ML19351G258
| ML19351G258 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 12/31/1980 |
| From: | Talwani P SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC |
| To: | |
| Shared Package | |
| ML19351G255 | List: |
| References | |
| 80-4, NUDOCS 8102230364 | |
| Download: ML19351G258 (24) | |
Text
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Technical Report 80-6' SEISitIC ACTIVITY NEAR THE V. C. SUMMER NUCLEAR STATION For the Period
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October - December 1980 '
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by Pradeep Talwani Principal Investigator Geology Department University of South Carolina Columbia, S. C. 29208 l
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Contract No. N230519
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SloR2 3036y
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. INTRCDUCTION This report presents the analysis of seismic data recorded near the V. C. Summer Nuclear Power Station in South Carolina. During the reporting period (October 1 - December 31,1980) shallow microearthquake activity averaged one locatable event every four days. Only one event of magnitude > 2.0 was recorded (12/27/80) for this reporting period.
INSTRUL7 NTATION 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 seismograthic network and a portable digital event detector (station JIM). These seismic stations are shiwn in Figure 1 and listed in Appendix I. '
mTHOD Events were located using a computer program HYP0-71 (Lee and Lahr, 1972) and a 'calocity model developed for the Monticello Reservoir ared (Appendix II). Tb: event magnitudes are calculated frem the signal
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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 10 E = 11.8 + 1.5 Mt
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. __ __ _ . _ . . _ . . . .. _ _ _ _ -.- _ .- _ _ _--~ -- _ -__._ _ .
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RESULTS
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In the reporting period (October 1 - December 31, 1980) 23 locatable
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l . events were recorded. These are listed in Appendix III. Figure 2 shows a
the cumulative events recorded in October, f;ovember and December 1980.
A group of events occurred in a tight cluster on the western edge of
the reservoir with a loose band of events occurring in a general ti-S
direction between Parr and Monticello reservoirs. A cross section, 2.0
.i j miles in width from A to B is shown in Figure 3, showing the shallow I
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(< 3.0.km) character of the events. The monthly locatiens are shown in t Figures 4 - 6. All 1980 located events are shown in Figure 7 with cross
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section taken along C-D (Figure 8). A cumulative (from December 1977 to December 1980) location map is shown in Figure 9. In Figures 2 - 9 4
only events with an RMS of < 0.1 see have been plotted.
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- CoMPisRISON OF SEISMICITY WITH RESERVOIR LEVELS ffonticello 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 dsy between the maximum and minimum
- water levels. Figure 10 shows the corparison of water level to seismicity.
i The top two graphs show the average i ater level and also the change of water
! level per day. The log energy per day and number of events per day are i
shown on the lower graphs.
, During the reporting period, seismic activity and corresponding energy release were <elatively low. This can be observed more clearly
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3 by comparison with the seismic activity and energy release for the
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entire year (Figure 11).
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b-VALUES ine 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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s log e
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IMj - s?!s
- where fig = sum of magnitude of all earthquakes having magnitudes equal to or larger than lis
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s = total number of those earthquakes
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and -
10-bAM n=
1 baM where n = factor for correcting the effort of the length of the magnitude interval AM. bAtt is given in Table 18, p. 388 t (Utsu,1971).
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The b-values for 3 month periods are shown in Figure 12.
l CONCLUSION Low level seismicity has continued to occur at tionticello reservoir.
Comparing the activity of 1980 with that of 1979 there is a marked decrease in frequency of events. 1979 figures show an average of 41 events per month, excluding the October swarm. In 1980, activity has dropped even 4
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4 more with a total of 151 events. Of the 151, 43 occurred in the July swarm. Excluding this July activity the per month frequency rate becomes 9 events. The total number of earthq 'akes of magnitude > 2.0 also decreased in 1980 with a total of 8 (total o f 21 in 1979).
These 1980 and 1979 data together with 1978 data ;rdicate a decrease in the level of seismicity after initial impoundment. This continuing decay in the frequency of seismic acti,ity coupled with the shallow nature seems to suggest further stablization of events at
- 3ther low levels.
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17
. REFERE.VCES Gutenberg, B. and Richter, C. F. (1956). Macnitude and energy of
. earthquakes, Ann. Geof. 9. p. 1-15.
Lee, H. H. K. and Lahr, J. C. (1972) . A computer progran for determining hypocenter, ragnitude and first motion pattern of local earthquakes, Revisions of HYPO 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 l'niv. Series VII (Geophysics), 3, no. 5.
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APPENDIX I
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STATICil LOCATION
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f:0. STN. LAT. N. L0ilG. W.
