Work Package 3: Physical interpretation of scale dependence

One of the present challenges in earthquake source mechanics is to reconcile laboratory experiments, seismological measurements, geological observations in order to obtain a coherent understanding of the physical processes governing earthquake rupture across 15 units of magnitude. To gain deeper insight into the dynamic processes before, during, and after an earthquake rupture, high-fidelity near-source observations of various physical parameters (e.g. displacement/strain in the volume, particle accelerations around the source) are needed. In FEAR, we will utilize microseismicity data and a range of near-source observations at unprecedented levels of resolution to better constrain and calibrate earthquake source models and simulations and investigate the scale dependence of earthquake source parameters at all relevant scales. With dense instrumentation, we will be able to close the loop “observed data - source kinematics - rupture dynamics - predicted data”, based on data-analysis, parameter estimation (e.g. source inversion) and high-performance-computing-enabled forward modelling. The project will allow us to constrain the in-situ constitutive relationship of the fracture process and provide fundamental insights into the scale-dependency problem of earthquake physics. Laboratory scale models, simulations, and inverse modeling will be used for estimating mechanical, frictional, and hydrogeological parameters relevant for constitutive equations. On the Bedretto scale, models of how hydrogeological and mechanical processes and their resultant stress variations lead to fault activation, as well as models of preseismic (nucleation, foreshocks, transients, slow-slip, runaway ruptures) and coseismic processes will be developed. Models of seismicity evolution as influenced by stress preconditioning of the fault, in conjunction with the real-time data from the monitoring system, will be part of the adaptive traffic light (ATLS) risk-mitigation system. How to upscale insights gained from models on the laboratory and Bedretto scales to those of natural faults, with the ultimate goal of improving understanding of large earthquakes and their associated seismic radiation and shaking levels, is a central component of this work package.