ML20040G987

Technical Rept 81-3, Seismic Activity Near VC Summer Nuclear Station,Jul-Sept 1981.

ML20040G987
Person / Time
Site:	Summer
Issue date:	02/10/1982
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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ML20040G984	List: ML20040G983 ML20040G987 ML20040G989
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N230519, NUDOCS 8202160700
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TECHNICAL REPORT 81-3 l SEISMIC ACTIVITY NEAR 1 THE V.C. SUMMER NUCLEAR STATION ,

i For the Period July - September 1981 by Pradeep Taiwani Principal Investigator Geology Department

. University of South Carolina >

Columbia, S.C. 29208 Contract No. N230519

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Technical Report 81-3 L

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SEISMIC. ACTIVITY NEAR THE V. C. SUMMER NUCLEAR STATION i

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For the Period July - September 1981 1

i by Pradeep Talwani Principal Investigator Geology Department University of South Carolina Columbia, S. C. 29208 -

, . Contract No. N230519 i

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1 INTRODUCTION ltiis report presents a summary on seismic activity near the V. C. Summer Nuclear Power Station in South Carolina for a three month period betwcen July 1 and September 30, 1981. During this reporting period a total of seven locatable events were recorded, 1

out of which only one exceeded magnitude 2.0.

_ SEISMIC NETWORK The data were recorded by a four-station seismic network operated by S.C.E. and G. In addition, data were also obtained from JSC --

a permanent station of the South Carolina seismographic network, and a portable digital event detector (Station JIM). Location of all these stations is shown in Figure 1, and their coordinates are listed in Appendix I.

DATA ANALYSIS ,

Location of the events was determined using HYP071 program (Lee and Lahr,1972) and a velocity model developed for the Monticello Reservoir area (Appendix II). The event magnitude (M ) was calculated t

from signal duration at station JSC, using the following relation:

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

The daily energy release was determined using a simplified magnitude (M L ) energy (E) relation by Gutenberg and Richter,1956.

log 10E = 11.8 + 1.5 Mt O

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RESULTS Seven events located during this reporting period (July 1 -

September 30, 1981) are listed in Appendix III. Five of these events occurred between 1.8 to 2.0 km in depth. The other two occurred at a depth shallower than 1.0 km. The cumulative plot of the epicentral location of these events is shown in Figure 2. A monthly breakup of their location 'is also shown in Figures 3-5. A cumulative location map of all the events (with RMS 5,1.0 sec) between December 1977 'and -

September 1981 is shown in Figure 6.

b-VALUES The low number of recorded events in this three month period (July 1 - September 30, 1981) are too few to make meaningful estimates of b-values.

RESERV0IR WATER LEVEL AND ITS COMPARISON WITH SEISMICITY Monticello Reservoir is a pumped storage facility, and 'the decrease in reservoir level associated with power generation is recovered when water is pumped back into the reservoir. Consequently, there can be variations up to about 4 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 reser-voir level and the local seismicity. Figure 7 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 released per day are shown on the lower two graphs.

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3 CONCLUDING REMARKS During this reporting period the activity was very low.

Figure 8 shows the monthly number of events from December 1977 to September 1981. The seismicity has occurred in discrete swarms after the initial spurt in January - February,1978. The level of seismicity has decreased considerably since its inception and appears to be completely dying out. At present the plans are to continue to monitor the seismicity to the end of 1982.

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 HYP0 71, U.S.G.S. Open-file report, 100 pp.

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. APPENDIX I STATICN LOCATION

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NO. STN. LAT. N. LONG. W.

1 001 34 19.91' 81 17.74' 2 002 34 11.58' 810 13.81' 3 003 34 21.09' 810 27.41' 4 004 34U 25.72'- 810 12.99' 5 JSC 34U 16.80' 81 15.60' 6 JIM 34 20.21' ~810 19.47' h

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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

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APPEllDIX III LOCATION OF EVENTS Cc=puter printout of HY?O71. showing dsts for location of events.

Colu=n 1 Date.

Cole =n 2 Origin time - (UCT) h.m.sec.

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Colu=n 3 Latitude (11) degrees, min.

Colu=n 4 Lon;itude (W) degrees, min.

Colt =:n 5 Depth (k=).

Colu=n 6 Local duration cagnitude.

Colu=n 7 Ilo. of station readings used to locate event.

P and S arrivals from sa=e stations are regarded as 2 readings.

Colt =n 8 Largest azi=uthal sepsrstion in degrees between stations.

Colt:n 9 Epicenersi distance in km to nearest station.

Colu=n 10 Root mean square error of time residuals in sec.

EMS =)R//1!O,whereR.isthetimeresidusifor,

.1 the ith station. .~-

Colu=n 11

• Standard error of the epicenter in km .

Colu=n 12 Standard error of the focal depth in km* .

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• Statistical interpretation of sesndard errors involves assu=ptions which may not be met in earthquske locations. Therefore standard errors may nct represent accust error limits.

If ERH or ERZ is bisnk, this mesns that it cannot be computed, becsuse of insufficient data.

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g JULY THROUGH SEPTEf1BER 1981 DATE ORIGIN LAT N LONG W DEPTH MAG N0 GAP Df1IN RMS ERH ERZ ~QM 810732 67 4.21 34-17.78 81-19.61 1.88 0.0 8 155 4.9 0.09 0.5 1.7 B1 810715 9 1 57.83 34-23.12 81-18.72 0.78 -0.11 10 167 6.1 0.15 0.6 3.6 C1 810718 21 6 9.77 34-19.68 81-18.50 0.27 0.21 10 126 1.2 0.08 0.3 0.8 B1 810719 118 10.39 34-20.42 81-20.47 1.96 0.29 10 133 4.3 0.09 0.4 1.6 B1 810730 2153 6.90 34-17.37 81-19.92 1.81 1.18 10 162 5.8 0.08 0.4 2.0 B1 810816 1531 30.29 34-19.71 81-19.50 1.96 2.03 10 132 2.7 0.09 0.4 1.1 B1 -

810822 8 4 43.53 34-21.49 81-19.45 1.96 0.37 8 145 3.9 0.06 0.4- 1.2 B1 THE NUMBER OF EVENTS IN THE LIST IS 7

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