1 001 34U 19.91' 81 17.74' 2 002 34U 11.58' 81U 13.81' 3 003 34 21.09' 81U 27.41'
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4 004 34 25.72' 81 12.99' 5 JSC 34U 16.80' 810 15.60' 6 JIM 34U 20.21' 81 19.47'
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. APPEllDIX II MONTICELLO RESERVOIR
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VELCCITY 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.I0 30.00
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APPEilDIX III *
. LOCATION OF EVENTS Cc=puter printout of ET?O71 showing data for loca:ica of events.
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Cole == 1 Date.
Colu=n 2 Origin ti=e (UCT) h.=.sec.
Cole =n 3 Latitude (U) degrees, =in.
Column ? Longitude (W) degrees, =in.
Cole =n 5 Depth (k=).
, Cole =n 6 Local duration =agnitude. '
Cole =n 7 No. of s:stion readings used to locate event.
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P and S arrivals frc= sa=e staticas are regarded as 2 readings.
Cole =n S Largest asi=uthal separatica in degrees between stations.
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, Cole =n 9 Epicentral. distance in k= to nearest station.
-Colu=n 10 ,
Root =ean scuare ' error of ti=e residuals in sec.
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RMS =9IRt '/MO, where R is the time residual- for the ith station.
Colu=2. 11 +
Standard error of the epicenter in k= .
Cole =n 12 Standard error of the focal depch in k=* .
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- Statistical interpretation of standard errors involves assumptions which may not bc =ec in earthquake locations. Therefore standard errors
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=ay nc: represent actual error li=its.
- 11 ERH or ER2 i= blank, this =' cans that D: cannot be computed, because of insufficient data. -
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OCTOBER Tli R O U G l! D E C L:!D E R 1930 DATE ORIGI:1 LAT :I LO!!G V DE P Til llAG !!O GAP DIIIII IGIS ERil ER2 Q:1 G01006 1830 54.25 34-17.55 81-18.04 0.20 1.27 7 236 4.7 0.06 1.3 2.0 C1 S01010 1313 11.63 34-19.U5 81-20.98 1.87 0.44 9 139 5.0 0.03 0.4 2.1 C1 301016 20 3 41.70 34-20.02 81-20.11 1.15 0.12 11 132 1.1 0.06 0.3 0.4 61 001017 5 0 21.58 34-16.97 31-20.39 1.90 1.64 10 171 6.G 0.00 0.3 2.5 C1 LO1024 454 21.09 34-20.31 81-19.39 1.00 1.29 12 129 0.7 0.09 0.5 0.5 B1
'301024 548 57.93 34-20.29 G1-19.3S 1.95 -0.40 9 127 0.2 0.0G 0.4 0.4 El S01029 311 24.94 34-20.u4 81-20.28 1.92 ->.11
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9 136 1.5 0.07 0.4 u6 L1 G01029 1240 45.93 34-19.76 81-20.37 0.33 -0.11 11 136 1.u 0.07 0.4 a.9 ni S01029 1245 16.88 34-20.20 G1-20.06 1.40 1.44 10 129 3.6 0.09 0.4 1.7 di LO1031 1338 46.28 34-20.23 L1-20.01 1.78 0.99 8 129 3.5 0.08 0.4 2.4 El 801105 655 5.18 34-17.86 81-20.62 2.41 1.24 9 162 5.8 0.05 0.3 1.1 31 801105 1149 49.95 34-17.35 81-19.79 4. O.73 6 lol 6.5 0.03 0.3 0.8 B1 801106 1046 33.75 34-17.97 81-20.14 1.91 0.44 6 190 5.1 0.04 0.3 1.4 C1 G01107 329 44.16 34-17.45 81-20.60 1.91 0.21 7 167 6.3 0.05 0.3 3.1 C1 S01109 647 1.29 34-20.35 U1-19.33 1.67 0.37 9 123 2.6 0.07 0.4 J.9 U1 801112 2116 55.05 34-19.54 31-19.44 2.59 -0.11 5 2s1 2.7 0.02 0.6 0.3 C1 801113 1531 2.67 34-18.88 01-17.99 1.33 0.7S 7 131 1.9 0.07 0.3 1.4 31 S01210 19 6 12.49 34-25.11 31-23.57 .1.93 0.87 9 228 9.5 0.09 U.6 4.0 C1 001215 59 12.75 34-13.71 81-20.54 1.35 0.87 3 151 4.3 0.u9 0.4 2.2 c1 301226 1 0 43.21 34-20.12 81-20.18 1.79 0.01 3 131 3.8 0.06 0.2 1.0 ul 5b5h 001227 840 27.53 34-19.23 G1-20.97 0.05 2.23 5 147 5.1 0.04 U.5 10.3 J1
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