Understanding complex faults: Rupture propagation during the 2010 El Mayor-Cucapah earthquake

Date:
March 24, 2022
Source:
University of Tsukuba
Summary:
Researchers have identified irregular rupture propagation during
the 2010 El Mayor-Cucapah earthquake in Mexico by incorporating
teleseismic P waveform inversion with traditional modeling, allowing
resolution of the rupture process and its relation to the complex
fault system while mitigating modeling errors. Reducing errors
made because of inaccurate assumptions about fault geometry is
critical for robust interpretation of complex slip histories.



FULL STORY ==========================================================================
On 4 April 2010, the Mw 7.2 El Mayor-Cucapah earthquake shook northeastern
Baja California, Mexico, along the Pacific-North American plate margin,
an area known for its complex fault systems with diverse geometries that
are often poorly understood. But now, researchers from Japan have shed
new light on irregular rupture propagation in the 2010 earthquake while reducing potential modeling errors.


==========================================================================
In nature, it is rare for the faults that cause earthquakes
to be completely planar, and they are typically subject to some
complexities. These complexities, or geometric discontinuities, affect
the distribution of stress along faults, and they result in diverse
rupture behaviors during earthquakes.

Such complexities understandably present challenges for robust geophysical interpretations.

"Understanding earthquake rupture processes and their relationship to
fault geometries is critical in the study of earthquake source physics,"
says Professor Yuji Yagi, lead author of the study. "However, conventional modeling approaches rely on modelers making some assumptions about
fault geometry that may introduce errors, making robust interpretation challenging." The conventional modeling approach, known as finite-fault inversion, estimates the spatiotemporal evolution of an earthquake to reconstruct its slip history.

To provide a more accurate interpretation of the rupture pattern
during the 2010 El Mayor-Cucapah earthquake, the researchers used
teleseismic P(or "primary") waveform data from the earthquake, which
contain information on true fault orientations. This information can be directly extracted, thereby mitigating potential modeling errors caused
by uncertainties on fault geometry and assumptions made during modeling.

"By using a potency density tensor approach to invert the teleseismic Pwaveforms from the El Mayor-Cucapah earthquake, we were able to
estimate the rupture process and fault geometry simultaneously and
identify an irregular rupture sequence," explains Professor Yagi. "The earthquake ruptured multiple faults with various faulting mechanisms,
and geometric discontinuities in the fault geometry caused irregular
rupture behavior." Sensitivity and reproducibility tests conducted by
the researchers yielded consistent results, including determinations
of the timing and propagation directions of different ruptures. Even
small changes in the data did not affect the results of the P waveform inversion, further indicating the reliability of the modeling approach.

Given the irregular rupture propagation of the El Mayor-Cucapah
earthquake, and earthquakes with similarly complex slip histories
worldwide, suppressing potential modeling errors is crucial for
identifying complex rupture behavior that would be difficult to determine
using traditional methods. Investigating complex fault geometries using
robust modeling techniques that don't rely on assumptions is thus critical
to our understanding of earthquake source physics.


========================================================================== Story Source: Materials provided by University_of_Tsukuba. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Shinji Yamashita, Yuji Yagi, Ryo Okuwaki. Irregular rupture
propagation
and geometric fault complexities during the 2010 Mw 7.2 El
Mayor-Cucapah earthquake. Scientific Reports, 2022; 12 (1) DOI:
10.1038/s41598-022- 08671-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220324104456.htm

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