ML20246P213

Seismic Activity Near VC Summer Nuclear Station for Period Oct-Dec 1988

ML20246P213
Person / Time
Site:	Summer
Issue date:	12/31/1988
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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ML20246P202	List: ML20246P199 ML20246P213
References
88-4, NUDOCS 8903280159
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TECHNICAL REPORT 88-4 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION' i

, e For the Period October - December 1988 by y Pradeep Taiwani i

Principal investigator Department of Geological Sciences University of South Carolina Columbia, SC 29208 Contract No. N482355

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TECHNICAL REPORT 88-4 s

1 s SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD OCTOBER-DECEMBER 1988 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR KEVIN SEVERANCE VINITA ARORA l l

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DEPARTMENT OF GEOLOGICAL SCIENCES UNIVERSITY OF SOUTH CAROLINA' COLUMBIA, S.C. 29208 CONTRACT NO. N482355 l

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l' 9 l-2 INTRODUCTION )

- Analysis'of the seismic activ3ty near.the V.C. Summer Nuclear Station in South Carolina between October 1 and December 30, k

1988 is presented in this report. During this period a total of I twenty-six events were recorded, nineteen of which were located.

The largest shock was of magnitude 1.4 and occurred on October 19 at 1950 UTC. Fourteen earthquakes had magnitudes less than zero. Three shocks were of B quality none of which located at depths greater than 2 km.

SEISMIC NETWORK Earthquakes recorded during this period were located using stations of the Monticello Reservoir and South Carolina 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 ANALYSI.S l

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

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

An estimate or daily energy release was determined using a simplified magnitude (Mg ) energy (E) relation by Gutenberg and

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log 10 E = 11.8 + 1.5 M g.

l OBSERVED SEISMICITY FOR THE PERIOD OCTOBER-DECEMBER 1988 During this period twenty-six events were recorded, nineteen of which were located (see Appendix III).. This level of activity was similar to that observed during the previous reporting period, and the long-term decline in seismicity is continuing (Figure 2). The largest event of this quarter (Mg =1.4) occurred on October 19 at 1950 UTC. Two shocks (8%)

were of magnitudes greater than one.

The epicenters of earthquakes located during this quarter and during each month are presented in Figures 3, 4, 5, and 6.

The majority of the earthquakes during this period occurred in October. Temporal clustering of events was observed on October 1, and October 23. Three earthquake locations were of quality L or better. These events were located between depths of 0.0 km and 1.7 km. The depth of the deepest event was 6.8 km.

CORRELATION OF RESERVOIR WATER LEVEL WITH SEISMICITY

- Monticello Reservoir is a pumped storage facility. Any decrease in reservoir ?evel associated with power generation is recovered when water if pumped back into the reservoir. There can be normal variatic.s up to approximately five feet per day between the maximum at.d 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 i

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Fi.gure 6. Seismic activity at Monticello Reservoir during December 1988.

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u. 9 the local seismicity. Water level was compared with seismicity in Figure 7. The top two plots show the median water'1evel and

-the change in water level each day. The number of events'per day.

and the. log of the energy released per_ day are.shown in the lower two histograms. . There is no apparent correlation between the change in median water level or daily water level fluctuations and' seismicity during this quarter.

CONCLUSIONS The. level of activity observed during the fourth quarter of' 1988 was . low and not significantly different from that observed during the third quarter of 1988. The largest event was of magnitude 2.4. Two of the twenty-six earthquakes were of magnitudes greater than 1.0. The three quality B earthquake Incations range in depth from 0.0 to 1.7 km.

SUBS 6ARY OF 1988 SEISMICITY Seismic activity during 1988 (87 events) was approximately half of that of the 177 events of 1987 (Figure 2). The number of' events per day recorded during 1988 is shown in. Figure 8. The majority of the activity occurred during the last part of the year. A total of 87 earthquakes were recorded 69 of which were located (82%). The majority of the earthquakes were concentrated beneath the center of the reservoir (Figure 9). Twenty-six percent (19) of the located events were of B quality and one l event was of A quality. Depths calculated for the B quality events all were within 2.7 km of the surface. The majority of the B quality earthquakes were located at depths between 1.5 and f.

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f 2.0 km and between 0.5 km and the surface (Figure 10). The depth of the A quality earthquake was approximately 1 km.

