ML20148L326

Seismic Activity Near VC Summer Nuclear Station for Period Oct-Dec 1987

ML20148L326
Person / Time
Site:	Summer
Issue date:	12/31/1987
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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87-4, NUDOCS 8804010240
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l TECHNICAL REPORT 87-4

SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION For the Period October - December 1987 ,

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! . Pradeep Taiwani Principal Investigator Department of Geological Sciences

!- University of South Carolina l} Columbia, S.C. 29208

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! Contract No. N449678  ;

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TECHNICAL REPORT 87-4 ,

SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD OCTOBER-DECEMBER 1997 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR STEVE ACREE KEVIN SEVERANCE DEPARTMENT OF GEOLOGICAL SCIENCES UNIVERSITY OF SOUTH CAROLINA COLUMBIA, S.C. 29208 s

CONTRACT No. N449678

INTRODUCTION Analysis of the seismic activity near the V.C. Summer Nuclear Station in South Carolina between October 1 and December 31, 1987 is presented in this report. During this period a total of' twenty-four events were recorded, fourteen of which were located. The largest chock was of magnitude 2.0 (October 4 - 1830 UTC). Seventeen percent (4) of the earthquakes were of magnitudes greater than zero. Two shocks were of B quality and were located at depths of 0.3 and 0.4 km.

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 Hypocentral locations of the events were determined using the computer program HYP071 (Lee and Lahr, 1972) and the velocity model listed in Appendix II. The event magnitude (M g) was determined from the 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

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Tigure 1. Location map of Monticello Reservoir area showing seismic scacions used in locating activity during this period.

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3 simplified magnitude (Mg) energy (E) relation by Gutenberg and Richter (1956).

log 10 E = 11.8 + 1.5 M g .

j OBSERVED SEISMICITY FOR THE PERIOD OCTOBER-DECEMBER 1987 During this period twenty-four events were recorded and fourteen were located (see Appendix III). This level of activitf was slightly greater than that observed during the previous reporting period, but the overall decline in seismicity is continuing as shown in Figure 2. The largest event of this quarter (M g=1.0) occurred on October 4 at 1830 UTC. Four shocks (17%) were of magnitudes greater than zero.

The epicenters of earthquakes located during this quarter and during each month are presented in Flgure 3 and Figures 4, 5, and 6, respectively. Most epicenters are located on the western shore of the reservoir. Only two earthquake locations were of quality B or better. These events were located at depths of 0.3 km and 0.4 km, respectively.

CORRELATION OF RESERVOIR MATER LEVEL WITH SEISMIOITY 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 miniarm water level. We have been monitoring the water level to see if there is any correlation

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. Figure 3. Seismic activity at Monticello Reservoir during October-December 1987.

6 MONTICELLO EARTHOUAKES OCTOBER 1987 ,

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Tigure 4. Seismic activity at Monticello Reservoir during October 1987.

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

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. and the local seismicity. Water level was compared with seismicity j in Figure 7. The top two plots show the 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 the lower two histograms which reveal four small earthquake swarms. These charts include both located and unlocated events around the reservoir. There is a possible correlation between the drop in l median water level and higher daily fluctuation on November 1 - 6 l (days 87.305 - 87.310) and seismicity.

1 CONCLUSIONS 1 The level of activity observed during the fourth quarter of J

{ 1987 was not significantly higher than that observed during the third quarter. No event was of a magnitude greater than 1.0.

Four of the twenty-four earthquakes were of magnitudes greater than 0.0. Depths of both quality B earthquake locations were J

1ess than 0.5 km.

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SosMARY OF 1987 SEISMICITY i

Seismic activity during 1987 (177 events) was not significantly greater than that recorded during 1986 (144 events)

. (Figure 2). The number of events per day rect.ded during 1987 is shown in Figure 8. The majority of the activity occurred during the f2rst quarter of the year. A total of 177 earthquakes were recorded, 147 of which were located (83%). The majority of the

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la earthquakes were concentrated beneath the center of the reservoir (Figure 9). Thirty-seven percent (65) of the located events were of B quality. Depths calculated for the B quality events all were within 3.5 km of the surface. The majority of the B quality earthquakes were located at depths between 1.5 and 2.0 km (Figure 10). ,

t The largest earthquake of the year was of magnitude Mg = 1.9 (January 13 - 0545 UTC). Only four events were of magnitudes greater than or equal to 1.0.

In summary, seismicity at Monticello Reservoir was of low magnitude during 1987. With the exception of earthquake awarms in January and February, the activity rate was low throughout the year.

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 notion pattern of local earthquakes, Revisions of HYP071, U.S. Geolosteal Survey. Open-File Report, 100 pp.

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MONTICELLO EARTHOUAKES JANUARY - DECEMBER 1987 ,

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'. 15 APPENDIX I STATION LOCATIONS No. STN. LAT.*N LONG.*W 1 JSC 34+ 16.40' 41+ 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' 7 010 34+ 20.18' 81+ 20.25'

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i APPENDIX II l

1 j MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth to top km/sec km 1.00 0.00 8.40 0.03 5.90 0.18 4.10 0.46 6.30 0.82 8.10 30.00 4

r - _ ___ ___ _ _ _ _________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

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I APPENDIX III t

MONTICELLO EARTHQUAKES OCTOBER-DECEMBER 1987 MYP071 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 magnitude.

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.

Column 10 error of time residuals in Root sec. mean RMS =squarg/NO, R where R, is the time residual for tke ith statiog Column 11 Standard error of the epicenter in km*.

- Column 12 Standard error of the focal depth in km*.

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

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18 NONTICELLO EARTNQUAEES OCTOSER-D8CEMBER 1987 i

.- DATE ORIGIN LAT N LONO W DEPTH NAC N0 GAP DNIN RMS ERH ERZ QN 871003 1138 31.69 34-22.33 81-19.60 1.00 0.01 4 307 0.2 0.06 C1 i 871004 1830 18.45 34-18.08 81-19.89 2.03 0.95 10 210 3.9 0.06 0.5 1.3 C1 871008 853 24.20 34-21.25 81-20.72 1.02 -0.86 7 246 2.1 0.05 0.4 0.8 C1 l 871101 1621 55.99 34-19.27 81-19.09 0.41 0.82 10 163 2.4 0.06 0.2 0.5 81 871104 1123 54.22 34-20.71 81-19.31 0.40 -0.86 5 246 1.7 0.03 0.0 0.0 C1 871105 14 1 1.73 34-20.44 81-20.66 2.10 -0.60 5 257 0.8 0.02 0.5 0.4 C1 871105 14 6 52.81 34-20.57 81-20.77 2.14 -0.24 8 245 1.1 0.09 0.8 0.6 C1 871106 11 1 53.35 34-19.25 81-19.39 0.33 0.82 10 173 2.2 0.06 0.3 0.6 B1 871203 9 8 23.96 34-20.68 81-20.09 1.73 -0.86 7 183 1.0 0.02 0.1 0.2 C1 871214 2346 42.23 34-19.25 81-20.35 0.80 -0.24 5 243 1.7 0.08 2.0 3.2 C1 871216 051 38.68 34-29.28 81-20.35 1.00 -0.86 4 315 0.2 0.09 C1 871217 035 33.07 34-17.33 81-18.98 1.89 -0.24 5 125 2.9 0.07 1.0 3.6 C1 871223 047 49.49 34-19.59 81-21.60 0.14 -0.24 5 274 2.3 0.08 1.6 4.3 C1 871224 1345 47.47 34-20.28 81-21.76 1.81 -0.24 6 240 2.3 n.06 0.8 0.8 C1 l

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