Stress heterogeneity on faults

Stress heterogeneity in ten laboratory shear configurations

Stress heterogeneity on rock discontinuities is critical in shear friction evolution and earthquake nucleation, whereas the local stress distribution has seldom been applied for shear analyses in laboratory shear tests. Instead, the average stress on rock joints was usually taken as an indicator. Thus, we investigated stress conditions on rock discontinuities in various laboratory shear tests numerically to account for the influence of stress heterogeneity on shear behaviors.

Effects of fault roughness on dilatancy behavior

We perform laboratory shear tests on rough faults with millimeter-scale asperity heights and analyze the four types of dilation or compaction behavior observed during stick-slip cycles. In the stick phases, dilatancy behavior inferred from the asperity contacts agrees well with the variation of normal displacement. The locations of acoustic emission (AE) events are also consistent with the potential surface damage regions estimated from the evolution of asperity contacts at various shearing displacements. Stick-slip events with compaction-dominant interseismic slip usually occur at large shear displacements on interlocking faults when overriding high asperities. In those stick-slip events, the proportion of large-magnitude AEs is lower, resulting in higher Gutenberg–Richter b values. A generalized schematic model is also proposed for the complex dilatancy behavior during stick-slip cycles.

Delayed seismicity caused by stress heterogeneity

We observed staged friction/stress drop during the slip phases of stick-slip cycles on rough laboratory faults. Numerical simulations were conducted to investigated the effect of stress heterogeneity. Two-dimensional ruptures on the heterogenous fault were analyzed via the distribution of local shear slip and stress.

Planetary science

Possible lunar seismicity infered from lunar landslides

We investigated the possibility of moonquake-induced crater landslides by numerical simulations incorporating modified seismic loadings from Apollo lunar seismic ground motions. The lunar geomorphology of nearby faults was taken as complementary evidence for the potential moonquakes. Numerical results with detailed parameter analyses reproduced rotational and translational landslides in either double-side or single-side sliding patterns. The seismic source location can induce directional landslides, with large-displacement landslides on the loading side and small-displacement landslides or stable slopes on the opposite side. Those landslide sliding patterns and surrounding faults contribute to locating the possible moonquakes. A feasible framework is also proposed for landslide and paleoseismicity dating when more lunar samples are returned in the future.