[S-SS07] Fault Rheology and Earthquake Physics

[SSS07-18] Dynamic simulations of coseismic slickenlines on non-planar and rough faults

*Takumi Aoki¹, Yoshihiro Kaneko¹, Jesse Kearse² (1.Kyoto University, 2.Victoria University of Wellington)

Knowing the directions of rupture propagation of paleo-earthquakes is a challenging, yet important task for our understanding of earthquake physics and seismic hazard, as the rupture direction significantly influences the distribution of strong ground motion. Recent studies proposed a relationship between the direction of rupture propagation and curvature of slickenlines formed during seismic slip (Kearse et al., 2019; Kearse and Kaneko, 2020). The relationship was established using a global catalogue of historical surface-rupturing earthquakes and dynamic models of idealized, planar faults. In their models, the slip direction changes within the cohesive zone of propagating rupture, resulting in curved slickenlines, consistent with the mechanism of Spudich et al (1998). At the same time, some slickenlines previously documented on geometrically complex fault segments show their convexity opposite from the simple model prediction, which we refer to as 'abnormal convexity'. To explain such observations, we perform simulations of spontaneous earthquake ruptures on non-planar and rough faults. We find that our models with non-planar fault geometry can lead to abnormal convexity of slickenlines under certain conditions. For strike-slip faults, non-planar faults combined with a homogeneous tectonic stress field induce locally non-zero vertical prestresses, causing the slickenlines to have abnormal convexity. Our results also show that it is difficult to reproduce abnormal convexity of slickenlines near the Earth's surface, especially when the fault strength and initial shear stresses increase with depth. This is consistent with observations that most of slickenlines have the same convexity as predicted by the planar-fault models. Our results imply that the effect of non-planar fault geometry on the curvature of slickenlines may be important when inferring the rupture direction of paleo-earthquakes from the trenching of curved slickenlines.