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UNAVCO Geophysical Event Response to the Mw=7.2 El Mayor-Cucapah Baja California, Mexico, Earthquake April 4, 2010

A magnitude 7.2 earthquake occurred at 3:40 p.m. PT on Sunday, April 4th, 2010, 39 miles (63 km) SSE of Calexico, CA, in the upper Baja California peninsula of Mexico. Tremors lasted 40 seconds causing extensive damage to buildings in the area. The earthquake has been named the El Mayor-Cucapah earthquake.

Community Response

The UNAVCO community has been analyzing incoming data and coordinating a response accordingly. Event response coordinator is Chris Walls, wallsunavco.org.

UNAVCO Community Geophysical Event Response Web page

Event Response Forum - community communication and coordination. Check in here for links to relevant data sets including GPS, Strainmeter, Seismic, and InSAR.

Supersite Web Page (for latest InSAR and other data & maps).

GPS Data: UNAVCO has downloaded and archived 5 Hz data from all Plate Boundary Observatory GPS stations with 97% data completeness within 200 km of the northern end of the April 4, 2010 El Mayor-Cucapah earthquake rupture. The time period covered is from April 2 - 6.
5 Hz data is available via anonymous FTP at:
ftp://data-out.unavco.org/pub/highrate/rinex/2010/, organized by day-of-year and by site ID.
1 Hz data is available from the California Real Time Network (CRTN) which includes many PBO stations and real-time SCIGN stations via FTP: ftp://sopac-ftp.ucsd.edu/pub/highrate/cache/rinex/2010

USGS: has a good general web page on the earthquake including location details, a shakemap, a maps aftershocks, and tectonics.

SCSN: the Southern California portion of the California Integrated Seismic Network (CISN) has a tremendous amount of nicely organized and detailed inrformation on this earthquake including updates on and maps of aftershocks, photos, and a map showing feedback from ~75,000 people on "Did you feel it?"

SCEC: the Southern California Earthquake Center forum has up-to-the-minute postings from on field observations, incoming data, models, and more. Email response@scec.org to request an individual user/password to access their forum.

GPS Explorer: JPL and Scripps maintain a data portal for higher order CGPS products and time series modeling. (login: guest, password: guest) The California Real Time Network (CRTN) of continuous GPS stations collected 1 Hz RINEX files during the event. On-the-fly 1 Hz relative displacements were computed in 9 sub-networks with overlapping stations. These were combined in a network adjustment to produce 1 Hz total displacement waveforms over the entire network (waveforms, plots), a movie of 1 Hz displacements, and rapid coseismic horizontal displacements (values, map). Be sure to watch the movie of 1 Hz displacements.

Long baseline strainmeter plots: these instruments are called ‘‘longbase’’ sensors because they produce high-quality data by measuring strain over distances of hundreds of meters at the surface of the Earth. Plots by Frank Wyatt and William Hatfield at UCSD. Go to their home page for more details.

Coseismic interferograms by Yuri Fialko at IGPP & SCRIPPS, UCSD.

Photos of liquifaction and other features by Yuri Fialko at at IGPP & SCRIPPS, UCSD.

Recent Results from the Community

See Figures. Additional information for certain figures is provided below.

Figure 2 - Interferogram based on ALOS PALSAR acquisitions.  Interpretation of interferograms over the northern end of the rupture reveals a combination of right-lateral strike slip motion and east side down normal faulting in agreement with field observations of the fault scarp.  The most recent interferogram collected on April 17 along an ascending T211 shows the southwest end of the rupture.  More importantly, it reveals the boundaries of the liquefaction zone in the agricultural areas southeast of the fault zone.  

This zone of liquefaction is bounded on the east by the Cerro Prieto fault and on the west by the Laguna Salada fault.  The zone is 18 kilometers wide and 60 km long.  Field observations show that the roads have undulations with vertical amplitudes of 20-50 cm and many of the concrete lined aqueducts are fractured.  There is a sharp line of deformation along the Cerro Prieto fault that could represent either triggered slip or localized subsidence.  Note that the Cerro Prieto fault passes directly beneath the Cerro Prieto geothermal power plant which is the largest in the world with 720 megawatts.   The data were processed by Matt Wei and David Sandwell at IGPP/SCRIPPS using GMSTAR. One fringe (color cycle) is 11.6 cm of line of sight deformation. Link to the KMZ file.

Figure 4 - Surface Rupture Along Fault was observed on April 6th, when scientists from the USGS, CICESE, SDSU, and Caltech Seismological Lab took a helicopter flight to make observations and take photos. Figure 4 shows the surface rupture across a highway along the Borrego fault. The group estimated that the total slip vector length was 2.5 m +- 0.75 m of oblique slip with dominantly east-down motion and also a significant component of right-lateral motion.

