'Segment-jumping' ridgecrest earthquakes explored in new study
Seismologists use supercomputer to reveal complex dynamics of multi-fault earthquake systems

Date:
May 24, 2023
Source:
University of California - San Diego
Summary:
Seismologists used a powerful supercomputer that incorporated data-
infused and physics-based models to identify the link between the
2019 Ridgecrest earthquakes.


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==========================================================================
FULL STORY ==========================================================================
On the morning of July 4, 2019, a magnitude 6.4 earthquake struck the
Searles Valley in California's Mojave Desert, with impacts felt across
Southern California. About 34 hours later on July 5, the nearby city
of Ridgecrest was struck by a magnitude 7.1 earthquake, a jolt felt
by millions across the state of California and throughout neighboring communities in Arizona, Nevada, and even Baja California, Mexico.

Known as the Ridgecrest earthquakes -- the biggest earthquakes to
hit California in more than 20 years -- these seismic events resulted
in extensive structural damage, power outages, and injuries. The M6.4
event in Searles Valley was later deemed to be the foreshock to the M7.1
event in Ridgecrest, which is now considered to be the mainshock. Both earthquakes were followed by a multitude of aftershocks.

Researchers were baffled by the sequence of seismic activity. Why did
it take 34 hours for the foreshock to trigger the mainshock? How did
these earthquakes "jump" from one segment of a geologic fault system
to another? Can earthquakes "talk" to one another in a dynamic sense?
To address these questions, a team of seismologists at Scripps Institution
of Oceanography at UC San Diego and Ludwig Maximilian University of Munich (LMU) led a new study focused on the relationship between the two big earthquakes, which occurred along a multi-fault system. The team used a powerful supercomputer that incorporated data-infused and physics-based
models to identify the link between the earthquakes.

Scripps Oceanography seismologist Alice Gabriel, who previously worked
at LMU, led the study along with her former PhD student at LMU, Taufiq Taufiqurrahman, and several co-authors. Their findings were published
May 24 in the journal Natureonline, and will appear in the print edition
June 8.

"We used the largest computers that are available and perhaps the most
advanced algorithms to try and understand this really puzzling sequence
of earthquakes that happened in California in 2019," said Gabriel,
currently an associate professor at the Institute of Geophysics and
Planetary Physics at Scripps Oceanography. "High-performance computing
has allowed us to understand the driving factors of these large events,
which can help inform seismic hazard assessment and preparedness." Understanding the dynamics of multi-fault ruptures is important, said
Gabriel, because these types of earthquakes are typically more powerful
than those that occur on a single fault. For example, the Turkey-Syria earthquake doublet that occurred on Feb. 6, 2023, resulted in significant
loss of life and widespread damage. This event was characterized by
two separate earthquakes that occurred only nine hours apart, with both breaking across multiple faults.

During the 2019 Ridgecrest earthquakes, which originated in the
Eastern California Shear Zone along a strike-slip fault system, the
two sides of each fault moved mainly in a horizontal direction, with no vertical motion. The earthquake sequence cascaded across interlaced and previously unknown "antithetic" faults, minor or secondary faults that
move at high (close to 90 degrees) angles to the major fault. Within the seismological community, there remains an ongoing debate on which fault segments actively slipped, and what conditions promote the occurrence
of cascading earthquakes.

The new study presents the first multi-fault model that unifies
seismograms, tectonic data, field mapping, satellite data, and other space-based geodetic datasets with earthquake physics, whereas previous
models on this type of earthquake have been purely data-driven.

"Through the lens of data-infused modeling, enhanced by the capabilities
of supercomputing, we unravel the intricacies of multi-fault conjugate earthquakes, shedding light on the physics governing cascading rupture dynamics," said Taufiqurrahman.

Using the supercomputer SuperMUC-NG at the Leibniz Supercomputing Centre
(LRZ) in Germany, the researchers revealed that the Searles Valley and Ridgecrest events were indeed connected. The earthquakes interacted
across a statically strong yet dynamically weak fault system driven by
complex fault geometries and low dynamic friction.

The team's 3-D rupture simulation illustrates how the faults considered
strong prior to an earthquake can become very weak as soon as there is
fast earthquake movement and explain the dynamics of how multiple faults
can rupture together.

"When fault systems are rupturing, we see unexpected interactions. For
example, earthquake cascades, which can jump from segment to segment,
or one earthquake causing the next one to take an unusual path. The
earthquake may become much larger than what we would've expected," said Gabriel. "This is something that is challenging to build into seismic
hazard assessments." According to the authors, their models have the
potential to have a "transformative impact" on the field of seismology
by improving the assessment of seismic hazards in active multi-fault
systems that are often underestimated.

"Our findings suggest that similar kinds of models could incorporate
more physics into seismic hazard assessment and preparedness," said
Gabriel. "With the help of supercomputers and physics, we have unraveled arguably the most detailed data set of a complex earthquake rupture
pattern." The study was supported by the European Union's Horizon 2020 Research and Innovation Programme, Horizon Europe, the National Science Foundation, the German Research Foundation, and the Southern California Earthquake Center.

In addition to Gabriel and Taufiqurrahman, the study was co-authored
by Duo Li, Thomas Ulrich, Bo Li, and Sara Carena of Ludwig Maximilian University of Munich, Germany; Alessandro Verdecchia with McGill
University in Montreal, Canada, and Ruhr-University Bochum in Germany;
and Frantisek Gallovic of Charles University in Prague, Czech Republic.

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========================================================================== Story Source: Materials provided by
University_of_California_-_San_Diego. Original written by Brittany
Hook. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Taufiq Taufiqurrahman, Alice-Agnes Gabriel, Duo Li, Thomas Ulrich,
Bo Li,
Sara Carena, Alessandro Verdecchia, Frantisek
Gallovič. Dynamics, interactions and delays of the
2019 Ridgecrest rupture sequence. Nature, 2023; DOI:
10.1038/s41586-023-05985-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230524181903.htm

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