Downtown Los Angeles Tehipite Dome, Kings Canyon National Park Theme Building, Los Angeles International Airport Joshua Tree National Monument Vincent Thomas Bridge, Los Angeles Harbor

Bombay Beach Earthquake Swarm

at 10:00:00AM on 03/24/09

Report by the California Integrated Seismic Network (Caltech/USGS) - Anthony Guarino, Egill Hauksson, Kate Hutton, Ellen Yu, Seismological Laboratory, Caltech, and Bob Dollar, Doug Given, Susan Hough, Ken Hudnut, and Lucy Jones, USGS.

The ShakeMap above displays a maximum intensity (MMI) of V.

An earthquake swarm near Bombay Beach in the Salton Sea area began on March 21st, 2009, with a M1.8 earthquake, located 3km SSE of Bombay Beach. The swarm has continued through today, with the largest event having occurred yesterday morning at 04:55AM PDT, a M4.8 earthquake, located 4km S of Bombay Beach. So far, there have been more than 250 events between M0.8 and M4.8, and the events continue through 3/25/09, despite a five-hour lull in activity from 06:47PDT through 11:41PDT on 3/25/09.

The M4.8 moment tensor solution displays strike-slip motion, with the preferred nodal plane strike of N57E, with an uncertainty of 8 degrees. This is consistent with a fault or faults orthogonal to the San Andreas fault, located in the northern Brawley Seismic Zone. As time has progressed, the events have migrated slightly southeast. Before 2001, there were few events that had occurred in the northern Brawley Seismic Zone. The southern Brawley Seismic Zone is much more active, with events occurring on a regular basis.

From 1932 to 2008, we recorded 722 events within a 5km radius of this current swarm. Most of the historical events recorded within 5 km of the current swarm were portions of earlier Bombay Beach swarms. Historically, the larger events (>M3.0) occurred less frequently, but still total 22. Prior to this sequence, the largest event recorded in this 5km region of Bombay Beach was a M4.2 earthquake. This event occurred on 11/13/99, and was triggered by the Hector Mine Earthquake, which occurred on 10/16/1999. The list of current events for the swarm can be viewed below. We will continue to monitor the area, and post any new information here at SCSN.org.

The Hauksson-Shearer relocations of historical events (in white) display a ladder-type structure in the plan view, with the current sequence at the northwesternmost portion of the zone. These southwest to northeast trending events may be an extension of the Extra fault zone (shown in orange), but is more commonly referred to as the Brawley Seismic Zone.

The latest events are shown as red circles (precisely re-located as of 3/24/09 noon local time by Egill Hauksson of Caltech). The activity occurred near the intersection of the San Andreas fault and the northeastward projection of the Extra fault zone, near the northern end of the Brawley Seismic Zone. This area has been seismically active previously in Oct. 1999 (Hough and Kanamori, 2002) and Nov. 2001. It has also been noted as being potentially significant for future rupture of the southern San Andreas fault (e.g., Hudnut et al., 1989). Active faults are shown in red if they have ruptured historically (the Elmore Ranch fault zone broke in Nov. 1987, and the Coyote Creek fault broke in 1968). Also shown in orange are faults that have been mapped and that have exhibited triggered creep during regional earthquakes. These include the San Andreas fault and Extra fault zone [data of Susanne U. Janecke, unpublished mapping, Kirby 2005 MS thesis, and Kirby et al. (2007).  Additional faults are being mapped.] Other features shown are volcanic centers (orange circles) and various mud pots, carbon dioxide vents (green symbols; from Lynch & Hudnut, 2008).

The image above shows the events which have been re-located using the Hauksson/Shearer method. Note that the events create a linear feature orthogonal to the San Andreas fault.

