SCSN Earthquake Commentary

August 31, 2002

Commentary

Filed under: Old Commentary — kate @ 7:06 pm

We had a small swarm in the northern Imperial Valley this morning,
about one mile northeast of Westmorland. The swarm began with a
M2.9 at 7:55 am & culminated with a M3.6 at 9:24 am. There was also
another M2.8 at 9:56 am. The total number of events in the swarm
is probably about 30. The M3.6, at least, was felt in the
Westmorland & Calipatria areas.

August 30, 2002

Commentary

Filed under: Weekly — kate @ 12:00 am

Southern California Earthquakes in the Past Week

Kate Hutton ,

Seismological Laboratory

Lucy Jones,

U. S. Geological Survey

California Institute of Technology

August 30, 2002

The time period covered is 5 pm on Thursday, August 22 (PDT)

through 5 pm on Thursday, August 29 (PDT). During this period

we dectected and analysed 174 earthquakes. Click

here to see a map.

The table below lists the quakes during the past week

that were M2.0 or larger in the central part of the coverage area.

Times are local times; if you want Greenwich Mean Time, add 7 hrs

to the Pacific Daylight Time or 8 hrs to the Pacific Standard Time

listed.


          Mag. Local Date Local Time Lat.      Long.    Depth  Descriptive location

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

 9813485  2.0  2002/08/22 19:29:33 33 28.2 N 116 32.1 W 14.5   16 km (10 mi) SE   of Anza, CA
 9813505  2.0  2002/08/22 21:34:41 32 37.3 N 115 46.7 W  0.0   24 km (15 mi) ESE  of Ocotillo, CA
 9813509  2.2  2002/08/22 21:35:56 32 37.6 N 115 46.8 W  0.1   23 km (15 mi) ESE  of Ocotillo, CA
 9813529  2.9  2002/08/23 00:51:37 33 10.3 N 117 38.8 W 14.4   25 km (15 mi) W    of Oceanside, CA
               FELT in Oceanside area
 9509974  2.2  2002/08/23 01:57:41 35 45.0 N 118 29.2 W  4.7   13 km ( 8 mi) N    of town of Lake Isabella, CA
 9813573  2.5  2002/08/23 01:57:44 35 45.7 N 118 29.1 W  5.6   14 km ( 9 mi) N    of town of Lake Isabella, CA
 9813585  2.2  2002/08/23 02:19:14 34 18.7 N 116 51.8 W  4.5    5 km ( 3 mi) N    of Big Bear City, CA
 9813833  2.3  2002/08/23 14:28:07 32 21.8 N 115 11.9 W  7.0   44 km (27 mi) SE   of Calexico, CA
 9814041  2.2  2002/08/24 02:02:18 33 10.7 N 115 39.1 W  2.4    2 km ( 1 mi) WNW  of Obsidian Butte, CA
 9510062  2.0  2002/08/24 10:44:01 33  7.1 N 116  6.4 W  5.7    4 km ( 2 mi) SE   of Ocotillo Wells, CA
 9814349  2.0  2002/08/25 02:27:40 33 11.8 N 115 34.2 W  3.1    7 km ( 4 mi) SW   of Niland, CA
 9814353  2.4  2002/08/25 02:32:20 35 56.2 N 118 40.7 W 12.2   35 km (21 mi) ESE  of Porterville, CA
 9815313  2.2  2002/08/26 16:35:03 36  2.6 N 118 49.5 W  9.2   18 km (11 mi) ESE  of Porterville, CA
 9815321  2.1  2002/08/26 17:02:13 32 17.1 N 115 15.2 W  7.0   48 km (30 mi) SSE  of Calexico, CA
 9815821  2.1  2002/08/27 11:52:41 34 20.9 N 116 28.0 W  4.5   26 km (16 mi) N    of Yucca Valley, CA
 9816269  2.0  2002/08/28 03:28:26 33 59.6 N 116 56.8 W  9.7    8 km ( 5 mi) NNE  of Beaumont, CA
 9816273  2.0  2002/08/28 03:34:50 34 16.7 N 118 25.9 W 13.1    1 km ( 0 mi) SE   of Pacoima, CA
 9816453  2.6  2002/08/28 08:11:48 35 34.7 N 117 10.1 W  9.4   28 km (17 mi) SE   of Trona, CA
 9816449  2.6  2002/08/28 08:11:48 35 34.7 N 117 10.1 W  5.6   28 km (17 mi) SE   of Trona, CA
 9816497  2.2  2002/08/28 10:14:06 33 59.6 N 116 56.9 W 10.4    8 km ( 5 mi) NNE  of Beaumont, CA
 9816561  2.1  2002/08/28 14:12:49 32 22.7 N 115 14.2 W  7.0   40 km (25 mi) SE   of Calexico, CA
 9816785  2.4  2002/08/29 03:25:11 36 39.7 N 115 38.2 W  0.0   95 km (59 mi) NE   of Shoshone, CA
        -------------------------------------------------------------------------------------------

