Acoustic Emission Accompanying Nucleation of Dynamic Slip on a Model Heterogeneous Fault of Meter Scale

Abstract—Regularities in the distribution of sections with different frictional properties govern fault slip dynamics to a great extent. Since it is impossible to directly study the structure of a fault at a seismogenic depth, developing fault diagnostics methods that can yield information on structural peculiarities of the zone where an earthquake source nucleates, in addition to a specific fault dynamics, is of primary interest. This article presents results of laboratory experiments directed at studying the regularities of elastic wave emission during shear deformation of a model fault with a spatially inhomogeneous structure of the slip interface. The model fault was a loaded contact of diabase blocks 750×120 mm2 in size. Two round zones, each 100 mm in diameter, were made at the interface. Those zones had high strength, showing the property of velocity weakening, so-called asperities. The relative position of asperities varied in experiments. The process of dynamic slip nucleation and emergence, caused by asperity disruption, was accompanied by emission of a large number of acoustic pulses that were recorded in the 20–80 kHz frequency range. The data on spatial distribution of pulses make it possible to detect two separate contact regions only when the distance between these regions exceeded 20 mm. Differences in the statistics of pulses emitted at different asperities were observed.