 1 to Nov. 

ilt (Wl-STK) 

(seconds) 

15, 1968---Continued 

Magnitude 

Change to single channel operation 

November 13 0430 -0.5 

1041 -0.5 

November 14 0905 -.1 

1136 .5 

1142 -.7 

1143 -.7 

1214 -.7 

1223 -.5 

1223 -.5 

1224 1.4 

1230 .7 

1231 -.7 

1234 .1 

1235 -1.0 

1240 -.7 

1342 -.8 

INTERI(J;:,>- "t.OLOGICAL SURVEY, WASHINGTON. D.C.-i969 

35