ML20153C536

Technical Rept 88-2, Seismic Activity Near VC Summer Nuclear Station, for Apr-June 1988

ML20153C536
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Site:	Summer
Issue date:	06/30/1988
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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NUDOCS 8809010172
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• 1 TECHNICAL REPORT 88-2 l

t SEISMIC ACTIVITY NEAR 1 ,

THE V.C. SUMMER NUCLEAR STATION l l

FOR THE PERIOD APRIL - JUNE 1988 BY 4

PRADEEP TALWANI PRINCIPAL INVESTIGATOR STEVE ACREE ,

ANDhEA CONKLE '

, VINITA ARORA DEPARTMENT OF GEOLOGICAL SCIENCES -

UNIVERSITY OF SOUTH CAROLINA COLUMBIA, S.C. 29208 i

CONTRACT No. N482355 8809010172 880829 i DR ADOCK0500gg95

. --__ -. - -. - _ - _ _ .- .-. . - - _ . -_ . - = . - - - - -

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I INTRODUCTION ,

4 Ana3ysis of the seismic activity near the V.C. Summer  !

Nuclear Station in South Carolina between April 1 and June 3C.

, 19tB ir presented in this report. During this period a tota 3 of 1 sixteen events were recorded. All but one of the events were

ocated. The largest shock was of magnitude 0.95 (June 27 - : P 3 F.

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"!C;. Thirty-one percent (5) of the earthquakes were of l magnitudes greater than zero.- Three shocks were of F quality.

j None of these were located at depths greater than 2 km.

f SEISMIC NETWORK  !

j Earthquakes recorded during this period were located using l 1

stations of the Monticeollo Reservoir and South Caroline networks. The configuration of the stations utilized to Jocate the events in this report is shown in Figure 1 and station  !

coordinates are listed in Appendix I.

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i DATA ANALYSIS

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] Hypocentral locations of the events were deterr.ined using-  !

'l the computer program HYPO 71 (Lee and Lahr, 1972) and the velocity l i

] model listed in Appendix II. The event maDnitude (Mg) was l determined from the signal duration at station JSC, using the I i

i following relation. ,

l Mt = -1.03 + 2.04 tog D where D is the signa) duration (seconds). -

. An estimate of daily energy release was determined using a f simplified magnitude (Mg ) enercy (E) relation uy Gutenberg and

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SOUTH 0 SKM =

A CAROLINA 2 ,

Figure 1. Seismic stations utilized to locate earthquakes near Monticello Reservoir during April - June 1988.

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Michter (1956):

200 0 E= 21.8 A :.5 M g .

OBSERVED SEISMICITY FOR THE PERIOD APRIL-JUNE 1988 i During this period sixteen events were recorded and all but one were located (see Appendix III). This level of activity wes i 4

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 =0.95) occurred on June 27 J

at 1838 UTC. Five shocks (31%) were of magnitudes greater than [

zero, f

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

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! The majority of the earthquakes during this perled occurred in  !

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April and were clustered on the western shore of the reservoir.

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]

Three earthquake locations were of quality B or better. These  !

events were located between depths of 0.2 kn and 1.8 km. '

i j CORRELATION OF RESERVOIR WATER LEVEL WITH SEISMICITY t

l Monticello Reservoir is a pumped storage facility. Any decrease in reservoir 'evel a9sociated with power generation is l recovered when water is pumped back into the reservoir. There can be normal variations up to approximately five feet per day  !

I between the maximum and minimum water level. We have been i f monitoring the water level to see if there is any correlation

, between the daily or seasonal changes in the reservoir level l J

and the local seismicity. Water level was compared with seismicity I

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1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1

Figure 2. Earthquakes per month between reservoir impoundment a.,d June 1988.

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MONTICELLO EARTHOUAKES april - JUNE 1988 ,

22.0 21.0 20.0 19.0 18 0 17.0 16 0 t I f l I I f I  ! I f I I l

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0 KILOMETERS 5  ;

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• t e i a a 4 e i a a e a e  !

MAGNITUDE DEPTH (KM)

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I Figure 3. Seismic activity at Monticello Reservoir during April - June 1988. I I

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MONTICELLO EARTHOUAKES i APRIL'1988 .

• 81 22 0 21.0 20.0 19 0 19.0 17 0 16.0 i f f I f f f 1 I t t i t f I _ 24 0 l . 23.5

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. I 3 I I I & I I I i i i i I 34 l D KILOMETERS 5 j a m' a D E) D 0 A + x o l j -i e i a a e e i e a e e e i I* MAh!TUDE DEPTH (KM)

Figure 4. Seismic activity at Monticello Reservoir during April 1988.

