Earthquake Commentary for July, 2000

Map of recent earthquake activity

Send comments and suggestions

09:17 PDT, Monday, July 31

At 2:01 am on Sunday morning, northern Baja experienced another feelable quake, a M3.4 located 70 miles south of Ocotillo. Insomniacs in Imperial Valley or even San Diego might possibly have felt it.

Two small quakes in the Yucaipa area, 5 miles east-northeast of Yucaipa, occurred a few minutes later: a M2.6 at 2:14 am and a M3.2 at 2:21 am. The larger one was probably felt (guessing from its location and magnitude), but we don't have any reports.

16:25 PDT, Saturday, July 29

A M3.0 quake occurred last night at 8:01 pm, located 13 miles south-southwest of Frazier Park. It is a remote area, and there are few landmarks. It's about 15 miles west of Pyramid Lake. It might have been felt in the Gorman or Frazier Park areas, but we've received no inquiries.

There was also a M2.8 Hector aftershock this morning, at 10:59 am. The epicenter was 39 miles south-southwest of Baker.

17:32 PDT, Thursday, July 27

The week's earthquake list totals 262 this week. Click here to see a summary and map .

09:01 PDT, Wednesday, July 26

There was a M3.8 quake in northern Baja last night at 8:01 pm, located 42 miles south-southeast of Calexico, or 48 miles southwest of Yuma. It could concievably have been felt in southern Imperial Valley, which is why we mention it.

09:06 PDT, Tuesday, July 25

There was a small quake (M2.6) last night at 11:07 pm, located 4 miles southwest of Niland, near Obsidian Butte in the northern Imperial Valley. No-one has reported feeling it.

10:26 PDT, Monday, July 24

Most of the seismic action over the weekend belonged to the Hector sequence. Largest was a M3.5 at 4:56 pm on Sunday, located 38 miles south of Baker. The focal mechanism was strike-slip. There is a small spike in our web hit statistics around that time, so it may have been felt. This quake looks like it actually occurred slightly (about 10 miles) to the east of the Hector aftershock zone. Other Hector aftershocks include a M2.6 at 11:20 am on Saturday (36 miles south-southwest of Baker) and a M2.6 at 11:32 pm on Sunday (34 miles north of Joshua Tree).

There was also a M2.5 quake in San Bernardino Mtns., 6 miles north of Mt. San Gorgonio, at 8:44 am. Due to its small size, it probably was not felt.

17:25 PDT, Thursday, July 20

The week's earthquake list totals 291 this week. Click here to see a summary and map .

12:26 PDT, Wednesday, July 19

All the action overnight was in the Hector aftershocks. The largest was a M3.1 at 6:22 pm last night, located 36 miles south-southwest of Baker.

11:33 PDT, Tuesday, July 18

At 8:57 pm last night, a small quake was felt in the greater Santa Barbara area. The magnitude was M3.4, and the epicenter was located under the Santa Barbara Channel, 16 miles south of Santa Barbara. There were two small aftershocks: a M2.5 at 10:10 pm and another M2.6 at 10:37 pm. The focal mechanism of the M3.4 is strike-slip.

08:23 PDT, Monday, July 17

There was a M3.0 last night at 11:50 pm, located 11 miles south-southwest of Ocotillo, actually in Mexico a few miles south of Inkopah County Park. We have no indications that it was felt.

16:03 PDT, Friday, July 14

A M3.8 Hector aftershock occurred this afternoon at 3:24 pm. The epicenter was 36 miles south-southwest of Baker, at the northern end of the mainshock rupture zone. Most of the other aftershocks of this magnitude have been felt in Barstow and surrounding areas, and this one probably was, too.

08:03 PDT, Friday, July 14

A M2.7 quake occurred this morning at 5:56 am, located 7 miles west-northwest of Castaic Lake dam. This epicenter is a mile or so west of the I5, near the Templin Highway exit. This is well north of the Northridge aftershock zone, so it's not an aftershock. It did, however, have an aftershock of its own: M2.2 at 6:44 am. We've gotten no "felt" reports on either quake.

