ML20090A331
| ML20090A331 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 09/30/1991 |
| From: | WESTON GEOPHYSICAL CORP. |
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| NUDOCS 9203020276 | |
| Download: ML20090A331 (48) | |
Text
I .
l I
l EIGHTEENTH QUARTERLY REPORT I
I ;
CEI Seismic Monitoring Network -
! April 1 Through September 30,1991 .
i I
I Prepared for l CLEVELAND ELECTRIC ILLUMINATING COMPANY -
I I
I rebruary 1992 L .-__ - - __- _ _ _ _
Wes on Geopbygcgl '
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[8RR88nZ8888jgo
TAlli,E OF CONTENTS l'nge LIST OF TABLES i LIST OF FIGURES il
1.0 INTRODUCTION
1 2.0 SEISMIC NETWORK 1 1
3.0 OBSERVED SEISMICITY 1 l 3.1 E pleentral Area ofJanuary 31,1986 1 l 3.2 The Corridor between the January 31,1986 Epicenter and the injection Wells -
2 3.3 Other events Recorded by AUTOSTAR 2
- 4.0 ' DISCUSSION AND llEVIEW OF DATA ACQUIRED SINCE Tile BEGINNING OF TIIE SEISMIC MONITORING 2 4.1 - Epicentral Area ofJanuary 31.1986 3
- 4.2 The Corridor between the January 31,1980 Epicenter and the Injection Wells 4 4.3 Other events Recorded by AUTOSTAR 5
5.0 CONCLUSION
7 6.0 ACKNOWLEDGEMENT 8 TABLES FIGUltES APPENDIX A 101 AMERICASPRESSURE AND VOLUMETRIC INJECTION DATA l APPENDIX B
SUMMARY
OFINVESTIGATIONS OF LOCAL CRUSTAL MODEL l
l '
1 t ,
15773-44 Weston Geophysical I-
l, LIST O F'I'A llLES !
t i
TABLE 1 l'arameters of the January 31,1986 Earthquake Sequence ,
TAllLE 2 Microcarthquakes Inside the CEI Micronet Aperture or in the immedinte Vicinity (February,1986 - September,1991)
TAllLE S Microcarthquskes Outside the CEI Micronet Aperture (February,1986 - I September,1991) t b
15773 44 Weston Geophysical
_- . . . _ _ . . . . -~. _ _ . _ . . _ , . . . _ . - . _ - _ _ . . . . _ . . . . . _ . - . . _ . _ _ . . _ . _ . . . _ . . . _ . . _ . _ . , _ , , . . _ . . . _ . _ _
i r
I.lST Olt IIG UltlCS .
Figure 1 Epicenters of the January 31,1986 Earthquake Sequence Figure 2 Seismicity: April to Septeinber 1991 Figure 3 Cumulative Seismicity (1/31/86 - 9/30/91) 1 l
r l
15773 44 Weston Geophysical j
QU AllTl?ltl,Y ltEl'OllT NO.18 1.0 INTitODUCTION In accordance with its agreement with the U.S Nuclear llegulatory Commission, Cleveland Electric illuminating (CEI) continues to monitor the seismic activity in a restricted region of Northeastern Ohio, encompassing the locale of the Perry Nuclear Power Plant, two deep injection wells operated by 101 Americas Inc.,(formerly CAL 1110), and the epicentral area of the January 31,1986 earthquake. This eighteenth Quarterly Report covers the monitoring period from April 1 to September 30,1991, in addition, Appendix A provides the volumetric data from the two injections wells for the two quarters; Appendix 11 gives a brief summary of the efforts made by CEI to verify the seismic crustal model used in its routine hypocentral determination.
This report also includes a summary of the conclusions reached since 1986 when CEI began its seismic monitoring. After almost six years ofinvestigations, CEI believes it has acquired the data necessary to answer the original questions, and that further monitoring at the same low level will not add any substantial new information.
2.0 SEISMIC NETWOllK During the second and third quarter of 1991, the Auto.aated Seismic Telemetering Itecording System (AUTOSTAll) and the Geneva station performed with their usual reliability; the total uptime percentage was 93E Most of the downtime was caused by telephone line problems.
3.0 OllSEltV ED Sl?!SMICITY 3.1 Epicentral Area of tho January 31,1980 Earthquaho There was no seismic activity observed in the Leroy area during the six nwnths of this monitoring period. For sake of review, Figure 1 and Table 1 presenting the cumulative observations since the main shock of 1986 are included.
15773 44 1 Weston Geophyucal
3.2 Tho Corridor between the January 31,1986 epleenter and the in.lection wells.
l During the six month period, several (10) small events occurred in the cluster located east and southeast of the injection wells. The two largest occurred on May 31,(Me = 1.6 and 1.3), in the northeast corner of the cluster. Two very small ones (Me = 0.1 and .2) on -
September 24 and 27 were located within one kilometer north of the wells. The six others, with Me between 0.4 and 1.2 occurred to the southeast of the wells. Figure 2 shows the i
activity observed during the six month period. The location parameters are included on Table 2 which lists all events recorded in this area and immediate vicinity since 198G.
3.3 Other events recorded by AUTOSTAlt.
AUTOSTAR triggered on a 4.2 mblg earthquake from the Western Quebec zone on June 16 and on a 3.9 mbig from New York state on June 17. One event from the Ashtabula source (Mc= 1,7) was recorded on May 2. A similar size event occurred on July 2, about 16 km cast of Ashtabula. As in the past, some low level activity (Mc = 0.3 and 1.0) was observed in the Lake, but the location accuracy for these small events outside the network aperture is not as good. Finally, one small event (Mc= 0.G) occurred in the Fairport Harbor area on June 10.
Figure 3 presents the cumulative seismicity as observed by the CEI not since January 31, 1986. Table 3 lists all events since 1986 outside the network aperture for which locations were calculated.
