“Aftershock Faults” and what they could mean for seismic hazard assessment

The Seismic Record
By: , and 



We study stress‐loading mechanisms for the California faults used in rupture forecasts. Stress accumulation drives earthquakes, and that accumulation mechanism governs recurrence. Most moment release in California occurs because of relative motion between the Pacific plate and the Sierra Nevada block; we calculate relative motion directions at fault centers and compare with fault displacement directions. Dot products between these vectors reveal that some displacement directions are poorly aligned with plate motions. We displace a 3D finite‐element model according to relative motions and resolve stress tensors onto defined fault surfaces, which reveal that poorly aligned faults receive no tectonic loading. Because these faults are known to be active, we search for other loading mechanisms. We find that nearly all faults with no tectonic loading show increase in stress caused by slip on the San Andreas fault, according to an elastic dislocation model. Globally, faults that receive a sudden stress change respond with triggered earthquakes that obey an Omori law rate decay with time. We therefore term this class of faults as “aftershock faults.” These faults release ∼4% of the moment release in California, have ∼0.1%–5% probability of M 6.7 earthquakes in 30 yr, and have a 0.001%–1% 30 yr M 7.7 probability range.

Study Area

Publication type Article
Publication Subtype Journal Article
Title “Aftershock Faults” and what they could mean for seismic hazard assessment
Series title The Seismic Record
DOI 10.1785/0320220036
Volume 3
Issue 1
Year Published 2023
Language English
Publisher Seismological Society of America
Contributing office(s) Pacific Coastal and Marine Science Center
Description 11 p.
First page 1
Last page 11
Country United States
State California
Google Analytic Metrics Metrics page
Additional publication details