18:01 PDT, Thursday, July 13

The week's earthquake list totals 395 this week. Click here to see a summary and map .

09:20 PDT, Thursday, July 13

A M2.6 quake occurred yesterday evening, at 8:27 pm, 2 miles north-northwest of Big Bear City.

This morning, at 8:37 am, there was a M3.2 quake 13 miles southwest of Pt. Conception, under the western end of Santa Barbara Channel. Neither of these two quakes generated any phone calls or any significant spike in the web hit statistics.

09:14 PDT, Tuesday, July 11

At 10:02 pm last night, there was a small quake, M2.8, located 15 miles north of Barstow. It was followed at 12:13 am by a M2.6 quake 16 miles southeast of Calexico. The latter quake was actually in Mexico, but it might conceivably have been felt in the Imperial Valley. We got no inquiries about either quake.

15:30 PDT, Monday, July 10

Here are the Quarterly Statistics! We are still not finished with the backlogged Hector aftershocks, so the "+" means that the figure is a minimum number.

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 1999 2,253 35 2,546 58 2,555 36 8,962+ 498+ 2000 5,295 72 4,441 75 --------------------------------------------------------------------

11:02 PDT, Monday, July 10

The main seismic action over the weekend was a swarm along the eastern Sierra front, 3 miles west-northweast of Olancha. This swarm actually started last Friday. The largest events so far have been: a M2.9 at 8:58 pm on Saturday, a M3.4 at 9:02 pm on Saturday, a M3.2 at 6:32 am on Sunday, and a M3.1 at 6:58 am on Sunday. We have had no inquiries. The quakes could easily have been felt in Olancha and Lone Pine, however.

There was also a small event, M2.6, at 1:39 pm on Sunday, located 4 miles east-northeast of Obsidian Butte, in the northern Imperial Valley. It was not felt, either, as far as we know.

11:08 PDT, Friday, July 07

A small Northridge aftershock was just felt in Sylmar a few minutes ago. The magnitude was M2.4, and the location 2 miles northeast of Granada Hills. Time was 10:43 am.

09:31 PDT, Friday, July 07

There was some minor seismic action yesterday evening in southern Owens Valley: a M2.5 at 8:45 pm and a M2.7 at 11:03 pm, both located 3 miles northwest of Olancha, along the eastern front of the Sierra Nevada. There were a few other small ones at the same location, the largest being M2.0. We have gotten no inquiries about any of these quakes.

18:36 PDT, Thursday, July 06

The week's earthquake list totals 285 this week. Click here to see a summary and map .

08:45 PDT, Wednesday, July 05

Seismicity was reasonably quiet over the long weekend. The largest quake was a M2.9 at 7:59 am on Monday morning. It was a Hector aftershock, located 34 miles south-southwest of Baker.

The only quake that was reported felt over the weekend occurred at 3:36 pm on Sunday. It was located 2 miles north-northeast of Granada Hills and had a magnitude of M2.8. The hypocenter was within the aftershock zone of the Northridge quake. Noticable seismicity (felt by the public) has been sporadic at best in the San Fernando Valley in the past few months, however, so it is a little problematic whether or not Sunday's quake should be called an aftershock or not. We normally continue to refer to quakes in such a sequence as aftershocks as long as the seismicity rate (number of quakes per week, month, or whatever) remains higher than what it was prior to the initial activity. Since aftershocks die off slowly, sometimes that is a difficult call. I see a small "blob" of activity in the Valley on every weekly map for the past few months, so my own call would be that the activity is still higher than it was before January 1994; therefore, the quake is an aftershock. Now you know more than you ever wanted to about aftershocks!

A couple of other small quakes occurred also. At 11:36 pm last night, there was a M2.6 located 6 miles east of Desert Hot Springs. Also, there was another Hector aftershock, a M2.8 located 32 miles north of Joshua Tree, at 4:27 am this morning. Neither was reported felt.

This page is
Last updated 09:17 PDT July 31, 2000.