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MONTICELLO EARTHOUAKES MAY 1988 ,

22.0 21.0 20.0 19.0 18.0 17.0 . 15.0 ,

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0 KILOMETERS 5 i f I I i 1 e

ml0 0 @ G O A + X &

• t 0 t 7 3 4 0 1 2 3 4 5 6 MAGN!IUDE DEPiv (KM) ,

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Figure 5. Seismic activity r.t Monticello Reservoir during May 19n8. l

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MONTICELLO EARTHOUAKES JUNE 1988 .

22.0 21.0 20.0 19.0 18.0 17 0 16.0 i t  ! I n i i l 1 I t t I l

- _24.0

- _23.5

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. I I I I 1 1 I I I i l i i i i 34 O KILOMETERS 5 I i t e i i i l m 0 0 0 C O O A + X 0 )

-t e i J 3 4 o i a a 4 s s NAGNITbO2 DEPTH (KM) l l

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Figure 6. Seis4.c activity at Monticello Reservoir during June 1988.

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• 30.092 se.ict se.122 se'.137 se'.152 8s'.167 88.182 JULI AN DATE Figure 7. Comparison of the median daily lake level and daily change in water level with the nt:mber of earthquakes per day and the log of the energy released.

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10 in. Figure 7. The top two plots show tte median water level 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 t?v 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 observe.1'during the second quartar of 1988 was low and not significantly different from that observed during the first quarter of 1989. The largest event was of magnitude 0.95. Five of the sixteen earthquakes were of magnitudes greater than 0.0. The three quality B earthquake 1

locations range in depth from 0.2 to 1.8 k..

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 HYPOT1, U.S. Geolosteal Survey. Open~ Tile Reporta 100 pp.

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7 11 APPENDIX I STATION LOCATIONS NO. STN. LAT.*N LONG.*W 1 JSC 34* 16.80' 81* 15.60'

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2 001 34* 19.91' 81* 17.74' 3 002 34* 11.58' 81* 13.81' 4 005 04* 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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APPENDIX II MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth to top km/see 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 1

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MONTICELLO EARTHQUAKES APRIL-JUNE 1988 HYPO 71 FORMAT Column 1 Date.

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

Column 3 Latitude (N) degrees, min.

Column 4 Longitude (W) degrees, min.

Column 5 Depth (km).

Column 6 Local duration nagnitude.

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. L Column 10 Root mean square error of time residuals in sec. RMS = R 2/NO, where R is the time residual for t e ith station $

Column 11 Standard error of the epicentar in km*,

Column 12 Standard error of the focal depth in km'.

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• 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.

If ERM or ER: is blank, this means that it cannot be computed, because of insufficient data.

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14 MONTICELLO EARTHQUAKES JANUARY-MARCH 1988 DATF OR101X 1.AT N LONG h' DEPTH MAG No GAP DMIN RMc ERH ER7 QM 880110 '216 17.46 31-17.64 81-20.29 2.9) 0.37 9 222 4.7 0.08 0.7 1. 6 C1-880110 353 38.12 34-20.45 81-19.82 0.41 -0.86 4 232 3.3 0.05 C1 880130 7 0 19.04 34-24.97 81-21.10 7.00 0.37 5 339 5.6 0 09 3.9 1.9 D1 880212 1235 58.45 34-20.28 81-20.35 1.00 0.87 7 232 0.2 0.08 1.2 1.0 C1 880217 0 7 36.29 34-20.77 81-19.86 1.28 0.78 8-163 1.2 0.01 0.1 0.2 D1 880217 018 44.20 34-21.00 81-19.00 1.95 -1.22 4 150 1.8 0.02 C1 880223 1350 16.22 34-20.52 81-20.39 4.60 -0.60 5 222 0.7 0.02 0.4 0.5 C1 880223 1350 30.05 34-20.54 81-19.30 1.00 1,39 6 121 1.0 0.08 0.9 3.0 B1 880223 1354 7.72 34-20.65 81-19,80 3.92 -0.86 4 151 1.1 0.00 C1 l

880223 14 6 24.00 34-20.62 81-19.73 1.70 -0.60 6 143 1.1 0.05 0.5 1.0 B1 880223 1423 30.22 34-20.28 81-19.65 1.63 0.21 6 123 0.9 0.08 0.7 1.2 B1 880302 2146 43.04 34-21.52 81-19.60 1.89 0.01 *, .65 1.3 0.09 0.8 1.0 BJ  ;

880308 6 5 41.96 34-21.90 81-18.73 2.67 0.29 6 216 1.3 0.05 0.7 0.8 C1 880310 659 43.93 34-20.68 81-19.86 5.13 -0.40 5 158 1.1 0.00 0.1 0.1 C1 880315 631 1.77 34-20.28 81-20.35 2.78 -0.86 5 180 0.2 0.09 2.2 1.1 C1 880324 1251 37.15 34-19.81 81-18.91 1.00 -0.60 6 204 1.8 0.03 0.4 1.0 C1 ,

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