ML19316A136

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Rept on Seismic Activity at Lake Jocassee,770601-0831. Oversize Map Encl
ML19316A136
Person / Time
Site: Oconee Duke Energy icon.png
Issue date: 08/31/1977
From: Chiang J, Stevenson D, Talwani P
SOUTH CAROLINA, UNIV. OF, COLUMBIA, SC
To:
References
NUDOCS 7911280670
Download: ML19316A136 (26)


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  • A Report on the Seismic Activity at Lake Jocassee Between June 1, 1977 and August 31, 1977 Pradeep .Talwani, Principal Investigator and Don Stevenson, Jin Chiang, Jeanne Sauber and David Amick Geology Department University of Scuch Carolina
  .               Columbia, S. C. 29208 A
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     .                                                 INTRODUCTION During the reporting period seismicity was monitored at Lake Jocassee.
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Low level (averaging about two events per day), low magnitude (M t 62.0), shallow (Z 44.0 Km) activity was recorded in the vicinity. A week after the reporting period, on September 7, 1977, a magnitude 2.5 earthquake occurred in the middle of the lake. The preliminary results of investi-gations associated with this event have also been incorporated in this J report. SEISMIC STATION DEPLOYMENT o Up to five portable seismographs (Sprengnether MEQ 800 model) were used, together with Duke Power Company's permanent station at SMT. pp The location of sites occupied are listed in Appendix I and are shown in Fig. 2. In identifying the sites in later discussion and in tables, i

;                the location number (first column) is used. The deployment times at various sites are shown in Fig. I. After some repairs SMT vent on line 4

on June 6, 1977. The transmitter circuitry at SNT was damaged by lightning strikes on July 31, 1977 and had to be sent to Sprengnether company in 4 St. Louis for repairs. The station went back on line on September 15, i 1977. The data are sent from SMT to a recorder in the power house. Inspite of the fact that the permanent instrument was installed at SMI nearly six months ago there is no provision to record WWV time code on the seismograms of SMT station. Thus the data obtained are not of much 8- help in locating the events. 3

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1 1 3 Fig. 2 JOCASSEE EARTHOURKES

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MAGNITUCE

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      ,            The seismographs at ODL and PFS were removed at the end of the first week of June 1977 for seismic refraction studies in the Summerville area. They were returned to the Jocassee area in the last week of July.

Electronic problems in the instrument at KTS necessitated its removal in the second week of July. At about this time Duke Power Company purchased two additional seismographs, and these were deployed at ODL and KTS" . RESULTS Events were located by using a computer program, KYP071 (Lee and Lahr, 1972) and a velocity model develped for the Clark Hill reservoir area (Appendix II). The location accuracy is about + 200 m while the depths are usually good to + 400M. In the reporting period, (June 1 - August 31, 1977)l68 events were O recorded. In June when one of the three stations used for locating the events was SMT, (the S-P times were used), the location accuracy deter-iorated considerably. Events between September 1 and 8 have been also added in Appendix III. Of these about 40 events with a RMS error 6 0.05 see and ERH 41 Em were located and are shown in Fig. 2 and are listed in Appendix IV. The activity appears to be concentrated in the middle of the lake. In the period (June 1 - September 8, 19'77) 13 events with magnitude greater than 1 were recorded. The largest was a magnitude 2.5 event on September 7. (Table 1) Figure 3 shows the location of all the located events between November 27, i 1975 and September 8, 1977. Only those events located with an RMS valuef0.05seewereplotted. i' 5 y ,, -, p- w --, ,,,gy- m --m 1 - --- - ,

5 TABLE 1 e LIST OF EVENTS WITII M > 1 L DATE ( 1977) TIME (L'CT) :4

   . 06:17          18:33 06:20                                      1.9 08:30                       1.2 06:24          09:18                       1.3 07:01          19:55 07:19 1.0 00:02                       1.3 07:28          22:36 1.1 08:05          17:56 08:23 1.3 07:34                       1.5 08:31          11:03                       1.5 14:11                       1.6 15:15                       1.1 09:04          02:50                       1.1 10:43                       1.3 09:07          14:41                       2.5

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l l 6 I , Fig. 3 JOCRSSEE ERRTHOURKES ?

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     ,g        In Fig. 4, the seismicity is compared with water level in Lake Jocassee and its fluctuations. These data are plotted on the same time axis for the period June       1977 to Augu=t 31, 1977. Starting at the top are the daily watcr level readings at 8AM (local time).
                                ,                                         The bars indicate the maximum and minimum water level for that day.      In the ordinate, 100 ft. corresponds to a full pond elevation of 1110 ft. a.s.l.