4.0 DISCUSSION AND REVIEW OF DATA ACQUlitED SINCE Tile ILEGINNING OF Tile SRISMIC MONITOltlNG.
The activity observed during the present reporting period is verj similar to the usual pattern and thus no special comments seem necessary.
In the Quarterly Report no.13 dated March 1990, a review of four years of observations was presented; it included a summary evaluation of the local seismicity, a discussion of a possible relationship to deep well injection, and CEI conclusions. The additional two years of monitoring have not changed the observed patterns of seismic activity; as a consequence the conclusions remain the same. A brief summary of these findings follows.
15773-44 2 Weston Geophysico!
4.1 The 1.croy earthquake of.lanuary 31,1986.
The seismic monitoring of the Leroy epicentral area during almost six years has confirmed that the Leroy carthquake was most likely a purely tectonic event, with no causal relationship to the deep injection of Guids taking place ten kilometers away to the north.
This hypothesis had been proposed during regulatory hearings after the main shock, although it received only limited support at the time, To a large extent, the task of local seismic monitoring was imposed on CEI for the purpose of collecting local data that would either validate or disprove this hypothesis ofinduced seismicity.
The complete and accurate recording of the aftershock sequence followed by occasional small microcarthquakes in the same epicentral area during the next four yeara(Table 1 and Figure 1) suggest that the Leroy seismic activity is very similar to what is observed in other areas of the Northeast where other magnitude 5 events have occurred and where the absence ofinjection wells or local r eservoirs preclude the possibility of induced earthquakes.
The magnitude 5.0 Leroy event had relatively fe" aftershocks, and most of them within a month. After a year, there was a long period of silence of eighteen months, suggesting the end of the sequence. Later, few isolated small events have occurred, none with aftershocks.
This pattern seems characteristic of moderate size tectcmic events in the East. It clearly contrasts with the seismicity pattern usually observed in several cases of induced seismicity,in which even smaller main shocks are followed by relatively large number of tremors. _
llecause of the low detection and location thresholds achieved by AUTOSTAlt, CEI was able to comparc several instances ofinduced seismic sequences occurring near Ashtabula with the local activity at Leroy. This comparative analysis was included in Quarterly lleport no.13. In addition, several short and smaller sequences of what is most likely induced seismicity were observed in the vicinity of the Calhio wells, in all of these cases, the focal depths observed were all typically shallower (about two kilometers) than those associated with the Leroy source (between 5 and 6 kilometers). These comparisons lead to distinguishing two different seismic regimes, tectonic and induced.
Finally, a seismic gap that separates the activity at Leroy from other local events has been observed since the very end of 1986. The lack of continuity in the seismicity pattern observed between some small events that are probably associated with the injection wells
1 and the active Leroy area reinforces CEl's position expressed early on that the Leroy l carthquake was purely tectonic and not induced by the distant injection wells.
In terms of local tectonics, CEI considers that the Leroy event occurred during a strain release at the corner of a small crustal block. The concept of small crustal blocks was-gradually developed by observing the stereographic threc dimem,ional projection of the Leroy hypocenters (USAll 1992, Figure 2.5 - 69), certain lineations of small events ,
occurring in the cluster associated with the 101 wells, and noting the multiplicity of short wavelength anomalies in the aeromagnetic data that are mostly influenced by relatively near surface geology.
4.2 The corridor between Leroy and the Cnthio wells, including the immediato vicinity.
The hypothetical causal relation between the injection wells and the Leroy carthquake focused the attention on the corridor connecting the wells and the epicenter. When proposed, the hypothesis disregarded the fact that all microscismicity observed after the main shock was remarkably tightly clustered around the hypocenter, ten kilometers away.
The frequently observed " smoking gun" trail was not present between the wells and the epicenter. On March 12,1986, a very small event (Mc=-0.3) was detected by one digital unit of the USGS left near the wells. This occurrence was interpreted as supporting the i hypothesis of induced seismicity. In consequence, CEI accepted the task to monitor the corridor between the wells and Leroy at the very low threshold of Mc= .5. The temporary deployment of portable seismographs for monitoring the aftershocks was reconfigured to include this north-south corridor until a more permanent telemetered network could be installed in spring 1987.
On September 28,1986, a small event (Mc=0.3) was located five kilometers east of the wells. Over the next few months, other microcarthquakes in the range -0.5 and 0.5 occurred in that same general area, at the average rate of one event per month, gradually forming a irtheast trending cluster. With time, exceptions occurred south and north of the wells, but se expected north-south alignment never materialized. The largest Mc magnitude of these events surrounding the wells and vicinity never exceeded 1.0, during all six years.
For the purpose ofinvestigating any possible causal relationship between the deep injection and the occurrence of small events, detailed information on the daily volumes of fluids 15773 44 4 Weston Geophysical
- m. _ _ _ . _ _ , - _ . _ _ _ , _ _ _ . _ . ,
injected and the pressures used were obtained from Calblo. These data plotted against nearby seismicity were presented in the Quarterly Iteports, starting with no. 4, and synthesized in Quarterly Iteport no.13. No clear temporal correlation was found, even taking into account some time lags required for diffusion. Although an occasional seismic event seemed to be related to a specific injection pulse,it was never possible to establish a one to-one correlation valid for all observed events.
I I
Despite the lack of a strict temporal correlation from which a cause and effect reintion could be surely inferred, the fluid injection is still considered to be probably responsible, in some manner, for those events occurring in the vicinity around the wells, and for the group of events forming a northeasterly trending cluster about four kilometers to the southeast.
This view is based on the spatial correlation and on the fact that all these events have roughly the same shallow focal depth, about 2 km, very similar to the injection depth (1.85 km),~ given the focal depth uncertainty. Since the Paleozoic-Precambrian interface is dipping gently to the southeast, fluid migration is facilitated in that direction. A system of fractures and joints usually pervasive in rocks subjected to various episodes of tectonism and several glaciation cycles can safely be postulated. This constitutes an adequate ;
environment for pore pressure changes and reduction of the frictional forces to allow sudden releases of strain energy.
