Laboratory Earthquakes: Characterization of Ground Motion and Stress States in Complex Rupture Scenarios Using High Resolution Optical Diagnostics

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This award is funded under the American Recovery and Reinvestment Act 2009 (Public Law 111-5) The thrust of this research effort will focus on the advancement of a unique experimental capability for generating earthquake-like ruptures under controlled laboratory conditions. The experiment features a model specimen with an interface that simulates a natural fault in the Earth?s crust. The assembly is held together by static friction under the action of a an applied compressive load which mimics natural tectonic stresses. Seismic slip induced within the specimen results in a dynamic rupture that propagates along the fault while radiating seismic wave energy into the body of the specimen. A well instrumented laboratory earthquake setup provides a versatile testing capability for investigating complex seismological phenomena such as dynamic frictional sliding, radiated ground motion, supershear ruptures, and dynamic rupture processes associated with complex geometries. Work under the support of this grant will target the development and integration of new optical diagnostics for the precise measurement of the resulting particle (ground) motion and associated stress fields in these experiments. A full suite of optical diagnostics, such as time resolved interferometry techniques and high speed digital photography will enable high resolution measurements of stress and ground motion at an array of fixed measurement stations in addition to full field characterization of radiated wave fields. Collectively, these advanced laboratory earthquake capabilities will permit the experimental investigation of numerous long standing problems of seismological relevance. Research findings will help to bridge the gap between empirical evidence obtained from the field and computational predictions with obvious potential benefits to seismology. The interdisciplinary nature of this research necessarily involves assigning priorities to the many goals within individual disciplines. In particular, two main characteristics are reflected in the design of the new experiments. Firstly, the experimental design is intended to be as relevant as possible to the geophysical systems that they model. Secondly, the experimental configuration is kept as basic as possible so that real-time data collection and analyses can produce, unequivocal, understanding of the phenomena under scrutiny. The proposed experimental investigations will address and resolve many controversies regarding the dynamics of earthquakes. New findings from such benchmark experiments will provide data to modelers that will subsequently aid in the validation of various kinematic inversion and dynamic rupture models. The research is designed to facilitate connections in seismology and earthquake hazard mitigation. The following list provides an overview of the proposed instrumentation enhancements and outlines the broader impacts of this proposal in a number of targeted areas of seismology. Primary research objectives are: Setting up highly instrumented Laboratory Earthquake experiments especially designed to study a variety of rupture phenomena and to serve as benchmarks for the validation of analytical and numerical models of dynamic earthquake rupture. Simultaneously measuring ground motion, slip velocity, and the complete stress tensor in the local vicinity of propagating ruptures. Combining high temporal resolution, point-wise measurements, obtained at multiple stations, along with spatially resolved full-field measurements to study dynamic frictional laws in the presence of non-uniform sliding. Utilizing the highly controlled laboratory environment to clearly identify the dominant and distinguishing signatures of radiated ground motion resulting from either sub-Rayleigh or supershear ruptures and from their transitions in both speed and mode (pulse-like vs. crack-like). Investigating the unknown effect of supershear events on seismic hazards. Studying rupture propagation through complex geometries and characterize the high frequency content of the strong ground motion from such events. Introducing complex and more realistic fault geometry benchmarks and measuring final slip distribution, in addition to time-resolved multi-station recordings, in order to validate kinematic inversion codes.