ML20211L626

Seismic Activity Near Virgil C Summer Nuclear Station, Jul-Sept 1986

ML20211L626
Person / Time
Site:	Summer
Issue date:	09/30/1986
From:	Nauman D, Talwani P SOUTH CAROLINA ELECTRIC & GAS CO., SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:	Harold Denton Office of Nuclear Reactor Regulation
References
86-3, NUDOCS 8612160109
Download: ML20211L626 (20)

Text

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TECHNICAL REPORT 86-3 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION i For the Period July - September 1986 i

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by Pradeep Taiwani

Principal Investigator ,

t Geology Department

- University of South Carolina

Columbia, S.C. 29208 Contract No. N418202

TECHNICAL REPORT 86-3 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD JULY - SEPTEMBER, 1986 BY PRADEEP TALNANI PRINCIPAL INVESTIGATOR GEOLOGY DEPARTMENT UNIVERSITY OF SOUTH CAROLINA COLUMBIA, S.C. 29208 s s s CONTRACT NO. N418202 I

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1

. INTRODUCTION Analysis of the seismic activity near the V.C. Summer Nuclear Station in South Carolina between July 1 and September 30, 1986 is presented in this report. During this period a total of 24 events

. were recorded of which 22 were located. The largest shock was of 1 magnitude 1.9 (860901 1402 UTC). Of the remaining earthquakes, eleven were of magnitudes greater than 0.0. All of the B-quality events located at depths not exceeding 2 km.

SEISNIC NETWORK Earthquakes recorded during this period were located using stations of the SCE&G and USGS/USC networks. The configuration of the stations utilized to locate the events in this report is shown in Figure 1 and station coordinates are listed in Appendix I.

DATA ANALYSIS Hypocentral locations of the events were determined using the computer program HYPO 71 (Lee and Lahr, 1972) and the velocity model listed in Appendix II. The event magnitude (M ) was determined from signal duration at station JSC, using the following relation:

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

l l An estimate of daily energy release is determined using a l

, simplified magnitude (M L) energy (E) relation by Gutenberg and Richter (1956).

log 10 E = 11.8 + 1.5 M g.

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. OBSERVED SEISMICITY FOR THE PERIOD JULY-SEPTEMBER, 1986 During this period, twenty-four events were recorded of which 22 (924) were located (see Appendix III). The current level of activity is of the same magnitude as that observed in the previous

. reporting period (Figure 2). Fifty percent of the recorded earthquakes occurred in September, including the largest event of this quarter (M "I*8' Eeptember 1, 1986). This was the only event L

with a magnitude of 1.0 or greater. Twelve shocks (50%) were of magnitudes greater than 0.0.

During this quarter approximately half (11) of the earthquakes located in an east-west trending band beneath the central portion of the reservoir. Four earthquakes were located along the northern perimeter of the lake. The remainder of the events were scattered throughout the reservoir region. A cumulative plot of epicenters of all the events located during this period is shown in Figure 3. Epicentral locations for each month are shown in Figures 4-6.

Thirty-six percent (8) of the located events were of B quality. All of these earthquakes located within 2 km of the

! surface (Figure 7).

CORRELATION OF RESERVOIR NATER LEVEL 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 approximately five feet per day between

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. the maximum and minimum water level. We have been monitoring the water level to see Sf there is any correlation between the daily or seasonal changes in the reservoir level and the local seismicity. Water level was compared to seismicity in Figure 8.

. The top two plots show the average water level and the change in water level per day. The number of events per day and the Icg of the energy released per day are shown in the lower two histograms. These charts include both located and unlocated events around the reservoir. No correlation between seismicity and lake level is readily apparent.

CONCLUSIONS The level of activity observed during the third quarter of ,

1986 was comparable to the level of the previous reporting period.

No earthquake with a magnitude greater than 2.0 was recorded.

i Only one event was of a magnitude greater than 1.0 (M "I*'I*

L Fifty percent of the earthquakes were of magnitudes between 0.0 and 1.0. All of the accurately located shocks were within the upper 2 km of the crust. The majority of the epicenters were clustered in two groups, an east-west trending band beneath the central portion of the reservoir and along the northern perimeter of the lake.

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12 marsasacas l 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.

4

13 l APPENDIX I ,

STATION LOCATIONS NO STN. LAT.*N LONG.*W i

1 001 34* 19.91' 81* 17.74' 2 002 34* 11.58' 81* 13.81' 3 JSC 34* 16.80' 81* 15.60' 4 06A 34* 17.32' 81* 18.15' 5 007 34* 22.23' 81* 19.50' 6 008 34* 24.53' 81* 24.55' 7 09A 34* 17.24' 81* 19.75' 8 010 34* 20.18' 81* 20.25' e

1 I. _ _ _ - _ . - . -

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APPENDIX II h0NTICELLO RESERVOIR VELOCITY MODEL Velocity Depth to top km/sec km 1.00 0.00 5.40 0.03 6.90 0.18 6.10 0.46 6.30 0.82 8.10 30.00 t

15 APPENDIX III MONTICELLO EARTHQUAKES JULY - SEPTEMBER, 1986 HYPO 71 FORMAT Column 1 Date.

Column 2 Origin time (UCT) h.m.sec.

