From: cowen@jade.ucdavis.edu
Newsgroups: ca.earthquakes,sci.geo.geology
Subject: Weekly Caltech Report, 21 August 1992
Date: 21 Aug 92 23:02:16 GMT
Reply-To: cowen@jade.ucdavis.edu
Followup-To: ca.earthquakes
Organization: Geology Department, University of California, Davis

Here is the text of the Caltech weekly report. It accompanies a postscript
map that I can't or won't re-post because it's a very big file. You can
ftp the text and map from seismo.gps.caltech.edu under successive
directories pub and ca.earthquakes. 
I've edited the text very lightly, but the information is unaffected.

Weekly Earthquake Report for Southern California, August 13 - 19, 1992

By Kate Hutton, Seismological Laboratory (kate@bombay.gps.caltech.edu)
Lucy Jones, U.S. Geological Survey
California Institute of Technology

This document is a commentary on current seismic activity. The earthquakes
discussed have been detected and processed automatically. All epicenters and
magnitudes have been reviewed to exclude obvious blunders; however, they must
still be considered preliminary. For further information, please contact 
the authors or the Caltech Public Relations Office at (818) 356-6326.

			--------------------------------

This week's Report covers the 7 days to midnight Wednesday night, August 19,
Pacific Daylight Time. Aftershocks of the Landers earthquake continue, as 
they will for several months at least. The activity is still so high that we
cannot keep up with the data processing. The map includes a nearly complete 
set of earthquakes of M2.5 or larger, plus many smaller ones that happen to

have made it through the system: 267 in all.
 This week the most significant event was the M5.2 aftershock (of the M6.5 
Big Bear quake) that occurred on Monday afternoon near the town of Big Bear
Lake. It was widely felt, at least as far away as Caltech, but apparently

caused no significant damage.  We received many questions along the lines	of
"Why so large, so late?", which point out the common misconception that
aftershocks always decrease in magnitude. Actually, they generally become 
less frequent with time but still come in a wide range of magnitudes.  
As always, the smaller ones are more frequent. However, it is possible, even
probable, to have decent-sized aftershocks months or years later, especially

after a main shock as large as MS7.5. In fact, given the way this sequence 
has been behaving, there is an 85% chance of another M5.0+ aftershock within

the next year.
 The M3.6 near Cabazon on Saturday night, although it is very close to if 
not on the San Andreas, is in an area that commonly produces earthquakes.  
The same is true of the cluster of M2.0+ quakes near the intersection of the
Banning and San Jacinto faults.
	The Table lists only earthquakes of M2.5 or larger. Times are local times; 
if you want GMT, add 7 hrs. to the PDT listed.

	Table 
	-------
	Date  Time     N Lat.   W Long.   Mag

	-------------------------------------------------------------
         8/13 12:25 am  34  6.9  116 59.2  3.0  9 mi. SE of Running Springs
         8/13  1:14 am  34 37.4  116 39.9  3.3  20 mi. NE of Lucerne Valley
         8/13  2:45 am  34 38.6  116 31.0  3.1  27 mi. ENE of Lucerne Valley
         8/13  8:10 am  35 50.3  117 39.9  2.5  15 mi. N of Ridgecrest
         8/13 10:40 am  34  6.7  116 59.1  2.8  9 mi. SE of Running Springs
         8/13 11:23 am  34  9.0  116 25.2  2.7  2 mi. NNE of Yucca Valley
         8/13 11:45 am  34 37.4  116 39.5  2.5  20 mi. NE of Lucerne Valley
         8/13 12:37 pm  34 37.4  116 40.0  2.6  	"
         8/13 12:53 pm  34 37.1  116 39.6  3.3  	"
         8/13  5:59 pm  34 17.9  116 26.5  2.6  12 mi. N of Yucca Valley
         8/13  6:31 pm  34 13.9  116 51.2  2.9  2 mi. S of Big Bear City
         8/13  8:53 pm  34 59.0  116 56.7  2.6  7 mi. NE of Barstow
         8/14  1:34 am  34 33.7  116 33.3  2.7  23 mi. ENE of Lucerne Valley
         8/14  2:03 am  34 55.8  116 51.5  2.5  9 mi. ENE of Barstow
         8/14  3:50 am  34  6.2  116 26.5  3.2  1 mi. S of Yucca Valley
         8/14  5:21 am  34 36.5  116 37.7  2.5  21 mi. ENE of Lucerne Valley
         8/14  7:43 am  34  5.4  116 22.1  3.9  4 mi. ESE of Yucca Valley
         8/14 10:37 am  32 40.4  115 55.7  2.8  5 mi. SE of Ocotillo
         8/14  3:32 pm  35  8.5  116 50.3  2.6  14 mi. S of Goldstone (dry)