The initial interpretation was that the rupture process likely began on Pescadores fault (aligned N40°W from the epicenter), paused, and then a larger rupture along the Borrego fault was then triggered. The group also observed liquefaction-related features along canal-levees, widespread shattering along levee crusts, and minor flooding, ground failure or cracking, and sand blows. (John Fletcher and Javier Gonzalez-Garciaat CICESE, Tom Rockwell at SDSU, Ken Hudnut at the USGS, and Anthony Guarino at Caltech Seismological Lab). For more fantastic photos, go to the SCEC forum. (You need a username and password for access. Email response@scec.org).

Figure 6 - Plot of 1 Hz real-time GPS total displacement waveforms versus broadband seismic velocities at co-located GPS (PIN1 and P494) and broadband seismic stations (PFO and WES) by Yehuda Bock at UCSD and Sharon Kedar at JPL. The plot shows that the real-time GPS did not clip, while broadband seismic stations did for this earthquake, even at Pinon Flat Observatory, at about 180 km from the epicenter. These examples demonstrate the power of real-time high-rate data from a regional CGPS network during a medium to large earthquake: they measure displacements directly, they do not clip and they are also able to detect the permanent (coseismic) deformation. Go to GPS Explorer for more plots, maps, and other information.

Tectonic Setting

The magnitude 7.2 northern Baja California earthquake of Sunday, April 4th, 2010, occurred approximately 40 miles south of the Mexico-USA border at shallow depth near the principal plate boundary between the North American and Pacific plates. This is an area with a high level of historical seismicity, though this is the largest event to strike in this area since 1892.

The plate boundary in northern Baja California represents transition zone from the ridge-transform boundary in the Gulf of California to the continental transform boundary in the Salton Trough.  Most of the active faults in this area are northwest-trending right-lateral strike-slip faults that are separated by transtensional basins.  The April 4 main-shock occurred along a strike-slip segment that coincides with the southeastern part of the Laguna Salada fault, though this has not yet been confirmed by observations. It seems that the rupture occurred directionally, propagating towards the northwest along strike with the Elsinore fault in the United States. Aftershocks appear to extend in both directions along this fault system from the epicenter of the main event, with the largest aftershock measuring M 5.7.

Faulting in this area is complex and there are several examples of historical earthquakes. The area is somewhat unique in terms of strain partitioning and in the fact that the fault system is quite young. The 1892 surface rupture occurred along the Laguna Salada fault system, but significantly northwest of the April 4 epicenter. It produced a complex rupture that left the Laguna Salada fault, which was almost perfectly oblique, with striations and offsets indicating ~45 degree rake, parallel to the intersection of the two faults that were activated. The rupture then bent abruptly southward onto the Canon Rojo normal fault, where slip was almost perfectly dip slip (Mueller & Rockwell, 1991, 1995).

The scarp from 1892 on the Canon Rojo fault connects southward to a series of curving scarps along the east side of Laguna Salada that may represent an active low-angle normal fault (Axen et al., 1999). However, evidence from the southernmost reaches of those scarps that suggest that the master fault there steepens with depth at its southern end (Fletcher and Spelz, 2009). Just to the east are the Cerro Prieto fault and active spreading center south of Mexicali.

The area is therefore unique in both its long- and short-term strain partitioning. Also, the aftershocks have filled in all the way to the Yuha Desert, which is a complex discontinuity in the overall dextral part of the fault system where the Laguna Salada fault connects through to the southern Elsinore. Both faults are relatively young (the Elsinore fault near Vallecito is only ~900 ka old), so we are "seeing" the evolution of a youthful system in action.

The 1940 Imperial Valley earthquake, which approached M 7, occurred farther to the north on the Imperial fault. Both the 1892 and 1940 earthquakes were associated with extensive surface faulting. An event of M 7.0 or 7.1 occurred in this region in 1915, and a M 7.0 to 7.2 in 1934 broke the Cerro Prieto fault to the east with up to several meters of surface slip.

Co-, post-, and inter-seismic deformation measurements in this area will provide unique opportunities for improved understanding of the earthquake cycle, lithospheric rheology, and the mechanisms of large, destructive earthquakes along the San Andreas plate boundary system.

References

Axen, G.J., J. M. Fletcher, E. Cowgill, M. Murphy, P. Kapp, I. MacMillan, E. Ramos-Velázquez, and J. Aranda-Gómez. 1999. Range-front fault scarps of the Sierra El Mayor, Baja California: Formed above an active low-angle normal fault?, Geology, 27, 247-250.

Fletcher, J.M.and R.M. Spelz. 2009. Patterns of Quaternary deformation and rupture propoagation associated with an active low-angle normal fault, Laguna Salada, Mexico: evidence of a rolling hinge? Geosphere; 5: 385-407. doi:10.1130/GES00206.1.

Mueller, K.J. and Rockwell, T.R. 1991. Late Quaternary structural evolution of the western margin of the Sierra Cucapa, Baja California Norte: in Dauphin, J., and Simoneit, B., (ed) The Gulf and Peninsular Province of the Californias, AAPG Memoir 47, 249­260.

