ML20090B130

Seismic Activity Near VC Summer Nuclear Station, Technical Rept 84-1 for Jan-Mar 1984

ML20090B130
Person / Time
Site:	Summer
Issue date:	07/06/1984
From:	Rawlins J, Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
Shared Package
ML20090B118	List: ML20090B116 ML20090B130
References
84-1, NUDOCS 8407120304
Download: ML20090B130 (17)

Text

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i i TECHNICAL REPORT 84-1 l l

SEISMIC ACTIVITY NEAR l THE V.C. SUMMER NUCLEAR STATION }

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For the Period l January - March 1984 i L

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l by Pradeep Talwani Principal Investigator Geology Department University of South Carolina Columbia, S.C. 29208 Contract No. N355486 8407120304 840706 i PDR ADOCK 05000395 ,

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Technical Report 84-1 l

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.' i SEISMIC ACTIVITY NEAR r

THE V. C. SUMMER NUCLEAR STATION l

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For the Period [

i' January - March 1984  ;

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I by  :

Pradeep Talwani, Principal Investigator and 1 Jill Rawlins, Research Assistant Geology Department ,

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

i i Contract No. N355486 .

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1 INTRODUCTION

,. This report presents a summary of seismic activity near the 4

V. C. Sumer Nuclear Power Station in South Carolina for the three month period between January 1 and March 31, 1984. During this reporting period, a total of 31 locatable events were recorded. The largest event was of magnitude 2.0 on March 7, four events had magni-tudes between 1.0 and 2.0, and the renaining events were small (ML < l .0).

SEISMIC NETWORK 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 pemanent station (JSC) of the South Carolina seismographic network are also used.

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

- DATA ANALYSIS Location of the events is determined using HYP071 program (Lee and Lahr,1972) and the velocity model given in Appendix II. The event magnitude (M L ) is determined from signal duration at station JSC, using the following relation:

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

An estimate of daily energy release is determined using a simpli-fied magnitude (M ) energy (E) relation by Gutenberg and Richter (195G).

L log 10E = 11.8 + 1.5 M L RESULTS

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The 31 located events recorded during this period are listed in Appendix III. One event was of magnitude 2.0 (March 7,1984), four u

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3 had magitudes greater than 1.0 (Table 1), and the rest were small.  ;

l TABLE 1 Date Magnitude March 7 1.09 March 7 2.00 ,

i March 18 1.02 ,

l March 18 1.18 l March 20 1.32 f

i Depth analyses for this reporting period were not divided into  ;

0.5 km increments as in the past year's reports due to the low number l of events. However, 87% of all the events located during this period occurred within the top two kilometers and the deepest event occurred at 2.53 km.

A cumulative plot of epicenters of events located during this period is shown in Figure 2 and a cross section in Figure 3, which ap-pears to show a southwest dipping plane defined by the events within 1.0 km of the cross section. A monthly breakdown of epicentral locations is shown in Figures 4-6. Most of the activity occurred in mid-March in a broad east-west band across the center of the reservoir.

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 O

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

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. local seismicity. Figure 7 shows the comparison of water level to

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I seismicity. The top two graphs show the water level and the change of a

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

CONCLUSIONS Monticello Reservoir experienced a low level of seismic activity for the January 1 thrcugh March 31, 1984 reporting period, with increased seismicity in the middle of March. A trend of discretr swarms separated by relatively quiet periods has been apparent for approximately five years (Figure 8) and the seismicity level for this period continues to agree with the trend, including a general decline in activity. Depth of seismicity for this reporting period was primarily within the uppermost two kilometers.

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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. STATION LOCATION I NO.- STN. LAT. N. LONG. W. [

0 l 1 001 340 19.91' 81 17.74' I

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2 002 34 11.58' 81 13.81' I 0

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VELOCITY MODEL  :

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Velocity Depth l km  :

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.u . .,. . _ . . .o i APPENDIX III DATE ORTGIN LAT N LONG W DEPTH MAG NO GAP DMIN RMS ERM ERZ GM 840203 945 11.10 34-18.91 81-19.18 0.80 n.44 628 2.9 0.04 0.6 1.0 1 840208 350 39.42 34-20.78 81-19.21 1.92 0.12 9 127 2.4 0.06 0.3 1.1 1

! 840200 112 14.69 34-20.01 81-1P.70 0.29 01 9 124 1. 0.09 0.4 0*9  : ,

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840320 156 45 34-19.54 A1-18.75 1.51 1.32 10 129 1.7 0.06 0.2 0.5 81

{ 81-19.50 1.78 -0.43 7 159 5.4 0.04 0.2 1.2 B1

840323 103763 57 840327 7M1490 34-20.28 35 05 1.73 81-19.30 34-17.37 0.37 to 127 2.5 0.05 0.2 0.6 B1 i

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