Lake
         8/14  3:37 pm  34 35.0  116 34.0  2.5  23 mi. ENE of Lucerne Valley
         8/14  4:25 pm  34 25.0  116 30.2  3.1  20 mi. N of Yucca Valley
         8/14  4:27 pm  35 50.3  117 40.2  3.5  14 mi. N of Ridgecrest
         8/14  4:38 pm  34 31.7  115 59.6  2.9  27 mi. N of Twentynine Palms
         8/14  5:19 pm  33 55.8  116 18.3  3.4  11 mi. E of Desert Hot 
Springs
         8/14  7:57 pm  34 26.7  116 29.5  3.1  22 mi. N of Yucca Valley
         8/14  9:40 pm  34  8.6  116 25.9  3.0  1 mi. NNE of Yucca Valley
         8/14 11:12 pm  32 41.0  115 55.5  2.9  5 mi. SE of Ocotillo
         8/15 12:07 am  34  5.2  116 24.4  2.5  3 mi. SE of Yucca Valley
         8/15 12:37 am  34 21.5  116 27.3  3.1  16 mi. N of Yucca Valley
         8/15  1:24 am  34  5.3  116 24.3  2.6  3 mi. SE of Yucca Valley
         8/15  1:24 am  34  5.3  116 24.1  4.8  	"
         8/15  1:33 am  34  5.8  116 24.1  2.6  	"
         8/15  1:54 am  34 25.2  116 28.6  3.3  20 mi. N of Yucca Valley
         8/15  2:27 am  34  5.5  116 24.0  3.3  3 mi. SE of Yucca Valley
         8/15  6:16 am  34 23.5  116 27.4  2.5  18 mi. N of Yucca Valley
         8/15  6:34 am  34 58.4  116 57.7  3.0  6 mi. NNE of Barstow
         8/15  8:50 am  34 23.3  116 27.6  2.7  18 mi. N of Yucca Valley
         8/15  9:21 am  34 33.0  116 33.3  2.7  23 mi. ENE of Lucerne Valley
         8/15  9:47 am  34 36.5  116 38.3  3.3  20 mi. ENE of Lucerne Valley
         8/15 10:35 am  34 16.5  116 26.3  2.7  10 mi. N of Yucca Valley
         8/15 11:18 am  34  6.9  116 59.3  3.6  9 mi. SE of Running Springs
         8/15 12:09 pm  34  6.8  116 59.4  3.5  	"
         8/15 12:18 pm  34 31.9  116 32.0  2.8  21 mi. ENE of Lucerne Valley
         8/15  2:35 pm  34  5.4  116 24.6  2.5  2 mi. SE of Yucca Valley
         8/15  2:46 pm  34  6.7  116 59.2  2.5  9 mi. SE of Running Springs
         8/15  3:15 pm  34 36.6  116 39.8  2.8  19 mi. NE of Lucerne Valley
         8/15  7:37 pm  34 34.6  116 35.7  2.6  22 mi. ENE of Lucerne Valley
         8/15 11:15 pm  34 25.2  116 28.6  3.1  20 mi. N of Yucca Valley
         8/15 11:30 pm  34  1.8  116 40.6  3.6  9 mi. NE of Cabazon
         8/16 12:09 am  34 29.6  116 29.8  2.8  26 mi. N of Yucca Valley
         8/16  4:06 am  35 10.3  116 49.2  2.8  13 mi. SSE of Goldstone 
(dry) Lake
         8/16  7:47 am  34  7.8  116 23.9  2.5  2 mi. ENE of Yucca Valley
         8/16  9:08 am  34  6.8  116 59.3  2.5  9 mi. SE of Running Springs
         8/16 11:57 am  34 35.8  116 35.8  2.9  22 mi. ENE of Lucerne Valley
         8/16  8:11 pm  34 33.1  116 31.7  2.5  24 mi. ENE of Lucerne Valley
         8/16  9:20 pm  34 47.2  116 34.9  3.3  26 mi. ESE of Barstow
         8/16 10:04 pm  34 13.2  116 26.0  2.5  7 mi. N of Yucca Valley
         8/17  4:33 am  34 57.7  116 56.9  2.9  6 mi. NE of Barstow
         8/17  5:49 am  34  5.4  116 25.7  3.1  2 mi. SSE of Yucca Valley
         8/17 10:36 am  34 37.6  116 39.7  2.6  20 mi. NE of Lucerne Valley
         8/17 11:20 am  34 30.1  116 30.5  2.5  26 mi. N of Yucca Valley
         8/17 11:24 am  33 47.7  118 34.8  2.5  8 mi. W of Palos Verdes 
Point
         8/17 11:37 am  34  6.7  116 59.7  2.5  8 mi. SE of Running Springs
