ML20137N051

Seismic Activity Near Virgil C Summer Nuclear Station, for Period Jul-Sept 1985

ML20137N051
Person / Time
Site:	Summer
Issue date:	09/30/1985
From:	Evans C, Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
Shared Package
ML20137N046	List: ML20137N041 ML20137N051
References
85-3, NUDOCS 8601290141
Download: ML20137N051 (18)

Text

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TECHNICAL REPORT 85-3 4

SEISMIC ACTIVITY NEAR l

THE V.C. SUMMER NUCLEAR STATION For the Period

July - September 1985 i

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! Pradeep Taiwani j Principal Investigator l Geology Department University of South Carolina l Columbia, S.C. 29208 Contract No. N385310 1

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TECHNICAL REPORT 85-3 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION

. FOR THE PERIOD JULY - SEPTEMBER, 1985 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR AND CYNTHIA S. EVANS RESEARCH ASSISTANT GE.0 LOGY DEPARTMENT UNIVERSITY OF SOUTH CAROLINA COLUMBIA, S.C. 29208 CONTRACT No. N230519

1 1

INTRODUCTION An analysis of the seismic activity near the V.C.

Summer Nuclear Station in South Carolina during July-September, 1985 is presented in this report. A total of 32 events were located. Two events occurring in July had magni-tudes between 1.0 and 2.0, with the majority having magni-tudes less than 1.0. Forty percent of the B quality events located at depths within 2 km from the surface.

SEISMIC NETWORE The report is based primarily on data recorded by the four station network operated by S.C.E.&G. and the USGS/USC stations JSC, 6A, 7 and 9A. The locations of the stations are shown in Figure 1 and their coordinates are listed in Appendix I.

DATA ANALYSIS Hypocentral locations of the events are determined by using the HYPO 71 program (Lee and Lahr, 1972) and the velo-city model listed in Appendix II. The event magnitude (M g) is determined from signal duration at station JSC, using the following relation:

Mg = -1.83 + 2.04 Log D where D is the signal duration (seconds).

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log 10 E = 11.8 + 1.5 M g .

OBSERVED SEISMICITY FOR THE PERIOD JULY-SEPTEMBER, 1985 During this three month period 92, events wers recorded with 32 being locatable (see Figure 2 and Appendix III). Two swarms of events occurred, August 22-23 with 7 earthquakes, and September 8 with 14 earthquakes, for which only 3 were locatable due to poor or not enough records. In the report-ing period, no records were obtained for stations 1-4 for 12, 9, 9 and 13 days, respectively. Additionally, stations 1 and 4 were down for 3 and 28 days, respectively. If more data had been available, approximately half of the events would have been locatable.

The level of activity decreased from the early part of the year but was higher than that observed in recent years.

There were two events with magnitudes greater than 1.0 with the remaining events being less. Six events of B quality located at depths greater than or equal to 2.0 km. Although the seismic activity was scattered throughout the Monticello Reservoir area, the majority of the earthquakes located in the central western side of the reservoir. A cumulative plot i

of epicenters of all the events located during this period in shown in Figure 2 and a cross section of events located

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EARTHQUAKE BLOOPER-In Technical Report 85-1, the earthquake on January 19, 1985 (1409 UTC or 1009 EST) with a magnitude of 0.95 was computed from paper records to have a depth of 7.23 km with a B quality using 14 phases. A relocation of this event using tape data was conducted by Steve Acree and Jill Rawlins, Research Assistants. A new depth of 0.63 km using 11 phases was found while still keeping its B quality.

RESERVOIR NATER LEVEL AND ITS COMPARISON WITH SEISMICITY Monticello Reservoir is a pumped storage facility. Any decrease in reservoir level associated with power generation is recovered when water is pumped back into the reservoir.

There can be variations up to about five feet per day between the maximum and minimum water level. We have been monitoring this water level to see if there is any correlation between the daily or seasonal changes in the reservoir level and the local seismicity. Figure 7 shows the comparison of water level to seismicity. The top two graphs show the water level and the change of water level per day. The log of energy released per day and the number of events per day are shown on the lower two graphs. These histograms include the unlo-cated events around the reservoir.

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8 MONTICELLO EARTHOUAKES AUGUST 1985 22.0 21.0 20.0 89.0 15.0 37.0 35.0 81 "

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1 CONCLUSIONS i

Compared to the first half of 1985, the level of seis-micity decreased discernably. However, it remained higher than in the preceding two years (Figure 8). The third quar-ter of 1985 was characterized by a moderate level of activity of low magnitude earthquakes (Mg < 2), mostly within the upper 2 km. As seen in Figure 7, discrete swarms were dispersed throughout the three month reporting period.

REFERENCES Gutenberg, B. and Richter, C.F. (1956). Magnitude and energy of earthquakes, Ann. Geof. 9,

p. 1-15.

Lee, W.H.K. and Lahr, J.C. (1972). A computer program for determining hypocenter, magnitude and first motion pattern of local earthquakes, Revisions of HYPO 71, U.S.G.S. Open-File Report, 100 pp.