Mueller, K.J. and Rockwell, T.R. 1995. Late Quaternary activity of the Laguna Salada fault in northern Baja California, Mexico: Geological Soc. of America Bull., 107, 8­18.

Chris Walls of UNAVCO in California Reports...

"We've had a large earthquake just south of the border in Laguna Salada/Cerro Prieto extensional complex in the Salton Trough. The epicenter is about 60 km south of Mexicali. According to the USGS website the magnitude is a M7.2 and was 10+ km in depth. Aftershocks are ongoing. So far there has been one 5.1 triggered event/aftershock near P497 at Imperial Airport. Thus far I have confirmed connectivity to stations in the region via the Salton Trough radio network (T1 line), LanCell2 modems and Vsat. In the San Clemente Office we have enough equipment to build about 5+ SDBM and 5+ DDBM monuments (we would need more receivers and solar bracket hardware). I am canceling travel plans and will be standing by for any pending earthquake response discussion." - April 4, 2010

Photo of rupture at surface of a fault, which looks like cracks along the desert floor surface.

Figure 1 - Photo of ruptures along fault, by John Fletcher at CICESE, Mexico. See below for more photos. [View full scale image].

Figure 2 - An Interferogram based on ALOS PALSAR , by Matt Wei and David Sandwell at IGPP/SCRIPPS. One color cycle or fringe is 11.6 cm of line of sight deformation. [View full scale image]. See text for more details.

Figure 3 - A Map of coseismic offsets from the rapid PBO and USGS solutions two days before and two days after the mainshock, complete with error ellipses, derived by Tom Herring at MIT. [View full scale image] Download the table of cosesimic displacements. These solutions include all PBO and USGS final processing.

Figure 4 - The surface rupture defines the fault location - as observed during helicopter reconnaissance by USGS, CICESE, SDSU and Caltech personnel. See text for more details on the field observations and geologic interpretation. [View full scale image.]

Figure 5 - A 5Hz data plot showing slip for GPS site P496 about 70 km from the epicenter, provided by Kristine Larson at the University of Colorado at Boulder. Also see her plot from Station 744.

Figure 6 - A plot of 1 Hz real-time GPS observations versus broadband seismic GPS observations at co-located seismometers by Yehuda Bock at UCSD and Sharon Kedar at JPL. [View full scale image] See text for more information or go to GPS Explorer.

A plot of the vertical seismic channel from PBO BSM network for the Mw=7.2 - April 4, 2010, event.

Figure 7 - A plot of the vertical seismic channel for select stations from the entire PBO BSM network for the 7.2 Baja event. Seismograms at the bottom of the figure were recorded nearest to the event. Distance from the event increases as you move upward. Produced by Wade Johnson at UNAVCO. [View full scale image]

Figure 8 - Plot of the 1-sps pore pressure data recorded in Pinyon Flat and Parkfield PBO boreholes. Data are available via anonymous FTP from ftp://pore.unavco.org/pub/pore and in SEED format from the NCEDC and IRIS DMC. Data plot provided by Kathleen Hodgkinson at UNAVCO. [View full scale image]

Predicted horizontal displacements based on USGS moment tensor solution.

Figure 9 - Preliminary predicted horizontal displacements based on the USGS moment tensor solution (Rowena Lohman, at Cornell).

Main shock and 12 hours of aftershocks.

Figure 10 - Map showing fault slip rates with an overlay of the main shock and 12 hours of aftershocks, with yellow lines (<0.2), pumpkin (0.2-1), orange (1.5) and red (>5 mm/yr) lines (Ramon Arrowsmith at Arizona State University).

Main Coulomb Stress (Ross Stein, USGS, and Shinji Toda, Kyoto University).

Figure 11 - Map of preliminary uniform-slip Coulomb model showing Coulomb stress change (Ross Stein, USGS, and Shinji Toda, Kyoto University) . [View full scale image]

Main Coulomb Stress (Ross Stein, USGS, and Shinji Toda, Kyoto University).

Figure 12 - Shaking in the vicinity of the rupture radiated low frequency sound waves (called "infrasound") that were detected 125 miles away by two sensitive infrasound arrays shown here as green squares operated by the Laboratory for Atmospheric Acoustics at UCSD. Image produced by Kris Walker at UCSD. [View full scale image]

Photo of fault at surface, Mexico.

Figure 13 - Photo of ruptures along fault, by John Fletcher at CICESE, Mexico. [View full scale image]

Photo of fault at surface, Mexico.

Figure 14 - Photo of ruptures along fault, by John Fletcher at CICESE, Mexico. [View full scale image]

USGS ShakeMap Baja, Mexico - Mw=7.2 - April 4, 2010.

Figure 15 - USGS ShakeMap Baja, Mexico - Mw=7.2 - April 4, 2010. [View full scale image]

Figure 16 - Image of Baja California rupture, courtesy of Dick Proctor.

Last modified: Thursday, 06-Oct-2016 20:05:44 UTC

 

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