The following table lists all events M3 and larger that have occurred during this swarm:

#EVID
MAG
YYYY/MM/DD
HH:mm:SS
LAT
LON
Depth
       
Location
14432456
3.1
3/21/2009
13:12:18
33
18.8
N
115
43.8
W
4.7
4
km
(
3
mi)
S of
Bombay Beach, CA
14432496
3.3
3/21/2009
13:17:03
33
18.9
N
115
44
W
4.7
4
km
(
2
mi)
S of
Bombay Beach, CA
14432576
3.1
3/21/2009
13:40:06
33
18.9
N
115
44
W
4.9
4
km
(
2
mi)
S of
Bombay Beach, CA
14433456
4.8
3/24/2009
4:55:43
33
19.1
N
115
43.7
W
5.8
4
km
(
2
mi)
S of
Bombay Beach, CA
14433696
3.1
3/24/2009
6:52:51
33
18.8
N
115
44.2
W
4.2
4
km
(
2
mi)
S of
Bombay Beach, CA
14434264
3.1
3/24/2009
16:43:15
33
18.4
N
115
44.6
W
5
5
km
(
3
mi)
S of
Bombay Beach, CA
14434504
3
3/24/2009
22:50:55
33
17.4
N
115
43.5
W
6
7
km
(
4
mi)
S of
Bombay Beach, CA
14434688
3.6
3/25/2009
0:51:23
33
17.4
N
115
43.3
W
4.4
7
km
(
4
mi)
S of
Bombay Beach, CA
14435296
3.7
3/25/2009
12:59:44
33
17.5
N
115
43.2
W
6.5
7
km
(
4
mi)
S of
Bombay Beach, CA
14435776
4
3/25/2009
20:25:21
33
17.6
N
115
43.3
W
7.4
6
km
(
4
mi)
S of
Bombay Beach, CA
10111842
3.4
3/25/2009
20:25:50
33
18.1
N
115
42.4
W
5
6
km
(
4
mi)
SSE
of Bombay Beach,
CA
14436024
3
3/25/2009
22:12:33
33
17.5
N
115
43.1
W
11
7
km
(
4
mi)
SSE
of Bombay Beach,
CA

The image below shows the relocations plotted using the Hauksson-Shearer method:

 

The graphs above represent the swarm and are color-coded by magnitude:

References:

Hough, S. E., Kanamori, H., Source Properties of Earthquakes near the Salton Sea Triggered by the 16 October 1999 M 7.1 Hector Mine, California, Earthquake Bull. Seis. Soc. Amer. , 92: 1281-1289, 2002. 

Hudnut, K.W., L. Seeber, and J. Pacheco, Cross-fault triggering in the November 1987 Superstition Hills earthquake sequence, southern California,  Geophys. Res. Lett. , v. 16, No.   2, pp. 199-202, 1989

Kirby, S.M., 2005, The Quaternary tectonic and structural evolution of the San Felipe Hills, California, [M.S. Thesis]: Logan, Utah State University, 182 p.

Kirby, S.M., Janecke, S.U., Dorsey, R.J., Housen, B.A., McDougall, K., Langenheim, V., and Steely, A. Jan 2007, Pleistocene Brawley and Ocotillo formations:  Evidence for initial strike-slip deformation along the San Felipe and San Jacinto fault zones, California: Journal of Geology, v. 115, p. 43-62.

Lin, G., P. Shearer and E. Hauksson (2007), Applying a three-dimensional velocity model, waveform cross correlation, and cluster analysis to locate southern California seismicity from 1981 to 2005, J. Geophys. Res., 112, B12309, doi:10.1029/2007JB004986

Lynch, D. K. and K. W. Hudnut, The Wister Mud Pot Lineament: Southeastward Extension or Abandoned Strand of the San Andreas Fault? Bull. Seis. Soc. Amer. , Vol. 98, No. 4, pp. 1720-1729, doi: 10.1785/0120070252, 2008 

 

home | about scsn | earthquakes | stations | data processing | software development

education and outreach | real-time information distribution | faq | contact

 

 

Questions or comments regarding this site may be directed to webmaster-scsn@gps.caltech.edu

The tool below will allow you to search the public SCSN files within this site:

Google
  Web www.scsn.org

Last Updated: 2011-02-28 © Copyright 2004, California Institute of Technology. All Rights Reserved. Permission required to reproduce any portion of this site.