ML19331C930

Seismic Activity Near VC Summer Nuclear Station, for Apr-June 1980

ML19331C930
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Site:	Summer
Issue date:	08/15/1980
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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ML19331C929	List: ML19331C928 ML19331C930
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80-2, NUDOCS 8008200157
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O TECHNICAL REPORT 80-2 THis DOCUMENT CONTAINS POOR QUAUTY PAGES SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION For the Period April - June 1980 I

by l

l Pradeep Taiwani Principal Investigator Geology Department University of South Carolina Columbia, S.C. 29208 Contract No. N230519 8008000157

_ _ _ _ _ _ . _ _ _ _ _ _ . . _ . _ _ _ _ _ . _ _ . . _ _ . _ _ _ , . _ _ _ _ . . ~ . _ . _ _ . . _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Technical Report 80-2 i

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

l For the Period

~

! April - June 1980 I .

1 1

by

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Tradeep Talwani Princip11 Investigator Geology Department University of South Carolina Columbia, S. C. 29208 ,

Contract No. N230519 i

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O

• 1 INTRODUCTION This report presents the analysis of seismic data recorded near the V. C. Summer Nuclear Power Station in South Carolina. During the reporting period (April 1 - June 30,1980) shallow microearthquake activity averaged less than one locatable event per day (= 0.32 event / day).

Two events of magnitude > 2.0 were recorded for this reporting period.

INSTRUMENTATION The data were recorded by a four station seismic network operated by S.C.E. and G. Data were also obtained from JSC, a permanent station of the South Carolina seismographic network and a portable digital event detector (station JIM or DW1). These seismic stations are shown in Figure I and listed in Appendix I.

METHOD Events were located using a computer program HYp071 (Lee and Lahr, .

1972) and a velocity model developed for the Monticello Reservoir area (Appendix II). The event magnitudes are calculated from the signal durations at station JSC, where the duration (D) and magnitude (ML )

. relation is ML = -1.83 + 2.04 log D The daily energy release was calculated using a simplified magnitude

(ML ) energy (E) relation (Gutenberg and Richter,1956) log 10E = 11.8 + 1.5 ML l

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, 2 RESULTS In the reporting period (April 1 - June 30,1980) 29 locatable events were recorded. These are listed in Appendix III. Figure 2 shows the cumulative events recorded in April, May and June 1980. Most events occurred in a loose band through the center of the reservoir with a small number occurring to the southwest. A cross section, 2.0 km in width from A to B is shown in Figure 3, enowing the shallow (1 3.0 km) character of the events. The monthly locations are shown in Figures 4 - 6.

A cumulative (from December 1977 to June 1980) map is shown in Figure 7.

In Figures 2 - 7 only etants with an RMS of 1 0.1 sec have been plotted.

COMPARISON OF SEISHICITY WITH RESERVOIR LEVELS Monticello reservoir is a pumped storage facility and the decrease in reservoir levels associated with power generation is recovered when water is pumped back into the reservoir. Correspondingly there can be Variations up to about 8 feet per day between the maximum and minimum water levels. Figure 8 shows the comparison of water level to seismicity.

The top two graphs show the water level and also the change of water level per day. The log energy per day and number of events per day are shown on the lower graphs.

During the reporting period there was only one seismicity peak, occurring in April.

b-Values The b-values were obtained for events occurring in approximately two week periods. As the number of events was not large Utsu's (1971)

, method was used. In this method:

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IMj - sMs where My = sum of magnitude of all earthquakes having magnitudes equal to or larger than Ms s = total number of those earthquakes and

-baM 10 y ,

1 - 10' where n = factor for correcting the effort of the length of the magnitude interval all. baP is given in Table 18, p. 388 (Utsu,1971) .

The b-values for 2 week periods (Figure 9) suggests a slow increase

! in the b-value which began in mid April.

coxcwszou During this reporting period seismicity was at a low level with a relatively large seismicity peak occurring in April (Figure 8, Events / day).

During the end of July and the first of August, there was an increase in seismicity. This increased activity is presently being studied and will l

be covered in the next report.

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REFERENCES Gutenberg, B. and Richter, C. F..(1956). Magnitude and energy of i

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.

Utsu,T.(1971). Aftershocks and Earthquake Statistics (III);

Analysis of the distribution of earthquakes in magnitude, time, and space with special consideration to clustering characteristics of earthquake occurrence (1): Journal of the Faculty of Science, Hokkaido Univ. Series VII (Geophysics), 3, no. 5.

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i APPEflDIX I STATICfl LOCATION i

?!0. STN. LAT. ?!. LONG. W.

1 001 34 19.91' 81 17.74' i

2 002 34 11.58' 81 13.81' 3 003 340 21.09' 81 27.41'

.i 4 004 340 25.72' 810 12.99' 5 JSC 340 16.80' 810 15.60' 6 JIM 34 20.21' 81 19.47' 7 DW1 34 20.50' 81 20.42' -

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APPENDIX II MONTICELLO RESERV0IR 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 30.00 e

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• APPENDIX III LOCATION OF EVENTS FROM April 1 - June 30,1980 Computer printout of HYP071 showing data for location of events.

Colu=n 1 Date.

Colu=n 2 Origin ti=e (UCT) h.m.sec.

Cole =n 3 -*'***d e (N) degrees, min.

Cole =n 4 ,agitude (W) degrees, min.

Colu=n 5 Depth (km).

Cole:n 6 Local duration magnitude.

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

P and S arrivals from same stations are regarded as 2 readings.

Colu=n 8 Largest a:i=uthal separation in degrees between stations.

l Colu=n 9 Epicentral distance in km to nearest station.

l Colu=n 10 Root mean squarc ' error of time residuals in sec.

RMS = 0, where R is the ti=e residual for the ich station.

l 1

Colu=n 11 Standard erro.r of the epicenter in km .

Column 12 Standard error of the focal depth in km .

• Statistical interpretation of standard errors involves assumptions which may not be met in earthquake locations. Therefore standard errors l may nc: represent actual error limits.

If ERll or ERZ is blank, this means that 2:cannot be computed, because of insuf ficient data.

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