GAUK project No. 200426 (Charles University Grant Agency)

Summary:

Dynamic (physics-based) earthquake models describe how elasticity and friction law govern rupture propagation along tectonic faults. Determining parameters that influence the rupture process for a specific earthquake involves solving a nonlinear inverse problem, requiring a large number of time-consuming dynamic simulations. Our project will use the computationally efficient code fd3d_tsn_pt (Gallovic et al., 2019), which is, however, so far, limited to a planar fault perpendicular to the free surface. The project's primary goal is to enable the application of dynamic rupture inversions to normal/reverse faults with a shallow rupture by incorporating a dipping (inclined) fault geometry in the code. We will implement the so-called vacuum formulation of the free surface (Zeng et al., 2012) in the finite-difference code to permit modeling surface topography and dipping faults (first year). The influence of topography on rupture dynamics will be studied on the 2016 Mw 6.1 Tottori earthquake (first year). We will test the performance of the dipping fault implementation using community benchmarks (second year), and then perform a dynamic seismic source inversion of the Mw 6.3 2009 L Aquila earthquake in a relatively low-frequency range, <~1 Hz (second year). Eventually, we will enhance the resulting models with random small-scale heterogeneities to model the observed data in a broad frequency range (0-10 Hz), important for engineering applications and seismic hazard (third year).

Project Objectives:

The project's primary objective is to enable the application of dynamic rupture inversions to normal/reverse faults with a shallow rupture by incorporating a dipping fault geometry in the dynamic rupture simulation code fd3d_tsn_pt (Gallovic et al., 2019). In the first part of the project, we will implement the vacuum formulation of a free surface (Zeng et al., 2012) in the code. Using this method, we will study the influence of surface topography on rupture dynamics in a model with a vertical fault. We will use the vacuum formulation to model dipping faults and validate the new code in the publicly available USGS/SCEC community benchmarks (Harris et al., 2018). We will perform a dynamic inversion of the Mw 6.3 2009 L Aquila earthquake in a relatively low-frequency range (<~1 Hz). Subsequently, we will attempt to enrich random small-scale heterogeneities to model the observed data in the frequency range up to ~10 Hz, important for engineering applications and seismic hazard assessment.

Keywords:

Earthquake Modeling. Seismic Source Inversion in a Bayesian Framework. Dynamic Rupture Propagation. Improving a Finite-Difference Code.

Method illustration