Earthquake Commentary for January, 1999

Map of recent earthquake activity

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18:00 PST, Saturday, January 30

There was a quake felt this afternoon in the Fontana area. It was a M3.6, located 1 miles south of Fontana, and it occurred at 3:24 pm. The focal mechanism was strike-slip. There have been a handful of small aftershocks, the largest one so far a M2.3 at 3:59 pm.

We also recorded a M2.5 at 1:35 pm this afternoon, 7 miles west-northwest of Fillmore.

There was also a M2.9 this morning, at 6:43 am, located 24 miles southwest of Visalia.

The Fontana quake was the only one that was reported felt.

09:36 PST, Friday, January 29

We recorded and analysed 173 earthquakes in the past week. Click here to see a summary and map .

We apologize that we are so far behind in "mentioning" earthquakes. Here are a few: a M2.4 (normally too small to mention, but it was felt) at 4:41 pm last Friday, under Baldwin Hills; a M2.5 at 7:32 pm on Tuesday, 9 miles east-southeast of Coso Junction; a M2.5 at 12:19 pm yesterday, 4 miles west of Valencia. Not much, in other words.

10:58 PST, Monday, January 25

At 2:24 pm yesterday, there was a M2.8 quake in the northeastern San Fernando Valley, 2 miles northwest of Lake View Terrace. This epicenter is at the very far eastern edge of the Northridge aftershock zone.

Following that quake, at 3:58 pm, there was a M3.4 located 4 miles north of Big Bear City. This is the location of the M4.9 Whiskey Springs quake of October 26 last year. Although we haven't had much there in the last month or two, yesterday's event should probably be considered an aftershock. It has a strike-slip focal mechanism.

17:07 PST, Friday, January 22

Today's action included a M3.1 quake located 16 miles north-northwest of Tehachapi. It occurred at 3:50 pm. The focal mechanism was oblique thrust.

Yesterday evening, at 6:18 pm, there was another M2.5 quake 4 miles east of Ocotillo. As far as we know, neither this quake nor the Tehachapi quake was felt by anyone.

18:03 PST, Thursday, January 21

We recorded and analysed 261 earthquakes in the past week. Click here to see a summary and map .

09:17 PST, Thursday, January 21

At 11:52 am and 11:58 am yesterday, there were two small Santa Barbara Channel quakes, M2.6 and M2.7 respectively. As with previous events in this swarm, the epicenters were about 13 miles north of Santa Cruz Island.

At 8:58 pm yesterday evening, there were two small Landers aftershocks, located 16 miles north of Yucca Valley. They were a little more than one minute apart, and had magnitudes of M2.6 and M2.7. As far as we know, none of the quakes just mentioned were felt.

10:41 PST, Wednesday, January 20

There has just been a M3.2 at 10:10 am this morning, located in the Port Hueneme area, 2 miles east of Port Hueneme or 13 miles southeast of Ventura. There have been two other small quakes nearby this month: a M2.5 on January 10th and a M2.7 on January 18th, both of which, surprisingly for their size, were felt. Today's quake was also felt, in the Oxnard area.

09:20 PST, Wednesday, January 20

The only Coso quake of note since yesterday afternoon was a M2.9 at 5:23 am. Like the others, it was located 6 miles east of Coso Junction. There have been 66 automatically located Coso events, including yesterday and today (as of 9:10 am).

In addition, we have had a little more activity 13 miles north of Santa Cruz Island, beneath the Santa Barbara Channel. The largest overnight was M2.9, at 4:09 am, but there were also M2.6's at 12:16 am and 3:54 am, with a total of six automatically located events. We have had a couple of other M2+ quakes at this location earlier this month.

18:03 PST, Tuesday, January 19

Oops, another one! This time the magnitude was M3.6, the time was 4:53 pm, and the epicenter, again, was 6 miles east of Coso Junction. This epicenter is very close, within 1 km, of the epicenter of the earlier M3.3, apparently very close to the boundary between "east" and "east-southeast" of Coso Junction, as some of the descriptive locations are coming out one and some the other. As of 6 pm, there have been 48 quakes that have been automatically located at this particular site today. (The analysts will certainly find more small ones!) What we've seen so far definitely qualifies it as a "Coso swarm", although a small one.

