ML20029A427

Seismic Activity Near VC Summer Nuclear Station,Jul-Sept 1990.

ML20029A427
Person / Time
Site:	Summer
Issue date:	09/30/1990
From:	Rajendran K, Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
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ML20029A426	List: ML20029A425 ML20029A427
References
90-03, 90-3, NUDOCS 9102220068
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e TECHNICAL REPORT 90 3

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SEISMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD JULY-SEPTEMBER,1990 BY PRADEEP TALWANI Principalinvestigator and Kusala Rajendran

,. Department of geological Sciences l Universtity of South Carolina l Columbia, SC 29208 9102220068 910213

{DR ADOCK 05000395 f'DR

l TECHNICAL REPORT 96 3 O

. SEIBMIC ACTIVITY NEAR THE V.C. SUMMER NUCLEAR STATION FOR THE PERIOD ,

JULY-SEPTEMBER 1990 BY PRADEEP TALWANI PRINCIPAL INVESTIGATOR and KUSALA RAJENDRAN I

DEPARTMENT OF GEOLOGICAL SCIENCES '

UNIVERSITY OF SOUTH CAROLINh COLUMBIA, SC 29208 CONTRACT NO. N536490 l .-

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1 INTRODUCTION Analysis of the seismic activity near the V.C. Summer Nuclear O

Station in South Carolina between July 1 and September 30, 1990,

. is presented in this report. During this period, 23 events were recorded in the vicinity of Monticello Reservoir, sixteen of which were located. The largest shock was of magnitude (M )L 1.5 which occurred on September 15, at 04:01:23.05 UTC.

SEISHIC NETWORK Earthquakes during this period were recorded on stations of Monticello Reservoir and South Carolina networks. The configura-tion of the stations utilized to locate Monticello events is shown in Figure 1 and station coordinates are listed in Appendix I. The operational status of the network in given in Appendix II. During this report period, two of the Monticello stations, 007 and 10 were down most of the time.

DATA ANALYSIS Hypocentral locations of the events have been determined using the computer program HYP071. The velocity model used in earthquake locations is given in Appendix III. The format of the output of HYPO 71 is given in Appendix IV (Lee and Lahr,1972).

The event magnitude was determined from the signal duration at 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 was determined using a l

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O 5KM V Figure 1. Location of Monticello Reservoir area showing seismic stations used in locating seismicity.

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simplified magnitude (M L) -

energy (E) relation by Gutenberg and Richter (1956):

Loggo E = 11.8 + 1.5 Mg.

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- OBSERVED SEISMICITY FOR THE PERIOD JULY-SEPTEMBER 1990 During this period 23 earthquakes were recorded, of which sixteen were located (Appendix V). The other events were within 8.5 km of the station JSC. One event on September 14 was also recorded at station 005 at 02:56329.55 (Appendix VI). Located events were of poor quality (C and D).

i Thirteen events occurred in a swarm on September 14. The l l

largest .- event in - this _ quarter was of magnitude (M L ) 1.5 which I occurred on September 15, following this swarm. This event l occurred in the southern part of the reservoir (Figure 2) . - The spatial distribution of located earthquakes in this swarm is shown in Figure 3. The earthquake sequence (Numbers 1-8 in Figure 3 )

l did not show any definite pattern. However, all of them, except I

the aftershock on September 15 (No 8t in Figure 3) fall in a narrow linear segment.

There were.three additional' events of magnitude >fl.0 in this quarter. One of these occurred on August 01 (00:34:45. 87 UTC)-and the other two during the swarm of September-14-15.

The' seismicity in-this period is comparable to that of the previous quarter, both in number - as well . as in the magnitude range. The:long term decline in seismicity observed in the

' earlier periods is continuing (Figure 4).

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6 MONTICELLO EARTHOUAKES JULY- SEPTEMBER 1990 ,

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. _l5.5 O 34 i . i i i i e i i i i i i 4 0 KILOMETERS 5 I i 1 i t i Figure 2. Earthquakes located near Monticello Reservoir during July- September 1990. Filled circles are earthquakes of magnitude 2 0.0. Open circles are earthquakes of magnitude < 0.0 4

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I-The earthquake sequence during 14-15 September 1990.

l. Figure 3 3 The numbers correspond to the sequence that started on l*

September 34, lisced in Appendix V. Filled circles are earthquakes of magnitude >0.0. Open circles are earthquakes of magnitude <0.0.

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l OORRELATION OF RESERVOIR WATER LEVEL WITH BEISMIOITY I Monticello Reservoir is a pumped storage facility. Ar.y 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 por day between the maximum and minimum water levels. The water level has been monitored to see if there is any correlation between the daily or seasonal changes in the reservoir level and the local seismicity. Water level is compared with seismicity in Figure 5.

The top panel shows the average water level; the error bars show the maximum and minimum water levels each day. The second panel shows the change in average water level from day to day. The number of events per day and the log of the energy released por day are shown in the lower two histograms. These charts include all reported earthquakes listed in Appendices V and VI.

No systematic correlation was observed between the seismicity and the lake level fluctuations. The swarm of activity during

' September 14-15 was not preceded by any significant lake icvel changes.

