Correlating Rayleigh-wave Breakout Phases with Source Parameters from 2-D Dip-slip Fault Geometries Under Equivalent Prestress Conditions

Abstract:

The asymmetric geometry of dip-slip faults (i.e., thrust and normal faults) leads to greater slip and greater peak slip rate near the free surface (e.g., the surface of the Earth) [Nielsen, 1998; Oglesby et al., 1998; Oglesby and Archuleta, 2000, Oglesby et al., 2000] than analogous vertical faults. Furthermore, when rupture travels updip along a dip-slip fault and reaches the free surface, it produces a Rayleigh-wave breakout phase, a pulse traveling back downdip and along the free surface [Savage, 1965; Burridge and Halliday, 1971; Oglesby et al., 1998; Madariaga, 2003; Kozdon and Dunham, 2013] that has the potential to be readily observed. Properties of the Rayleigh-wave breakout phase are undoubtedly related to the fault slip distribution, the details of this relationship are not well understood. In particular, these breakout phases may be correlated to fault slip near the free surface, which efficiently generates tsunamis when submarine faults rupture [Okal, 1988; Geist and Bilek, 2001]. We propose to constrain 2-D earthquake source parameters from characteristics of the Rayleigh-wave field by running suites of 2-D dynamic rupture forward models on dip-slip faults that vary in dip angle and fault curvature, and with equivalent prestress conditions such as constant traction across the fault and stochastic prestress distributions. We will compare traveling Rayleigh-wave breakout properties (e.g., amplitude) with fault rupture parameters (e.g., slip distribution) for a variety of fault geometries and prestress conditions. Preliminary results on thrust faults indicate that shallower dip angles produce slip distributions that are more preferentially weighted updip, and larger amplitude breakout phases, with implications for early estimation of far-field tsunami amplitude.