Research

The mechanics and frequency of rupture propagation through zones of fault geometrical complexity

Zones of geometrical complexity can act as conditional barriers to rupture propagation, where material properties, rupture dynamics, and the availability and geometry of neighboring faults control the probability of throughgoing rupture. We use a combination of paleoseismic trenching, numerical modeling, and analysis of historical surface rupture maps to understand how frequently zones of geometrical complexity are breached, allowing a propagating rupture to continue growing, and the mechanics of this process. We study both the general mechanics of geometrical complexity in rupture propagation, using global surface rupture maps, and the multi-cycle mechanics and frequency of specific zones of geometrical complexity, such as the Cajon Pass step-over in Southern California or segment boundaries on the Wasatch fault in Utah.

Collaborators: Mike Oskin (UC Davis), Tom Rockwell (SDSU), Irina Delusina (UC Davis), Drake Singleton (USGS), Emily Brodsky (UCSC), Kelian Dascher-Cousineau (UC Berkeley), SCEC SOURCES interns: Vanessa Herrera (SDSU), Sophia White (UCSC)

Publications: Rodriguez Padilla et al. (2022), Rodriguez Padilla et al. (2024)

The influence of elastic interactions on long-term fault dynamics

Paleoseismic evidence from parallel, neighboring faults across the world suggests that fault synchronization and alternation are frequent behaviors in the geologic record. We model a simple two-fault system to examine the role of the elastic interactions between the faults in establishing these behaviors.

Collaborators: Jean-Philippe Avouac and Alexis Saez (Caltech)

The distribution of inelastic strain during earthquakes and over multiple earthquake cycles

Inelastic deformation constitutes a permanent sink of strain energy during earthquakes, modifies the elastic properties of the shallow crust, threatens lifelines, and amplifies ground shaking during earthquakes. We use field observations and remote sensing (often drone images) to characterize the spatial distribution of fracturing and folding around faults during individual earthquakes and over multiple earthquake cycles to investigate the mechanisms that accommodate permanent strains within the rock volume and the evolution of the mechanical properties of that volume. We have applied this to individual earthquakes (e.g., Ridgecrest 2019, Landers 1992), and to fault zones that record a cumulative record of normal faulting spanning millenia (e.g., the Volcanic Tableland in Bishop or the Modoc Plateau in northern California).

Collaborators: Mike Oskin (UC Davis), Chris Milliner (Caltech), Andreas Plesch (Harvard), SCEC SOURCES interns: Mercedes Quintana, Brian Castillo, Ruth Prado, Tom Shea, UC Davis undergraduate: Leslie Garcia

Publications: Rodriguez Padilla et al. (2022a), Rodriguez Padilla et al. (2022b)

Probabilistic displacement hazard assessment for strike-slip faults

Fracturing and surface displacements during earthquakes threaten infrastructure and lifelines. We have been working to expand probabilistic displacement hazard models to account for the hazard posed by distributed fracturing, such as that observed in immature earthquakes in the Eastern California Shear Zone. Because surface processes erase the record of faulting, limiting the development and application of hazard models to fault zones that have not hosted a recent earthquake, we also work to quantify the loss of information for mapping fault zones as a function of the time elapsed since the most recent earthquake (see collaborations section for more info on this work, led by PhD candidate Mindy Zuckerman).

Collaborators: Mike Oskin (UC Davis), Ramon Arrowsmith (ASU), graduate student: Mindy Zuckerman (ASU)

Publications: Rodriguez Padilla and Oskin (2023)