ML20214U416

Seismic Activity Near VC Summer Nuclear Station, for Period Jan-Mar 1986

ML20214U416
Person / Time
Site:	Summer
Issue date:	03/31/1986
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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ML20214T184	List: ML20214T183 ML20214U416
References
86-1, NUDOCS 8609300606
Download: ML20214U416 (18)

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. . ___ . . _ _ _ . .

l TECHNICAL REPORT 86-1 1 ,

l SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION l For the Period January - March 1986 l

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by Pradeep Taiwani Principal Investigator ,

i Geology Department .

University of South Carolina ii Columbia, S.C. 29208  !

l Contract No. N418202 B

!DR ADO 5 00 95 R PDR

1 TECHNICAL REPORT 86-1 4

SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD JANUARY - MARCH, 1986 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR GEOLOGY DEPARTMENT UNIVERSITY OF SOUTH CAROLINA COLUMBIA, S.C. 29208 CONTRACT NO. N418202

t INTRODUCTION Analysis of the seismic activity near the V.C. Summer Nuclear Station in South Carolina between January 1 and March 31, 1986 is presented in this report. During this period a total of 48 events were recorded of which 32 were located. The largest snock was of magnitude 1.3 (860207 2304 UTC). The remaining earthquakes were of magnitudes less than 1.0. Seventy eight percent of the B-quality events located at depths not-exceeding 2 km below the surface. This level of activity represents a decline from that observed during January-March 1985.

SEISMIC NETWORK This 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 and 7. 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 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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An' estimate of daily energy release is determined using a simplified magnitude (M{} energy (E) relation by Gutenberg and Richter (1956).

log E = 11.8.+ 1.5 M g 10 .

OBSERVED SEISMICITY FOR THE PERIOD JANUARY-MARCH, 1986 During this period, 48 events were recorded of which 32 were located (see Appendix III). Instrument down time was a major factor in the relatively poor ratio of located to recorded events.

Sixty-five percent of the recorded activity occurred in February.

Fifteen of these events were recorded in a single swarm (February 7-9). The largest event of this quarter (M g=1.3) occurred on February 7, 1986 and was the only event with a magnitude of 1.0 or greater. The seismic activity decreased substantially from the level observed during the same period in 1985 in which 216 events were recorded. The current level of activity is concor-dant with the decline observed between 1978 and 1984. The in-creased seismicity recorded in 1985 was anomalous (Figure 2).

During this quarter the majority of the earthquakes located in an east-west trending band beneath the' west-central portion of the reservoir and the western shoie. 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 shown in Figures 4-6.

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9 Nine events were located with a quality of B. Of these, seven (~ 78%) located within 2 km of the surface. The remaining events (~ 22%) located within the top 3.5 km (Figure 7).  ;

l 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 bp 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 Activity during the first quarter of 1986 was low in comparison to that experienced during the same period in 1985 but is comparable to the levels of 1983-1984. The majority of the

. earthquakes (984) were of magnitudes less than 1.0 and 78% of the accurately located shocks located within the upper 2 km of the i

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, crust. The epicenters clustered mainly in a broad east-west trending band beneath the west-central portion of the reservoir and the western shore. ,

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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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 06A 34* 17.32' 81* 18.15' 7 007 34* 22.23' 81* 19.50'

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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 0.82 8.10 30.00

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E 15 APPENDIX III MONTICELLO EARTHQUAKES JANUARY - MARCH 1986 860105 312 35.67 34-23.37 81-18.45 2.75 -0.86 5 170 6.5 0.01 0.1 0.3 C1 860118 1558 5.12 34-20.36 81-17.84 1.00 -0.60 6 227 0.8 0.06 1.3 0.7 c1 8S0126 2359 51.43 34-20.53 81-19.72 2.97 -0.60 4 132 11.8 0.09 C1 860201 9 4 56.71 34-20.03 81-19.72 1.44 -0.24 10 125 3.1 0.06 0.2 0.9 B1 860204 19 8 47.39 34-20.02 81-20.96- 1.97 0.01 6 155 10.1 0.09 0.7 7.3 C1 860204 2324 53.78 34-19.91 81-21.04 6.97 0.12 5 158 10.0 0.01 0.2 0.4 C1 860207 936 55.05 34-20.44 81-18.73 0.87 -0.11 6 131 8.3 0.09 0.6160.8 C1 860207 1543 11.22 34-20.58 81-22.61 0.99 -0.40 5 154 7.4 0.09 2.1 98.2 D1 860207 1543 34.58 34-20.36 81-20.77 0.89 -0.60 4 148 10.3 0.05 C1 860207 1547 44.91 34-208.01 81-21.38 0.87 0.51 6 158 9.5 0.04 0.3 73.2 C1 860207 16 6 48.51 34-20.61 81-21.64 0.82 0.78 5 148 8.9 0.05 0.5108.9 D1 860207 17 7 34.08 34-20.44 81-20.93 3.51 0.21 6 147 10.0 0.01 0.1 0.5 B1 860707 1948 0.20 34-20.01 81-21.42 0.89 0.87 6 159 9.4 0.05 0.4 65.5 C1 l 8G0207 23 4 6.81 34-20.57 81-21.12 1.93- 1.29 5 146 9.7 0.02 0.3 2.9 C1 860209 1325 37.13 34-19.80 81-19.26 4.22 0.01 5 146 7.9 0.01 0.1 0.4 C1 860211 742 29.08 34-20.52 81-19.62- 1.95 0.12 10 132 3.1 0.08 0.3 0.8 B1 860212 019 25.63 34-20.30 81-20.82 0.90 -0.40 9 132 4.8 0.08 0.4 11.0 C1 860215 027 5.05 34-20.33 81-19.17 1.95 -0.86 5 212 2.3 0.06 0.7 0.9 C1 860218 830 34.89 34-19.93 81-21.14 1.95 -0.24 7 247 4.9 0.08 0.8 2.1 C1 860221 428 43.06 34-20.59 81-21.68 0.11 -1.22 5 281 4.5 0.06 0.1 0.2 C1 860221 524 9.07 34-20.46 81-19.60 1.75 -0.40 6 211 3.0 0.07 0.8 1.2 C1 860222 1 4 49.55 34-20.34 81-18.84 0.30 -1.22 5 201 1.9 0.00 0.0 0.1 C1 860223 657 12.35 34-20.01 81-19.25 2.79 -0.60 8 203 2.3 0.05 0.4 0.4 C1 860227 3 1 13.63 34-20.14 81-19.11 1.56 -0.40 10 198 2.1 0.05 0.3 0.4 C1 860304 940 5.56 34-22.95 81-19.32 1.48 -0.24 8 168 1.4 0.03 0.1 0.2 B1 860310 1837 5.73 34-20.12 81-20.77 2.73 0.12 11'134 4.4 0.07 0.2 0.6 B1 860318 747 53.22 34-21.55 41-20.26 3.28 -0.60 4 262 1.7 0.00 C1 860320 2130 29.57 34-20.44 81-20.23 0.63 0.21 11 132 3.9 0.08 0.3 1.2 B1 860321 21 1.20 34-20.19 81-20.00 1.68 0.12 11 128 3.5 0.08 0.3 1.1 B1 860321 211 34.16 34-20.28 81-20.11 0.69 0.91 12 130 3.7 0.05 0.2 0.5 B1 860323 943 39.88 34-19.64 81-18.98 5.86 -0.60 6 247 2.0 0.09 1.5 0.9 C1 i 860326 3 0 20.41 34-20.44 81-20.45 0.77 0.68 10 133 4.3 0.08 0.3 1.9 B1

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