The daily variation of water level (computed for r2ndings at 8AM and plotted midway between them) is shown on the next row. The daily A 4 energy release and the number of events are shown in the two bottom " $ rows. There appears to be no obvious correlation between the seismicity and water level or its fluctuations. ON THE CAUSE OF JOCASSEE EARTHQUAKES The seismic activity around Lake Jocassee - an area generally p8% considered aseismic appears to have been induced by the impoundment of the lake behind the Jocassee dam. Growth of epicentral area, well developed foreshock-after-shock sequences were interpreted as indicating the seismicity to be induced (Taiwani and others,1976.) However the mechanism of how the lake was responsible for the seismicity, if indeed it was, is not well understood. An attempt to do so is made in Fig. 5. The figure shous data over a two year period (January 1975 - August 1977). Each data point represents a 10-day period. From top to bottom: first row shows the average water level in Lake Jocassee over a 10-day period, with the bars indicating the maximum and minimum water level in that 10-day l period. The change in water level between the 10 day mean water levels is l shown in the next row. In order to quantify this change, the area in each segment, below and above the zero (or no change) line was calculated D . _,,_,.----deee

) i 4 8 in arbitrary units. This ' change time' then represents the duration and i i ! amount of change is plotted in the next row. This was compared with the ) total number of events (in 10 day periods), and the times of events with i

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I magnitude greater than 2 were noted. t On comparing the third and fourth rows, we note that, the two i events in January 1976 (M t l 2.0) occurred towards the end of the period of large positive " change time", i.e. the water level in the lake had been going up for over 20 days. Similar causal relationships are suggested by the events in June 1976 and February 1977. However there is a large

            " change time" in August 1976 with anomalous decrease in seismicity.

\ When the change time is compared with the average seismic energy release, (bottom row Fig. 5) we note that there is a possible correlation 1 i with it.(Fig. Sj. s I CONCLUSIONS Low Level seismicity is still continuing and is continuing to be observed. I l i i l l 3 l l l i )

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e t APPENDI.CEs

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AI APPENDI;I I

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STATION LOCATIONS No. Stn. Lat. N. Lonc. W. 1 BL2 34 57.92 82 57.24 2 KTS 34 56.00 82 53.08 < 3 BG3 34 59.58 82 55.90 4 ODL 34 55.82 82 57.26 5 MCS 34 57.12 83 00.45 6 PFS 34 58.50 83 00.29

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A2 , APPENDIX II VELOCITY MODEL " HYP071 was used to locate various events. The crustal model used is Velocity Depth km/see km 5.75 0 6.2 0.5 S.1 30.0 This model was developed for the Clark Hill reservoir - also located on gneissic rocks in the South Carolina Piedmont (Talvani, 1975). 4

A3 APPENDIX III LIST OF EVENTS FROM JUNE I - AUGUST 31, 1977 In column 3 the " station of cax. duration" refers to the location of a station where the recorded duration event was maximum. The station number corresponds to that listed in Appendix I. The maxi =u recorded duration for any event is given in cole =n 4 In column 5 are listed the total number of stations recording the event. The daily energy release is listed in colunn 6. The daily energy is calculated using a simplified magnitude - energy relation (Cutenberg and Richter, 1956), i.e., log E = 11.8 + 1.5 M t 10 where Mg - calculated duration magnitude. For Jocassee (Talwani and others, 1976), M = -1.83 + 2.04 log D L where D = duration of event in seconds. Events with magnitude 2_ 1 are listed in column 7. 1 1 1 1 l

A4 f DATE TI>T ST:i. OF DURATIC: !!O. OF E!ERGY  ?!.>l.0 lux. ST :. '

     -                                                             PER DAY DURATIO:;            REC.         (ERCS)

H:M:S (SEC) EVE:T 770601 04:07:16 2 5 3 08:43:53 3 3' 1 17:31:38 2 15 2 17:45:00 4 5 2 23:39:22 4 2 1 23:50:30 4 3 1 4.89 x 1012 0602 07:01:18

  • 2 5 2 15:30:57 4 5 1 #

15:53:58 4 2 1 , 22:45:45 4 3 1 3.54 x 1011 0603 02:07:32 2 10 4 1 09:20:04 2 3 1 ! 12:14:40 2 8 2 13:14:41 4 3 3 2.02 x 10 ', 0604 10:06:06 4 6 1 2.73 x 1011 j 0605 15:53:36 3 7 3 4.33 x 10 11 0607 04:56:51 2 10 4 17:49:46 3 2 1 1.30X10 - ~ l 0608 11:19:15 3 3 1 { 11:52:37 3 5 1 1.SSX1011 0610 10:55:41 2 7 2 9.47X10 9 i 0611 10:16:23 2 16

3 12
16:26 2 15 3 1X1013 0613 09:41:56 3 5 2 1.5X10 11 0614 22:50:27 2 7 2 4.3SX1011 0616 09:05:23 2 5 2 1.56X10ll 0617 18:38:49 3 71
  '                                                   3     5.25X1014        1.95 0613      05:16:15         3        3        1     3.27X1010 0619      05:16:01         2        4       2      789X1010