The largest earthquake of-the year was of magnitude Mg = 2.4 (September 30 -- 174 6 UTC) . Eleven of the located events (15%)

were of magnitudes greater than or equal to 1.0. In summary, seismicity at Monticello Reservoir continued to decline and was of low magnitude during 1988.

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. Geological Survey, Open-File Report, 100 pp.

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l' APPENDIX I e

STATION LOCATIONS

'l LONG.*W NO. STN. LAT.*N 1 JSC 34+ 16.80' 81+ 15.60' 2 001 34+ 19.91' 81+ 17.74' 3 002 34+ 11.58' 81+ 13.81' 4 005 34+ 16.05' 81+ 20.05 5 007 34+ 22.23' 81+ 19.50' 6 010 34+ 20.18' 81+ 20.25' l

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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 O.46 ,

6.30 0.82 8.10 30.00 l

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i APPENDIX III MONTICELLO EARTHQUAKES-OCTOBER-DECEMBER 1988 A

HYPO 71 FORMAT Column 1 Date.

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

Column 3- Latitude (N) degrees, min.

4- Column-4 Longitude (W) degrees, min. .

Column 5 Depth-(km).

Column 6 Local duration magnitude.

Column 7 No.Lof station readings.used to locate event.

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

Column 8 Largest azimuthal separetion in degrees between stations.

Column 9 Epicentral distance in km to nearest. station.

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

=. R where Rg.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*.

. *Statistica1' interpretation of standard errors involves assump-tions which may not be met in earthquake locations. Therefore standard errors may not represent actual error limits.

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

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MONTICELLO EARTHQUAKES OCTOBER-DECEMBER 1988 s DATE ORIGIN LAT N LONO W DEPTH MAG NO GAP DMIN RMS ERH ERZ QM 881001 0451 39.81 34-22.92 81-18.30 2.80 -1.22 5 282 2.5 0.06 1.4 2.6 C1

' I 881001 0514 24.43 34-20.35 81-17.84 1.54 -0.11 5 189 0.8 0.07 1.4 1.7 C1 881001 0549 37.82 34-19.13 81-19.57 2.09 -1.22 4 184 2.2 0.05 -- -- C1 881001 0810 21.32 34-19,68 81-17.84 1.63 0.68 7 128 0.5 0.09 1.4 1.5 B1 881019 1515 48,10 34-19.95 81-20.35 1.00 0.37 6 249 0.5 0.03 0.7 0.7 C1 881019 1950 22.94 34-19.21 81-19.04 0.04 1.39 6 164 2.4 0.02 0.1 0.2 B1 881023 0954 18 21 34-19.43 81-18.57 0.83 -0.60 5 162 1.6 0.08 1.7 5.9 D1 881023 0954 44.99 34-18.99 81-19.11 1.00 0.01 5 195 2.7 0.09 1.7 11.3 D1 8'81023 1024 05.83 34-19.53 81-18.37 0.60 -0.40 5 153 1.2 0.08 28.3 61.1 D1 881023 1201 09.79 34-20.01 81-17.84 1.00 -0.24 5 173 0.2 0.09 1.7 1.4 C1 881023 1600 43.04 34-20.08 81-18.35 0.47 0.01 5 169 2.9 0.05 0.6 3.8 C1 881112 2034 20.92 34-19.92 81-19.69 1.01 -0.86 5 167 1.0 0.03 0.9 1.4 C1 881125 2329 10.53 34-20.01 81-17.84 6.78 0.21 5 173 0.2 0.02 0.9 0.5 C1 881201 1759 49.05 34-20.46 81-18.48 2.65 1.32 4 158 1.5 0.00 -- -- C1 881225 1351 19.87 34-19.48 81-18.96 1.72 0.01 6 170 2.4 0.08 0.9 1.8 D1 881225 1716 23.47 34-20.01 81-17.84 1.00 -0.24 4 178 0.2 0.06 -- -- C1 881227 1116 15.87 34-21.63 81-17.53 4.76 0.37 5 231 3.2 0.01 0.5 0.5 C1 881227 1202 45.71 34-20.62 81-17.84 1.76 0.91 6 195 1.3 0.06 0.9 1.7 C1 881227 1905 51.16 34-20.01 81-18.28 1.00 -0.11 4 187 0.9 0.07 -- -- C1

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