ML20210L307

Seismic Activity Near VC Summer Nuclear Station, for Apr-June 1986

ML20210L307
Person / Time
Site:	Summer
Issue date:	06/30/1986
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
Shared Package
ML20210L212	List: ML20210L206 ML20210L307
References
86-2, NUDOCS 8610010595
Download: ML20210L307 (18)

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l TECHNICAL REPORT 86-2 l

SEISMIC ACTIVITY NEAR i

. THE V.C. SUMMER NUCLEAR STATION For the Period ,

April - June 1986 j i

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l TECHNICAL REPORT 86-2 '

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SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD APRIL - JUNE, 1986 DY PRADEEP TALWANI PRINCIPAL INVESTIGATOR GEOLOGY DEPARTMENT UNIVERSITY OF SOUTH CAROLINA Y COLUMBIA, S.C. 29208 l

l CONTRACT NO. N418202 l

1

. INTRODUCTION Analysis of the seismic activity'near the V.C. Summer Nuclear Station in South Carolina between April 1 and June 30, 1986 is presented in this report. During this period a total of 39 events were recorded of which 30 were located. The largest shock was of magnitude 2.2 (860509 2026 UTC). The remaining earthquakes were of magnitudes less than 1.0. Seventy-five percent of'the B-quality events located at depths not exceeding 2 <m below the surface.

SEISMIC NETWORK The station configuration changed during this period. Two stations of the SCE&G network were abandoned and the instruments moved to sites previously occupied as USGS/USC stations. The instrument at statien 003 was moved to USGS site 007 and station 004 was relocated to station 010. The configuration of the stations utilized to locate the events in this report are shown in Figure 1 and their coordinates are listed in Appendix I.

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DATA ANALYSIS l

!. Hypocentral locations of the events are determined by using the HYP071 program (Lee and Lahr, 1972) and the velocity model listed in Appendix II. The event magnitude (Mg) 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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OBSERVED SEISMICITY FOR THE PERIOD APRIL-JUNE, 1986 During this period. 39 events were recorded of which 30 were located (see Appendix III). The current level of activity is concordant with that observed in the previous reporting period (Figure 2). Forty-six percent of the recorded activity occurred in May, including the largest event of this quarter (Mg =2.2, May 9, 1986). This was the only event with a magnitude of 1.0 or greater. It is interesting to note that this event was apparently not followed by a swarm of aftershocks as often observed in past sequences.

During this quarter the majority of the earthquakes located in a broad east-west trending band beneath the central portion of the reservoir and the western shore. A cumulative plot of epi-centers of all the events located during this period is shown in Figure 3. Separation of all epicentral locations by month are i

. shown in Figures 4-6.

Twenty-four percent (8) of the located events were.of B quality. Of these, six (~ 75%) located within 2 km of the surface. The remaining events (~ 25%) located within the upper 3.4 km (Figure 7).

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. RESERVOIR WATER 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 approximately five feet per day between the maximum and minimum water level. We have been monitoring the water level to see if 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 log 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 second quarter of 1986 was substantially less than that experienced during the same period in 1985 but is comparable to the level of the previous

,, reporting period. One earthquake with a magnitude greater than 2.0 was recorded. The majority of the earthquakes (97%) were of magnitudes less than 1.0 and 75% of the accurately located shocks were within the upper 2 km of the crust. The epicenters were diffused in a broad east-west trending band beneath the central portion of the reservoir and the western shore.

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l 12 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 HYP071, U.S.G.S. Open-File Report, 100 pp.

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13 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* 15.60' 6 005 34* 16.05' 81* 20.05' 7 06A 34* 17.32' 81* 18.15'-

8 007 34* 22.23' 81* 19.50' 9 008 34* 24.53' 81* 24.55' ,

10 09A 34* 17.24' 81* 19.75'

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14 APPENDIX II MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth to top km/sec km 1.00 0.00 5.40 0.03 5.90 0.18 6.10 0.46 6.30 0.62 8.10 30.00

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- APPENDIX III MONTICELLO EARTHQUAKES APRIL - JUNE 1986 HYP071 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 Root-mean sec. 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.