OONCLUSIONS The level of seismic activity during the third quarter of 1990 was low and comparable to that of the previous quarter. Fifteen of the 23 recorded earthquakes during this quarter occurred over two days (September 14-15). The largest event was of magnitude (ML) 1.5, which occurred on September 15. There were three other events of magnitude ( Mg ) >, 1. 0 .

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182 196 211 226 241 256 271 JULY AUGUST SEPTEMBER Figure 5 Comparison of daily lake level, variation in lake level, number of earthquakes and log of energy release (ergs per day) at Monticello Reservoir. Error bars in the top panel indicate daily fluctuations in lake level, 8

. l REFERENCES Gutenberg, B. and Richter, C.F. (1956). Magnitude and energy of earthquakes, Ann. Geof. 9, 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 HYP071, U.S. Geological Survey, Open-File Report, 100 pp.

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APPENDIX I STATION LOCATIONS NO. STN. LAT. N LONG. W

. 1 JSC 34 16.80' B l* 15.60' 2 001 34* 19.91' 81* 17.74' 3 002 34' 11.58' 81* 13.81' 4 005 34' 16.05' B l* 20.05' 5 007 34* 22.23' 81* 19.50' 6 010 34 20.18' 81* 20.25' 7 09A 34* 17.24' 81' 19.75' e

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i APPENDIE II i

SEISMIC STATION OPERATIONAL STATUS ,

JULY 01-SEPTBNBER 30, 1990

• STATION PERCENT DOWNTIME JSC 3%

001 30%

002 1%

005 25%

007 75%

010 100%

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APPENDIX III i l

MONTICELLO RESERVOIR VELOCITY MODEL 0

- Velocity Depth to top km/sec lan l 1.00 0.00 5.40 0.03 5.90 0.18 6.10 0.46 6.30 C.82 8.10 30.00 2,

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APPENDIX IV MONTICt _s EARTHQUAKE 8 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 betwesn stations.

I Column 9 Epicentral distance in km to nearest station.

l Column 10 error of time residuals in l Root sec. meanRMS squarg/NO,

= R; where R1 is the time l residual for tfie ith station. l Column 11 Standard error of the epicenter in km*.

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

Column 13 Quality of the epicentral location.

• 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,

.bocause of insufficient data.

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APPENDIX Y MONTICELLO EARTNQUhKES l' JULY-SEPTEMBER 1990 DATE. ORIGIN LAT N LONG W DEPTH MAG No GAP DMIN RMS ERH ERZ QM E - 900702 1546 19.79 34-19.69 81-20.30 4.89 0.95 5 275 4.0 0.00 0.0 0.0 C1  !

900705 1431 49.38 34-20.01 81-16.67 1.00 0.21 6 261 1.6 0.18 2.6 7.4 D1 900708 0826 23.17 34-20.01 81-17.84 0.08 -0.40 4 343 0.2 0.36 D1

• 900708 1901 46.62 34-20.01'81-16.74 1.72 -0.40 4 260 1.5 0.10 C1 900710 1223 32.75 34-15.32 81-17.84 2.89 0.01 4 309 4.4 1.11 D1  !

900720~1713 26.02 34-20.92 81-15.52 1.57 0.82 4 308 7.6 0.00 .

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900724 2056 34.39 34-19.15 81-18.11 0.23 0.82-6 283 4.3 0.02 0.4 1.0 C1 1 4

900801.0034 45.87 34-20.93 81-18.28 1.00 1.02 4 353 8.7 0.03 C1 900914 0251 05.22 34-19.66 81-18.05 0.84 1.02 6 300 6.5 0.10 1.4 1.0 D1 900914 0256 28.52 34-15.13 81-16.57 3.56 -0.40 4 262 3.4-0.06 C1

• 900914 0315 59.34 34-17.24 81-17.41 5.80 0.91 5 225 2.9 0.00 0.1 0.0 C1 1 900914 0336'50.69.34-16.42 81-17.20 5.97 0.21 5 173 2.6 0.00 0.1 0.1 C1 900914 0354 16.26 34-19.50 81-17.65 0.90 0.91'6 298 5.9'O.11 0.8 D1z 900914 0528 21.07 34-20.42 81-17.52 0.92 1.18 5 311 7.3 0.07 1.9 D1

- 900915-0401.23.05 34-18.55 81-18.38 0.29 1.54 6 278 5.3 0.05 2.6- D1 900915 0737 39.52 34-20.56 81-19.45 1.00 0.82 3 313 8.4 0.18 C1

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A APPENDIX VI LIST OF EVENTS WITH 8-P q 2.5 BEC RECORDED AROUND

. MONTICELLO DURING 1 JULY 1990 - 30 SEPTEMBER 1990

• DATE STATION P-ARRIVAL TIME S-P EP.DIST DUR MAG H MIN SEC SEC s-p*8.5km SEC 90 09 14 JSC 01 36 24.25 0.10 0.9 5.0 -0.4

" JSC 02 49 07.20 0.10 0.9 3.0 0.9

" JSC 02 36 29.45 0.60 5.1 20.0 0.8 005 29.55 1.00 8.5

" JSC 03 00 25.45 0.10 0.9 5.0 -0.4

" JSC 03 07 22.75 1.00 8.5 10.0 0.2

" JSC 03 36 09.00 1.00 8.5 5.0 -0.4

" JSC 09 09 49.40 0.20 1.7 5.0 -0.4 9

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