Studying the Viability of Kinematic Rupture Models and Source Time Functions with Dynamic Constraints

Earthquake is one of the greatest natural hazards and a better understanding of the physical processes causing earthquake ruptures is required for appropriate seismic hazard assessment. Kinematic modelling is a standard tool for providing paramount information about the complexity of the earthquake rupture process and for making inferences on earthquake mechanics. Despite recent advances, kinematic models are characterized by uncertainties and trade-offs among parameters (related to the non-uniqueness of the problem). It has been shown that, for the same earthquake, source models obtained with different methodologies can exhibit significant discrepancies in terms of slip distribution, fault planes geometry and rupture time evolution.

One of the crucial assumptions in kinematic modelling on causative faults is the source time function, because it contains key information about the dynamics. Such function is nonetheless one of the most poorly observationally constrained characteristics of faulting. Recently, slip velocity time histories have been studied with laboratory earthquakes, and it has been observed that a systematic change of mechanical properties and traction evolution corresponds to a change in the shape of slip velocity. However, in kinematic inversions this function is a-priori assumed using simplified shapes, although functions compatible with rupture dynamics should be preferred.

In this work, we run a series of forward and inverse modelling to investigate the effect of the assumed slip velocity function on the ground motion and on the inverted slip history on the fault plane. We generate spontaneous dynamic models and use their ground motion as real events, inverting these data with kinematic models. Kinematic inversions have been conducted using both single-time and multi-time windowing. Uncertainties have been investigated assuming four different source time functions (i.e., triangular, box, regularized-yoffe and exponential functions). In this way we examine how the slip velocity function influences the slip distribution on the fault plane, and test if the inferred kinematic parameters (rise time and rupture velocity) are consistent with the dynamic models. Also, for a dense grid of phantom receivers, we examine the variability of the peak ground velocity (PGV) of synthetic seismograms up to 1 Hz. The latter have been obtained with forward models assuming the same slip distribution, rise time and rupture velocity but changing the source time functions.

Finally, we use the retrieved kinematic history on the pseudo-dynamic models to examine how different kinematic assumptions lead to a variability in the shear stress evolution. We focus on dynamic parameters such as breakdown work, stress drop, and Dc parameter. Our results provide a glimpse of the variability that kinematic source time functions (dynamically consistent or not) might have when used as a constraint to model the earthquake dynamics.