i If ERH or ERZ is blank, this means that it cannot be computed,

! because of insufficient data, i

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16 MONTICELLO EARTHQUAKES APRIL - JUNE, 1986 DATE ORIGIN LAT N LONG W DEPTH MAG NO GAP DMIN RMS ERH ERZ QM 860401 21 2 26.95 34-20.24 81-19.83 1.91 -0.24 5 256 3.3 0.06 2.1 2.1 C1 860408 8 3 11.04 34-20.17 81-20.29 1.88 -0.24 7 131 3.9 0.07 0.3 1.3 B1 860408 932 31.51 34-20.43 81-21.35 0.27 -0.40 5 150 5.6 0.00 0.0 0.1 C1 860411 2119 11.38 34-19.32 81-20.35 3.42 0.57 6 259 5.0 0.07 1.3 1.3 C1 860427 146 20.50 34-19.72 81-18.44 0.97 0.01 7 223 1.1 0.08 0.9 0.9 C1 860427 146 49.26 34-19.56 81-18.99 0.62 -0.86 5 247 2.0 0.04 0.8 0.7 C1 860427 226 40.43 34-19.63 81-17.84 1.01 -0.24 8 190 0.5 0.05 0.5 0.4 C1 860429 2312 45.47 34-20.01 81-17.84 1.00 0.21 8 210 0.2 0.07 0.8 0.4 C1

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860504 836 41.25 34-20.18 81-17.48 0.86 -1.22 4 175 0.6 0.03 C1 860505 736 58.58 34-20.46 81-18.45 0.17 -1.22 7 225 1.5 0.02 0.3 0.4 C1 860509 2026 53.49 34-19.90 81-20.99 2.08 2.20 11 159 1.2 0.05 0.3 0.3 B1

-860515 1741 26.90 34-19.01 81-19.01 0.26 0.01 9 240 2.6 0.04 0.4 0.4 C1 860518 1053 38.18 34-20.58 81-20.49 1.99 -0.40 5 262 4.4 0.07 3.0 3.2 D1 860525 552 30.63 34-19.61 81-20.99 1.83 0.01 11 142 5.0 0.09 0.3 1.5 B1 860527 844 40.98 34-19.70 81-20.85 3.27 -0.40 10 140 4.8 0.08 0.3 0.8 B1 860527 20 6 45.65 34-20.01 81-21.13 1.86 -0.40 8 137 5.2 0.07 0.4 1.7 B1 860528 1037 36.81 34-20.96 81-19.04 0.28 -0.60 6 251 2.8 0.03 0.5 0.5 C1 860528 1056 43.72 34-20.73 81-17.84 0.63 -0.60 5 224 1.5 0.02 0.7 0.5 C1 860528 12 4 36.33 34-21.10 81-18.91 0.48 -0.40 6 251 2.8 0.03 0.5 0.6 C1 860529 1250 7.35 34-19.80 81-19.46 1.96 0.12 10 125 2.7 0.07 0.3 0.7 B1 860529 1526 18.90 34-19.88 81-19.55 0.79 -0.40 10 125 2.8 0.06 0.2 0.6 B1 860529 1528 33.49 34-19.99 81-19.20 1.74 -0.11 12 123 2.3 0.07 0.2 0.6 B1 860530 132 9.52 34-20.26 81-19.86 1.69 -0.86 5 272 3.3 0.03 0.8 1.1 C1 860602 553 20.63 34-20.09 81-19.60 2.43 -0.40 9 212 2.9 0.07 0.5 0.6 C1 860603 440 34.07 34-20.17 81-19.13 0.51 0.21 12 187 2.2 0.07 0.3 0.8 C1 860611 553 49.55 34-17.45 81-15.70 6.94 -0.11 4 200 1.2 0.07 C1 860618 2146 25.62 34-18.65 81-20.93 5.47 -0.11 8 238 4.9 0.07 1.0 0.9 C1

. 860623 436 17.71 34-17.50 81-20.44 3.33 0.73 12 226 3.5 0.05 0.4 0.5 C1 860627 531 29.41 34-19.83 81-20.14 0.09 -0.86 8 216 0.7 0.05 0.5 0.6 C1 860627 2250 14.41 34-20.98 81-17.84 2.52 -0.60 8 204 2.0 0.05 0.6 0.5 C1 i

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