A Major Earthquake Along the San Andreas Fault Looms Along its Southern Segment in Coachella Valley and Scientists try to Put Together Different Pieces of the Puzzle

A major earthquake along the San Andreas Fault looms, as portended by the 2019 Ridgecrest quakes in the Southern California desert.

Now, seismologists are rushing to parse together different pieces of the puzzle that is the next big rupture in the San Andreas Fault.

san andreas earthquake overdue for a big one
Aerial view of the San Andreas Fault in the Carrizo Plain. Image credit: John Wiley

The San Andreas Fault runs more than 800 miles (1,200 kilometers) north to south through the state of California.

Although the dangerous fault is responsible for some of California’s most notorious earthquakes such as the 1906 San Francisco earthquake it remains a mystery to scientists.

The central and northern segments of the fault have seen recurring earthquakes as frequently as every 22 years.

The southern segment of the San Andreas Fault in Coachella Valley is overdue for a ‘Big One’ has not had a major shakeup in the last three centuries. This is far past its recurrence period of 180-200 years.

The segment’s proximity to the Los Angeles Basin worries residents that an inevitable rupture will be deadly and costly, affecting millions of lives.

Studies have shown that the southern segment has accumulated sufficient stress to trigger a magnitude-7 earthquake.

Two weeks ago, scientists had already warned that the risk of big San Andreas earthquake had increased.

New research: fault geometry

One team of researchers, led by seismologist Roby Douilly of the University of California, Riverside, is studying various factors, such as fault geometry, to model the evolution of a not-so-hypothetical future earthquake on the San Andreas’s southernmost segment.

As reported in Geosphere, the researchers altered the intersection angles and directions of five rupture-prone strands branching from the main San Andreas Fault line to determine the most likely rupture pathway.

The fault in our data

Though the San Andreas is one of the most well-mapped faults in the world, it is still not yet fully understood.

The exact configuration of the intertwining fault branches, the pent-up stress levels and the friction laws between the tectonic plates are still open questions.

Parts of the San Andreas Fault extend 10 miles (16 kilometers) underground, deeper than our current mapping and seismic methods can plumb.

With an incomplete picture of the San Andreas Fault, scientists have to rely on computer simulations to estimate the range of possible rupture outcomes, such as which fault branches will slide and how the seismic energy will be released.

Computer simulations

Douilly and his colleagues used computerized simulations called finite element analyses to simulate how a rupture would propagate from the Coachella Valley segment of the San Andreas, should that segment slip. The method involves constructing a complex 3D geometric model from smaller “discretized” units called elements, similar to how a digital photo is made up of pixels.

Results show a slight change in the parameters of the fault could produce drastically different outcomes, with propagations running along different types of faults, including the more dormant faults.