! 0620 I -03:50:37 2 31 3 09:16:29 2 1.21 5 3 15:11:40 2 4 1 4.17X1013 0621 18:56:52 2 S 2 6.5SX10 0623 16:39:09 2 7 2 4.3SX10ll

A5 DATE TIME STN. OF DURATION NO. OF ENERGY Mg> 1. 0 MAX. STN. PER DAY DURATION REC. H:M:S (ERCS) (SEC) EVENT

 .      0624   09:18:10      2       36        3 17:26:57      3 1.34 4       1    1.39X1014             -

0625 05:05:56 2 4 1 7.89X1010 0626 13:46:10 3 3 1 19:40:07 2 16 2 5.49X1012 0627 02:42:06 2 5 1 03:27:08 2 15 1 23:49:04 2 3 y, 2 4.69X10 ~ 0630 01:32:47 2 10 2 1.30X1012 , 0701 19:24:48 3 4 1 19:46:23 3 7 2 19:55:25 2 25 2 19:59:06 2 1.02 6 2 2.2X1013 0702 13:40:30 3 3 1 22:19:37 3 5 1 1.88X10ll 0703 10:40:48 3 4 1 7.89X1010 0704 03:49:38 3 2 1 04:41:41 3 4 10 1 8.39X10 0706 03:26:56 3 6 1 07:04:31 3 5 1 14:48:57 3 3 1 4'.67X10ll 0707 11:55:21 3 3 1 3.27X10 10 0710 13:15:13 3 3 1 3.27X1010 0711 16:10:31 3 8 1 6.58X1011 0712 07:44:15 3 7 1 22:42:11 3 11 5 1 7.82X10 l 0716 13:47:28 2 4 3 18:43:55 3 3 2 1.16X1011 0717 07:11:21 4 3 1 - 11:16:22 4 3 1 9.81X10 10 , 0718 04:39:57 3 3 1 3.27X1010 0719 00:02:33 2 36 3 11:03:23 2 2 2 1.89X10 10 0720 00:42:15 3 3 2 3.27X1010 0722 12:31:42 3 2 2 9.47X10 9

A6 DATE TIME STN. OF DURATION NO. OF

     <                                                  ENERGY     M >1.0 MAX.               STN.

t PER DAY DURATION REC. (ERGS) H:M:S (SEC) EVENT 0723 02:36:47 3 3 1 02:38:16 3 2- 1 05:27:24 3 1 1 4.33 x 1010 0724 21:45:32 2 8 2 6.58 x 10 11 0725 00:04:27 3 2 1 00:32:21 '2 3 2 12:01:30 2 2 1 5.16 x 10 10 0727 18:03:31 2 13 4 21:51:26 2 10 4 4.21 x 10 12 0728 22:36:27 2 28 3 3.04 x 10 13 1.12 0731 12:48:37 2 15 5 4.51 x 10 12 0801 17:47:40 3 1 1 21:18:42 3 2 1 1.06 x 10 10 0802 00:34:16 1 4 1 04:45:53 ~1 4 1 04:46:01 1 4 1 04:54:7 1 4 1 14:53:36 3 12 3 2.59 x 1012 - 0803 02:21:30 1 4 4 11:58:49 1 3 1 14:40:33 1 4 3 18:27:12 1 3 1 22:58:22 1 4 , 3 3.20 x 1011 0805 06:22:36 6 3 4 17:56:26 2 26 4 1.34 22:39:30 3 20 4 3.52 x 1013 0806 08:28:01 2 2 1 08:41:06 6 4 1 09:51:20 3 1 1 09:51:36 3 1 1 18:49:17 11 1 5 1 2.46 x 10

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1 ~5 4 5.08 x 1011 l 0808 01:06:00 1 7 5 01:07:16 1 3 3 01:22:14 1 2 1 4.8 x 1011

1 1 a 9 . A7 DATE TIb!E STN. OF DURATION NO. OF ENERGY Pg>1.0 MAX. STN. PER DAY , DURATION REC. (ERCS) H:M:S (SEC) EVENT .i 0809 15:50:47 1 3 1 18:42:09 1 6 2 22:52:03 1 5 1 4.61 x 10 11 0810 00:52:00 1 3 1 4 00:52:26 1 3 1 00:56:50 1 2 1 1.53 x 10 11 i 02:26:09 *1 4 1 02:27:28 1 3 1 02:27:31 1 3 1 06:35:13 3 2 1

