Abstract
Pulse-like ruptures tend to be more sensitive to stress heterogeneity
than crack-like ones. For instance, a stress-barrier can more easily
stop the propagation of a pulse than that of a crack. While crack-like
ruptures tend to homogenize the stress field within their rupture area,
pulse-like ruptures develop heterogeneous stress fields. This feature of
pulse-like ruptures can potentially lead to complex seismicity with a
wide range of magnitudes akin to the Gutenberg-Richter law. Previous
models required a friction law with severe velocity-weakening to develop
pulses and complex seismicity. Recent dynamic rupture simulations show
that the presence of a damaged zone around a fault can induce pulse-like
rupture, even under a simple slip-weakening friction law, although the
mechanism depends strongly on initial stress conditions. Here we aim at
testing if fault zone damage is a sufficient ingredient to generate
complex seismicity. In particular, we investigate the effects of damaged
fault zones on the emergence and sustainability of pulse-like ruptures
throughout multiple earthquake cycles, regardless of initial conditions.
We consider a fault bisecting a homogeneous low-rigidity layer (the
damaged zone) embedded in an intact medium. We conduct a series of
earthquake cycle simulations to investigate the effects of two fault
zone properties: damage level D and thickness H. The simulations are
based on classical rate-and-state friction, the quasi-dynamic
approximation and the software QDYN (https://github.com/ydluo/qdyn).
Selected fully-dynamic simulations are also performed with a spectral
element method. Our numerical results show the development of complex
rupture patterns in some damaged fault configurations, including events
of different sizes, as well as pulse-like, multi-pulse and hybrid
pulse-crack ruptures. We further apply elasto-static theory to assess
how D and H affect ruptures with constant stress drop, in particular the
flatness of their slip profile, which is an indicator of pulse-like
rupture. We find qualitative agreement between our theoretical and
computational results regarding the range of damaged zone properties
that enable pulse-like rupture.