         8/17 11:39 am  34  7.3  116 23.6  3.4  2 mi. E of Yucca Valley
         8/17  1:17 pm  34  1.9  116 20.7  2.5  8 mi. SE of Yucca Valley
         8/17  1:41 pm  34 11.7  116 51.7  5.2  4 mi. SE of town of Big 
Bear Lake; Felt as far as Pasadena
         8/17  1:44 pm  34 11.6  116 52.8  2.5  	"
         8/17  1:44 pm  34 11.8  116 53.0  2.6  	"
         8/17  1:51 pm  34 11.8  116 51.8  2.5  	"
         8/17  1:55 pm  34 11.9  116 52.5  3.0  	"
         8/17  2:01 pm  34 11.6  116 52.6  3.6  	"
         8/17  2:03 pm  34 12.0  116 52.7  2.5  	"
         8/17  2:06 pm  35  1.3  116 49.9  2.8  14 mi. NE of Barstow
         8/17  2:25 pm  34 11.8  116 52.0  3.2  4 mi. SE of town of Big 
Bear Lake
         8/17  3:04 pm  34  3.1  116 23.0  3.2  5 mi. SE of Yucca Valley
         8/17  3:33 pm  34  3.4  116 23.0  2.6  	"
         8/17  6:13 pm  34 56.1  116 47.1  2.6  13 mi. ENE of Barstow
         8/17  6:19 pm  34  0.3  116 19.9  2.8  10 mi. SE of Yucca Valley
         8/17  7:48 pm  34 11.7  116 52.4  2.9  3 mi. SSE of town of Big 
Bear Lake
         8/17 11:19 pm  34  6.6  116 59.4  2.6  9 mi. SE of Running Springs
         8/17 11:51 pm  34 20.1  116 38.6  2.5  12 mi. ENE of Big Bear City
         8/18 12:26 am  34 15.3  116 26.0  2.6  9 mi. N of Yucca Valley
         8/18  2:46 am  34 11.9  116 51.7  4.0  4 mi. SE of town of Big 
Bear Lake; Felt.
         8/18  4:16 am  33 53.7  116 17.1  2.5  13 mi. NNW of Indio
         8/18  4:37 am  34 22.5  116 27.5  2.7  17 mi. N of Yucca Valley
         8/18  1:33 pm  34 58.5  116 57.5  2.8  7 mi. NNE of Barstow
         8/18  3:35 pm  33 56.0  116 19.9  2.6  9 mi. E of Desert Hot 
Springs
         8/18  6:26 pm  34 15.6  116 43.5  2.8  7 mi. E of Big Bear City
         8/18  7:00 pm  34  5.5  116 25.7  2.7  2 mi. SSE of Yucca Valley
         8/18  7:16 pm  34 21.5  116 28.0  2.5  16 mi. N of Yucca Valley
         8/18  8:10 pm  34 29.8  116 31.1  3.1  26 mi. N of Yucca Valley
         8/18  9:00 pm  34 58.8  116 57.4  2.6  7 mi. NNE of Barstow
         8/18 10:00 pm  34 29.9  116 31.1  2.7  26 mi. N of Yucca Valley
         8/19 12:50 am  34 24.9  116 30.4  3.2  20 mi. N of Yucca Valley
         8/19 12:51 am  34 38.6  116 39.9  2.8  21 mi. NE of Lucerne Valley
         8/19  1:49 am  34  1.8  117  7.7  2.7  3 mi. ESE of Redlands
         8/19  2:45 am  36  2.8  117 35.2  2.9  21 mi. SSW of Panamint 
Springs
         8/19  3:19 am  35  1.2  116 58.5  2.5  9 mi. NNE of Barstow
         8/19  5:04 am  34 59.4  116 57.4  2.8  7 mi. NNE of Barstow
         8/19  5:25 am  34 36.3  116 38.8  2.6  20 mi. ENE of Lucerne 
Valley
         8/19  1:58 pm  34 16.2  116 25.0  2.6  10 mi. N of Yucca Valley
         8/19  3:25 pm  34 56.6  116 52.1  2.5  9 mi. ENE of Barstow
         8/19  4:41 pm  34 37.7  116 35.6  2.6  23 mi. ENE of Lucerne 
Valley
         8/19  4:53 pm  34 10.5  116 48.4  2.7  5 mi. NNE of Mt. 
San Gorgonio
         8/19  4:53 pm  34 22.3  116 27.1  3.0  17 mi. N of Yucca Valley
         8/19 10:45 pm  34 10.3  116 26.3  2.7  3 mi. N of Yucca Valley
	-------------------------------------------------------------
	
Richard Cowen
Newsgroups: ca.earthquakes