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. APPENDICES 4

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14 APPENDIX I

. STATION LOCATIONS NO STN. LAT.*N LONG.*W 1 001 34* 19.91' 81* 17.74' 2 002 34* 11.58' 81* 13.81' 3 003 34* 21.09' 81* 27.41' 4 004 34* 25.72' 81* 12.99' 5 JSC 34* 16.80' 81* 12.99' 6 06A 34* 17.32' 81* 18.15' 7 007 348 22.23' 81* 19.50' 8 09A 34' 17.24' 81* 18.15' 6

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15 APPENDIX II MONTICELLO RESERVOIR

, VELOCITY MODEL

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Velocity Depth to top km/sec km 1.00 0.00 5.40 0.03 i

5.90 0.18 6.10 0.46 6.30 0.82 8.10 30.00 4

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APPENDIX III If0NTICELLO 1ARTHQUAKES JULY - SEPTDiBER 1985 850701 1555 6.13 34-19.71 81-20.30 1.47 1.09 9 137 3.9 0.03 0.2 0.7 61 850703 1575 52.54 34-19.46 81-19.45 1.98 -0.11 8 134 2.7 0.04 0.5 1.0 61 850706 345 12.39 34-20.59 81-19.11 1.90 1.15 6 183 3.1 0.03 0.6 0.9 C1 850706 533 13.15 34-20.16 81-15.51 4.51 -0.60 6 243 6.2 0.01 0.2 0.2 C1 850708 555 0.64 34-18.41 81-20.25 0.84 -1.22 4 257 4.8 0.07 C1 850710 126 31.81 34-19.62 81-18.45 2.29 0 7 127 1.2 0.06 0.8 81 4 04 0.93 -0 51 5 262 7.4 0.04 0.2 90 1

D1 850719 2016 39.83 850719 2048 58.36 34-23 34-18 3)4 81-20 98 2.04 -0 8640 7 158 5.7 0.04 0.4 149 B1 850720 2344 33.37 34-20.94 61-20 36 81-17 3.26 -0.60 4 324 2.0 0.02 C1 E

850801 744 54.22 34-24.5d 81-16.47 1.00 -0.60 4 338 C1 850801 830 2.01 34-20.49 09 0.15 -0.24 4 239 81.2 0.068 0.06 C1 850801 2016 38.33 34-19.74 81-18 84 H1-17 2.74 -0.24 4 228 0.3 0.01 C1 850817 12 4 13.16 34-19 81-18.64 2.24 -0.60 7 126 1 0.05 0.3 0.4 B1 850818 418 38.98 34-18,85 86 81-18.06 1.66 -0.40 5 151 240 0.04 0.3 0.6 C1 850818 22 3 4.49 34-18.85 61-18.20 3.11 -0.40 4 153 1 0.09 C1 850819 043 34.07 Ul-2 0. 66 61-17.93 2.75 40 6 161 23. 8 0.07 0.o 1 3 81 850907 3 8 34.29 3.4-19.44 81-20.70 0.44 -00 57 8 258 4.6 0.09 0.9 22C1 8 0907 354 6.50 34-19.98 81-19.65 0.10 -0 40 5 230 2.9 0.08 1.1 2.9 C1 8 0907 455 22.25 34-20.01 M1-20.34 0.48 -0 7 248 4.0 0.04 0.3 0.6 C1 8 0908 14?! 3'.16 34-21.07 81-19.60 3.37 0 60 44 4 222 1 0.02 C1 850908 1430 $.07 34-21.06 61-19.41 3.81 -0.11 4 213 2*2

2. 0.00 C1 650908 1430 36.52 34-20.17 81-2 .66 1.00 0 37 3 277 0 0.01 C1 8 0913 23T7 40.14 34- 15 61-1 85 0. 5 -0 24 8 234 53. 3 0.05 052 0.4 C1 8 0914 641 41.41 34- 93 61-1 44 0. 0 -0 6 224 2 0.05 0. 1.1 C1 8 0914 1018 40.82 34- 01 81-1 1. 3 -0*Bo 7 142 2*63 0.06 0.3 0.8 B1 850917 14 8 34.01 34- 79 81-19 23 68 1.78 -0 60 4 232 3.0 0.01 C1 850919 9T7 56.6% T4-

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,* 8 6 0.80 -0 *60 86 8 147 2.6 0.09 0.4 1.0 B1 850920 1271 39*21 34- 81 81-1 1.54 0.21 7 145 1*7 0.08 0.8 1.6 C1 850925 858 49 52 34- 83 81-1 . 77 2.85 0.57 108 132 31 0.07 0.3 0.6 81 850927 1114 5.58 34-21.24 81-2 .76 1.76 -0.24 270 2.7 0.03 0.3 0.3 C1 850928 18 5 24.84 54-20.01 81-19,46 0.18 -0 7 224 7 0.07 0.6 0.9 C1 850929 to 6 32.u1 34-20.01 81-19.39 2.57 -0 8640 9 144 2

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