  • f 07:53:59 6 4 4 09:41:50 1 3 1 1.86 x 1011 i 0812 01:32:52 4 2 1 j 04:10:31 1 5 5 04:17:33 6 3 5 06:00:49 1 4 2 1 09:16:53 1 2 1 l 19:01:51 1 3 1 3.51 x 10 11 23:10:14 1 3 1 0813 04:43:48 6 6 5
04
52:53 6 4 3 3.51 x 1011 0814 22:29:21 4 3 1 22:32:37 4 4 1 22:33:32 4 2 1 22:33:36 4 2 1 22:52:16 4 3 1 1.63 x 1011 0815 09:42:54 4 4 1 7.89 x 10 10 0816 03:23:27 4 3 2 03:26:25 4 2 2 4.21 x 10 10 0817 12:44:16 2 2 2

, 20:16:55 1 4 1 20:27:16 1 2 1 20:27:48 1 3 1 20:27:54 1 3 1 4.36 x 10 11

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23:17:45 1 6 2 . 0818 02:14:44 1 2 1 9.47 x 10 9 0819 05:32:26 1 3 5 05:36:30 1 5 5 06:13:39 1 3 4 13:18:43 1 4 4 21:27:00 1 3 5 I, 23:58:10 3 2 1 3.42 x 1011 i

                                ' A8 DATE    TIbE   STN. OF   DURATION NO. OF      ENERGY     F >1.0 MAX.                 STN. PER DAY DURATION               REC.      (ERGS)
 .               H:M:S             (SEC)   EVENT 0820 05:11:02    4          3         4 09:19:21    4          1         1     3.38 x 1010 0821 05:31:20    1          4         4   ,

05:46:7 1 3 4 23:04:33 3 2 3 1.21 x 1011 0823 00:39:53 1 2 2 02:23:29 1 2

  • 1 07:34:54 1 41 5 1.46 9.81 x 10 13 16:58:35 1 7 5 23:35:37 1 3 1 3.27 x 1010 15:49:48 3 4 1 7.89 x 1010 0826 22:30:02 1 2 1 9.47 x 109 0827 10:11:57 1 3 1 3.27 x 10 10 0828 16:11:51 1 2 1 9.47 x 10 9 0829 00:53:47 1 2 1 9.47 x 109 0830 20:21:42 2 27 3 2.43 x 1013 0831 11:03:11 2 45 3 1.54 11:51:46 2 6 3 14:11:11 2 48 3 1.60 15:15:54 2 26 4 3.12 x 10 14 1.06

A9 DATE TDE ST'I. OF Dt! RATION NO. OF ENERGY MAX. STN. M[1.0 PER DAY DURATION REC. (ERGS) H:M:S (SEC) EVENT 0901 11:57:50 1 3 4 12:24"59 1 1 2 12:27:41 1 6 5 12:42:52 1 6 4 12:54:48 1 1 2 6.59E11 0903 20:44:18 1 4 4 20:51:02 3 3 2 1.11 Ell 0904 02:48:10 1 8 5 C 02:50:15 1 27 5 1.09 02:54:45 1 1 2 02:57:55 1 3 4 02:59:58 1 10 5 03:03:35 1 1 2 05:10:19 1 8 5 05:12:17 3 2 2 05:20:47 6 4 4 05:21:11 3 2 2 05:22:28 3 1 2 06:35:28 1 13 5 06:45:21 3 2 2 10:43:45 3 34 5 1.29 21:03:36 3 2 1 0906 12:41:20 1 10 5 1.30E12 - 0907 03:53:08 4 4 5 14:41:33 6 143 5 2.56 14:43:34 1 15 5 14:44:10 1 7 5 14:45:13 3 5 5 14:5S:59 1 2 4 15:27:20 1 8 3 15:54:47 2 3 3 16:10:10 1 15 5 16:10:19 1 3 5 16:10:57 1 2 2 16:11:10 3 2 1 16:47:00 1 3 3 t 17:03:19 1 3 3 ! 17:37:20 3 14 5 i 20:13:49 1 7 5 21:20:57 1 4 4 4.37 EIS i 0908 01:17:45 1 2 1 ) 01:28:38 l' 10 4 14:45:56 3 2 1

A10 DATE TIME ST'I. OF DURATION NO. OF ENERGY Mt >1.0 MAX. STN. PER DAY DURATION REC. (ERGS) H:M:S (SEC) EVENT 14:45:56 3 2 1 16:02:54 3 2 1 16:56:37 3 12 2 18:26:02 2 4 3 23:41:55 3 5 1 3.84 E12 e O I f l l l L

4 All APPENDIX IV LOCATION OF EVENTS FROM JUNE 1 - SEPTEMBER 8, 1977 Computer printout of HYP071 showing data for locatien of events. Column 1 Date Column 2 Origin time (UCT) 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 .souare error of time residuals in sec.

RMS = '/ iR ' /NO, where gR is the time residual for the ith station. i 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 assuptions which may not be met in earthquake locations. Therefore standard errors i

may not represent actual error limits. If ERH or ERZ is blank, this means that it cannot be computed, because of insufficient data. 1 l 4

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