Under high co-seismic slip rates and normal stress, frictional melt may be generated, extensively weakening a fault and rendering classical rate-and-state friction laws ineffective. Pseudotachylytes (solidified frictional melt) created in laboratories and found in natural fault zones thus provide thermal and mechanical information critical to the study of dynamic shear zone processes, including thermal runaway, stress drop, and viscous braking. While existing geochemical and mineralogical evidence has suggested the occurrence of disequilibrium melting during pseudotachylite generation, few studies have leveraged it to resolve the kinematics of co-seismic slip. This study uses a numerical model to constrain the dynamics of frictional melt formation using pseudotachylyte surface micro-roughness inferred to form due to disequilibrium melting. We optimize the kinematic parameters of the Yoffe source time function using the micro-roughness data of a pseudotachylyte sample from Gole Larghe Fault Zone. We also perform a series of forward modeling experiments to examine the interplay between critical source properties such as melt growth, temperature, and shear stress. We find that the optimal slip rates and displacements are a magnitude larger than other independent estimates in order to compensate for a lack of heat production, and fault experienced a complete stress drop (~99%) with its average more than a magnitude less than laboratory experiments and field measurements. We argue that it is a consequence of melt superheating from ineffective heat transport, activating negative feedback between heat and viscosity. Additional forward modeling results reveal that lower melting power (100s of degrees) and higher thermal conductivity (<100 times) are effective means to achieve higher power density and drive melt growth, but are in contradiction with the steep temperature gradient inferred from the low topographic relief on the pseudotachylyte surface. The possibility of lower melting points implies more intensive pulverization and grain size reduction during frictional melting and consequently, higher fracture energy for the energy partition model. Finally, our simulations show that temperature gradient at the phase interface and power density are not correlated, which is at odds with previous theoretical assumptions. We suggest that coupling frictional melt dynamics with normal stress typical of natural faults in future modeling endeavors might be the key to resolving some of these contradictions.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Author-supplied Keywords","value":["Earthquake physics","Numerical modeling","Frictional melt"]},{"label":"Administrative Note","value":"Drupal Node ID: 24123