ML20209G582
| ML20209G582 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 01/15/1987 |
| From: | WESTON GEOPHYSICAL CORP. |
| To: | |
| Shared Package | |
| ML20209G580 | List: |
| References | |
| NUDOCS 8702050397 | |
| Download: ML20209G582 (14) | |
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QUARTERLY PROGRESS REPORT CEI SEISMIC MONITORING PROGRAM FOR NORTHEASTERN OHIO OCTOBER 15.1986 - JANUARY 15,1987 -
Prepared for CLEVELAND ELECTRIC ILLUMINATING COMPANY l'
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QUARTERLY PROGRESS REPORT
- k. SEISMIC MONITORING PROGRAM l POR NORTHEAST OHIO Submitted by CEI Frepared by Weston Geophysical Inc.
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1.0 INTRODUCTION
After the January 31, 1986 earthquake, Cleveland Electric Illuminating (CEI) has pursued nquerous studies to confirm the seismic design of the Perry Nuclear Power Plant. In an immediate response to the earthquake, which occurred 17 km from the plant, CEI embarked on an intensive seismic monitoring program, which began the very same night as the event.
Although several academic institutions and government agencies deployed a large number of portable seismographs, CEI (through its consultant, Weston j Geophysical) established and maintained its own 13-station portable array around the epicenter. The purpose of this monitoring was to obtain an accurate location of the January 1986 earthquake main shock by recording the aftershock sequence and tracking any potential migration of the j seismic activity.
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In addition, CEI has provided a separate permanent regional net for John Carroll University, to provide an independent monitor of future seismic
, activity in the region surrounding the PNPP and the January 31, 1986 epicenter. In response to the theory that two deep injection wells located 7 miles (11 km) north of the epicenter could have triggered the main shock, CEI also agreed to install a separate network in the vicinity of the injection wells. This net has a small aperture but a very low magnitude threshold, and covers the corridor extending from the injection wells down to the main shock epicenter.
This report represents the first quarterly report requested by the NRC staff in October 1986. Because this is the first report submitted on the ongoing seismic monitoring program, it covers several subjects. It includes an update of the seismic data previously reported by CEI in its June 16, 1986 submittal to the NRC. It also reviews the progress made with the seismic monitoring program undertaken by CEI, including both the microseismic and regional networks. Future reports will focus on the micronet operating data, which the staff has indicated to be ita primary area of interest in following with these quarterly reports.
Weston Geophysical
2.0 NETWORK DESCRIPTION l l
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- 1. The CEI Temporary Monitoring of the Regional Activity ;
During February, March and early April of 1986, a total of 13 portable MEQs were operated by Weston Geophysical for CEI. The configuration 7 changed very little during this period, as shown on Figures 3-6 and 3-7 of the June report. By the middle of April, as the aftershock sequence had almost died out, the number of stations was reduced to nine, as shown on r
Figure 1. This nine-station configuration was maintained until the John y Carroll University system commenced operation in late September.
) 2. The CEI Micronet The principal objective of the CEI micronet is to monitor the corridor between the injection wells and the main shock epicenter, at a very low threshold (Mc=0.0 or lower). The configuration was expanded to include a
' the area north of the wells extending to the PNPP site. The data will be used to evaluate the validity of a theory originally proposed by the USGS that the wells could have triggered the January 31, 1986 earthquake. This position was later considered by the USGS, the NRC and CEI to have only a low probability (SSER No. 10). SSER No 10 also states that a microearthquake that occurred on March 12, 1986 (Mc=-0.3) and two small earthquakes (Mc=2.3 and 2.7) that occurred in 1983, all within two or three kilometers from the wells, could have been either induced by the injection wells or simply unrelated and tectonic. It is hoped that with time, both the CEI micronet and the John Carroll regional net will produce data that will help resolve this question.
Once the John Carroll regional network came in operation, Weston used the portable equipment from these stations to search for micronet site locations, while maintaining adequate coverage of the wells-main epicenter corridor. Figure 2 shows the selected sites for the five network stations for the CEI micronet, which are presently occupied by portable equipment.
