ML20245A148
| ML20245A148 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 03/31/1989 |
| From: | WESTON GEOPHYSICAL CORP. |
| To: | |
| Shared Package | |
| ML20245A145 | List: |
| References | |
| NUDOCS 8906210119 | |
| Download: ML20245A148 (26) | |
Text
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TENTH QUARTERLY REPORT CEI SEISMIC MONITORING NETWORK JANUARY 1 THROUGH MARCH 31,1989 Prepared for CLEVELAND ELECTRIC ILLUMINATING COMPANY JUNE 1989 9,
Weston Geophysical CORPORATION K gh R
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i ABLE,QF CONTENTS Ease LIST OF TABLES .i LIST OF FIGURES . ii
1.0 INTRODUCTION
-1 2.0 SEISMIC NETWORK 1 3.0 OBSERVED SEtSMICITY 1 3.1 Epicentral Area of January 31,1986 1 3.2 The Corridor between the January 31,1986 Epicenter i
and the injection Wells 1 3.3 Other Events Recorded by AUTOSTAR 2 4.0 DISCUSSION 2
5.0 CONCLUSION
4 l
6.0 ACKNOWI,EDGEMENT 4 FIGURES i APPENDIX A: CALHIO VOLUMETRIC INJECTION DATA APPENDIX B:
SUMMARY
OF AN INTENSITY SURVEY OF THE
( DECEMBER 28,1988 EVENT y
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IJSLQEIABIES TABLE 1 Microcarthquakes Within the CEI Micronet Aperture or its immediate Vicinity i
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1 LIST OF FIGURES- l I
FIGURE 1 Seismicity, January - February. . March 1989 :
FIGUllE 2 Cumulative Seismicity 1/31/1986 -3/31/89 i i
FIGURE 3 Analog recordings of the March 22,1989 event, Mc=1.9 FIGURE 4 Di 6ital recordings from stations ANT and SCH, March 22,1989 FIGURE 5. Digital recordings from stations FORD and WIL, March 22,-1989 )
FIGURE 6 Digital recordings form station RAD, March 22,1989 FIGURE 7 Focal Mechanism Data, March 22,1989 i
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1.0 INTRODUCTION
In accordance with its agreement with the U.S Nuclear Regulatory Commission, j Cleveland Electric Illuminating (CEI) continues to monitor the seismic activity in 'I a very small regiou of Northeastern Ohio, encompassing the locale of the Perry Nuclear Power Plant, two deep injection wells operated by CALHIO, and the j l
epicentral area of the January 31,1986 earf.hquake. This tenth Quarterly Report l covers the period from January 1 to March 31, 1989. An update of the CALHIO i vol:: metric injection data is also provided in Appendix A.- A summary of an.
irrtensity survey of the December 28, 1988 microearthquake, Mc = 2.8, is presented in Appendix B.
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2.0 SEISMIC NETWORK l
During the first quarter of 1989, the Automated Seism 3c Telemetering and Recording System (AUTOSTAR) performed in a very reliable manner, achieving an uptime for network operation of 97.7%. Most of the downtime, calculated in station / hour units, was related to individual telephone line troubles and periodic j maintenance of the system.
i 3.0 OBSERVED SEISMICITY 3.1 Eoicentral Area of the January 31.1986 Earthouake l There was no microcarthquake activity detected during the quarter. The last -
event reported occurred on December 28,1988. !
i 3.2 The Corridor betwcen the January 31.1986 Eoicenter and the Iniection Wells i !
l' During this quarter, AUTOSTAR detected eight microcarthquakes above the Mc = -0.5 threshold, four within the network aperture and the four others just -
l outside. The standard location parameters of all these events are listed on Table l 1 and the epicentral locations are plotted on Figure 1. Station and injection well locations are included on the same figure. Figure 2 presents the cumulative i
seismicity since January 31,1986.
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3.3 Other Events Recorded by AUTOSTAR The digital system triggered on many local and regional quarry blasts, but did not record any regional or teleseismic events.
4.0 DISCUSSIQE 1
The lack of microseismicity during the last three months ir. the immediate area of the January 31,1986 earthquake is not surprising; during 1987 and 1988, there l was an absence of seismic activity over an 18-month period.
Three of the four events located within the network aperture are very small, with Mc magnitudes less than zero. The fourth one, on March 22, 1989, with an Mc = 1.9, is the largest microcarthquake to occur in the corridor since seismic monitoring began, excluding aftershocks in the January 31,1986 epicer. tral area.
The event was'not recorded by any in-plant strong motion instrumentation at PNPP located 8 km from the epicenter. The estimated location is approximately l two kilometers south of the two CALHIO injection wells. Figure 3 presents the five helicorder seismograms of the vertical components used for the Me duration measurements. Figures 4, 5, and 6 i.how the first five seconds of all 15 digital channels. Impulshce P-motions on the vertical and well developed S-phases on.
l the horizontal components should be noted. Figure 7 summarizes the focal mechanism data, suggesting a predominantly strike-slip motion, probably on a
! NNE plane. The epicentral location of this March 22,1989 Mc - 1.9 event is close to the epicenter of the March 12,1986, Mc = -0.3 microcarthquake originally detected by the USGS. All injection well data, including all injection ;
volumes and operating pressures, must be thoroughly examined before concluding. l that a causal relationship exists between the wells and the obsetved seismicity.
