ML20237E934

Seismic Activity Near VC Summer Nuclear Station for Period Jul-Sept 1987

ML20237E934
Person / Time
Site:	Summer
Issue date:	09/30/1987
From:	Acree S, Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
Shared Package
ML20237E927	List: ML20237E926 ML20237E934
References
87-3, NUDOCS 8712290268
Download: ML20237E934 (16)

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$ g TECHNICAL REPORT 87-3 ,

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SELSMIC ACTMTY NEAR THE V.C. SUMMER NUCLEAR STATION il

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TECHNICAL REPORT 87-3 f' ]

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i SE.ISMIC ACTIVITY NEAR .-

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THE V.C. SUMMER NUCLEAR STATION ,

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PRADEEP TALWANI m PRINCIPAL INVESTIGATOR ,

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STEVE ACREE '

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INTRODUCTION Analysis of the seismic activity near the V.C. Summer Nuclear Station in South Carolina between July 1 and September 30, 1987 is presented in this report. During this period a total of eight events were recorded, all of which were located. The largest eJhock was of magnitude 0.6 (July 7-0711 UTC). Twenty-

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five pehcent (2) of the earthquakes were of magnitudes greater than zero. One shock was of B quality and was located at a depth of less than 0.1 km.

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1 SEISMIC NETWORK Earthquakes recorded during this period were located using stations of the SCE&G and USGS/USC 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 ANALYSIS l

Hypocentral locations of the events were determined using the computer program HYPO 71 (Lee and Lahr, 1972) and the velocity  ;

model listed in Appendix II. The event magnitude (ML) was 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).

An estimate of daily energy release is determined using a m -- .. .

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MONTICELLO RESERVOIR

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A Figure 1. Location map of Monticello Reservoir area showing seismic stacions used in locating activity during this period. I

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simplified magnitude (M ) energy (E) relation by Gutenberg and Richter (1956). ]

l log 10 E = 11.8 + 1.5 M L

• 1 OBSERVED SEISMICITY FOR THE PERIOD JULY-SEPTEMBER 1987 During this period eight events were recorded and located.

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(see Appendix III). This level of activity again was significantly less than that observed during the previous reporting. period. The level of activity continued to decline l

during this period, consistent with the trend observed in Figure

2. The largest event of this quarter.(M g=0.6). occurred on July.7 1

at 0711 UTC. Two shocks (25%) were of magnitudes greater than zero.

The epicenters of earthquakes located during this quarter and during each month are presented in Figure'3 and Figures 4, 5, and 6, respectively. The earthquakes were neither spatially nor temporally clustered. Only one earthquake location was of quality B or better. This event located at a depth of approximately 0.1 km.

CORRELATION OF RESERVOIR WATER LEVEL WITH SEISMICITY

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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 normal variations up to approximately five feet per day between the maximum and minimum water level. We have been i

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MONTICELLO EARTHQUAKES JULY - SEPTEMBER 1987. ,

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Figure 3. Seismic activity at Monticello Reservoir during July - September 1987.

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i MONTICELLO EARTHQUAKES JULY 1987 ,

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MONTICELLO EARTHQUAKES ]

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Figure 5. Seismic activity at Monticello Reservoir during August 1987.

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MONTICELLO EARTHQUAKES SEPTEMBER 1987 ,

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Figure 6. Seismic activity at Monticello Reservoir during September 1987..

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9 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

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in Figure 7. The top two plots show the. median water'1evel.and the change in water,Ievel each day. The number of events per day. l 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 water level and seismicity is readily apparent.

CONCLUSIONS The level of activity observed during the third quarter;of

, 1987 was significantly lower than that observed during either the l

first or the second quarters, consistent with the.long term decline in seismicity. No event was of a magnitude greater than O.6. Two of the eight earthquakes were of magnitudes greater than 0.0.

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REFERENCES i

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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11 APPENDIX I STATION LOCATIONS NO. STN. LAT.*N LONG.*W 1 JSC 34* 16.80' 81* 15.60' 2 001 34* 19.91' 81* 17.74' 3 002 34* 11.58' 81* 13.81' 4 007 34* 22.23' 81* 19.50' 5 008 34* 24.53' 81* 24.55' 6 09A 34* 17.24' 81* 19.75' 7 010 34* 20.18' 81* 20.25' O

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APPENDIX II' 1a MONTICELLO RESERVOIR-VELOCITY MODEL-Velocity Depth to top

.km/sec km 1.00- 0;00 5.40 0.03-5.90 O'.18 6.10 0.46 6.30 0.82 8.10 30.00-t--- - - _ - - - - _ _ - - - - _ . - . - - _ - - - _ - - - _ - - _ - - - _ _ - - _ _ _ _ _

t 13 APPENDIX III MONTICELLO EARTHQUAKES JULY - SEPTEMBER 1987 HYPO 71 FORMAT-i Column 1 Date. I Column 2- Origin' time _(UTC) h.m.sec. l I

Column 3 Latitude (N) degrees, min. I Column 4 Longitude (W) degrees, min.

l Column 5 Depth (km), j 3

Column 6 Local duration magnitude.

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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 error of time residuals in Root sec. mean squarg/NO, RMS = R where R is the time residual for tbe ith station.g l Column 11 Standard error of the epicenter in km*.

i Column 12 Standard error of the focal' depth in km*. j I

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

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I-14 MONTICELLO EARTHQUAKES JULY - SEPTEMBER 1987 DATE ORIGIN LAT N LONG W DEPTH MAG NO GAP DMIN RMS ER!l ERZ QM 870707 711 52.79 34-18.78 81-18.70 0.77 0.57- 5 245 2.6 0.07*0.4 1'.1 C1 870801 917 37.50 34-20.01 81-17.29 1.00 -0.60 6 242 0.7 0.09 1.4 1.2 C1 870801 10 2 45.99 34-19.47 81-17.50 0.14 0.21 5 173 0.9 0.02 0.2 0.5 C1 870818 242 57.88 34-20.81 81-19.79 1.99 -0.40 5 186 6.6 0.08 1.2 10.1 D1 870819 024 54.59 34-20.23 81-20.49 1.14 -0.24 6 175 4.3 0.05 1.5 7.7 C1 870902 1724 23.36 34-20.14 81-18.89 0.06 -0.40 7 131 1.8 0.03 0.1. 0.5 B1 870909 2357 1.06 34-22.03 81-19.60 2.64 -0.40 6 186 0;4 0.05 1.0' O.5 C1 1 870929 2251 22.68 34-22.00 81-20.12 4.76 -0.40 5 243 1.0 0.02 .0.5 0.5-C1 l

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