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== SHAKEOUT SCENARIO PRELIMINARY EARTHQUAKE REPORT ==

                   California Integrated Seismic Network

                          http://www.cisn.org

                     USGS/Caltech/CGS/UCB/UCSD/UNR

 

Version 1: This report supersedes any earlier reports about this event.

 

This is a computer-generated message and has not yet been reviewed by a

seismologist.

 

PRINCIPAL EARTHQUAKE PARAMETERS

______________________________

_

  Magnitude       :   6.7  Ml

 Time                :    15 October 2009   10:15:00 AM PDT

                        :   15 October 2009   18:15:00 UTC

 Coordinates      :   33 deg. 25.2 min. N,  115 deg.  50.4 min. W

Depth                :    6.3 miles (   10 km)

Location Quality  : Excellent

 

                  1 mi.  Coachella Valley, CA

                  5 mi. Bombay Beach, CA

 

 

More Information about this SCENARIO  event and other earthquakes is available at

 

http://earthquake.usgs.gov/eqcenter/eqinthenews/2008/shakeout/

 

ADDITIONAL EARTHQUAKE PARAMETERS

________________________________

rms misfit                   :  0.47 seconds

horizontal location error    :   0.3 km

vertical location error      :   0.6 km

maximum azimuthal gap        :    28 degrees

distance to nearest station  :   6.0 km

event ID                     : 999

 

SOURCE OF INFORMATION/CONTACTS

________________________________

 

CISN Southern California Management Center

 

        Caltech Seismological Laboratory

        U.S. Geological Survey

 

        http://www.cisn.org/scmc.html

 

________________________________

_______________________________________________

Duty mailing list

Duty@scsnmail.gps.caltech.edu

http://unix1.gps.caltech.edu/mailman/listinfo/duty

This new version overlays all of the previous layers plus updated seismicity (thanks again to Egill Hauksson for re-locations and to Duncan Agnew and Bob Dollar for KMZ files). The caption is copied below. The Extra fault zone mapping by Susanne Janecke and others on-land has been augmented with mapping from the offshore work in the Salton Sea by Danny Brothers, Graham Kent and Neal Driscoll of UCSD/Scripps. This work is as-yet-unpublished, and is compiled here along with other data for use in earthquake response, scientific coordination and planning purposes. Please contact Danny Brothers with any questions or requests for additional information about this important new data set - this map was presented at the Fall 2008 AGU meeting (abstract attached below) and has been provided with a request for proper attribution. They are preparing a paper on this, and for now please cite the AGU abstract as follows: Brothers, D., N. Driscoll, G. Kent (2008), New constraints on the tectonic evolution of the Salton Trough, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract T11A-1840 EM: dbrother@ucsd.edu AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0225, United States AU: Driscoll, N EM: ndriscoll@ucsd.edu AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0225, United States AU: Kent, G EM: gkent@ucsd.edu AF: Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0225, United States AB: The Salton Trough is a critical structure where two very different styles of deformation meet; spreading-center dominated deformation to the south in the Gulf of California and dextral strike-slip deformation along the San Andreas fault system(SAF) to the north. Seismic CHIRP data acquired in the Salton Sea provide new constraints on the interaction between the San Andreas, San Jacinto and Imperial fault systems and reveal distinct changes in deformational style from north to south. Based on the stratal geometry observed in CHIRP profiles, we propose three distinct phases of tectonic deformation: (1) Late- Pleistocene transpression north of the Extra Fault Zone (EFZ) replaced by (2) late-Holocene differential subsidence south of the EFZ and (3) recent formation of the Brawley Seismic Zone (BSZ), a through-going crustal shear zone. An angular unconformity is observed to separate the folded and faulted (late?) Pleistocene strata of the Brawley Formation from the overlying Holocene Cahuilla Formation (CF). North of the EFZ reflectors in the CF suggest little to no active deformation. Conversely, south of the EFZ reflectors exhibit marked divergence with their dip systematically increasing with depth. Such a pattern of divergence indicates that the rate of sedimentation has kept pace with the rate of tectonically-induced accommodation. As such, it appears that the EFZ is a tectonic hinge zone delineating the northern limit of active subsidence, high heat flow, and volcanism. Furthermore, given the observed subsidence pattern, we predict the existence of a NE trending basin-bounding normal fault, or series of normal faults, near the southern shoreline of the Salton Sea. In our conceptual model, the early distributed faulting and transrotation between the San Andreas and San Jacinto faults accounts for the compressional folding observed in the Brawley Formation, but later gave way to extension-dominated deformation as significant slip became focused along the Imperial Fault. Reactivation of Miocene extensional structures by the Imperial � San Andreas releasing bend may account for the differential subsidence in the southern sea. In addition, we propose that the BSZ is a young feature similar to through-going shear zones formed in pull-apart basin analog models. We suggest that seismicity patterns in the BSZ do not reflect the dominant tectonic processes or kinematics occurring beneath the Salton Sea, but rather short-term, low magnitude stress release. Finally, we have established a chronostratigraphic framework for the Salton Sea by correlating seismic horizons in the CHIRP data with Lake Cahuilla stratigraphy observed in onshore paleoseismic excavations. The EFZ shows evidence for multiple events during the last ~1,500 years, and the most recent event occurred ~1700 AD, suggesting the potential for coincident ruptures along the SAF and EFZ. Initial estimates suggest that the vertical subsidence rate across the EFZ has been ~ 6 mm/yr for the last 800 years. Modified version of figure caption: The latest events are shown as blue circles (precisely re-located as of 3/26/09 9 a.m. local time by Egill Hauksson of Caltech). In red are the Nov. 2001 sequence events. The latest 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).

Here is a plot that shows the magnitude distribution & rate vs. time plot for the Bombay Bech swarm activity as of this morning. -- Morgan Page

Ken: Here is the NS data from DHL. The gap was caused by the 4.8 event. The burst of low-frequency noise before and after the start of day 82 is from wind: note that this is 1-s data, not the filtered 5-m data we usually show, so the thickness of the trace comes from microseisms; symmetrical spikes are earthquakes, and downward spikes are trains going by. No signal that I can see! Note also that since we couldn't record a coseismic offset, the offset across the gap is just set to zero. I still can't get into the SCEC Response area, but you are welcome to post this and the seismicity KMZ file. Thanks Duncan

it's just the skewness in the time domain (i.e. normalized third-central moment of the moment-rate history). We haven't done any magnitude anomaly detectors for this one yet, but based on experience this swarm would be way beyond 2-sigma in terms of being an anomaly on a standard ETAS transformed-time plot.

I like this way of displaying sequences. I assume it's a time skewness and not a skewness in moment distribution (e.g., relative to a nominal beta value). Have you also plotted the latter?