The close examination of the epicentral distribution of these events suggests indeed the presence of sublineations, possibly defining the boundariec of small crustal blocks. Minor readjustments between these blocks are most likely facilitated or triggered by the presence of fluids.
Another characteristic of these events suggesting that they are induced is the tendency of some events to cluster in the time domain. Such tendency has been observed near l Ashtabula, Oli where the July 13,1987 sequence, considered induced by Armbruster et Al.
(1987) took place. Since then, several other isolated short sequences have occurred there, comprising foreshocks, main shock, and aftershocks. This temporal distribution is usually not observed for small magnitude events that are purely tectonic.
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4.3 Other events detected by CEI monitoring.
During the six years of operation, AUTOSTAlt triggered several times on small events originating from the Fairport llarbor area near 41.75N and 81.25W, where deep and 16773-44 5 Weston Geophysicci
shallow injection wells are located. llecause of the close proximity, a causal relationship has been ruspected; no attempt has been made to obtain daily logs for each of the injection wells ad investigate potential temporal correlation.
Several events were located offshore. The largest one, Mc = 3.5, occurred just few kilometers north of Euclid, a suburb of Cleveland, on January 26,1991 and was discussed in Quarterly ,
I lleport no.17. A small sequence of events (Mc=2.7) was recorded June 1988,just north of Painesville. Three smaller ones were also loented north northeast of Madison.on the Lake.
The location accuracy of all these offshore evects is variable with the distance from the network aperture, size of events, and azimuthal gup; given the small dimensions of the array, the location error may well be in the order of several kilometers at times. .
l One important fact learned from this local monitoring exercise is the confirmation of offshore seismicity on the basis of instrumental data. The historical record lists several tremors with inland locations along the lake shore, based on felt reports only. Some of these events may have occurred offshore, as suggested in Appendix 2D D of the USAlt. This fact was confirmed by the small earthquake that occurred offshore Euclid, on January 26,1991.
This event, studied in detail by CEI, was located offshore on the basis ofinstrumental data from the two networks.- Yet, on the basis of intensity reports alone collected through a
( telephone survey, the exact epicentral location was not evident. in fact, without the instrumental data, the event could well have been mislocated inland by several miles. For example, the National Earthquake Information Service reported a maximal intensity V at Brecksville and Broadview IIcights, more than twenty miles south of Euclid. The apparent randomness of these small offshore events seems to suggest again stress releases along boundaries of small crustal blocks, as supported by the short wavelength aeromagnetic anomalies. This conceptual model of small crustal blocks was discussed in Quarterly Report no.13, in reference to a crisscross pattern of seismic lineations observed in the cluster of
! microcarthquakes located east of the injection wells, and probably applies to a large portion l
of the site region.
Other significant observations include the recording and locationing of small events I onshore, e.g. near Aurora, Willoughby, Fostoria, Madison-on the-Lake, Ashtabula, Ohio, and also south of Erie, PA. Several of these new epicenters confirm historical locations based on felt reports only.
15773-44 G-Weston Geophysicol-
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The triggering of AUTOSTAll on a multiplicity of events occurring in the vicinity of an l Injection welljust east of Ashtabula was also enlightening. (See Quarterly lleport no.15).
Although the distance from the network aperture and the relative short dimensions of the network did not permit the detailed tracking of the spatial migration of the induced seismicity, the detection threshold was low enough to capture the temporal distribution of-the events. The periodic pattern of brief seismic episodes provided a useful criterion to distinguish purely tectonie events from induced ones. The best example illustrating the contrast of the two seismic regimes: a Mc=2.8 occurring at Leroy on December 28,1988 without any aftershock at all versus a Mc= 2.8 at Ashtabula on August 1,1989, followed by at least 12 events with Mc greater than 0.5 over a period of Ove days (Quarterly lleport No.
15).
5.0 CONCl,USIONS With almost six years ofintensive seismic monitoring of the area encompassing the Perry Nuclear Power Plant, two ICI Americas deep injection wells, and the January 31,1980 Leroy earthquake, with a highly sensitive network, CEI has gathered sufficient information to answer questions raised about the nature of the Leroy event and the local microscismicity.
First, the seismic activity in the Leroy area continued to remain extremely well contained in space around the main shock hypocenter. The aftershock sequence was relatively briefin time, as typical of other similar size tectonic events in the Eastern United States and Canada. In addition, the cluster of activity at Leroy has remained spatially isolated from other seismic events considered as probably induced. The corridor connecting the epicentral area and the two ICI Americas injection wells never developed as a seismic lineament, as hypothetically predicted. It is interesting to note that a long period of observations has corroborated the evaluation made by CEI one month after the main shock,i.e that the Leroy event was a natural tectonic event and not induced by injection. Equally relevant is the fact that Nicholson et al. (1988) of the USGS reached the same conclusica after a detailed study,
_ using similar observations "to argue for a natural origin" Secondly, the detailed monitoring of an area larger than the corridor revealed th.it some low level activity exists in the vicinity of the two wells, particularly to the southeast. Certain -
characteristics of this activity, such as the shallow focal depth, the temporal distribution, and the proximity to the wells suggest strongly a causal relationship. in the same manner 15773-44 7 Weston Geophysicol
,,4ruster et al.(1987) concluded the seistnic activity netu un 'njection well owned by p/,<
re nearEnvironunental Ashtabuh are almostidenticalnear to those used Ashtabula by ICl. to be most probably ind
,3rdly, the occurrence of small events near injection wells in the Fairport liarbor area has Leo been suspected to be induced.
'inally, several small earthquakes, some felt locally, have confirmed that low level activity, pssibly associated which minor readjustments of small crustal blocks suggested in the bromagnetic data, exists both onshore and offshore, as suspected in CEI original ssessment of the historical seismicity. (Appendix 2D D of USAR)
.0 A C KNOWI.EI)G EM RN'I' 1El and Weston Geophysical are grateful to Rev. W.R. Ott, S.J. of the John Carroll Iniversity Seismological Observatory for contributing data from his network. Considering he small aperture of CEl's network, the additional data are critical to the locationing of 1
everal events.
