UCERF3: Significant Advancements Made in Earthquake Forecasting

3D Perspective showing the likelihood of a magnitude 6.7 or larger earthquake based on location, over the next 30 years in CA.

California’s new earthquake forecast model, UCERF3 (Third Uniform California Earthquake Rupture Forecast), provides authoritative estimates of the magnitude, location and likelihood of earthquake fault rupture, over a period of 30 years (length of a typical home mortgage).

Earthquakes are a constant threat to the geologically-complex and active Golden State. This model will be used by a variety of industries to better understand California’s earthquake hazards, namely those from the insurance, engineering, and emergency management sectors, in order to reduce damage and save lives.

Although we cannot predict earthquakes, we can assess their likelihood, which is the aim of UCERF3. Another component of understanding the earthquakes in our future is ground motion prediction modeling, which is modeling that anticipates ground velocity (speed) and acceleration (rate of change) from seismic waves generated by an earthquake. With UCERF3 and ground motion prediction modeling, scientists can better understand earthquake hazards in California.

Simply put, earthquake forecasts are probabilities of "where and when", ground motion prediction modeling describes "how."

UCERF3 was developed by the 2014 Working Group on California Earthquake Probabilities (WGCEP), a multi-disciplinary collaboration of leading experts in seismology, geology, geodesy, paleoseismology, earthquake physics, and earthquake engineering. UCERF3 involved numerous public meetings and included formal evaluations by five separate review panels.

The development of earthquake rupture forecasts by the WGCEP (in 1988, 1990, 1995, 2003, and 2007) shows progress towards more accurate representations of the very complex California fault system. The earlier model, UCERF2, has been confirmed by findings in UCERF3, along with a few improvements and technical innovations:

Major Findings

  1. Overall, the chance of moderate-sized earthquakes had slightly decreased. For example, a magnitude 6.7 earthquake (size of the 1994 Northridge Earthquake) has changed probability from one per 4.8 years to one every 6.3 years.
  2. The chance of a big earthquake (magnitude 8 or larger) has increased from 4.7% to 7% within the next 30 years. The southern San Andreas is the most likely to host such an event.
  3. Southern California, particularly the Los Angeles region, is at a greater risk of large earthquakes since the region has more faults and can host multi-fault ruptures.
  4. Northern California, particularly the San Francisco region, has an greater risk of large earthquakes due to the Calaveras and Hayward-Rogers faults not having a large earthquake in a long time, as compared to the northern San Andreas, whose last rupture was the 1906 Great San Francisco Earthquake.

Innovations and Improvements

  1. More than 350 fault sections are now included in UCERF3. Detailed history of faults has generally been limited, but due the inclusion of space-based geodesy (GPS), scientists working on UCERF3 have been able to produce more data.
  2. In UCERF3, earthquakes can now be understood as multi-fault ruptures. We know from several recent events that an earthquake can cause another part of a fault or an entirely different fault in the vicinity to rupture.
  3. High-performance computing, of which SCEC is a leader in the earth sciences, has been used to run calculations for modeling that would take more than 8 years on a desktop.

Evolution of the Community Fault Model

Led by the Working Group on California Earthquake Probabilities (WGCEP), with oversight and support from the U.S. Geological Survey, the Southern California Earthquake Center, and the California Geological Survey, and the California Earthquake Authority.

Learn more: http://ceo.scec.org/ucerf/index.html