||On 4 April 2010, a large earthquake (Mw = 7.2) struck the northern part of Baja California in Mexico. The official name for the earthquake is the El Mayor-Cucapah Earthquake.
New results published online in Science on 9 February 2012:
Near-Field Deformation from the El Mayor–Cucapah Earthquake Revealed by Differential LIDAR
- Michael E. Oskin1,
- J Ramon Arrowsmith2,
- Alejandro Hinojosa Corona3,
- Austin J. Elliott1,
- John M. Fletcher3,
- Eric J. Fielding4,
- Peter O. Gold1,
- J. Javier Gonzalez Garcia3,
- Ken W. Hudnut5,
- Jing Liu-Zeng6,
- Orlando J. Teran3
The paper (online here) describes analysis of LiDAR data to examine the detailed folding and breaking of rocks near the main fault ruptures during the 2010 Mw 7.2 earthquake. See also NASA news note, JPL news note, and UC Davis news release. Para Español, ver nota de CICESE.
Summary of paper:
Large [moment magnitude (Mw) ≥ 7] continental earthquakes often generate complex, multifault
ruptures linked by enigmatic zones of distributed deformation. Here, we report the collection
and results of a high-resolution (≥nine returns per square meter) airborne light detection and
ranging (LIDAR) topographic survey of the 2010 Mw 7.2 El Mayor–Cucapah earthquake that
produced a 120-kilometer-long multifault rupture through northernmost Baja California, Mexico.
This differential LIDAR survey completely captures an earthquake surface rupture in a sparsely
vegetated region with pre-earthquake lower-resolution (5-meter–pixel) LIDAR data. The postevent
survey reveals numerous surface ruptures, including previously undocumented blind faults within
thick sediments of the Colorado River delta. Differential elevation changes show distributed,
kilometer-scale bending strains as large as ~10^3 microstrains in response to slip along discontinuous
faults cutting crystalline bedrock of the Sierra Cucapah.
Oblique View of Borrego Fault
This 3-D airborne light detection and ranging (LiDAR) oblique view of the Borrego Fault, taken from the post-earthquake topographic survey, shows a wide zone of numerous small faults that slice the ground surface and offset the floor of a desert wash surrounding the main fault. The various colors in the landscape represent elevation changes during the earthquake. Image generated in Crusta (keckcaves.org) with 2x vertical exaggeration.
Image credit: Michael Oskin, UC Davis, www.keckcaves.org
Previous results published as Advance Online Publication in Nature Geoscience on 31 July 2011:
Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico
- Shengji Wei,
- Eric Fielding,
- Sebastien Leprince,
- Anthony Sladen,
- Jean-Philippe Avouac,
- Don Helmberger,
- Egill Hauksson,
- Risheng Chu,
- Mark Simons,
- Kenneth Hudnut,
- Thomas Herring
- & Richard Briggs
The paper (online here) describes analysis of InSAR, GPS, fieldwork and seismic data to unravel the complex fault ruptures of the Mw 7.2 earthquake. See also JPL news release and Caltech news release.
Wei, S., Fielding, E.J., Leprince, S., Sladen, A., Avouac, J.-P., Helmberger, D.V., Hauksson, E., Chu, R., Simons, M., Hudnut, K.W., Herring, T. & Briggs, R.W., 2011. Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico, Nature Geosci, 4, 615-618.
summary of paper
The geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation, propagation and arrest of seismic ruptures. The fault system that runs from southern California into Mexico is a simple strike-slip boundary: the west side of California and Mexico moves northwards with respect to the east. However, the Mw 7.2 2010 El Mayor–Cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike-slip fault. Here we use geodetic, remote-sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake. We find that the earthquake produced a straight 120-km-long fault trace that cut through the Cucapah mountain range and across the Colorado River delta. However, at depth, the fault is made up of two different segments connected by a small extensional fault. Both segments strike N130° E, but dip in opposite directions. The earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike-slip motion. We show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves. We conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone.
NASA has obtained permission from the Mexican government to fly the NASA/JPL radar UAVSAR on its Gulfstream III airplane over the area of the 2010 earthquake in Baja California and Sonora, Mexico. The first flights were during the nights of 31 January to 1 February (northern part) and 2 February to 3 February 2012 (southern part).
The first polarimetric UAVSAR images processed by the UAVSAR team are exciting:
False-color composite polarimetric image over the fault ruptures (red lines) of the April 2010 El Mayor Cucapah earthquake in northern Baja California, acquired Feb. 3, 2012 by NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), overlaid on a Google Earth map. The U.S.-Mexico border is shown by a yellow line extending horizontally across the upper third of the image. The Gulf of California is in the lower right. Gray circles denote large historical earthquakes, with yellow and orange dots show earthquakes within the last week and day, respectively. In the enlargement below, taken from the central part of the fault rupture, greenish shades are rocks and gravel in the Cucapah Mountains, while purplish tones are smoother soil in the Mexicali valley to the east. This image will be combined with other images of the same area to be acquired during future flights in order to measure the motion of Earth's surface during the time between images using a technique called interferometry. The interferometric measurements will allow scientists to study the pressures building up and being released on faults at depth.
Credit: NASA-JPL/Caltech/USGS/Google Earth
Credit: NASA-JPL/Caltech/USGS/Google Earth
Horizontal motion measured from radar images reveals the faults that moved in the 2010 magnitude 7.2 earthquake in Baja California, Mexico. Motion in the direction along the track of the JAXA ALOS satellite (roughly north, parallel to the side of the colored image) was extracted by comparison of PALSAR images acquired before and after the earthquake. Colors show the amount of motion of the ground surface, the sharp line between the orange or red colors and the green or blue colors is the location of the fault rupture. Red star shows the epicenter where the earthquake rupture started. The fault that extends to the southeast from the epicenter has been named the Indiviso Fault and was previously unknown before the 2010 earthquake. Blue line shows the Colorado River and dashed black line shows the USA-Mexico border. Light gray filled areas are the water of the Salton Sea to the north and Gulf of California to the south. Image credit: JAXA/METI/NASA/JPL-Caltech
Eric J. Fielding, Section 324, Jet Propulsion Laboratory, California Institute of Technology,
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