One additional station at YMC is operated to strengthen the portable array of vertical instruments.
Weston Geophysical
To achieve a reliable level of detection and location, the micronet will have five 3-component stations. All instruments will be placed in boreholes. This required the selection of 4-hz geophones. All stations transmit by phone lines digitized signals to the recording center located at PNPP. Disk and tape will store seismic signals arriving simultaneously; visual recorders will continuously preserve one channel from each station. At present, boreholes have been drilled and telephone / power lines are installed.
Hardware and software are under preparation, anl testing is expected to start soon.
3.0 MONITORING RESULTS
- 1. The January 31, 1986 Aftershocks t 5 Since the June 1986 report, only two more aftershocks have occurred in the epicentral area. One occurred on June 17, (Mc=0.8) and the last one on July 17, (Mc=0.3). Both of them are contained within the boundaries of the original cluster defined by the first 13 aftershocks. Table 1 gives an update of all aftershock parameters and Figure 3 shows their locations, including the two additional events.
- 2. Other Microearthquake Activity The CEI micronet covers an aperture of approximately 50 sq. km., about ten times smaller than the John Carroll net. The location threshold is neer Mc=-0.5. At this low magnitude level, not all events are detected at all stations; consequently the epicentral accuracy of located events varies in quality. 1 i
On October 2, 1986 CEI notified the NRC staff of a small microearthquake recorded by the portable array on September 28, 1986. Since that time, other small events have occurred in the same area, at the rate of one event per month. Table 2 presents the typical location parameters of these events. Figure 4 shows the microearthquake epicentral locations as Weston Geophysico!
well as the locations of the two injection wells and the main epicenter of January 31, 1986. It also shows the local distribution of oil and gas wells. At this time, it is premature to attempt any conclusive spatial correlation between Ehe microearthquakes and either the injection wells or the oil / gas wells. Detailed developmental information and operating data on these oil / gas wells is presently being obtained to evaluate their ,
potential role.
Because the focal depth estimates are influenced by the distance to the nearest station as well as the chosen geological model, it is not possible to use them to determine with absolute confidence the cause of these events. It should be noted on Table 2 that large azimuthal gaps exist for several events reducing confidence in the epicentral location estimates.
Two other microevents were detected on November 3, 1986 (Mc=0.0) and on j December 24, 1986 (Mc=0.1). They have not been accurately located at this time, being too small and completely outside the micronet and are, therefore, not included on Table 2. The first one seems to be about 15 kilometers to the southwest, while the second is about 10 kilometers to the west.
4.0 CONCLUSION
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One conclusion can be drawn at this time: there is no association between the small events in the vicinity of the wells and the January 31, 1986 epicenter, as evidenced by the lack of activity in the corridor leading to the main epicenter as shown on Figure 4. At present it is felt that, because of their infrequent occurrences, their small magnitudes and the
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location uncertainty, that these events have little significance for Perry. As discussed in SSER No. 10, events of this nature could be either induced or tectonic. When the CEI micronet is operational and additional operating information is available, more definitive conclusions can be l made.
