CHARACTERIZING INTERACTIONS BETWEEN EARTHQUAKE RUPTURE AND FAULT ZONE STRUCTURE (Invited Presentation)

Earthquakes usually occur in damaged fault zones, which can be detected from the propagation of seismic waves. The weaker materials in fault zones cause the trapped waves and produce distinct signatures in seismic waveforms. Most major fault zones are found to be 100-400 m wide with seismic velocities 20%-65% lower than the surrounding medium. They may reach as deep as ~10 km or may only exist in the top ~3-4 km [Ben-Zion, et al., 2003; Li et al., 2007]. Damaged fault zones also show temporal healing after the occurrence of large earthquakes [Vidale and Li, 2003].

To understand how such fault structures affect earthquakes and how earthquakes influence the structural evolution of fault zones, we develop numerical simulations of dynamic earthquake ruptures in damaged fault zones. The trapped waves reflected from the fault zone boundaries generate slip pulses as rupture propagates [Huang and Ampuero, 2011]. The rise time of such slip pulse is proportional to the travel time of reflected waves. In other words, the final slip can be scaled with the width of the damaged fault zone in certain cases. The trapped waves propagating along the fault zone boundaries can also produce much faster rupture, or the so-called supershear rupture [Huang et al., 2016]. Such fast earthquakes can enhance ground shaking and induce the extensive rock pulverization in major fault zones [Doan and Gary, 2009].

To further investigate the fault zone deformation after large earthquakes, we include the off-fault plasticity of damaged fault zones [Huang et al., 2014]. We find most plastic deformation tends to occur in the damaged fault zone, though some damage can accumulate outside the fault zone. The rupture styles of earthquakes can also leave a permanent and characteristic pattern in the fault zone deformation. These results show that earthquakes have a significant influence on the structural evolution of fault zones. We will extend our numerical simulations to multiple earthquake cycles in damaged fault zones and advance our understanding on these relations between earthquake rupture and fault zone structure.