16:19 PST, Tuesday, January 19

At 2:25 pm this afternoon, there was a M3.3 quake in the Coso Range, 6 miles east-northeast of Coso Junction, followed by at least ten smaller aftershocks. As far as we know, the quake was not felt. The Coso area is a very prolific source of quakes, mostly small but occasionally above M5.

09:57 PST, Tuesday, January 19

There was a small Northridge aftershock just after midnight this morning, a M2.5 at 12:44 am. As far as we know, it was not felt.

15:58 PST, Monday, January 18

There have been two quakes of possible interest this afternoon. The first was at 2:12 pm, 3 miles east-southeast of Port Hueneme (which is near Oxnard). The magnitude was M2.7, and it was felt. Last Tuesday, there was a M2.5 at the same location, which was also felt.

The other quake was a M3.0, at 2:52 pm, at the now familiar location 5 miles east-southeast of Ocotillo, at the site of last Wednesday's M4.4 event.

09:20 PST, Monday, January 18

The weekend's activity included a M2.9 at 11:49 am on Saturday, 4 miles east-southeast of Ocotillo. That makes it an aftershock of last Wednesday's M4.4 quake in the same area.

At 2:20 pm on Sunday, there was an unrelated M2.6 located 12 miles south-southeast of El Centro.

Just after midnight this morning, at 12:48 am, central California experienced a M4.3 quake. The epicenter was about 26 miles south-southeast of Hollister. For more information about this and other quakes in northern and central California, visit Menlo Park's web site .

08:27 PST, Friday, January 15

We recorded and analysed 165 earthquakes in the past week. Click here to see a summary and map .

There was a pair of small quakes overnight in the Sierras, 22 miles southwest of Olancha: a M2.7 at 9:48 pm and a M2.5 at 10:26 pm. Because of the isolated area where they occurred, they are unlikely to be reported felt.

08:48 PST, Thursday, January 14

A M3.4 quake occurred offshore last night at 10:44 pm, 13 miles north of Santa Barbara Island, or 29 miles south of Pt. Mugu. Note that there was a M3.9 at nearly the same location on December 18, 1998. Historically, this epicenter is close to that of a small mainshock-aftershock sequence that began with a M5.5 on September 4, 1981. Because of the time lapse, however, the quakes in the past month cannot be considered related to the 1981 series.

08:58 PST, Wednesday, January 13

Western Imperial County saw some action early this morning, the largest ones being a M3.8 at 2:02 am and a M4.4 at 5:20 am. There were more: the M3.8, a M2.5 at 4:03 am, a M2.7 20 seconds later, a M2.3 at 4:15 am, the M4.4, and a M2.3 at 5:23 am followed 23 seconds later by a M3.1. All were located between 3 and 4 miles east of the town of Ocotillo. This area is a common source of small quakes. The M4.4 was reported felt as far away as Ramona.

If you felt it and would like to contribute your observations toward an intensity map, visit the Community Internet Intensity Map site.

We also had another small one in the Santa Barbara channel (see Saturday's update), at 1:12 am. It had a M2.6 magnitude and was located 14 miles north of Santa Cruz Island.

12:58 PST, Tuesday, January 12

At 2:08 am today, there was a M2.5 quake located 3 miles southeast of Port Hueneme, which is near Oxnard. It was small; nevertheless, it was felt by a few local residents.

Here's one that might possibly have been felt, however, even though it was only M2.4: at 5:58 pm yesterday, located 1 mile northwest of Panorama City. This quake was just outside the Northridgs aftershock zone, so probably not an aftershock.

There was also a M2.4 at 8:50 pm in the Big Bear area, 6 miles east-southeast of Big Bear City, part of a small cluster that began yesterday morning with a M2.6 at the same location.

At 10:21 am today, another small quake (M2.6) occurred 15 miles south-southwest of Pt. Arguello, or 57 miles west of Santa Barbara. There have been no indications as yet that it was felt.

