The Effect of Depth‐Dependent Stress in Controlling Free‐Surface‐Induced Supershear Rupture on Strike‐Slip Faults

Abstract

The state of stress in the upper crust plays a crucial role in determining the earthquake dynamic rupture process, and in particular, the rupture velocity, which further exerts a great influence on near-fault ground motion. With a combination of direct stress measurement methods such as hydraulic fracturing, overcoring, or wellbore breakouts, several scientific drilling projects (e.g., San Andreas Fault Observatory at Depth project, Parkfield, California (Zoback et al., 2011), the Wenchuan Earthquake Fault scientific Drilling Project Hole-1, Dujiangyan, Sichuan, China (Li et al., 2013)) have measured the state of stress and pore pressure in and near the fault zone. A common feature in these experiments is that in-situ stresses in the upper crust are depth-dependent (e.g., Brudy et al., 1997). The Earth's free surface, where the phase conversion of upward SV to horizontally diffracted P waves occurs, has the capability to trigger free-surface-induced (FSI) supershear ruptures on strike-slip faults with the aid of the generalized Burridge-Andrews (BA) mechanism (Kaneko & Lapusta, 2010). With the assumption of a uniform shear and normal stress regime, the supershear daughter crack of FSI supershear ruptures with a low stress drop value or shallow hypocenter locations may transition to a sub-Rayleigh daughter crack (Hu et al., 2019) (We note that daughter crack, propagating ahead of the main crack, can travel at a sub-Rayleigh speed). Depth-dependent stress, with lower stress near the surface, can make FSI-mediated supershear rupture less likely to proceed over the

Dynamic Rupture Simulation of the 1833 Songming, Yunnan, China,M8.0 Earthquake: Effects From Stepover Location and Overlap Distance

“…Moreover, we identify that supershear ruptures may have occurred during the Songming earthquake. However, we cannot identify whether the mechanism of supershear rupture was the Burridge–Andrews mechanism (Andrews, 1976) or free surface‐induced supershear (Hu et al., 2021; Kaneko & Lapusta, 2010). All the above situations need to be further investigated.…”

“…Hence, we set the σ V as increasing from the surface to 5 km below the free surface, below which it remains constant. This kind of stress scheme could be physically explained by the hydrostatic increase in pore fluid pressure down to a critical depth, below which the pressure increases lithostatically (Hu et al., 2021; Rice, 1993). Figure 4a presents an example of the distributions of the effective initial stresses varying with depth.…”

Non-typical supershear rupture: fault heterogeneity and segmentation govern unilateral supershear and cascading multi-fault rupture in the 2021 Mw 7.4 Maduo Earthquake

“…The surface rupture initiates a supershear transition by P-wave diffraction at the free surface (e.g., Kaneko & Lapusta, 2010;J. Xu et al, 2015;Hu et al, 2021;Tang et al, 2021). The supershear rupture front then dynamically triggers coseismic slip on F2 and F3 at about 14 and 18.5 s, respectively (Figure 2F).…”