ML20237H273

Technical Rept 87-2, Seismic Activity Near VC Summer Nuclear Station for Apr-June 1987

ML20237H273
Person / Time
Site:	Summer
Issue date:	06/30/1987
From:	Acree S, Talwani P, Ward C SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
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ML20237H265	List: ML20237H263 ML20237H273
References
87-2, NUDOCS 8708240415
Download: ML20237H273 (17)

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TECHNICAL REPORT 87-2 SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION 4

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.For the Period April - June 1987 By Pradeep Talwani Principal investigator Steve Acree Chris Ward l

Department of Geological Sciences University of South Carolina Columbia, S.C. 29208 Contract No. N449678 kogsaggggggggggg95 R

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TECHNICAL REPORT 87-2' l

SEISMIC ACTIVITY NEAR THE V.C.

SUMMER NUCLEAR STATION FOR THE PERIOD APRIL-JUNE 1987 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR-l STEVE ACREE CHRIS WARD DEPARTMENT OF GEOLOGICAL SCIENCES UNIVERSITY OF SOUTH CAROLINA

COLUMBIA, S.C.

29208 CONTRACT NO. N449678 a

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1 1

INTRODUCTION i

Analysis of the seismic activity near the V.C.

Summer Nuclear Station in South Carolina between April 1 and June 30, o

1987 is presented in this report.

Imring.this period a total of twenty-two events were recorded of which eighteen were located (82%).

The largest shock'was of magnitude 1.1 (April 22-2014 UTC).

Approximately twenty-seven percent (6) of the earthquakes were of magnitudes greater than zero.' Twenty-two percent (4) of the located shocks were of B quality.

All' of the B quality events located at depths less than 2.0 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 (Mg) 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).

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A MONTICELLO RESERVOIR 7

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,JSC STUDY AREA

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

3 An estimate of daily energy release is determined using a simplified magnitude (M ) energy (E) relation by Gutenberg and g

Richter (1956).

log E = 11.8 + 1.5 M 10 g

OBSERVED SEISMICITY FOR THE PERIOD APRIL-JUNE 1987 j

During this period, twenty-two events were recorded, of which eighteen (82%) were located (see Appendix III).

This level of activity was significantly less than that observed during the previous reporting period.

The level of activity continued to decline during this period, consistent with the trend observed in Figure 2.

The largest event of this quarter (M =1.1) occurred on April 22 at 2014 UTC.

This was the only g

event with a magnitude of 1.0 or greater during this period.

Six shocks (27%) were of magnitudes greater than zero.

The epicenters of earthquakes located ourjng this quarter and during each month are presented in Figure 3 and Figures 4, 5,

and 6, respectively.

Spatially, the earthquakes were concentrated beneath the center and western shore of the reservoir.

Temporally, the maiority of the events occurred during late April.

Only four earthquake locations were of quality B or better.

All of these earthquakes located within 2 km of the surface.

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During this period an earthquake of magnitude 2.6 (April 25 I

- 1430 UTC) occurred near Newberry, S.C.

(approximately 20 km west of Monticello Reservoir) and was followed by eight aftershocks

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Figure 3.

Seismic activity at Monticello Reservoir during April - June 1987.

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MONTICELLO EARTHQUAKES APRIL 1987 O

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y 34 16.5' Figure 4 Seismic activity at Monticello Reservoir during April 1987.

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Seismic activity at Monticello Reservoir during May 1987.

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MONTICELLO' EARTHQUAKES AME 1987 P

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Seismic activity at Monticello Reservoir during June 1987.

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with magnitudes.of 0.7 - 1.8.

The activity located within the epicentral area defined by earlier swarms (Rawlins, 1986).

The

largest event (M 2.6) was no greater than events associated with L

these swarms.

CORRELATION OF RESERVOIR WATER LEVEL WITH SEISMICITY 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 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 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.

These charts include both located and unlocated events around the reservoir.

A temporal correlation between the onset of activity in mid-April and a rapid decline in water level below an elevation of 422 ft is noted.

The decline in water level followed a sustained period of levels above 423 ft accompanied by minor daily changes.