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l To date, any relationship between the Calhlo injection 'wells and the microseismicity remains unclear. This is partly due to the fact that the injected volumes - as shown in Appendix A, initially reported with the Fourth Quarterly ;
Report - are fairly constant as a function of time, with only brief interruptions-2722J 2 Weston Geophysical
and small seasonal variations. Thus the corresponding f(t) is relatively flat and does not resemble et all the somewhat unpredictable time function s(t) describing the seismic sctivity.
In the spact domain, the seismicity distribution has evolved over the last three years. Although there are a few epicenters within 1 km north of Well No.1, the more apparent and active clut.ter observed through intensive monitoring at the low threshold of Mc = -0.5, remains east of the wells at a distance of 4 km. With such an aseismic zone between the wells and this northeas: trending linear cluster, the causal influence remains in doubt. Whh this quarter, three events have subtly changed the pattern. First, the January 3 and March 22 microearthquakes have partially filled an aseismic area to the south of the wells, suggesting an east-west lineation at a distance of 2 to 3 km. from the wells.
Secondly, an event occurred on January 30, just north of Station Williams, in a'n area which priorly had been aseismic. It is possible to visualize an alignment made of this event and four others previo0 sly located along a northeast trending azimuth. These last two lineations are still highly subjective and will need to be confirmed through additional seismicity.
With microseismicity observed aloing these three different lines, all within the influence radius of the wells, the hypothesis of some relationship cannot be ruled out, particularly in view of the fact that most of these small events have a nominal focal depth of 2 km, approximately the injection depth. Nonetheless because these events are very small, rather infrequent, and several of them of dubious origin, i.e. possible blasts or gas well related, it reinains premature at this time to conclude that a causal link surely exists. Three small events occurred 6n March 9,10, and 12, almost 3 kilometers east of Station Ford, close to the epicenter of another microearthquake recorded on October 22,1988. This i represents a new cluster of activity detected; for this reason, an area reconnaissance was made. Several new gas wells with recently initiated production were found in the vicinity. At this time, a definite causal link cannot j be substantiated, but the hypothesis of a possible gas wellinfluence continues to be considered for some part of the local seismicity.
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i Finally, one small event occurred on March 25,1989, in close proximity of a deep j injection well, in .the Fairport Harbor Area. This is the fifth instance of small I microcarthquakes in this area, over the last thirty months. Noticeably, these events seem to occur nearer to the wells than at Calhio; however they are very j infrequent. .
5.0 CONCLUSION
q Eight microcarthquakes were detected by AUTOSTAR during the first quarter of ;
1 1989. Four were located within the network aperture, in a somewhat scattered' j distribution. The largest event, with Me = 1.9 has its epicenter two kilometers )
south of the injection wells, but no causal relationship has been established.
Four other small events occurred outside the aperture; three of them were i spatially related to new gas wells found in the vicinity; the other event is located )
close to an injection well in Fairport Harbor. Although the cumulative microseismicity may suggest the existence of crosstrending lineations in the area of the wells, there is no reason at this time for CEI to change its original position that the Leroy earthquake of 1986 was probably not induced.
6.0 ACKNOWLEDGEMENT .
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CEI and Weston Geophysical are grateful to Rev. W.R. Ott, S.J.,.of the John Carroll University Seismological Observatory, for contributing additional phase j arrival times for several seismic events detected by the CEI network.
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Well #2 did not operate.
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l APPENDIX B i
SUMMARY
OF AN INTENSITY SURVEY OF THE DECEMBER 28.1988 LEROY MICROEARTHOUAKE 1
i INTRODUCTION On December 28,1988, at 23:28:24.5 (U.T.) or 6:28 p.m. (E.T.), a small earthquake, M c
- 2.8, occurred in Leroy Township, Lake County, Northeastern Ohio. The Cleveland Electric Illuminating Company local network and the John Carroll University regional
'l network recorded the trerr or very clearly. The event was readily identified as originating ; j from the same area as tne January 31, 1986, seismic sequence. In the Ninth Quarterly Report, the location parameters were presented and discussed. Because the event was felt widely in two coun;:ies, an intensity survey was done; a summary of this survey follows.
INTENSITY SURVEY l
It is not uncommon in Eastern North America for small earthquakes in the magnitude ra g 2 to 3 to be felt locally. As expected, the December 28 tremor was felt but the i number of phone calls placed to police stat!9ns and newspapers seemed relatively larger than normal for a small 2.8 M cshock. Some reports originated from Painesville, Perry, and Mentor, all locations with lower elevations and softer soil conditions than those prevailing in the epicentral area.
