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Technical Rept 83-4, Seismic Activity Near VC Summer Nuclear Station,Oct-Dec 1983 & Summary for 1983
	ML20088A874
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Site:	Summer
Issue date:	12/31/1983
From:	Rawlins J, Talwani P; SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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	83-4, NUDOCS 8404130253
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TECHNICAL REPORT 83-4 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION

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For the Period October - December 1983 s

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by Pradeep Talwani Principal Investigator Geology Department University of South Carolina Columbia, S.C. 29208 Contract No. N301315

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Technical Report 83-4

-SEISMIC ACTIVITY NEAR 1;

THE V. C. SUMMER NUCLEAR STATION For the Period October - December 1983 and Sumary for the Year 1983 by Pradeep Talwani, Principal Investigator and Jill Rawlins, Research Assistant Geology Department University of South Carolina Columbia, S.C.

29208 l

Contract No. N230519 w

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1 INTRODUCTION This report presents a summary of seismic activity near the V. C. Sumer Nuclear Power Station in South Carolina for the three s

month period between October 1 and December 31, 1983, as well as a brief summary of seismicity for the entire year of 1983. Between g

1 October 1 and December 31, a total of twelve locatable events were recorded, the largest of which occurred on November 3,1983, with a magnitude equal to 1.18.

A total of 190 events were located in the Monticello Reservoir area during the entire year of 1983, two of magnitude greater than 2.0 and 14 with magnitudes between 1,0 and 2.0.

4 i

SEISMIC NETWORK j

The report is based on the data recorded by a four-station network operated by S.C.E. and G.

In addition, data from a permanent station (JSC) of the South Carolina seismographic network are also used.

l Location of all these stations is shown in Figure 1, and their coor-l dinates are listed in Appendix 1.

1 DATA ANALYSIS

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Location of the events is determined using HYP071 program (Lee and i

' Lahr,1972) and the velocity model given in Appendix II. The event magnitude (M ) is detennined from signal duration at station JSC, g

using the following relation:

M ~= -1.83 + 2.04 Log D g

where D is the signal duration (seconds).

An estimate of daily energy release is determined using a simpi-fled magnitude.(M ) energy (E) relation by Gutenberg and Richter,1956.

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3 RESULTS The twelve located events recorded during this period are listed in Appendix III. Two of the events had magnitudes greater than 1.0 (Nov. 3,

= 1.02), and the remaining events were small ML = 1.18; Nov. 30, Mg (M < 1.0). Half of.the activity occurred within two kilometers of t

the surface, the other half at greater depths with the maximum depth at 3.9 km.

Further depth studies are included with the analysis for the entire year.

A cumulative plot of the epicenters located during this reporting period is shown in Figure 2, and separation by month is shown in Figures 3-5.

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 about i-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 6 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 number of events per day and log of energy 7

released per day are shewn on the lower two graphs. The histograms showing events per day and log of energy release include the unlocated events around the reservoir.

$LNtARY OF 1983 SEISMICITY' A histogram of seismic activity for the year 1983 is presented in g

Figure 7, showing the total number of events per day. A total of 190

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locatable events were recorded in the Monticello Reservoir area during the year. A cumulative plot of epicenters is shown in Figure 8 and a cross section of events located within one kilometer of AA' is showr in Figure 9.

No depth correlation is noted. The events with magnitudes greater than 2.0 are listed in Table 1, and Table 2 is a listing of the events with magnitudes between 1.0 and 2.0.

The remaining events were small (M < l.0).

L Most of the seismic activity for the year occurred over a broad period from February to May with no significant peak in the level of seismicity. Spatially, the major portion of the seismicity was con-centrated near the center of the west side of the reservoir.

Depth variations based on quality B or better events are shown in Figure 10. The depth ranges were divided into 0.5 km increments up te 3.0 km, and events occurring at greater depths were grouped to-gether. The largest percentage of events occurred in the 1.5 to 2.0 km increment in every year, and since 1981 the percentage of events occurring in the 3.0 and deeper-increment has been significant.

_ Approximately 15 miles west of the V. C. Summer Nuclear Station, near Newberry, S.C., a. swarm of 103 locatable events occurred within two weeks from April 27 to May 11. Their epicentral locations and proximity to the Monticello Reservcir are shown in Figure 11. The larger events of the swarm occurred on April 28 (M = 2.20) and May 7 (ML=2.45).

CONCLUSIONS Seismic activity during the.0ctober through December,1983, reporting period was extremely low. A plot of the total number of events per

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month from December,1977, through December,1983.(Figure 12) indicates

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TABLE 1 l

ML > 2.0 Date Magnitude i

February 19 2.00 June 11 2.20 TABLE 2 1.0 < M, t < 2.0 Date Magnitude January 31 1.50 February 8 1.09 February 9 1.06 February 20 1.25 1

April 3 1.27 April 3

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a trend of discrete swarms separated by relatively quiet periods. The peak levels of the swarms have decreased continually while the time span has increased, and the overall level of seismicity has dropped.

t The seismicity levels for 1983, in general, and for the last three months in particular, reinforce the observed trend of tapering off of g.

activity. The depth variations, however, bear continued monitoring and the Newberry swarm appears to have no direct association with the reservoir.

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 O

STATION LOCATION

. NO.

STN.

LAT. N.

LONG. W.

0 34 19.91' 81 17.74' 1

001 0

2 002 34 11.58' 81 13.81' 0

3 003 34 21.09' 81 27.41' 0

'4 004 34 25.72' 81 12.99' 0

0 34 16.80' 81 15.60' 5

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APPENDIX II MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth 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 i

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APPENDIX III 6

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