15773-44 8 Weston Geophysical
in i ispis upu i
'I'AlilES Weston Geophysical
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Table 1 A.81 t R $ H O C A PARAN!f1R$ CF THI JANUARY 31, 1986 E LR 7HOUAK E * ,
Y E ARMODY HRMISEC LAT11UDE LONGITUDE DEPTH NP GLP RMS LRN [R2 Mc
- 1. 19860201 185449.35 41N38.67 81W 9.17 4.35 20 94 .09 .3 .5 1.5
- 2. 19860202 32248.67 41 38 72 81 9.55 4.86 37 72 .07 .1 .2 .9
- 3. 19860203 194719.77 41 38.92 81 9.48 5.83 52 75 .08 .2 .2 2.0
- 4. 19860205 634 2.47 41 38.90 81 9.27 3.73 31 52 .08 .2 .3 .1
- 5. 19860206 183622.44 41 38.72 61 9.61 5.A0 50 67 .07 .1 .2 2.5
- 6. 19860207 152020.38 41 39.03 81 9.22 3.76 44 62 .07 .1 .3 1.1
- 7. 19860210 200613.61 41 39.10 81 9.39 4.73 29 70 .06 .1 4 .9
- 8. 19860223 32948.50 41 39.18 81 9.09 5.48 22 76 .06 .2 4 .1
- 9. 19860224 1655 6.48 41 30.85 21 9.60 3.25 to il .09 .5 2.7 .1
- 10. 19860228 13934.21 41 39.23 81 9.61 3.91 12 il .06 .3 .5 .1
- 11. 19860308 204249.68 41 38.67 81 9.20 3.12 20 55 .10 .3 .7 .1
- 22. 19860324 134241.24 41 38.43 81 9.11 5.30 11 30 .06 .3 .8 1.4 l
- 13. 19860410 65805.71 41 38.91 81 9.55 5.11 22 $3 .08 .2 .3 .1 14 19860617 221633.20 41 38.91 81 9.55 3.40 16 33 .09 .3 .8 .8
- 15. 19860714 075423.12 41 38.69 81 9.13 4.93 12 99 .08 .3 .B .3
- 16. 19870212 011056.67 41 39.10 61 9.11 3.87 13 196 .09 .8 1.0 1.8
- 17. 19880805 222632.99 41 39.07 81 9.11 4.60 12 170 .04 .2 .3 0.1
- 18. 19881011 063132.33 41 39.20 81 8.78 5.33 13 147 .04 .2 .3 .2
- 19. 19881228 232824.52 41 38.17 81 9.97 5.87 18 90 .05 .1 .2 2.8
- 20. 19900901 135054.46 41 38.87 01 9.09 4.56 17 B2 .05 .2 .3 1.5
- 21. 19910117 071153.29 41 39.33 81 8.91 6.13 8 159 .02 .1 .2 .2 Vp184.2 $ k m/s Thickness a 2 km vp2=6.5 km/s Thicknees = 33 km rev. APR. 1991 vp/Vss1.78
- The m or e recent events sn a y not be true af tershock s Weston Geophy5ical j
Tabis 2 MICROC AR THQU At f 5 IN51DE TH E M1CR DNET APERTURT OR IN THE IMME01 ATE VICIN!7 Y (2/1986-9/19?!)
NO.Y E AR MO OT HRMIS(C LA7.N LONG.W D RM5 EH El NP N5 GAP MC 50 1R.40.
- 1. 1985 0312 085526.6 41.7272 81.1707 2.0 0.06 0.7 0.4 10 6 216 .3 G5
- 2. 1986 0928 103604.2 41.7247 81.1091 2.3 0.04 0.3 0.4 11 6 174 .3 WG
- 3. 1986 1020 105944.7 41.7587 81.1453 3.00.071.7 2.0 6 4 337 .6 WG 4 1986 10 2 T 122555 5 41.7435 81.0944 2.9 0.07 2.7 1.5 6 3 221 .2 WG
- 5. 1986 1103 085449.6 41.7098 81.1292 1.8 0.06 0.5 0.5 7 5 145 .3 WG
- 6. 1986 1201 050317.5 41.7120 81.1195 2.1 0.0706 5.8 7 5 188 .2 WG
- 7. 1987 0102 026114.8 41.7472 81.1027 2.0 0.06 0.3 0.5 10 6 174 . 6 WG
- 8. 1987 3128 2J5829.8 41.7399 81.0974 2.1 0.03 0.4 07 8 5 199 .7 WG 9 1987 0223 114556.4 41.7284 81.1197 2.00.030.1 0.3 10 7 100 .5 WG 10.1987 0228 204644.5 41.7451 81.0932 2.4 0.07 1.0 1.7 7 4 239 .4 WG 11.1987 0501 211332.3 41.7466 81.0372 1.9 0.06 0.3 0.2 7 4 196 .6 WG 12.1987 3501 211352.1 41.7466 81.0921 2.4 0.08 0.2 0.8 15 9 100 1.3 WG 363 13.1987 3502 183307.7 41.7475 81.0932 2.0 0.02 0.1 3.0 6 4 174 .6 WG 14.1987 0502 202526.5 41.7424 '81.0889 2.7 0.08 0.3 0.6 14 8 115 4 WG 366 15.1987 0708 034835.2 41.7392 81.1037 2.7 0.07 0.7 1.1 8 5 166 .2 WG 16.1987 0815 052637.7 41.6994 81.1472 2.8 0.06 0.2 1.0 10 6 133 .1 WG 1061 17.1987 1010 000610.4 41.7430 91.1030 1.9 0.04 0. 3 0.2 7 5 166 .6 WG 18.1987 1014 195924.8 41.7250 81.1318 3.4 0.04 1.6 0.7 6 3 190 .7 WG 19.1987 1122 *74916.9 41.6989 81.1447 2.2 0.04 0.2 38 9 5 120 .1 WG 1720 20.1988 0116 22403. *41.747 81.098 2 .6 WG 21.1988 0116 223010. 441.747 81.098 3 .6 WG 22.1988 0116 231704.4 41.7474 81.0981 2.0 0.05 0.5 0.3 9 5 185 1 8 WG 18 79 23.1988 0117 024821.7 41.7467 81.0997 1.90.060.5 0.3 10 5 180 0.5 WG 1881 24.1988 0117 092236. *41.747 81.098 3 .6 WG 25.1988 0117 09:400. *41.747 81.098 2 .6 WG 26.1988 0117 131551. 641.747 81.098 2 .6 WG 27.1988 0205 155837.0 41.7351 81.0907 2.0 0.04 0.4 0.2' 10 5 195 0.5 WG 1971 28.1988 0820 005423.1 41.7026 81.1121 2.4 0.05 0.2 1.6 8 4 162 .2 WG 3011 29.1988 0927 154639.1 41.7716 81.1334 3.20.030.2 0.3 11 6 292 0.1 WG 3076 30.1988 1022 201132.9 41.7150 81.0578 2.5 0.06 1.3 0.7 13 7 193 0.1 WG 3136 31.1988 1031 063428.7 41.7290 81 1035 21 0.04 0.2 0.5 10 5 120 .0 WG 3412 32.1988 1103 190335.4 41.7133 81.1232 2.1 0.05 0.2 7.9 9 5 126 .2 WG 3437
