Understanding earthquake source processes with spatial coherence

Speaker: Seok Goo Song
Song et al. (2009) show that spatial coherence analysis tools, commonly used in geostatistics, can be successfully applied to characterizing earthquake source processes. Earthquake rupture is described by key kinematic source parameters, such as slip, rupture velocity, peak slip velocity, and slip duration (rise time). The heterogeneity of each source parameter is characterized with auto-coherence while the linear dependency (coupling) between parameters is constrained with cross-coherence. Both zero and non-zero offset spatial coherence can be considered in the form of cross-coherence. This study shows that the non-zero offset coherence analysis method can capture many interesting features of earthquake rupture, which may be difficult to analyze, or even detect by zero offset coherence only. For instance, the correlation maximum between slip and rupture velocity can be shifted from zero offset, i.e., large slip may generate faster rupture velocity ahead of the current rupture front, which may be important for rupture directivity. This spatial coherence analysis method may have potential not only for understanding earthquake source characteristics, but for generating physics-based kinematic rupture models for strong motion simulation. Both kriging and sequential conditional (Gaussian) simulation from geostatistics can be used in generating a number of realizations of earthquake source models that reproduce target coherence structures. This type of coherence analysis may also help us perform kinematic source inversion in a more physics-based way. The spatial coherence structure, i.e., auto- and cross-coherence of key kinematic source parameters, can be used both in testing the reliability of currently available kinematic source inversion methods and in developing physically-guided regularization methods in actual inversion procedure.