ML19323D940

Seismic Activity Near VC Summer Nuclear Station, Technical Rept 80-1 for Jan-Mar 1980

ML19323D940
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Site:	Summer
Issue date:	05/20/1980
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
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80-1, NUDOCS 8005220573
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e Technical Report 80-1 SEISMIC ACTIVITY NEAR THE V. C. SUMMER flUCLEAR STATION For the Period j January - March 1980 i -

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! by i Pradeep Talwani Principal Investigator

, Geology Department University of South Carolina Columbia, S. C. 29208 i

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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 (January 1 - March 31,1980) shallow microearthquake activity averaged less than one locatable event per day (= 0.36 event / day).

Only one event of magnitude > 2.0 was recorded (03/20/80) 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. These seismic stations are shown in Figure 1 and listed in Appendix I.

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j METHOD 4

Events were located using a computer program HYP0-71 (lee and i

Lahr,1972) and a velocity model developed for the Monticello Reservoir.,

area (AppendixII). The event magnitudes are calculated from the signal durations at stations JSC, where the duration (D) and magnitude (M )

L relation is:

Mt = -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 10 E = 11.8 + 1.5 ML e

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2 RESULTS In the reporting period (January 1 - March 31,1980) 33 locatable events were recorded. These are listed in Appendix III. Figure 2 shows the cumulative events recorded in January, February and March,1980. Most events occurred on the western edge of the reservoir with a group of events occurring in three loose clusters in the northern, central and southwestern parts of the reservoir. Two cross sections, 2.0 miles in width through the central and southwestern clusters are shown in Figure 3, showing the shallow (1 3.0 km) character of the events. One event, on 3/04/80, occurred at a depth of 5.0 km. Though the epicentral locations of these events are accurate, their depths are not. Thus the depths

, shown in Figure 3 are probably the maximum depths. The monthly locations and cross sections are shown in Figures 4 - 8. A cumulative (from December 1977 to March 1980) map is shown in Figure 9. In Figures 2 - 9 only events with an RMS of 1 0 1 sec have been plotted.

DISCUSSION '-

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 5 feet per day between the maximum and minimum water levels. Figure 10 shows the comparison of water level to seismicity.

The top two graphs show the average water 1.evel and also the net change of water level per day. The log energy per day and number of events per day are shown on the lower graphs. Only events with a duration of 10 seconds (M L S 0.2) were considered, as the seismic energy release associated

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C with smaller events is significantly smaller. Only one event with ML > 2.0 occurred in the reporting period on March 20 (Julian day 80).

We do not see any obvious changes in the water level which would indicate an association.

b-Values The b-values were obtained for events occurring in two week periods.

As the number of events was not large Utsu's (1971) method was used. In this method:

s log e b =

IMj - sMs where Mj =

sum of magnitude of all earthquakes having magnitudes equal to or larger than Ms s = total number of those earthquakes and n = 10' ^ + bAM/ log e ,,

-0 1 - 10 where n =

factor for correcting the effort cf the length of the magnitude interval AM. baM is given in Table 18, p. 388 (Utsu,1971).

The b-values for 2 week periods (Figure 11) indicate a slow increase in the b-value which began in mid January 15.

CONCLUSIONS Low level seismicity is still continuing at Monticello reservoir and is continuing to be monitored.

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. b-VALUES FOR MONTICELLO

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15 REFERENCES Gutenberg, B. and Richter, C. F..(1956). Magnitude and energy of earthquakes, Ann. Geof. 9, p. 1-15.

Lee, H. 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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APPEflDICES O

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APPENDIX I i .

I STATICN LOCATION NO. STN. LAT. N . LONG. W.

i 1 001 340 19.91' 81U 17.74' i

, 2 002 34 11.58' 81 13.81' l! 3 003. 340 21.09' 810 27.41'

! 4 004 340 25.72' 810 12.99'

5 JSC 34 16.80' 81 15.60' 1

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, APPEllDIX II MONTICELLO RESERVOIR VELOCITY MODEL Veloci ty 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 O

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APPENDIX III~

LOCATION OF EVENTS FROM January 1, 1980 - March 31 ,1980 Computer printout of HYP071 showing data for location of events.

Colu=n 1 Date. ' '

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

4 Colu=n 3 Latitude (N) degrees, min. ~

Column 4 Longitude (W) degrees, min.

Colu=n 5 Depth (km).

Coluan 6 Local duration magnitude.

, Colu=n 7 No. of station readings used to locate event.

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

Colu=n 8 Largest a imuchal separation in degrees between stations.

Cole =n 9 Epicentral. distance in km-to necrest station.

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

A _

RMS=[R t /NO, where R is the time residual for a the ith station.

