Dynamics and Near‐Field Surface Motions of Transitioned Supershear Laboratory Earthquakes in Thrust Faults

Abstract

We study how the asymmetric geometry of thrust faults affects the dynamics of supershear ruptures and their associated trailing Rayleigh ruptures as they interact with the free surface, and investigate the resulting near‐field ground motions. Earthquakes are mimicked by propagating laboratory ruptures along a frictional interface with a 61° dip angle. Using an experimental technique that combines ultrahigh‐speed photography with digital image correlation, we produce sequences of full‐field evolving measurements of particle displacements and velocities. Our full‐field measurement capability allows us to confirm and quantify the asymmetry between the experimental motions of the hanging and footwalls, with larger velocity magnitudes occurring at the hanging wall. Interestingly, because the motion of the hanging wall is generally near‐vertical, while that of the footwall is at dip direction shallower than the dip angle of the fault, the horizontal surface velocity components are found to be larger at the footwall than at the hanging wall. The attenuation in surface velocity with distance from the fault trace is generally larger at the hanging wall than at the footwall and it is more pronounced in the vertical component than in the horizontal one. Measurements of the rotations in surface motions confirm experimentally that the interaction of the rupture with the free surface can be interpreted through a torqueing mechanism that leads to reduction in normal stress near the free surface for thrust earthquakes. Nondimensional analysis shows that the experimental measurements are consistent with larger‐scale numerical simulations as well as field observations from thrust earthquakes.

Fault structure mapping using satellite-based remote sensing technology in Mindoro

“…With the technology of automated feature detection, edge detection and pattern recognition, were employed to identify linear features consistent with typical fault signatures [8] . In addition, such as digital elevation models (DEMs) and geological maps, were integrated with the satellite imagery to aid in the interpretation of surface features and their relation to potential fault structures [9] .…”

How Fault‐Normal and Shear‐Parallel Stiffness Influence Frictional Sliding Behavior

“…During stick‐slip motion, thought to be the laboratory equivalent of earthquakes, faults generally dilate during the “sticking” phase when shear stress builds up and compact during the slip event, when the stress drops (Rice & Rudnicki, 1979; Scuderi, Carpenter, et al., 2016; Segall & Rice, 1995). In addition, lab studies and numerical models of elastodynamic rupture show that fault normal strains are significant during rupture propagation (Bodin et al., 1998; Rosakis et al., 2020; Tal et al., 2022; Xia et al., 2004). Such changes in fault normal stress could impact frictional strength (Bedford & Faulkner, 2021; Linker & Dieterich, 1992; Shreedharan et al., 2019) and cause dynamic weakening or complex changes in strength as fault slip begins.…”