—————————–7d21e41af4016e–

August 23, 2002

Commentary

Filed under: Old Commentary — kate @ 7:45 am

Two small quakes may have been felt overnight. The first was a M2.9
located offshore 15 miles west of Oceanside, at 12:51 am. The other
was a M2.5 at 1:57 am, located 9 miles north of Lake Isabella.

August 22, 2002

Commentary

Filed under: Weekly — kate @ 12:00 am



Southern California Earthquakes in the Past Week


Nick Scheckel ,

Seismological Laboratory
Lucy Jones,

U. S. Geological Survey
California Institute of Technology

August 22, 2002

The time period covered is 5 pm on Thursday, August 15 (PDT)
through 5 pm on Thursday, August 22 (PDT). During this period
we dectected and analysed 186 earthquakes. Click
here to see a map.

The table below lists the quakes during the past week
that were M2.0 or larger in the central part of the coverage area.
Times are local times; if you want Greenwich Mean Time, add 7 hrs
to the Pacific Daylight Time or 8 hrs to the Pacific Standard Time
listed.

          Mag. PST Date   PST Time  Lat.       Long.    Depth  Descriptive location
-------------------------------------------------------------------------------------------
 9810369  2.2  2002/08/16 18:23:00 33  9.2 N 115 37.1 W  4.5    3 km ( 2 mi) SE   of Obsidian Butte, CA
 9810373  2.0  2002/08/16 18:23:47 33  9.5 N 115 36.3 W  7.0    3 km ( 2 mi) ESE  of Obsidian Butte, CA
 9810421  2.3  2002/08/16 19:10:55 33 49.0 N 116 59.9 W 12.2    8 km ( 5 mi) NNW  of Hemet, CA
 9810485  2.6  2002/08/17 03:11:37 32 17.0 N 115 13.8 W  7.0   50 km (31 mi) SSE  of Calexico, CA
 9810509  2.9  2002/08/17 04:39:52 32 15.9 N 115 16.0 W  7.0   50 km (31 mi) SSE  of Calexico, CA
 9810585  2.5  2002/08/17 05:19:26 32 17.3 N 115 17.8 W  7.0   46 km (29 mi) SSE  of Calexico, CA
 9810661  2.0  2002/08/17 10:09:21 33 14.7 N 116  4.4 W 10.7   11 km ( 7 mi) WSW  of Salton City, CA
 9811301  2.4  2002/08/19 01:26:22 32 39.5 N 115 53.0 W  1.8   13 km ( 8 mi) SE   of Ocotillo, CA
 9811465  2.6  2002/08/19 07:31:43 36  1.0 N 117 48.6 W  2.4   13 km ( 8 mi) ESE  of Coso Junction, CA
 9811497  2.1  2002/08/19 08:57:27 33 17.8 N 116 45.4 W 10.6    6 km ( 4 mi) N    of Lake Henshaw, CA
 9811773  2.0  2002/08/19 22:20:51 34 27.9 N 116 13.8 W  8.7   37 km (23 mi) NNE  of Joshua Tree, CA
 9811889  2.5  2002/08/20 04:37:38 36  3.0 N 117 33.1 W  1.4   35 km (22 mi) NNW  of Trona, CA
 9812393  2.2  2002/08/20 16:10:48 34 18.9 N 116 26.9 W  2.4   22 km (14 mi) N    of Yucca Valley, CA
 9812461  2.0  2002/08/21 00:29:05 33 44.4 N 118  6.8 W 16.6    1 km ( 1 mi) WSW  of Seal Beach, CA
 9812505  2.1  2002/08/21 01:41:36 34 17.6 N 118 44.8 W 11.7    4 km ( 2 mi) WNW  of Simi Valley, CA
 9812973  2.1  2002/08/21 14:07:53 33 29.0 N 116 17.0 W 10.7   21 km (13 mi) WSW  of Mecca, CA
 9813009  2.2  2002/08/21 16:33:06 34  2.0 N 117 14.3 W 15.3    2 km ( 1 mi) SE   of Loma Linda, CA
 9813029  2.2  2002/08/21 18:21:03 36 52.8 N 118 16.1 W 11.6   11 km ( 7 mi) NW   of Independence, CA
 9813385  2.0  2002/08/22 14:51:55 34 45.8 N 116 47.3 W  8.1   26 km (16 mi) ESE  of Barstow, CA
-------------------------------------------------------------------------------------------


