ML20106G242

Seismic Activity Near VC Summer Nuclear Station for Period Jul-Sept,1984, Quarterly Seismic Rept

ML20106G242
Person / Time
Site:	Summer
Issue date:	09/30/1984
From:	Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
Shared Package
ML20106G239	List: ML20106G236 ML20106G242
References
84-3, NUDOCS 8502140289
Download: ML20106G242 (19)

Text

..

4 TECHNICAL REPORT 84-3 SEISMIC ACTIVITY NEAR L

THE V.C. SUMMER NUCLEAR STATION For the Period July - September 1984 h

by Pradeep Talwani Principal investigator Geology Department University of South Caro!!na Columbia, S.C. 29208 Contract No. N355486 hDR DO O O 5

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7 TECHNICAL REPORT 84-3 SEISMIC ACTIVITY NEAR.

THE V.C. -SU)DiER NUCLEAR STATION FOR THE PERIOD JULY - SEPTEMBER

-1984 m u l

+

1 , { .-

' BY '

PRADEEP TALWANI

, . . PRINCIPAL ' INVESTIGATOR 4

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.. ..AND

JILL:RAWLINS:

-.RESEARm. ASSISTANT:

. UNIVERSITY.OF SOUTH' CAROLINA COLUl!BIA,' S .C.' -29208 i -

. CONTRACT NO..N230519 .

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-Introduction This report presents a summary of seismic activity near the V.C. Summer Nuclear Power Station in South Carolina for the three month period between July 1 and September 30, 1984. 'During this reporting period, a total. of twelve locatable events were recorded. None of the events had magnitudes greater than 2.0 and three had magnitudes between 1.0 and 2.0. ' The largest events were of magnitudes 1.5 and occurred on July 20 and September 25.

Seismic Network.

The report is primarily based on data recorded by the four station network operated by S.C.E. and G. and the permanent station JSC. Because of poor records during~ September (Table 1),

the permanent stations 6A and 9A'were used to supplement the data. Locations of the. stations are shown in-Figure:1 and-their coordinates are listed in Appendix I. .

Table 1. Number of days per month station in operation =

Month Station No. of Days July 1 31 2 31 3 28 4 30 August 1 31 2 31 3 0 4 31

- September 1 24 2 10 3 -14 4 17 I

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Data Analysis Locations of the events are determined using HYP071 program' (Lee and Lahr, 1972) and the velocity model given in Appendix II. .The~ event magnitude (ML ) is 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).

An estimate of daily energy release is determined using

-a simplified magnitude (Mg) energy (E) relation by Gutenberg

~

and; Richter (1956).

log 10 E = 11.8 + 1.5 M g Results The -twelve locatable events recorded during this period are listed in Appendix III. There were no events with

- magnitudes greater than 2.0. The three events with magnitudes between 1.0 and 2.0 are listed in Table 2 and the remaining events were small (Mt.< l.0).

Table 2.

Date Magnitude .-

July 20- 1.46 July 27 1.09 September 25 1.52 Most of the seismic activity for'the three month reporting period was confined to within the reservoir in a

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northerly-linear trend. Depth estimates for all located

-events indicate that 75% of the activity occurred within two kilometers of the surface. The deepest event occurred at 3.5 km. A comparison of depth variations based on quality B or better events for the first nine months of 1984 and for the'past-five years is shown in Figure 2. The depth ranges

-were divided into one-half kilometer increments up to 3.0 km, 'and events occurring at greater than 3.0 km were grouped together. The largest percentage.of events occurred in the 1.5 to 2.0 km increment every yea r. None of the A or B quality events 'in 1984 occurred at depths greater than 3.0

'km; . the deepest event was a t -2.9 km.

A cumulative plot of epicenters of events located

- during this period is shown in Figure 3 and a cross section of events located' within one kilometer of line AA' is shown 4

~

in Figure 4. Separation of epicentral locations by month is-shown in Figures 5-7.

