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Unusual fault pattern surfaces in earthquake study

Date:
August 12, 2011
Source:
NASA/Jet Propulsion Laboratory
Summary:
Like scars that remain on the skin long after a wound has healed, earthquake fault lines can be traced on Earth's surface long after their initial rupture. Typically, this line of intersection is more complicated at the surface than at depth. But a new study of the April 4, 2010, El Mayor-Cucapah earthquake in Baja California, Mexico, reveals a reversal of this trend. Superficially, the fault involved in the magnitude 7.2 earthquake appeared to be straight, but at depth, it's warped and complicated.

Horizontal motion measured from radar images reveals the faults that moved in the magnitude 7.2 earthquake in Baja California, Mexico.
Credit: JAXA/METI/NASA/JPL-Caltech

Like scars that remain on the skin long after a wound has healed, earthquake fault lines can be traced on Earth's surface long after their initial rupture. Typically, this line of intersection is more complicated at the surface than at depth. But a new study of the April 4, 2010, El Mayor-Cucapah earthquake in Baja California, Mexico, reveals a reversal of this trend. Superficially, the fault involved in the magnitude 7.2 earthquake appeared to be straight, but at depth, it's warped and complicated.

The study, which was led by researchers at the California Institute of Technology with NASA Jet Propulsion Laboratory geophysicist Eric Fielding serving as a coauthor, is available online in the journal Nature Geoscience.

In a standard model, transform plate boundary structures -- where two plates slide past one another -- tend to be vertically oriented, which allows for lateral side-by-side shear fault motion. However, as the study found, the 75 mile (120 kilometer) long El Mayor-Cucapah rupture involved angled, non-vertical faults and the event began on a connecting extension fault between the two segments.

The new analysis indicates the responsible fault is more segmented deep down than its straight surface trace suggests. This means the evolution and extent of this earthquake's rupture could not have been accurately anticipated from the surface geology alone, says the study's lead author Shengji Wei. Anticipating the characteristics of earthquakes that would likely happen on young fault systems (like the event in the study) is a challenge, since the geologic structures involved in the new fault systems are not clear enough.

Jean-Philippe Avouac, director of Caltech's Tectonics Observatory and principal investigator on the study, says the data can be used to illustrate the process by which the plate boundary -- which separates the Pacific Plate from North America -- evolves and starts connecting the Gulf of California to the Elsinore fault in Southern California.


Story Source:

The above story is based on materials provided by NASA/Jet Propulsion Laboratory. The original article was written by Katie Neith. Note: Materials may be edited for content and length.


Journal Reference:

  1. 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. Superficial simplicity of the 2010 El Mayor–Cucapah earthquake of Baja California in Mexico. Nature Geoscience, 2011; DOI: 10.1038/ngeo1213

Cite This Page:

NASA/Jet Propulsion Laboratory. "Unusual fault pattern surfaces in earthquake study." ScienceDaily. ScienceDaily, 12 August 2011. <www.sciencedaily.com/releases/2011/08/110812094507.htm>.
NASA/Jet Propulsion Laboratory. (2011, August 12). Unusual fault pattern surfaces in earthquake study. ScienceDaily. Retrieved September 21, 2014 from www.sciencedaily.com/releases/2011/08/110812094507.htm
NASA/Jet Propulsion Laboratory. "Unusual fault pattern surfaces in earthquake study." ScienceDaily. www.sciencedaily.com/releases/2011/08/110812094507.htm (accessed September 21, 2014).

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El Mayor-Cucapah Earthquake Was Simple on Surface, Complicated at Depth, New Data Show

Aug. 11, 2011 Like scars that remain on the skin long after a wound has healed, earthquake fault lines can be traced on Earth's surface long after their initial rupture. Typically, this line of intersection ... read more
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