August 19, 2002

Commentary

Filed under: Old Commentary — kate @ 1:05 pm

Submitted by Kate Hutton

I’ve had a couple of e-mail inquiries about how exactly a deep teleseism can create “ghost” local earthquakes. There is probably enough general interest that I will take a shot at explaining it.

It happens when the P waves from the teleseism pass through our local network. (Some people may not realize that seismographs are incredibly sensitive & can pick up quakes above about Mw6.0 anywhere in the world. We refer to these as “teleseisms” or distant earthquakes.) Because the Fiji quake was a deep teleseism, the seismogram at each of our stations is relatively “impulsive”, jumps right out of the background noise, like a local earthquake. However, the arrival times are all wrong, so it (the real-time computer) can’t locate it as a local quake. One of the things it tries to do is “split” the arrivals into two or more quakes. It has to know to do that, because we sometimes have more than one local quake in the same minute. This was the result from the first (now called Mw7.5 by NEIC) Fiji quake. Three bogus local quake solutions were generated. All three were judged (again by the real-time computer) to be of poor quality, but two of them were still good enough to get onto the “Recent Eartthquakes” web site. We deleted those when we arrived at work this morning.

When the waves from the second quake came through 7.5 minutes later, there were still some other waves passing through from the first quake, so the arrivals were not as clean & “impulsive”. The real-time system detected the Mw7.7, but did not generated even any poor quality local solutions.

I hope this makes sense. It is the down side of generating earthquake data for the public in near-real time, which I think is generally agreed to be a good thing. The system does a good job about 99% of the time, but not 100%. That’s why we keep checking up on it. If you watch the web page closely, you may notice small quakes that disappear after working hours start. Most of these are actually telemetry (data transmission) noise that happens to (usually poorly) mimic the arrival pattern of a local earthquake. If we changed the software to be more selective, we would end up throwing out a few earthquakes, which we don’t want. Better to just keep an eye on the automatic results & fix them when needed.

Commentary

Filed under: Old Commentary — kate @ 7:20 am

Please note that the two M3+ quakes this morning at 4:12 am are not
accurate. They are our local Seismic Network’s misread on waves
coming in from a pair of deep M7’s in the Fiji Islands (Mw7.4 & Mw7.7). The events have been changed to “teleseisms” in our data
base, but I still need to figure out how to remove them from the web
page. Sorry.

August 16, 2002

Commentary

Filed under: Weekly — kate @ 12:00 am

Southern California Earthquakes in the Past Week

Kate Hutton ,

Seismological Laboratory

Lucy Jones,

U. S. Geological Survey

California Institute of Technology

August 16, 2002

The time period covered is 5 pm on Thursday, August 8 (PDT)

through 5 pm on Thursday, August 15 (PDT). During this period

we dectected and analysed 204 earthquakes. Click

here to see a map.

The table below lists the quakes during the past week

that were M2.0 or larger in the central part of the coverage area.

Times are local times; if you want Greenwich Mean Time, add 7 hrs

to the Pacific Daylight Time or 8 hrs to the Pacific Standard Time

listed.