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At the recommendation of Weston, CEI commissioned an intensity survey with the dual. ,
objective of defining the total felt area and identifying any anomalous isoseismal contour. It was hoped that some insight could possibly be gained from this exercise Anto l i
the interpretation of small historical events located mostly on the basis of felt reports, A l
two-. fold approach for the data collection was decided upon. First, Weston's personnel -l i
would condue, as soon as possible, interviews at locations along EW and NS traverses; !
secondly, CEI would use qtsestionnaires mailed to the majority of its local personnel, to fill in the coarsely gridded data collected by Weston. Table 1 gives a breakdown of the i i
2722J 1 Weston Geophysical )
. _ _ _ _ _ _ _ _--__-_-- - D
data in terms of felt reports versus modes of collection. The most frequently chosen level was Intensity Ill (MM), usually with the expressions " felt quite noticeably indoors" and
" vibration like passing of truck" underlined. These intensity III reports pervade the entire felt area; reports with intensity level I or 11 were very sparse, as previously noted in other intensity surveys. The maximum level observed in only several instances was intensity IV (MM), usually with the expression "like heavy truck striking building" selected. Most of these IV (MM) reports were located within 6 km of the epicenter.
Among the personal comments, the most common type of observations refer to some acoustical wave, of brief duration, and generally impulsive: " loud noise or bang", " sonic boom", " furnace exploding", " heavy thunder", " rumbling noise". Observers noted they
" heard but did not feel". One can infer that some of the high frequency energy of ground waves was conve: -d into a sound wave near the points of observations. There were more instances of " rattling windows" than " rattling dishes", possibly suggesting that the air wave was more effective than the elastic wave in moving structures. Vibratory motions reported were brief, 3-4 sec, and often referred to "a thud", "a slight jolt", " passing of a snowplow" or simple " shaking of the house". Several cases of " alarmed animals" were reported. Nobody was frightened or panicked.
Numerous reports, particularly from CEI retirees, noted that in the same house, "one person felt the event while another did not". This suggests that indeed the earthquake was " marginally felt". This observation is supported by the fact that within the felt area, more than 130 non-felt reports were recorded, almost as many as felt reports. Often, felt and non-felt data were reported within a few hundred feet along the same street.
Figure i shows the contour line separating the felt area from the non-felt area. Contrary to what had been inferred from early publicity reports, the felt area is generally symmetrical around the epicenter, with the exception of a rectangular lobe bounded to the south by the Grand River and extending in a northeastern orientation. It is not clear if this anomaly results from the effect of soil amplification, corresponds to a higher degree of alertness due to the proximity to PNPP, or a combination of both, and finally if it represents a truly preferential azimuth in seismic ground motion propagation. It has
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been noted by geologists that the prevalent orientation of bedrock jointing is indeed north-northeast; this would certainly support the preferential azimuth hypothesis.
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The present anomaly is also consistent with observed variations in calculated magnitude; it was noted for the Kentucky and the Leroy earthquakes that seismographic stations of 1 I
the Eastern Canadian Telemetered network, mostly located in the northeastern azimuthal '
quadrant, recorded larger ground motion amplitudes than along other azimuths. l l
I It should be noted that the fault plane solutions obtained for the December 28, 1988 microcarthquake are fairly similar to the one determined for the main shock of January 31, 1986. Figure B-2 presents the faulting mechanism data for both events. In view of this similarity of faulting, it is expected that the radiation and propagation of released energy would have similar pattern and characteristics.
)
One insight gained from this detailed survey that could be used in the re-evaluation of small historical events regards the accuracy of an epicenter based on felt reports only and l the minimum magnitude of felt microcarthquakes. Granted that the present survey is much more detailed than those of most historical events in the same region, one can nonetheless conclude that the center of the total felt area would be a good approximation of the true instrumental epicenter. Secondly, the calculated M = 2.8 of the December c
28,1988 event, for which the total felt area was near 475 sq. km. seems just above the threshold of felt events, considering that the December 25,1988 event near Madison with hic= 2A was also reported felt with an intensity III and III-IV, but only over an area less than 100 sq. km.
_ CONCLUSIONS i
The small seismic tremor (Mc = 2.8) of December 28, 1988 was located slightly to the southwest of the January 31, 1986 earthquake. An intensity level III - IV (MM) was observed near the epicenter. The total felt area was found symmetrical around the epicenter, except for an anomalous elongation to the northeast, which is possibly related :
to rock anisotropy. The event was just above the threshold of felt events clearly recognized as earthquakes.
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PERRY NUCLEAR POWER PLANT THE CLEVELAND ELECTRIC ILLUMINATING COMPANY TOTAL FELT AREA OF DEC. 28,1988 (23:28 UT)
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O PERRY HUCLEAR POWER PLANT THE CLEVELAND ELECTRIC ILLUMINATING COMPANY FAULT PLANE SOLUTIONS
., 12 28-88 Figure B 2
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