Organizers: Eric Dunham, Judi Chester
Location: Plaza Ballroom, Hilton Palm Springs Resort, Palm Springs, CA

Over the past several years there has been a surge of research on dynamic weakening mechanisms, i.e., processes by which fault strength is dramatically reduced during coseismic slip. Dynamic weakening offers a possible resolution of a number of outstanding issues in fault and rupture mechanics, including the heat flow paradox, the low stresses inferred to be acting on major faults, and why ruptures take the form of narrow slip pulses. A variety of weakening mechanisms have been proposed, including flash heating of asperity contacts, thermal pressurization of pore fluid, macroscopic melting, and thermal decomposition weakening. At this workshop, speakers will provide an overview of 1) the latest high velocity friction experiments; 2) theoretical predictions of fault strength as a function of slip rate, normal stress, and other variables; 3) consequences of dynamic weakening in spontaneous rupture models; and 4) field constraints. The objective of the workshop is to foster discussion between experimentalists, modelers, and geologists in order to determine which weakening mechanisms are active in natural earthquakes and how they influence rupture behavior.

SATURDAY, SEPTEMBER 12th

Introduction and Overview
10:00 - 10:10 Introduction, Eric Dunham and Judi Chester
10:10 - 10:40 Overview of Dynamic Weakening Mechanisms, Jim Rice

Session I: High Velocity Experiments and Understanding Weakening Mechanisms
10:40 - 11:10 Experimental constraints on coseismic slip David Goldsby
11:10 - 11:40 Laboratory experiments to understand slip weakening due to flash heating at seismic slip rates Vikas Prakash
11:40 - 12:10 Fault plasticity at seismic slip rates: Experiments and theory Kevin Brown

12:15 - 13:45 Lunch

13:45 - 14:15 Dynamic weakening by gouge lubrication: Experimental observations of granite friction at velocity range of 0.001-1.0 m/sZe'ev Reches
14:15 - 14:45 High-speed friction of Punchbowl Fault ultracataclasite in rotary shear: Characterization of frictional heating, mechanical behavior, and microstructure evolution Hiroko Kitajima
14:45 - 15:30 Session I Discussion, led by Terry Tullis

15:30 - 15:45 Break

Session II: Interpreting Observations and Integrating Dynamic Weakening into Rupture Models
15:45 - 16:15 Flash weakening and the onset of melting Alan Rempel
16:15 - 16:45 3D earthquake-sequence simulations with thermal pressurization of pore fluids: Effect of heterogeneous fault properties on slip complexity and interseismic stress Nadia Lapusta
16:45 - 17:00 Wrap-Up Discussion

18:30 - 20:00 Dinner

SUNDAY, SEPTEMBER 13th

Session II: Continued
08:30 - 09:00 3D earthquake-sequence simulations with thermal pressurization of pore fluids: Effect of heterogeneous fault properties on slip complexity and interseismic stress Giulio Di Toro
09:00 - 09:30 Semi-empirical constitutive relations for dynamic weakening based on high speed friction experiments Nick Beeler

09:30 - 09:45 Break

09:45 - 10:15 What can ground motion in the Chi-chi earthquake tell us about dynamic weakening? Joe Andrews
10:15 - 11:30 Session II Discussion, led by Nadia Lapusta

Moving Forward - What earthquake physics science priorities should SCEC4 pursue?
11:30 - 11:59 Open Discussion and Wrap-Up of Day 2, Eric Dunham and Judi Chester

Registrant List for the Dynamic Weakening Mechanisms Workshop