          Mag. Local Date Local Time Lat.      Long.    Depth  Descriptive location

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

 9807929  2.2  2002/08/09 10:30:49 33  9.9 N 115 39.6 W  8.4    2 km ( 1 mi) WSW  of Obsidian Butte, CA
 9808009  2.0  2002/08/09 16:58:38 32 13.0 N 115 19.1 W  7.0   53 km (33 mi) SSE  of Calexico, CA
 9808025  2.2  2002/08/09 20:08:45 35  0.5 N 118 50.5 W 13.3    9 km ( 6 mi) E    of Wheeler Ridge, CA
 9808089  2.4  2002/08/10 02:58:31 32 13.7 N 115 19.1 W  7.0   52 km (32 mi) SSE  of Calexico, CA
 9808205  2.1  2002/08/10 15:45:04 36  6.3 N 117 51.3 W  2.2   11 km ( 7 mi) NE   of Coso Junction, CA
 9808277  2.1  2002/08/10 20:59:25 33 42.0 N 116 44.6 W 17.2    6 km ( 4 mi) SSW  of Idyllwild, CA
 9808337  2.1  2002/08/10 23:01:34 34 13.0 N 117 24.9 W 14.5    1 km ( 1 mi) WSW  of Devore, CA
 9808421  2.2  2002/08/11 12:22:42 32 27.0 N 116 15.1 W 11.6   40 km (25 mi) SW   of Ocotillo, CA
 9808533  2.8  2002/08/11 22:21:25 32 17.0 N 115  7.2 W  7.0   55 km (34 mi) SE   of Calexico, CA
 9808577  2.0  2002/08/12 04:16:31 35 57.4 N 117 39.8 W  3.7   28 km (17 mi) ESE  of Coso Junction, CA
 9808641  2.2  2002/08/12 07:46:56 34 40.8 N 120 17.1 W  4.9   11 km ( 7 mi) NW   of Buellton, CA
 9808785  2.0  2002/08/12 18:42:31 33 11.2 N 115 36.2 W  2.5    4 km ( 2 mi) ENE  of Obsidian Butte, CA
 9808789  2.0  2002/08/12 19:13:09 32  6.9 N 116 25.0 W  7.0   76 km (47 mi) SE   of San Ysidro, CA
 9808837  3.0  2002/08/13 03:09:49 34 10.0 N 117 26.1 W  7.3    7 km ( 4 mi) N    of Fontana, CA
          FELT in Cajon Pass, Fontana & Rancho Cucamonga
 9808845  2.7  2002/08/13 03:15:04 34 10.0 N 117 26.0 W  3.1    7 km ( 4 mi) N    of Fontana, CA
 9808901  2.4  2002/08/13 03:28:58 34  0.0 N 118 24.0 W 12.4    0 km ( 0 mi) ENE  of Culver City, CA
          FELT in Culver City & Inglewood.
 9808913  2.0  2002/08/13 05:06:03 36 11.4 N 117 59.3 W  5.1   10 km ( 6 mi) S    of Olancha, CA
 9809025  3.1  2002/08/13 11:03:25 35 18.7 N 119 26.8 W 14.3   19 km (12 mi) N    of Taft, CA
          FELT in Taft & Tupman
 9809645  2.5  2002/08/14 18:24:10 34  9.8 N 117 26.6 W  9.8    6 km ( 4 mi) N    of Fontana, CA
 9809785  2.8  2002/08/15 07:57:22 34  5.3 N 117 19.1 W 17.3    3 km ( 2 mi) SW   of San Bernardino, CA
          FELT in San Bernardino, Rancho Cucamonga & Redlands.
        -------------------------------------------------------------------------------------------

August 15, 2002

Commentary

Filed under: Old Commentary — kate @ 8:49 am

A quake this morning at 7:57 am was felt in the San Bernardino,
Rancho Cucamonga & Redlands areas. It was a M2.8, 2 miles southwest
of San Bernardino, close to the San Jacinto fault.

August 13, 2002

Commentary

Filed under: Old Commentary — kate @ 12:51 pm

Oops. The two felt quakes that I submitted to the commentary report
earlier today didn’t make it. They were: a M3.0 at 3:09 am, located
in the Lytle Creek area 4 miles north of Fontana. It was felt in
the Cajon Pass area, Fontana & Rancho Cucamonga. The second one, a
M2.4, occurred a few seconds before 3:29 am, under Culver City. It
was felt in Culver City & Inglewood.

Commentary

Filed under: Old Commentary — kate @ 12:48 pm

A pair of M3.1 quakes happened mid-day today, in different locations.
The first occurred at 10:03 am, 12 miles north of the town of Taft,
in the western San Joaquin Valley. It was felt in Taft itself & in
Tupman.

Another M3.1 occurred at 12:20 pm, in the White Mtns. east of Owens
Valley, 17 miles east-northeast of Big Pine. It had a M2.7
aftershock at 12:23 pm. Due to its remote location, there have been
no “felt reports”.

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