Reservoir Water Level and its Comparison 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 variations up to about five feet per day.

L between the maximum and minimum water level. -We have been monitoringLthis water level to see if there is any-correlation between the daily or -seasonal changes in the-m

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6 MONTICELLO EARTHOUAKES JULY - SEPTEMBER 1984 81 "

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9 MONTICELLO EARTHOUAKES AUGUST 1984 81

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11 b reservoir level and the local seismicity. Figure 8 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

.re leased per day are shown on the lower two graphs. The histograms showing events per day and log of energy release include the unlocated events around the reservoir.

Conclusions Seismic activity in the Monticello Reservoir area generally occurs in a long term trend of discrete swarms

. separated by relatively quiet periods. Figure 9 is a histogram of the number of events per month from December, 1977, through September,1984. The low level of seismicity for this three month period is consistent with the previous years trend as again it was preceded by a swarm in the spring. However, the peaks of the swarms have decreased as ,

' has the general level of activity. tlo increase in depth of seismicity was noted during this period, end the spatial extent continued to be confine'd to within the reservoir area.

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

Lee W.H.K. and Lah r , J.C. (1972). A computer program for ,

determining hypocenter, magnitude and first motion pattern of local earthquakes, Revisions of HYP071, U.S.G.S. Open-File Report, 100 pp.

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.WPENDICES w

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APPENDIX I r- ,

h-STATION LOCATION u

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4 N O .' STN. LAT. N. LONG. W.

1 -

001 34' 19.91' 8P 17.74'

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2 002 . 34* 11.'58' 8P .13.81' .

3 003 34' 21.09' 8P '27.41'

-4 004 34' 25.72 8P 12.99' .

5 JSC 34' 16.80' ' 8P 12.09' 6 06A 34' 17.32' 8P. 18.15' t-

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APPENDIX II MONTICELLO RESERVOIR VELOCITY MODEL Velocity Depth km/sec km ,

1.00 0.00 S.40 0.03 5.90 0.18 6.10 0.46 6.30 0.82 ,

8.10 30.00 I

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APPENDIX III DATE RTGIN LAT N LOf4G W CEPTH T9AG tJO G AP 0'41N RilS ERH ERZ Qit 840702 1337 51.}7 34-20.80 61-20 712 32.67 34-19.o7 P1-18. 76 1.40 -0.11 to 141 5.0 0.03 0.1 0 840707 71 1.51 -0.40 8 192 0.3 0 5 B1 C1 8407 0 1723 41.62 33-15.82 81-21.83 1.97 -0.60 8 196 91 57 0.05 0.0a 0.2 24.0 C1 6407 0 1512 22.4a 34-2s. O ot-7.3.6% 1.36 1 to 227 9.2 0.07 0.8 4.8 C1 8407 7 1953 31.86 3u-17 13 41-19 2.43 1.a6

.r 9 to 158 5.2 0.08 0.3 1.0 81 840815 020 0.24 54-19 81-18 60 3.29 -0.24 7 130 1 4 0.05 0.0 0.4 Ct 8408?! est 56.47 14-19.73 R1-18 .21 a6 1.60 -0.40 5 242 '

. 2 0.02 0.5 0.2 C1 840629 11 2 3o.31 34-2c.?d 81-19.77 0.10 -0.60 5 25 3.2 0.02 0.3 0.5 C1 840901 1458 1.83 34-17.73 81-70.83 2.24 -0.60 7 26 6.2 0.03 0.4 0.9 C1 840907 452 10.25 54-20.54 M1-18.47 1.31 0.91 10 20 L. 0.07 0.6 0.6 C1 840907 1C59 35.39 34-20.15 81-18.6o 1.94 -0.86 8 20 L . 0.02 01 0.1 C1 840925 13 6 43.81 34-21.o3 81-19.00 0.76 1.52 jo 243 3. 0.08 0.7 1.1 C1 O

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