09:23 PST, Monday, January 11

There was a M2.9 quake at 7:20 am Sunday, in the Wheeler Ridge area, west of the Grapevine grade. The location was 17 miles west-southwest of Wheeler Ridge. The focal mechanism was thrust. As far as we know, the quake was not felt.

At 5:30 am today, there was a M2.6 quake located 5 miles south-southeast of Big Bear City. Although smaller than Sunday's quake, this one might have been felt because of its location. We have not reveived any reports, however.

13:23 PST, Saturday, January 09

At 4:27 pm yesterday, there was a M2.7 quake under the Santa Barbara Channel, 14 miles north of Santa Cruz Island. As far as we know, it was not felt.

16:27 PST, Thursday, January 07

We recorded and analysed 242 earthquakes in the past week. Click here to see a summary and map .

Our quarterly seismicity summary appears below. The total for 1998 was 11,427 quakes, 149 of which were M3.0 or larger, or, in other words, large enough for someone to easily feel.

Totals listed below apply to the area within a polygon bounded by
the following latitude, longitude pairs:
35.0N, 121.0W; 37.0N, 119.0W; 37.0N, 115.0W; 32.5N, 115.0W; and
32.5N, 121.0W.

1st quarter 2nd quarter 3rd quarter 4th quarter all 3.0+ all 3.0+ all 3.0+ all 3.0+ 1986 3,040 16 2,865 19 6,634 192 2,300 38 1987 1,679 24 1,887 36 2,341 38 5,748 198 1988 2,749 40 2,128 45 2,195 30 2,208 27 1989 2,528 46 2,340 21 2,323 19 2,335 26 1990 2,850 56 2,293 43 1,859 27 2,039 31 1991 1,679 10 1,843 32 2,081 21 2,337 27 1992 3,389 37 10,084 741 25,849 808 9,775 181 1993 4,799 41 5,152 58 5,039 46 4,419 34 1994 10,735 418 5,766 42 5,221 48 4,813 39 1995 3,639 28 3,788 37 8,252 88 7,733 49 1996 5,735 56 3,966 32 3,690 23 4,660 50 1997 3,699 39 3,276 54 3,193 31 2,443 27 1998 3,590 56 2,830 27 2,655 37 2,352 29

Northridge area --------------- 1/17/94 - 12/31/98

All events 14,907 (96 of them this quarter) 3.0 - 3.9 421 (none this quarter) 4.0 - 4.9 52 (none this quarter) 5.0 and up 11 (none this quarter)

Landers/Big Bear area --------------------- 4/23/92 - 12/31/98

All events 70,522 (382 of them this quarter) 3.0 - 3.9 1,657 (2 of them this quarter) 4.0 - 4.9 173 (none this quarter) 5.0 and up 23 (none this quarter) --------------------------------------------------------------------

16:00 PST, Monday, January 04

There have been a few quakes of interest in the past few days, starting with a M2.9 at 3:08 am on the 1st (Friday). It was located 11 miles north-northeast of Ojai. It was followed, at 4:21 am the same morning, by a M3.5, located 15 miles west of Wheeler Ridge. (Later that day, at 12:19 pm, there was another near Ojai, with a M2.3 magnitude.)

Also on the 1st, there was a small series on the western edge of Imperial Valley, 5 miles west-northwest of El Centro: a M3.2 at 11:31 am, a M2.9 at 11:32 am, and a M3.3 at 11:51 am. The two M3+ events were felt in the El Centro area.

At 1:16 am on Saturday, a M2.7 5 miles east-northeast of Big Bear City went unnoticed by the public, as did a M2.5 at 9:05 pm 19 miles northwest of Trona, a M3.2 at 9:37 pm 6 miles east-northeast of Coso Junction, and a M2.8 at 10:42 pm 8 miles east-southeast of Hemet.

On Sunday, at 10:24 am, there was a M3.0 located 25 miles west-southwest of Olancha, in the Sierras. Everything else has been small.

Hopefully, now that the holidays are over, we can get back to some regular commentary on this site.

Last updated 18:00 PST January 30, 1999
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