Column 3 Latitude (N) degrees, min.

Column 4 Longitude (W) degrees, min.

Column 5 Depth (km).

Column 6 Local duration magnitude.

Column 7 No. of station readings used to locate event. '

P and S arrivals from same stations are regarded as 2 readings.

Column 8 Largest azimuthal separation in degrees between stations.

Column 9 Epicentral distance in km to nearest station.

Column 10 error of time residuals in l Root sec. mean RMS squarg/NO,

= R where R is the time residual for t e ith station Column 11 Standard error of the epicenter in km*.

Column 12 Standard error of the focal depth in km*.

• Statistical interpretation of standard errors involves assump-tions which may not be met in earthquake locations. Therefore standard errors may not represent actual error limits.

If ERH or ERZ is blank, this means that it cannot be computed, because of insufficient data.

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. l MMITICELLO RARTBQUAKES JULY-SEPTEMBER, 1986 DATE ORIGIN LAT N LONG W DEPTH MAG NO GAP DMIN RMS ERH ERZ QM 860709 20 1 36.15 34-21.82 81-18.33 0.54 0.44 7 223 1.9 0.07 1.2 4.4 C1 860710 2031 32.60 34-17.06 81-20.29 1.76 0.82 9 225 3.3 0.07 0.6 1.9 C1 860718 4 2 41.82 34-19.90 81-18.51 0.55 -0.86 9 108 1.2 0.05 0.2 0.6 B1 860718 4 5 14.23 34-19.76 81-18.47 0.15 -0.60 10 112 1.2 0.05 0.2 0.7 B1 860723 1142 41.31 34-17.61 81-18.77 1.16 -0.86 5 235 1.1 0.05 1.1 0.7 C1 860809 6 3 29.25 34-19.76 81-19.06 0.41 0.78 8 141 2.0 0.06 0.1 0.3 B1 860809 655 27.78 34-19.37 81-19.75 0.87 0.82 10 185 1.7 0.07 0.4 1.2 C1 860810 1316 13.65 34-20.56 81-21.12 1.36 -0.86 8 269 1.5 0.04 0.4 0.3 C1 860814 836 3.90 34-19.61 81-19.11 1.72 -0.11 6 167 2.0 0.02 0.2 0.3 B1 860815 832 32.31 34-19.75 81-19.21 1.77 -0.60 8 106 1.8 0.06 0.3 0.6 B1 860818 1824 19.82 34-23.19 81-21.75 2.45 0.51 5 320 3.9 0.05 6.9 3.3 D1 860901 544 21.02 34-22.57 81-19.05 1.96 -1.22 5 286 0.9 0.01 0.2 0.2 C1 860901 14 2 36.62 34-23.00 81-18.98 1.52 1.87 9 306 1.6 0.08 1.0 0.9 C1 860912 528 54.90 34-19.70 81-18.95 1.61 0.44 8 99 1.9 0.06 0.3 0.6 B1 960913 18 0 7.95 34-22.66 81-18.43 1.14 -0.24 9 274 1.8 0.08 0.7 1.3 C1 860915 941 8.52 34-19.76 81-19.46 1.83 -0.24 10 117 1.4 0.06 0.2 0.5 B1 860922 931 31.93 34-17.62 81-21.42 0.36 0.82 9 245 2.7 0.08 0.7 0.8 C1 860922 933 9.73 34-17.34 81-20.87 1.59 0.68 9 336 1.7 0.0'3 0.6 0.7 C1 860922 1322 12.05 34-18.60 81-21.93 0.38 -0.40 5 274 3.9 0.04 1.6 4.0 C1 860923 1217 51.33 34-19.88 81-18.06 0.86 0.01 6 110 0.5 0.04 0.3 0.4 B1 860923 1548 44.00 34-19.81 81-18.53 0.85 0.37 5 216 2.7 0.04 0.0 0.2 C1 860923 2248 59.55 34-20.01 81-18.54 1.95 0.01 6 259 1.2 0.04 0.5 0.5 C1 e

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/ gm na Electric & Gas Company Dan A. n lumbia 29218 Nuclear Operations

~ * "

December 9, 1986 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Virgil C. Summer Nuclear Station Docket No. 50/395 Operating License No. NPF-12 Quarterly Seismic Report

Dear Mr. Denton:

South Carolina Electric & Gas Company, acting for itself and as agent for South Carolina Public Service Authority, herewith forwards five (5) copies of Technical Report 86-3 " Seismic Activity Hear the Virgil C. Summer Nuclear Station" for the Period July - September, 1986.

If you should have any questions, please contact this office.

Yr truly yours, l

.- . N Ni an h RBW/ DAN:jez Attachment l

l c: 0. W. Dixon, Jr./T. C. Nichols, Jr.

E. H. Crews, Jr.

W. A. Williams, Jr.

J. N. Grace (w/ attach.)

l Group Managers l 0. S. Bradham (w/ attach.)

C. A. Price C. L. Ligon (NSRC)

R. A. Stough G. Percival R. L. Prevatte J. B. Knotts, Jr. (w/ attach.)

H. G. Shealy NPCF

! File 1

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