The Current Unlikely Earthquake Hiatus at California’s Transform Boundary Paleoseismic Sites

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

If the average interval between paleoearthquakes at 16 high-resolution paleoseismic sites along the major transform faults in California range from 100 to 220 years, what are the odds that none of these sites has experienced an earthquake in the last 100 years? A similar question was posed by Jackson (AGU, 2014) who found the odds were exceptionally low. We revisit the question using full earthquake age uncertainties and subsets of high-resolution sites that sample the five major transform fault sections in California: the Northern and Southern San Andreas Fault, San Jacinto Fault, Hayward Fault, and Elsinore Fault (Biasi and Scharer, SRL, accepted). A 100-year hiatus can be observed in the 1000-year record of sets of a few proximal sites. In contrast, if a single site from each of the five major fault sections is assumed to reflect the complete behavior of that strand, a 100-year period without a major earthquake is not predicted by common time-dependent (lognormal) or time-independent (Poisson) recurrence models. If known rupture behavior complexity (e.g., partial section ruptures like 1812 and 1857) are included, the odds of the 100-year gap are further reduced. To examine the recurrence across all 16 sites, we remove possible double-counted ruptures and find time-independent probability of the current 100-year gap is of order 0.3%. We review published models of earthquake modulation due to post-seismic loading, viscous flow in the deep crust, and Coulomb stress transfer for potential explanations. We also invite discussion of earthquake recurrence for seismic hazard estimation, given that the current models seem, at least, incomplete.

Presenting Author: Katherine Scharer

Authors