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Table 1 '
AFTERSHOCK PARAMETERS Vp/Vs = 1.78 YE ARMC0Y HRMISEC LATITUL E LONGITUDE CEPTH NP GAP RMS ERH ERZ MAG 15860201 185449.35 41 38.67 81 9.17 4.35 20 94 .09 .3 .5 1.5 15860202 32248.67 41 38.72 81 9.55 4.86 37 72 .07 .1 .2 .9 19860203 194719.77 41 38.52 81 9.48 5.83 52 75 .08 .2 .2 2.0 15860205 634 2.47 41 38.50 81 9.27 3.73 31 52 .08 .2 .3 .1 15860206 183622.44 41 38.72 81 9.61 5.50 50 47 .07 .1 .2 2. 5 I 19860207 152020.38 41 39.C3 81 9.22 3.76 44 42 .07 .1 .3 1.1 i 15860210 200613.61 41 39.10 81 9.39 4.73 29 70 .05 .1 .4 .9 15360223 32948.50 41 39,.18 81 9.09 5.48 22 76 .05 .2 .4 .1 15860224 1655 6.48 41 38.15 81 S.63 3.26 10 91 .09 .5 2.7 .1
, 15860228 13934.21 41 39.23 81 9.61 3.91 12 91 .06 .3 .5 .1 1 15860308 204249.68 41 38.(7 81 9.23 3.12 20 65 .13 .3 .7 .1
' 15863324 134241.31 41 38.21 81 9.31 3.84 12 79 .12 .5 1.8 1.4 15860410 65805.71 41 38.91 81 9.55 5.11 22 63 .08 .2 .3 .1 15860617 221633.20 41 38.51 81 9.55 3.40 16 93 .09 .3 .8 .8 15860714 075423.12 41 38.(8 81 9.13 4.93 12 99 .08 .3 .8 .3 Vr1=4.25 k m/s Thicknes s = 2 km Vg2=6.5 km/s Thickness = 33 km e
l Table 2
,MICR0 EARTHQUAKES YE AR P0 DY HAMISEC , LAT.N LONG.W D RNS EH EZ NP NS GAP MC $0 1986 03 12 085526.6 41.l72 72 81.1707 2.0 0.06 0.7 0.4 10 6 216 .3 G5 1586 09 28 103604.2 41.7140 81.1090 1.9 0.02 0.3 0.1 7 7 173 .3 hG 1586 10 20 105944.6 41.,7594 81 1536 2.2 0.09 8.6 5.0 5 3 354 .6 WG 1586 10 27 122555.8 41.7437 81.1040 0.5 0.08 2.4 10.1 6 3 231 .2 WG 1586 11 03 085449.6 41.,7092 81.1292 18 0.06 0.5 0.5 7 5 145 .3 WG i 1186 12 01 050317.5 41 7120 81.1195 2.1 0.07 0.6 5.8 7 5 138 .3 WG 1987 01 02 024114.5 41.,7472 31.1027 2.0 0.06 0.3 0.5 10 6 174 .5 WG 1
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APPENDIX A
- 1. The John Carroll University Regional Network Weston Geophysical supplied consulting services in the design of the John Carroll network, particularly with respect to the selection of the sites.
It was agreed that some of the stations occupied by Weston could become part of the regional telemetered net. Stations KEL, TOM, and PAT, were i selected because of their corner locations. Station WC2, at Leroy, in the immediate vicinity of the January 31 epicenter was also included in the array. To achieve some symmetry in the aperture of the net, a station located to the northwest had to be found. The location of the existing station at the University had also to be considered. Mentor-on-the Lake seemed to be the correct area; unfortunately it is densely populated and characterized be deep alluvium. Several candidate locations were tested and had to be rejected; negotiations for one selected site failed. A site
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at the Waterplant (Figure 1 - Mentor-on-the Lake) was finally accepted and to reduce the effects of traffic noise, CEI agreed to assume the ,
additional cost of a borehole for the fifth station. Figure 1 shows the final configuration of the John Carroll University net.
4 Signals from four stations are transmitted by telephone lines to the fifth .
1 site at Chesterland, where they are multiplexed, and then proceed by phone to the University. The system commenced operation in September 1986. All stations are single component. Leroy, Thompson, and Mentor are equipped with 2-hz vertical seismometers, while E. Claridon and Chesterland have horizontal seismometers. All signals are reccrded on visual drums and on magnetic tape at John Carroll University.
- 2. Monitoring Results On Wednesday January 21, 1987 at 6:15 a.m. (E.S.T), John Carroll University recorded a small event (estimated Mc=1.5), probably tectonic, near Cleveland in Willoughby Hills approximately 15 miles west of the January 31, 1986 epicenter. This event was outside the existing Weston Geophysical temporary monitoring net but was still detected by the portable instruments. A final solution has not been developed yet.
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