Colu=n 11 Standard error 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 may na: represent actual error limits.

If ERH or ERZ is blank, this means that k cannot be computed, because of insufficient data.

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30 JAN. 01 - MAR. 31 80 DATE ORIGIN LAT N LONG H DEPTH MAG NO GAP DMIN RMS ERH ERZ QM 800107 723 42.21 34-19.57 81-18.70 0.56 0.57 9 129 1.6 0.07 0.3 1.0 B1 800112 1132 51.99 34-19.68 81-18.74 1.59 1.02 9 128 1.6 0.08 0.4 1.1 B1 800117 1113 51.63 34-19.95 81-18.70 1.28 0.82 8 125 1.5 0.05 0.3 0.8 B1 800118 11 9 37.70 34-19.49 81-20.35 0.09 0.21 10 140 4.1 0.06 0.2 0.6 B1 800122 1034 34.20 34-18.58 81-19.69 1.93 1.50 10 146 3.9 0.10 0.4 1.4 B1 800125 132 40.46 34-19.00 81-19.90 1.98 0.51 10 143 3.7 0.06 0.3 0.9 B1 800127 1210 16.68 34-21.26 81-20.69 1.76 1.84 5 147 5.2 0.02 0.3 1.4 Cl 800201 750 57.71 34-17.34 81-18.88 0.79 0.82 9 154 5.1 0.08 0.3 2.0 Cl 800207 253 9.63 34-17.52 81-20.21 1.35 1.21 10 163 5.8 0.06 0.3 2.6 Cl 800208 945 18.89 34-18.92 81-18.66 1.81 1.37 8 135 2.3 0.06 0.3 1.1 B1 800210 1048 14.50 34-20.01 81-19.73 1.78 0.63 10 130 3.1 0.10 0.4 1.4 B1

• 800211 950 27.74 34-20.01 81-29.69 1.80 1.77 10 135 4.5 0.09 0.5 1.6 B1

.800216 957 59.36 34-18.82 81-20.07 2.38 1.18 10 146 4.1 0.04 0.2 0.5 B1 800220 1454 28.95 34-20.18 81-20.84 1.12 1.37 10 134 4.8 0.08 0.4 3.4 B1 800224 641 22.78 34-22.84 81-18.59 1.92 0.57 10 162 5.6 0.06 0.3 1.5 31 800224 643 3.04 34-22.74 81-18.48 2.77 1.09 10 159 5.4 0.07 0.3 0.9 B1 800224 734 31.52 34-22.19 81-18.33 1.65 1.32 9 150 4.3 0.10 0.3 3.1 Cl 800224 926 36.74 34-22.91 81-18.50 1.90 0.99 10 162 5.7 0.05 0.2 1.1 B1 800226 2224 51.42 34-20.17 81-20.34 1.97 0.91 7 131 4.0 0.07 0.5 1.3 B1 800227 112 21.65 34-22.94 81-18.62 0.24 0.63 9 164 5.8 0.05 0.2 0.9 B1 800227 322 11.05 34-19.86 81-20.51 2.00 0.57 10 136 4.3 0.08 0.3 1.2 B1 800304 834 40.40 34-18.63 81-20.05 1.86 1.44 10 148 4.3 0.07 0.3 1.5 B1 800304 855 27.62 34-18.96 81-20.01 5.09 1.32 8 144 3.9 0.11 0.6 1.1 B1 800304 1656 10.49 34-18.57 81-19.75 2.73 1.18 8 174 4.0 0.05 0.3 0.6 B1 800306 1134 57.24 34-20.39 81-19.35 2.00 1.32 8 137 2.6 0.08 0.5 1.2 B1 800306 1154 39.87 34-19.02 81-20.03 1.78 1.54 10 143 3.9 0.06 0.2 1.1 B1 800310 2211 31.39 34-19.65 81-19.29 1.79 2.17 5 131 2.4 0.07 1.1 2.6 Cl 800312 13 7 56.91 34-18.75 81-19.85 0.12 1.77 5 145 3.9 0.05 0.2 1.9 Cl 800317 030 59.52 34-22.90 81-18.80 4.45 0.99 7 164 5.8 0.07 0.6 1.2 B1 800320 19 7 5.91 34-22.74 81-18.68 2.49 1.64 9 160 5.4 0.10 0.6 1.4 B1 800320 1927 51.90 34-22.89 81-19.05 1.93 0.91 10 165 5.9 0.05 0.2 1.1 B1 800321 2056 29.60 34-20.29 81-19.20 0.82 1.18 10 127 1.8 0.04 0.2 0.4 B1 800324 1110 14.33 34-18.38 81-19.93 1.98 0.82 10 150 4.4 0.10 0.5 1.9 B1

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