-33.1988 1205 055514.9 41.7578 81.1538 2.4 0.06 0.5 0.7 7 4 279 0.0 WG 3525 34.1989 0103 120244.5 41.7287 81.1328 2.1 0.06 0.2 11 0 8 5 226 .1 WG 3623 35.1989 0130 032527.0 41.7018 81.1846 2.0 0.04 0.4 18.2 10 6 182 .2 WG 3661 36.1989 0130 185020.8 41.7334 81.0983 2.0 0.04-0.2 0.4 11 5 155 .2 WG 4663 37 1989 0309 033045.8 41.7105 81.0581 2.00.040.2 15.1 13 8 187 0.6 WG 5719 38.1989 0310 165722.4 41.7107 81.0585 1.9 0.04 0.2 0.1 10 6 186 .2 WG $725 39.1989 0312 192349.6 41.7113 81.0596 2.0 0.04 0.2 13.2 13 8 185 0 4 WG 5729 40.1989 0322 201335.9 41.7269 81.1545 2.1 0.03 0.1 1.4 16 9 119 1.9 WG 5770 41.1989'0530 142039.6 41.7188 81.1223 2.1 0.04 0.1 3.0 7 4 115 .4 WG 5953
'42.1989 0719 085451.1 41.7261 81.1542 2.1 0.05 0.1 2.0 16 8 161 .) WG 4132 43.1989 1002 071123.5 41.6981 81.1447 2.2 0.04 0.2 4.7 8 5 163 .3 WG 4415 44.1990 0331 025526.6 41.7303 81.1001 2.0 0.05 0.3 0.6 9 5 134 .2 WG 493B
'45.1990 0505 212924.0 41.7111 81.0556 2.1 0.03 0.2 1.5 13 8 194 .2 WG 5086 4 6.19 9 C 0 519 222823.5 41.6901 81.1269 2.1 0.05 0.2 13.0 8 5 153 .2 WG 5153 47.1990 3522 140632.2 41.7026 81.1119 2.20.050.3 3.9 9 5 162 . 3 WG 5159 48.1990 3526 120735.4 41.7300 81.0774 2.30.030.2 0.2 10 5 236 .1 wG 5198 49.1990 0812 102352.0 41.7340 81.0761 2.3 0.02 0.1 0.2 10 5 237 .2 WG 5480 50.1990 1021 132813.8 41.7113 81.0552 20 0.04 0.1 0. 2 13 8 195 .5 WG 5795 51.1990 1022 122847.5 41.7127 81.0545 - 2. 0 0.04 0.2 3.0 14 9 146 .2 WG $796 52.1990 1112 142426.6 41.7125 81.0589 2.3 0.03 0.3 0.9 9 5 250 . 3 W G $ 919 l 53.1991 0424 091108.5-41.7052 81.1254 2.3 .04 0.2 2.9 9 5 137 0.2 WG 7022 54.1991 0531 210145.3-41.7550 81.0592 -2.2- .04 02 3.5 12 7 143 1. 6 WG 7149-55.1991 0531 212808.8 41.7562 81.058J 2.1 .04 0.2 9.3 12 7 144 1.3 WG 7150 56.1991 0604 053515.5 41.7283 31.1315 2.1 .05 0.2 2.5 9 5 120 0.5 WG 7162 57,.1991 0726 214949.9 41.7229 81.0959 2.0 .05 0.3 0.4 10 5 141 9.4 WG 7453 50.1991 0727 011739.1 41.7227 81.0952 2.0 .05 0.3 0.4 10 5 146 0.2 WG 7454 59.1991 0731 093968.3 41.7256 81.1227 1.9 .06 0.3 0.2 10 5 100 1.2 WG 7466 60.1991 0916 152956.3 41.6967 81.1469 2.8 .06 0.2 1.5 3 5 161 .4 WG 7558 61.1991 0924 230021.3 41.7579 81.1522 2.2 .06 0.3 0.6 10 5 179 0.1 WG 7564 <
62.1991 0927 174549.9 41.7575 81.1!25 2.3 .06 0.3 0.5 10 5 179 .2 WG 7567 i
- In dic at e s location by inference l
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I Al'I'ENDlX H CilUSTAL INVESTIGATIONS IN LAKE AND GEAUGA COUNTIES, N.E.01110 Weston Geophysical Im u. x x
o TAllLE OF CONTENTS ,
l'nge LIST OF TABLES LIST OF FIGURES l.0 INTRODUCTION 1
2.0 DESCRIPTION
OF THE CRUSTAL MODELINVESTIGATIONS 1 2.1 Objectives and Approaches 1 2.2 DifTiculties Encountered 2 3.0 PRESENTATION OF THE RESULTS 3 3.1 Shallow Refraction Lines 3 3.2 Long Refraction Lines 3 3.2.1 Quarry Blasts and SCH Explosives 3 3.2.2 Data l< rom Local Microcarthquakes 3 4.0 DISCUSSION 4 4.1 Inferred Crustal Model 4
5.0 CONCLUSION
5
6.0 REFERENCES
6 15773-44 weston Geophysical
LIST OF TAlilES TABLE B4 Three Crustal Models TABLE B 2 Model Testing - Best Sand Quarry, Novernber 2,1988 TABLE B-3 Model Testing - Best Sand Quarry, Septernber 20,1989 TABLE B-4 Aftershock Parameters of the January 31,198G Earthquake Using the Three-Layer Model 5
15773 44 Weston Geophysical
- 1.lST OF FIG UltES
. FIGURE B-1 Blast Locations and Dates FIGURE B-2 Shallow Refraction Travel Time Plot, Best Sand Quarry, December 12,1988 FIGURE B-3 Shallove Refraction Travel Time Plot, SCII, December 12,1988 FIGURE B-4 Travel Time Plot, Best Sand Quarry, November 2,1988 FIGURE B-5 Travel Time Plot, Best Sand Quarry, September 20,1989 FIGURE B-6 Travel Time Plot, SCll, December 13,1988 FIGURE B 7 Travel Time Plot, SCII, December 14,1988 FIGURE B-8 Travel Time Plot, Sidley Avarry, March 26,1990 FIGURE B Travel Time Plot, Madison on-the-Lake, December 25,1988 FIGURE 8-10 Travel Time Plots, Ashtabula Earthquakes, August 1,1989 l
15773 44 Weston Geophysical
l CitUSTA1,INVESTIG ATIONS IN 1 AKE AND GEAUG A COUNTIES, N.E. 01110 1.0 INTItODUCTION When Cleveland Electric illuminating (CEI) assumed the task of .nonitoring the microseismicity of the corridor between two Calhio injection wells and t'.ne epicentral area of the January 31,1986 earthquake, special efforts were made to obtain high quality data.
Starting with the aftershock program, up to 13 portable stations were deployed in the epicentral area and immediate vicinity. Within a year, a permanent digital telemetered network was installed, with three-component borehole sensors placed on rock, and a station distribution symmetrical around the area ofinterest, Close cooperation with the operator of the John Carroll University seismic network was initiated, thus assuring an optimal pool of arrival times.
