Sharan Shreedharan, Utah State University

The shallow portion of plate interfaces hosts a range of slip behaviors including dynamic ruptures and Slow slip events (SSEs) exhibiting a range of magnitudes and recurrence intervals. However, the frictional and mechanical behaviors of the shallow portion of plate interfaces remain enigmatic. In this talk, I explore two commonly measured parameters in brittle rock deformation experiments – frictional healing and the critical slip distance. Using samples obtained by drilling offshore of the N. Hikurangi subduction zone, I show that that the frictional healing rates of the likely fault material at the northern Hikurangi margin is nearly zero (< 0.0001/decade). In concert with relatively low loading rates near the trench, near-zero frictional healing rates, which are often associated with phyllosilicates, are a key ingredient in promoting frequent, quasi-periodic, low-stress-drop slip events in the forearc of subduction zones, including the increasingly common observations of shallow SSEs at subduction zones globally. Next, I show that laboratory faults with finite granular width can be well modeled by an extended elasto-frictional system with rate-state friction and radiation damping, conceptually similar to a Burridge-Knopoff model. This model reproduces slow and fast slip, period-doubling and deterministic chaos observed in rigid-block laboratory experiments at comparable effective stresses and strain rates. I propose a framework where seismological (LFEs, VLFEs, tremors) and geodetic (SSEs) slow earthquakes represent frictional instabilities at vastly different scales even on simple planar faults, with the SSEs providing the necessary elevated loading rates that help sustain VLFEs and LFEs on thinner shear zones with shorter Dc.

Short Biography
Srisharan is an Assistant Professor of geomechanics and geophysics in the Department of Geosciences at Utah State University. He is broadly interested in faulting, friction and the mechanics of how earthquakes start, propagate and stop, particularly at shallow plate interfaces and in subsurface energy systems. Srisharan uses a combination of friction experiments, ultrasonic monitoring, numerical modeling and machine learning techniques in his research to better understand faulting and friction at multiple scales. Before Utah, he was an Institutional Postdoctoral Fellow at the University of Texas Institute for Geophysics. Srisharan earned his PhD in Geosciences at Penn State, and an MS in Geological Engineering from the University of Arizona.