On the origin of earthquake complexity in continuum fault models with rate and state friction

Institute of Geophysics, ETH Zurich.
This work was sponsored by EC-Project RELIEF (EVG1-CT-2002-00069).

It is of great interest to isolate the fundamental physical mechanism controlling observed statistical properties of seismicity patterns. We present four numerical studies investigating the e ciency of uid related mechanisms and the role of fault zone heterogeneity in producing observed earthquake complexities. The 3-D models of the continuous class are governed by rate- and state-dependent friction and, depending on the problem, by elasto-hydraulic interactions or heterogeneous frictional properties on the 2-D fault plane. First, for certain ranges of hydraulically relevant parameters dilatant processes are shown to stabilize accelerating slip instabilities on a uid in ltrated fault, leading to nonuniform spatio-temporal slip evolution. The second model demonstrates the ability of heterogeneous pore pressure conditions in an undrained environment to produce complex slip pattern, where unstable sliding corresponds to regions with low degrees of overpressurization. In the third study we focus on the role of complex fault zone structure, parameterized by heterogeneous distributions of the rate and state slip weakening distance. The approach is shown to be a powerful and consistent method to generate seismicity patterns with properties similar to those of natural seismicity. Due to the e ciency of this parameterization we use it in the fourth study to investigate fault zones at di erent evolutionary stages and associated seismic response types. Using heterogeneous, correlated maps of the slip weakening distance we explore systematically the e ect of the range of size scales, correlation lengths and a statistical parameter related to roughness, on seismic response characteristics. In summary, we observe an increase in e ciency from the rst to the last study to generate synthetic seismicity with realistic statistical properties, suggesting that the range of size scales is the most fundamental parameter in explaining complex earthquake related phenomena. In the last part we analyze the generated synthetic seismicity catalogs with respect to their overall source scaling behavior. We nd that the general scaling trends of source properties of the simulated slip maps are in very good agreement with observations reported in the literature. We also show that the catalog of source models provides a useful resource on physically self-consistent scenario earthquakes for groundmotion simulations. We make use of this resource calculating waveforms and shake intensity maps for a suite of example events.

Hillers, G. ON THE ORIGIN OF EARTHQUAKE COMPLEXITY IN CONTINUUM FAULT MODELS WITH RATE AND STATE FRICTION, PhD-thesis, Institute of Geophysics, ETH Zurich, ETH No. 16430,