For processing the observed aftershocks and other local events, CEl consultant Weston Geophysical (WG) selected the first and simplest crustal model out of three available (Table B1). As pointed out by Nicholson et al. (1988), these models give similar results except for small variations in focal depth estimates. WG's preference was based on sensitivity tests and technical considerations, but still remained subject to further verification.
l-This appendix briefly summarizes a report on the activities undertaken over the last four years to assess the validity of the crustal model used (Weston Geophysical, September 1991).
- 2.0 - DESCitiPTION OFTIIE CitUSTAl,MODEl, INVESTIGATIONS 2.1 Objectives and Approaches i
The CEI network aperture is somewhat limited to _the corridor between the two deep .
injection wells and the main shock epicentral area. The John Carroll University (JCU)
-regional network has a larger aperture. For the local seismicity monitored by the two networks, travel paths of first arrivah never reach the MOllo discontinuity at the base of
- the crust. For this reason, only velocities of the upper crust needed to be investigated with l
relatively short refraction profiles. The planned strategy called for very short refraction -
lines to investigate the near surface rocks, and longer profiles using data from both local quarries and nearby microcarthquakes. Portable MEQ recorders were deployed on four 15773 44 1 Weston Geophysical
~_ , _ _ - _ _ _ _ _ _ _ . - , . . _ . _ _ _ _ _ _ . . . ._,
occasions to increase the number of data points collectcd, but the permanent stations of *.he two nety srks provided the bulk of usable data.
Figure El shows the locations of the two quarries used, BEST SAND and SIDLEY, and of
'the SCIIncider site where two special explosions were detonated in an attempt to reverse a ;
long profile between BEST SAND and ANTIOCll; it also gives blast dates, and station locations of two networks.
2.2. Difficulties Encountered The main difHeulty encountered regards the insufficient energy released by the quarry blasts and the two CEI explosions at Schneider. The distance between the-BEST SAND quarry and ANTioch is about 28 km. Because of the many delays in the firing sequence, arrivals from both quarries were often emergent beyond 10 km. In addition, shot sizes at SCIIncider were limited by the presence of nearby pipelines and residences; as a result, the crustal profile between BEST SAND and Scil could not be reversed. The deployment of portable stations at regular close spacing along the profile was abandoned after four
- attempts in 1988.- Only data from the permanent network stations on selected larger quarry
. blasts were used in 1989 and 1990.
A second important difficulty came from the large uncertainty attached to arrival time readings due to the poor resolution offered by analog recorders, either because of drum speed or internal clock limitations. With a possible cumulative error as large as 0.2 sec for individual data points, the. calculated velocities on the time-distance plots can have an uncertainty of about 0.2 km/sec. This is one order of magnitude less than what is obtained in formal crustal experiments using one or two thousand pounds of explosives and hundreds of digital recorders along reversed linear profiles.
. A third difficulty resulted from the lack of shallow nearby local microcarthquakes large
- enough to be seen at all stations. Deeper events do not give critically refracted arrivals and
. thus are not suitable for the current objective. Several events were examined but only a few were retained.
.I5773 44 2 Weston Geophysical
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i 3.0 PitESENTATION OF Tile ltESUl!!'S 3.1 Shallow itefraction 1.ines Two short (2500 ft and 1800 ft) reversed profiles were shot on December 12,1988 on the BEST SAND quarry floor and at SCIIncider. Figures B2 and B3 indicate average velocities of 3.5 and 3.7 km/sec, values that agree with local surficial geology. Although thicknesses could not be formally calculated, boring logs suggest that 0.1 to 0.2 km estimates are realistic.
