Regional Location:

Preliminary Magnitude:

Greenwich Mean Date:
Greenwich Mean Time:
Latitude:
Longitude:
Focal Depth:

WALKER PASS, EASTERN CALIFORNIA

4.1 (SCSN & NCSN)

01/05/017
22:56:45
34.226N:
117.440W
6.8 km

Seismo-Watch Significant Earthquake Reports- No. 01-015
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ISABELLA, CALIFORNIA, May 17, 2001 (Seismo-Watch) -- Preliminary data indicates that an earthquake measuring M4.1 (SCSN / NCSN) occurred at 22:56:45 UTC (3:56 p.m. local time), May 17 about 17 miles southwest of Coso Junction and 26 miles northeast of Isabella in the Southern Sierra, near Walker Pass.

It was the largest of a robust earthquake swarm which has included more than a hundred M1+ quakes in a short six-hour period, five of which were M3s and another was as large as M4.0 (21:53:45 UTC or 2:53 p.m. local time).

Subscribers to the Seismo-Watch EQ Flash! Alert Bulletins system were informed of these earthquakes within minutes of the shaking. You should subscribe to the service too! It's FREE and Fast!

The sequence were centered about 7 miles north of Walker Pass and 6 miles northeast of Canebrake in the upper reaches of Spanish Needle Creek, at Lamont Peak (See a TopoZone Epicentral Map).

The focal point for the M4.1 shock was placed at 8.1 km (5.1 miles) deep. The UC-Berkeley fault plane solution for the largest event (MT M4.1) shows a complex normal dip-slip motion along a northeast trending plane and the solution for the M4.0 temblor is predominantly strike-slip (MT 4.0).

Preliminary reports indicate the quake was widely felt in the Southern Sierra and as far away as Bakersfield and Ridgecrest (See USGS Felt Earthquake Maps: M4.1 and M4.0). We have no reports of light items (such as picture frames, books, etc.) toppling from tables and shelves.

Did you feel this earthquake? .

The sequence began with a M3.0 temblor at about 10 minutes before 1 p.m. local time and progressed at a brisk rate of 10-12 quakes per hour for the next two hours, culminating with the M4.0 at 2:53 p.m.

Seismicity then jumped to a rate of 20 quakes per hour and just a little more than an hour after the first M4 event came another sharp registering M4.1 at 3:56 p.m. Action raced on at the 20 quake per hour rate for the next two hours and dwindled to about 4-7 quakes per hour till the end of this report (see time at the bottom). The last M3 event triggered at 7:28 p.m. and measured M3.0.

(Note: Although there are three local seismic monitoring networks that triggered on the event, (Southern California, Northern California, University of Nevada, Reno), the earthquake sequence was located in a remotely monitored area, therefore, data processing of the smaller events will be a bit slower and seismic rates above may be off slightly pending further review.)

The quake was centered about 9 miles west of the prominent Sierra Frontal Fault Zone an in a region not well mapped for active faults. It appears to be centered north of the Pinyon Fault and perhaps along a northeast extension of the Canebrook Valley Fault, a discontinuous zone of faults which parallel the northeast-trending Canebrook Valley.

While most of Southern California has been going through a relaxed seismic period for the last several weeks and the only source of any significant action has been in the Coso-Isabella area. On April 14 and generally following a M3.8 temblor, a swarm north of Isabella in the Upper Kern Canyon shook with more than 70 events, including a few M3s. The following week and on and off there after, the Coso Volcanic Field at Coso Junction has shaken with dozens of quakes. Today's sequence was essentially centered between of the two sequences and slightly south.

The Walker Pass region is no stranger to earthquakes. On March 15, 1946, a strong M6.3 earthquake sharply jolted the region (see more info).

These were the first M4+ quakes recorded in the Southern California since the Big Bear M5.1 and M4.2 earthquake of February 10 - 15 weeks ago. This is a rather long seicmic gap for M4+ activity.

Additional Seismic information links:

Seismograms of the earthquake series from nearby stations:
Mainstream media news reports:
  • None at this time.
Report update: 9:23 p.m., Thursday, May 17, 2001
Click on the image to see a detailed map.
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