SCEC Award Number 14063 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Physics Based Models of Slow Slip Events and Possible Earthquake Triggering
Investigator(s)
Name Organization
Paul Segall Stanford University
Other Participants Andrew Bradley, Postdoc
SCEC Priorities 5d, 5e SCEC Groups FARM, Geodesy, Transient Detection
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Segall and Bradley [2012a] showed that slow slip events (SSE) can be hosted in a dilatant, velocity weakening region at low effective stress (σ ̄). SSE may be confined within this zone by the greater effective stress at shallower depth. We have observed that model earthquakes evolve from the final SSE. Late in the earthquake cycle SSE gradually penetrate into the high-σ ̄ region. Here we further explore dynamic rupture triggering by SSE, and in particular how the spatial dependence of σ ̄ and slip weakening distance dc control this behavior.
We show that artificially altering the distribution of dc to improve numerical efficiency can significantly alter predicted behavior, if not done carefully. We study how far a stable creeping zone can penetrate a velocity weakening region before going unstable. For the aging law this distance is close to the size of the longest fault that never generates dynamic slip, but for the slip law it can be considerably greater. We have further shown that how one smooths σ ̄ from low values (in the SSE region) to larger values (locked zone) also alters predicted behavior. Results depend on the transition widths, but for narrow transition we can predict roughly how far the creep zone will penetrate into the high normal stress region.
Intellectual Merit Slow slip events (SSE) are observed in many subduction zones, and it has
been recognized for some time that SSE incrementally stress the locked zone that generate
megathrust events. In the past we have explored how this could lead to nucleating a
dynamic rupture.
In this study we have shown that one cannot cut corners and transition
material properties (e.g., $) at the updip end of the SSE zone for numerical efficiency
without significantly altering the predicted behavior. We have further shown that how one
smooths the effective normal stress from low values (in the SSE region) to larger values
(locked zone) will also alters predicted behavior. Finally, we analyze how far stable creep
can penetrate a velocity weakening region before generating a dynamic instability and
show that this rationalizes numerical simulations.
Broader Impacts This work informs others on details of how to model slow slip events
and how they could trigger dynamic ruptures.
Exemplary Figure Figure 1. Penetration length of stable slip (circles) into a velocity weakening region as a function of velocity weakening length for aging and slip laws, with and without thermal pressurization. The dashed line shows
the updip edge of the v.w.~region, which is the upper limit on the penetration distance.