3.2 1.ong itefraction 1.ines Although the long linear profile could not be reversed as originally planned, the apparent velocities of the Paleozoic and upper Precambrian horizons remain informative since the 2 km-thickness of the Paleozoic and the gentle regional dip of the interface to the southeast are already known from borings.
3.2.1 Quarry tilasts and SCll Explosions Four blasts originating from the BEST SAND quarry were monitored, but only two were retained in last analysis. Figure B4 presents the results of the November 2,1988 survey.
The two velocities seen,4.72 and 6.17 km/sec, are inferred to represent the Paleozoic and Precambrian rocks respectively, Figure B5 gives the results of the September 20,1989 blast from which only a 6.25 km/sec velocity was read and assumed to be from the Precambrian horizon.
Two explosions made at the SCIIncider site, on December 13 and 14,1988, with limited explosives, provided information on the Paleozoic rocks only. Figures B6 and B7 present the respective results,4.76 and 4.81 km/sec.
Only one of the two monitored blasts from the SIDLEY quarry provided usable data.
Figure B8 shows the results of the March 26,1990 blast, with a Paleozoic velocity of 4.67 km/sec. 15773 44 3 Weston Geophysicol
-~. . . . _ _ _ . _________________ ___ _ _ _ _ ____
3.2.2 Data from 1 oeal Microcarthquakes In view of the limited seismic energy generated by quarry blasts, several local microcarthquake data sets were examined. Those selected had to be considered relatively shallow (about 2 km) and have a very stable solution. All Leroy aftershocks could not be used since they are relatively deeper (about 5 km); other locals within the CEI aperture were not large enough. The Madison-on-the-Lake event of December 25,1988, with Mc=2.4 was the only one local retained. Figure B9 suggests that observed first arrivals yield a 6.33 km/see apparent velocity over the distance range related to the Precambrian j rocks. i Beyond the two network apertures, one relatively well located source is associated with the Ashtabula activity, considered to be induced by injection (Armbruster, et al.1987). Three events recorded during the August 1989 sequence, assumed to be at the location and shallow depth determined by Armbruster for the main 1987 sequence, were examined. Figu.e BIO illustrates the relative consistency of three data sets, with a velocity of about 6.17 km/sec.
4.0 DISCUSSION 4.1 Inferred Crustal Model Given all limitations previously mentioned, the modest experiment is expected to give relatively imprecise velocity estimates, with only a 0.2 km/see accuracy, but still informative. With the data collected, a three layer model seems indicated, e.g., a thin surficial layer with a 3.5 km/see velocity, a Paleozoic column of about 1.9 km with a velocity of 4.8 km/sec, and a Precambrian sequence with a velocity of 6.2 km/see near the top.
To account for the velocity uncertainties, several variations of this basic model were tested to relocate the two quarry locations and the SCII site of two explosions. Tables B2 and B3 summarize a subset of the many tests perform ~ed on two recorded blasts from BEST SAND.
It is interesting to compare the relocation accuracy obtained with the preferred three-layer model derived from the experiment with that of the two-layer model used since 1986. There is indeed a definite improvement. Similar tests for the SCIIncider explosions and the SIDLEY blast confirm the same trend.
15773-44 4 Weston Geophysical
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In view of the observed improvement in the quarry relocation tests, the preferred three-layer model was then used to relocate all observed microscismicity within or near the network aperture. Table 114 presents all relocation parameters for the Leroy aftershock sequence. This Table 114 should be compared with Table 1 of the present Quarterly Report where the old two-layer model is used. There is little change in the epicentral coordinates, as expected when the station configuration is somewhat synunctrical around the source. On the other hand, the focal depth is systematically increased by an average 0.3 km. This change is not substantial.
-The effect of the three-layer model on the relocation of other events recorded by the network, even those sometimes outside the aperture, is similar: a pronounced tendency to increase the focal depth, usually by several tenths of a kilometer, a slight improvement in the RMS ?
residuals and standard errors ERil. i
5.0 CONCLUSION
Since the crustal model plays an important role in the hypocentral determination of observed seismic events, CEI has supported a modest experiment to validate the crustal modelin use since the January 31,1986 Leroy earthquake. The effort was spread over the
- last four years; ~ except for four special deployments of portable MEQ analog recorders, all the data were collected by the permanent network stations recording several local quarry blasts, two especially made explosions, and some local microcarthquakes.
The results of these crustal investigations have been very informative. Although several
- factors contributed to limit the accuracy of the collected data, nonetheless the observations were good enough to suggest that a three-layer model should be preferred to the two-layer model actually in use since 1986. This model separates the Paleozoie column in a thin surficial layer (0.1 km) and a thicker layer ( L9 km) with respective P-velocities of 3.5 and
'4.8 km/sec. The Precambrian column is given a velocity of 6.2 km/sec, the same 33 km .
thickness being retained. Several tens of variations of this observed model were tested systematically in relocating known quarry blasts. The observed basic model consistently-gave superior resultsin terms oflocation accuracy and RMS residuals.
-In a final stage, all observed microseismicity either in the Leroy source area or within the -
two network apertures was reprocessed with the preferred three-layer model. The epicentral coordinates show only a minimal change, and as expected a systematic increase 15773-44 5 Weston Geophysical
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in the focal depth _ estimates,0.3 km in the average. These results are most encouraging; the epicentral changes are small enough to be negligible, and the systematic increase in focal depth does not appear to be substantial and have new tectonic significance.
-- Consequently, conclusions reached previously need not to be modified. ,
6.0 ItEFEltENCES Armbruster, J.G., Seeber, L., and K. Evans (1987): TheJuly 1987 Ashtabula earthquake (mb=3.6) sequence in Northeastern Ohio and a deep fluid injection well; Abstracts of 59th annual meeting of E.S. of S.S.A.; St. Louis Urdversity, October 7-9.
