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7/11/2017 by mdc
David Jacobson and Ross Stein report that a new study on the California earthquake hazard model will be published soon, which shows, through computer simulations, that in the week following a M=7.0 earthquake, the likelihood of another M=7.0 quake is up to 300 times greater than the week beforehand. This dramatic jump in likelihood is due to the inclusion of the short-term probabilities associated with aftershock sequences, a factor never before used in statewide comprehensive model like this one.

The California earthquake hazard model, the Uniform California Earthquake Rupture Forecast Version 3 (UCERF3), was first published in 2015, and quantifies the hazard posed by tectonic forces unleashed on faults. The 2015 model was the first to include the possibility that an earthquake on one fault could jump to another fault in a matter of seconds, thereby creating multi-fault ruptures. In doing so, over 250,000 rupture scenarios were created for the state of California, vastly more than in the previous model. The reality of such falling-domino or cascading ruptures was demonstrated spectacularly in the 2002 M=7.9 Denali, Alaska, and the 2016 M=7.8 Kaikoura, New Zealand earthquakes.

It the study released tomorrow, dubiously dubbed UCERF3-ETAS (ETAS refers to epidemic-type aftershock sequence, a concept borrowed from medical research and successfully applied to earthquakes by Yoshihito Ogata of Japan) takes it a step further by attempting to capture the role of aftershocks of all sizes following a main shock. In a nutshell, for short times after a main shocks, aftershocks matter.

Main shocks, by changing the stress on surrounding faults, trigger aftershocks; if you like, the main shocks are the parents. But these aftershock daughters can in turn trigger grand-daughters aftershocks of their own, ad infinitum.

Read on ...

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