Earthquake Commentary for September, 1999

Map of recent earthquake activity

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17:23 PDT, Thursday, September 30

We recorded and analysed 237 earthquakes in the past week. Click here to see a summary and map .

09:56 PDT, Wednesday, September 29

The only quake overnight of any interest (ie. above M2.5) was a M2.8 at 6:47 pm, located 24 miles southwest of Santa Barbara, under the Santa Barbara Channel. As far as we know, it was not felt.

13:38 PDT, Tuesday, September 28

Here's one more: a M2.5 at 6:08 this morning, located 8 miles east-southeast of Coso Junction.

11:02 PDT, Tuesday, September 28

There were a few more small ones yesterday and today: a M2.5 at 1:36 pm on Monday, 3 miles north of Yucca Valley; a M2.5 at 11:02 pm Monday, 2 miles south-southeast of Big Bear City and felt by a local resident; and a M2.6 at 12:24 am today, 23 miles northeast of Lucerne Valley.

09:54 PDT, Monday, September 27

In addition to the above mentioned M2.9, there was some other activity over the weekend. The most notable was a pair of M4+ events over the border into Nevada: a M4.7 at 9:25 am and a M4.1 at 1:11 pm yesterday (Sunday). These events were 58 miles north of Stovepipe Wells, or 74 miles east of Bishop. They are aftershocks of a M6.0 that occurred on August 1. They may or may not be in our coverage area; however, the events in August were not reported to the map web page by anyone, so we are taking the liberty of doing so.

At 6:18 pm on Friday, there was another quake 8 miles southeast of Olancha, this time M3.0.

At 11:08 pm, also on Friday, there was a M3.3 in Mexico, 56 miles south-southwest of Calexico. Because of the distance, it probably was not felt in the U.S., but it is possible.

At 12:49 am on Saturday, there was a M2.6, located 10 miles east of Coso Junction.

Then, at 6:12 am on Saturday, there was a quake closer to Imperial Valley, only 11 miles south of Calexico. The magnitude this time was M2.9.

Believe it or not, as far as we know, none of the quakes this weekend were felt, except for the San Fernando M2.9.

09:26 PDT, Sunday, September 26

A Northridge aftershock that was felt occurred last night at 11:57 pm. The epicenter was 2 miles north-northeast of San Fernando, and the magnitude was M2.9. There were a couple of tiny foreshocks: a M1.6 at 11:46 pm and a M1.4 at 11:50 pm.

08:12 PDT, Friday, September 24

There has been some activity overnight in the southern Owens Valley, 8 miles southeast of Olancha, or a couple of miles east of the Haiwee Reservoir. The largest event was a M3.3 at 8:42 pm yesterday. There were a few small foreshocks, and a dozen or so small aftershocks so far. The largest aftershocks were a M2.8 at 7:21 am and a M2.5 at 7:26 am this morning. We have not had any "felt" reports on any of these quakes.

17:20 PDT, Thursday, September 23

We recorded and analysed 203 earthquakes in the past week. Click here to see a summary and map .

10:33 PDT, Monday, September 20

The largest quake in our area over the weekend occurred at 12:02 am this morning. The epicenter was 4 miles north of Big Bear City, and the magnitude was M4.2. It was felt in the Big Bear and Apple Valley areas, plus San Bernardino and Palm Springs. There was an aftershock of approximately M2.6 magnitude a few minutes later, at 12:05 am. This morning's quake might be considered a late Landers/Big Bear aftershock, except for the fact that the Big Bear section of that sequence has been pretty much "dead" for the last several years. In that circumstance, it is basically impossible to tell if a single quake is an aftershock or an unrelated "background" quake.

At 11:19 am on Sunday, there was a M2.5, located is the southern Owens Valley area, 8 miles southeast of Olancha. It was not reported felt.

At 6:38 am on Saturday, there was a M3.0 quake in the Imperial Valley, 7 miles east-southeast of El Centro, near the Imperial fault. This is close to the location of a small cluster that was going on on Friday morning. Saturday's event was the largest event in the cluster. It was not felt either, as far as we know.

11:20 PDT, Friday, September 17

There is a small cluster of earthquakes going on in the Imperial Valley this morning. There have been five so far, with the largest having a magnitude of M2.5, at 10:09 am. These quakes are located 7 miles east of El Centro, near the Imperial fault.