Nicholson, C.,lloeloffs, E., and It.L. Wesson (1988): The Northeastern Ohio Earthquake of January 31,1986: Was itinduced?; llull. Seismol. Soc. America, vol. 78, pp.188-217.
Weston Geophysical,1991: Crustallnvestigations in Lake and Geauga Counties, N.E.
Ohio; prepared for Cleveland Electric illuminating Co., September,50 p.
15773-44 6 Weston Geophysical '
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Table B-1 Depth Thickness P Velocity S Velocity Vp/P s Description *
(km) (km) (km/s) (km/s) 0.0 2.00 4.25 2.53 1.08 Paleozoic section 2.00 99.00 6.50 3.87 1.68 Granitic basement 0.0 1.00 3.70 2.06 1.80 Upper Sedimentary 1.00 1.00 5.00 3.20 1.75 Lower Sedimentary 2.00 35.00 6.33 3.06 1.73 Granitic crust 37,00 99.00 8.10 4.68 1.73 Mantle 0.0 0.05 1.80 0,00 3.00 Glacial till 0.05 0.45 3.00 1.58 1.90 Devonian shale 0.50 0.50 4.20 2.33 1.80 Silurian dolomite 1.00 0.75 -4.50 2.53 .1,78 Ordovician limestone and dolomite 1.75 0.35 4.75 2.70 1.76 Cambrian sandstone and dolomite 2.10 17.90 6.15 3.54 1.74 Precambrian granite 20.00 25.00 0.70 3.87 1.73 I,ower crust 40.00 99.00 8.15 4.63 1.75 Mantle after: Wesson and Nicholson,1986.
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Table B-3 MODELTESTING -- BEST SAND QUARRY Blast: 9-20-1989 Location:41.5440N 81.2090W MODELS SOLUTIONS Velocity Thickness Orig. Time Lat. Long. RMS NP Gap A Lat. ALong. !
km/s km UT N W sec 0 km km 3.5'4.8/6.2 0.1/1.9/33 191241.1 41.5405 81.2107 0.08 10 278 -0.39 0.14 (1.70/1.70/178) 3.5/4.8/6.2 0.1/1.9/33 191241.3 41.5471 81.2042 0.08 10 271 0.34 -0.40 (1.78/1.78/1.7S)-
l 3.5/4.8/5.9 0.1/1.9/33 191241.2 41.5505 81.2060 0.06 l') 270 0.72 -0.25 (1.78/1.78/1.78) 4.8/5.9 2/33 191241.2 41.5486 81.2098 0.08 10 273 0.51 0.07 (1.7S'1.73)
I 4 S'6.2 2/33 191241.4 41.5465 81.2040 0.10 10 272 0.2S -0.42 f 1.78/1.78) L 4.25/6.5 2/33 191241.3 41.5476 81.1949 0.13- 10 269 0.40 -1.18 :
(1.78/1.78)
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Table B-4 AFT ERSHOC K P AR A ME 1E RS Of 1HE JANUARY 31, 1996 E AR TH QU AK E C USING THREE-LAYER MODEL Y E ARMO DY HRMISEC LATITUDE LONGITUDE DE PTH NP GLP RMS ERH E (Z Mc
- 1. 19860201 185449.33 41N38.72 61W 9.22 4.65 20 95 .09 .3 .5 1.5
- 2. 19360202 32243.64 41 38.73 81 9.56 5.19 37 72 .07 .1 .2 .9
- 3. 19860203 19 719.77 41 38.92 81 9.49 6.28 52 75 .08 .2 .2 2.0 4 19860205 634 2.46 41 38.89 81 9.29 4.10 31 52 .09 .2 .3 .1
- 5. 19860206 183622.39 41 38.72 81 9.60 5.89 50 47 .07 .1 .2 25
- 6. 19860207 152020.34 41 39.02 81 9.21 4.42 44 62 .06 .1 .3 1.1
- 7. 19860210 200613.58 41 39.08 el 9.40 5.20 29 70 .07 .2 4 .8
- 8. 19860223 32949.47 41 39.15 81 9.10 5.74 22 76 .06 .2 4 .1
- 9. 19860224 1655 6.50 41 38.84 81 9.62 3.55 10 31 .10 .5 2.1 .1
- 10. 19860228 13934.i2 41 39.20 81 9.65 4.04 12 91 .06 .3 .5 .1
- 11. 19860308 204249.64 41 38.66 81 9.20 3.81 20 55 .09 .2 .5 .1
- 12. 19860324 134241.20 41 38.40 81 8.97 5.46 11 B1 .08 .3 '.0
. 1.4
- 13. 19860410 65805.70 41 38.78 81 9.53 5.04 22 53 .07 .2 .3 .1 14 19860617 221631.16 41 38.83 81 9.58 3.70 16 33 .10 .3 .8 .8
- 15. 19860714 075423.06 41 39.61 81 .22 5.40 12 98 .10 4 9 .3
- 16. 19870.'12 011056.68 41 39.22 81 9.3B 3.60 13 201 .10 .8 1.1 1.8
- 17. 19880805 222632.96 41 39.08 81 9.03 4.20 12 166 .04 .2 .1 0.1
- 10. 19881011 063132.30 41 39.22 81 8.69 5.40 13 142 .05 .3 4 .2
- 19. 19881228 232324.42 41 38.17 81 10.05 6.30 18 91 .08 .2 4 2.8
- 20. 19900901 135054.38 41 38.81 81 9.20 5.00 17 B3 .07 .2 4 1.5
- 21. 19910117 071153.29 41 39.40 81 8.84 6.10 8 153 .02 .1 .2 .2 Yp1=3.5 km/s thickness = .1 k m Vp2a4.8 k m/s Thicknos s = 1.9 km Vp2=6.2 k m/s Thicknos s = 33 km rev. Aug. 1991 Vp/Vs=1.78
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