CAREER: From slow to fast, micro to macro, single events to cascades: A multi-scale study of seismic event triggering in lab and nature

University Of Memphis, Memphis TN

Investigators

Abstract

"Earthquake triggering" refers to an earthquake causing other earthquakes to happen seconds to years later, both nearby and up to thousands of miles away. Most earthquakes are thought to result from this process, yet the underlying causes remain unclear. Earthquake triggering results in clustered "families" of earthquakes, with foreshocks, mainshocks and aftershocks. Foreshocks may provide information about possible upcoming, larger-magnitude mainshocks, and mainshock size and location may be used to forecast aftershocks. Still, there is much to learn, for example, what is it about a fault that makes it likely to be triggered by another earthquake, and can we use this knowledge to improve earthquake forecasts? Using newly-available instruments, Goebel and his group will record tiny earthquakes during abrupt fault slip between blocks of rock in their laboratory. They will see earthquake triggering as it happens in the lab, test conditions that make triggering more or less likely to occur, and apply this knowledge to real-world earthquakes. This research will contribute directly to improvements in assessing seismic hazard and forecasting aftershocks in real time. Earthquake triggering is ubiquitous throughout different tectonic and stress regimes. Triggering processes involve static and dynamic stress transfer, post-seismic creep, poroelastic effects, sub-critical crack growth and rate- and state-dependent friction; however primary mechanisms and conditions that amplify aftershock triggering remain largely unresolved. Is triggering solely controlled by mainshock characteristics or also by local conditions such as fault stress and damage, and are there specific crustal properties that enhance triggering? What controls changes in triggering time-scales and are such changes indicative of stress state and proximity to large failure events? To address these questions, this study will concentrate on a multi-scale investigation of stress relaxation and triggering in lab and nature. Only a few studies have focused on seismic triggering in controlled frictional-sliding experiments that mimic earthquake behavior. Full waveforms of sub-millimeter lab-fractures and slip can now be recorded using high-speed, broad-band seismic instrumentation. Based on such records, this work will advance the ability to detect triggering during natural stress relaxation in the lab and test the hypothesis that triggering is not only a function of source characteristics but also of fault stress and damage state. The proposed research addresses three primary questions: 1) What conditions and mechanisms amplify earthquake triggering? 2) Are triggering time scales indicative of fault stress state and proximity to large failure events? 3) Which laboratory processes are scale-invariant and thus help advance the understanding of fault constitutive behavior? To address these questions, a series of triaxial and direct-shear tests on lab-generated faults at mid-crustal stresses will be conducted. These tests will assess the roles of i) fault roughness; ii) normal stress, iii) fault damage, iv) pore fluid pressure and v) stiffness in enhancing or inhibiting triggering. This research aims to unravel how these components are linked and how lab results can be transferred to the natural system. The results are expected to help identify key factors that govern triggering and their implications for earthquake predictability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.