17:32 PDT, Thursday, September 16

We recorded and analysed 241 earthquakes in the past week. Click here to see a summary and map .

11:07 PDT, Thursday, September 16

The small swarm 3 miles east-southeast of Coso Junction produced its largest quake so far, a M3.6, at 8:02 pm last night. Since the epicenter is not far from Inyokern, Ridgecrest, and the China Lake Naval Weapons Station, the quake was probably felt, but we have received no reports. Another M3.1 occurred at the same location at 10:39 am today.

Closer to the towns mentioned above, there was an unrelated M2.4 at 5:29 am this morning, located 12 miles north of Ridgecrest.

09:48 PDT, Wednesday, September 15

Another quake, M2.9, occurred 3 miles east-southeast of Coso Junction at 10:20 pm last night. It was not reported felt.

14:07 PDT, Tuesday, September 14

The largest quake in our area overnight was a M3.2 at 4:57 am, located 3 miles east-southeast of Coso Junction. Also of possible interest: at 12:47 am there was a M2.5 Landers aftershock, located 26 miles north of Yucca Valley, and at 8:45 am today, there was a M2.5 aftershock of Saturday's Desert Hot Springs quake. We have received no "felt" reports on any of these quakes.

13:19 PDT, Monday, September 13

Since the Desert Hot Springs quake on Saturday (whose magnitude has now been revised to M3.2), there have been two more quakes of slight interest: a M2.6 at 7:45 pm on Saturday, 4 miles south-southwest of Idyllwild, and a M2.5 at 6:18 am on Sunday, located 7 miles north of the town of Lake Isabella. Neither of these was felt.

19:12 PDT, Saturday, September 11

There was a M3.1 quake early this evening, at 6:21 pm, located 8 miles east-southeast of Desert Hot Springs.

10:14 PDT, Friday, September 10

A M4.9 quake occurred this morning at 6:40 am, located in Mexico, 35 miles south-southeast of Calexico. It was slightly felt in the Imperial Valley area and in Yuma. Note that this epicenter is not the same as all the recent activity 45 miles south of Yuma.

17:19 PDT, Thursday, September 09

We recorded and analysed 162 earthquakes in the past week. Click here to see a summary and map .

12:03 PDT, Tuesday, September 07

Aside from a few more quakes 45 miles south of Yuma (a M3.0 at 6:17 pm on Saturday and a M3.0 at 6:28 pm on Sunday), the only quake of interest was a M3.4 at 9:42 am today, located 11 miles east-northeast of Borrego Springs (just east of Clark Dry Lake). This morning's quake took place in the complex San Jacinto fault zone and had a strike-slip focal mechanism, although the strike was somewhat more east-west (or north-south, depending on which plane you choose!) than the mapped fault traces are.

16:14 PDT, Friday, September 03

There were two more quakes of interest this afternoon. The first, at 12:49 pm, was a M2.8 located near Walker Pass in the southern Sierras, 20 miles south-southwest of Coso Junction. The second was a M3.7 at 2:10 pm, located 12 miles southwest of Ocotillo, near Jacumba, with a strike-slip focal mechanism. We have received no "felt" reports for either quake.

09:38 PDT, Friday, September 03

The largest quake in the area overnight was a M3.0 at 11:35 pm, located 8 miles north of the town of Lake Isabella. This is the same location where a small group of M2+ quakes occurred the night before.

Also perhaps of interest was a M2.5 quake at 3:27 am today, located 4 miles northwest of Palomar Observatory, in San Diego County.

We have no reports of either quake being felt, but the Lake Isabella quake could easily have been felt.

17:14 PDT, Thursday, September 02

We recorded and analysed 222 earthquakes in the past week. Click here to see a summary and map .

10:44 PDT, Thursday, September 02

We recorded a few quakes overnight in the Tehachapi Mountains area, 6 to 8 miles north of the town of Lake Isabella. These quakes were: a M2.5 at 5:54 pm, a M2.6 at 9:11 pm, and a M2.7 at 10:21 am this morning. None have been reported felt.

This page is Last updated 17:23 PDT September 30, 1999.