Connecting depth limits of interseismic locking, microseismicity, and large earthquakes in models of long-term fault slip

Junle Jiang, & Nadia Lapusta

Published August 15, 2017, SCEC Contribution #7171

Thickness of the seismogenic zone is commonly determined based on the depth of microseismicity or the fault locking depth inferred from geodetic observations. The relation between the seismic and geodetic estimates and their connections to the depth limit of large earthquakes remain elusive, while bearing importance for understanding the deep fault zone and assessing regional seismic hazard. We explore the seismic and geodetic observables in models of heterogeneous faults governed by laboratory-based friction laws, including quasi-static rate-and-state friction and enhanced dynamic weakening. Our models suggest that the transition between the locked and fully creeping regions can occur over a broad depth range. The effective locking depth (Delock), associated with concentrated loading and promotion of microseismicity, is located near the top of this locked-creeping transition zone; the geodetic locking depth (Dglock), inverted from surface geodetic observations, indicates the mid-depth of the transition zone. Following large earthquakes, Delock either stays in space or becomes shallower due to the creeping region recovering from deeper-penetrating coseismic slip, whereas Dglock deepens as the slip-deficit region expands, bounding the depth limit and potency release of large earthquakes in our models. Such processes lead to the two locking depths diverging toward the late interseismic period, consistent with seismic and geodetic observations from the Carrizo and Coachella segments in Southern California. However, the assumed layered distribution of fault friction and simple depth estimates are insufficient to characterize more heterogeneous faults, e.g., with along-strike variations. Improved observations and detailed models are thus needed to further illuminate deep fault conditions.

Key Words
fault mechanics, rate-and-state friction, dynamic weakening, microseismicity, geodetic locking, large earthquakes

Citation
Jiang, J., & Lapusta, N. (2017). Connecting depth limits of interseismic locking, microseismicity, and large earthquakes in models of long-term fault slip. Journal of Geophysical Research: Solid Earth, 122. doi: 10.1002/2017JB014030.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM), Stress and Deformation Over Time (SDOT)