The subsequent seismicity was also correlated with a sustained period of daily water level changes greater than ~ 2 ft.

Discernible correlations between seismic activity and the rapidly fluctuating l

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01 111 121 131 141 151 161 171 1g-JUUAN DAY 1987 Figure 7.

Qomparison ofthe median daily lake level and daily change in water level with the number of earthquakes per day and the log of the energy released.

11 lake level at Monticello are relatively rare.

Based on this and the low activity level, the seismicity during April may be unrelated to the observed changes in reservoir level.

CONCLUSIONS The level of activity observed during the second quarter of 1987 was significantly lower than that observed during the first quarter, consistent with the long term decline in seismicity.

Only one event was of a magnitude greater than 1.0 (M =1.1).

Twenty-seven percent of the earthquakes were of magnitudes greater than 0.0.

All of the accurately located shocks were within the upper 2.0 km of the crust.

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 HYPO 71, U.S.

Geological Survey, Open-File Report, 100 pp.

Rawlins, J.

(1986).

Seismotectonics of the Newberry, South Carolina earthquakes, Master's Thesis, Univ. of South Carolina, 68 pp.

8

12 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' r

5 010 34* 20.18' 81* 20.25' 1

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l APPENDIX II MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth to top 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 8

14 APPENDIX III MONTICELLO EARTHQUAKES APRIL - JUNE 1987 HYPO 71 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 Root mean square error of time residuals in sec.

RMS =

R 2 where R is the time residual for tAe/NO, g

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

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15 MONTICELLO EARTHQUAKES APRIL - JUNE 1987 DATE ORIGIN LAT.N LONG W DEPTH MAG NO GAP DMIN RMS ERH ERZ QM 870402 1156 35.64 34-20.03 81-19.64 1.71

--0.60 5 168 1.0 0.02 0.3 0.4 C1_.

870416 613 0.41.34-19.60 81-20.23 0.42

-1.22 5 232 1.1 0.01- 0.3 0.3 C1' 870418~ 835 5,82 34-19.92 81-19,27 1.87

-0,40 7 152 1.6 0.07- 0.5 0.'8 B1

- 870421 -455 37 40 34-22.33 81-18.43 1.97

-0.60 5 253. 1.7 0.08 1.6 2.0 C1 4

I 870422 545,27.71 34-20.28 81-19.11 1.11

-0.24' 7 124. 1.8 0.06 0.3 0.9 B1 870422 2014 32.69 34-20.01 81-18.79 2,41 1.06 7 191 1'.6 0.10 4.4 2.9 D1 870427 1918 21.93 34-18.22 81-20.35 0.32 0.73-6 253~ 3.6 0.04 0.7 0.9 C1-870429 626 20.01 34-19.59 81-19.11 1.00

-1.22 3 168 2.1 0.01 C1 870430- 533 1.69 34-20.27 81-19.60

.1.65

-0.86 4 134 1.0 0.05 C1 870502 2135 44.94 34-20.64 81-17.24 0.44

-0.11 6 210 1.5 0.01 0.1 0.2 C1 870503 1037 55.11 34-19.88 81-18.73 0.06

-1.22 4 144 1.5 0.03 C1 870503 1249 56.03 34-19.87 81-18.72 0.18

-0.24 6 144 1.5 0.04 0.2 0.6 B1 870504.229 40.43 34-19.57 81-20.09 1.65 0.82,9 201 1.1 0.05 0.3 0.6 C1

' 870513 1546 19.80 34-19.94 81-19.51-1.74

-0.60 7 158 1.2 0.02 0.2. 0.2 B1 870617 1354 19.45 34-17.18~ 81-17.68 0.95 0.91 5 209 3.3 0.06 1.0 5.3 D1 870618 4 2 23.95 34-16.39 81-18.86 0.83

-1.22 5 273 5.1 0.03 0.6 60.0 D1 870625 1941 0.68 34-19.90 81-20.40 1.30 0.78 5 303 4.1 0.04 0.2 0.7 C1 870629 1222-1 22 34-19.18 81-19.96 1.57 0.12 5 282 3.7 0.09 0.7 2.0 C1 i

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