My current research at Caltech focuses on the response of faults to transient stresses and fluids, both in natural settings and from controlled laboratory experiments. Here is a summary of projects that I have been working on during my Ph.D. program.
Driving mechanisms of earthquake swarms
Swarms are bursts of small magnitude earthquakes without complex time evolution. They are thought to be driven by aseismic slip and fluid flows, but the association is rarely quantitative. In this work, we choose a swarm near Westmorland, California as a case study. The swarm started on September 30, 2020, and lasted for approximately 150 hours. Using sub-daily GPS and InSAR, we found an episode of aseismic slip transient that preceded the swarm by approximately 12 hours. Using a stress-driven model, we discovered that the earthquakes were predominantly non-interacting and they were driven by an aseismic slip transient in the early stage and fluid diffusion in the later stage. The model also provides constraints on frictional parameters.
- Sirorattanakul, K., Ross, Z. E., Khoshmanesh, M., Cochran, E. S., Acosta, M. A. and Avouac, J.-P. (2022), The 2020 Westmorland, California earthquake swarm as aftershocks of a slow slip event sustained by fluid flow, Journal of Geophysical Research: Solid Earth, 127(11), e2022JB024693, doi:10.1029/2022JB024693.
Imaging slow-slip events in Costa Rica and Japan
Slow-slip events are episodes of accelerated fault slips that are too slow to produce seismic waves. As a result, they cannot be detected by seismometers leaving geodesy the only method. However, the ground deformations measured from geodesy are often resulting from a mixture of multiple physical sources that could include phenomena that are not related to fault slips like hydrological cycles. In our work, we rely on the variational Bayesian Independent Component Analysis (vbICA) to extract the signals related to fault slip. Then, we invert the surface deformations for slip on the fault using semi-analytical solutions of elastic dislocations in homogenous half-space. We apply this data processing workflow to image slow-slip events in the Nicoya peninsula Costa Rica and the Nankai subduction zone in Japan.
Related conference presentation:
- Sirorattanakul, K., Gualandi, A. and Avouac, J.-P., Imaging Slow-slip Events in Costa Rica, American Geophysical Fall Meeting, San Francisco, CA, USA, December 9-13, 2019, Poster Presentation T13D-0308.
Injecting fluids into laboratory-scale earthquake faults
Fluids permeate the crusts and can be added on faults by both natural and industrial processes. Once added to the faults, fluids will reduce friction locally leading to instability. However, fluid-induced fault slips do not need to always be fast earthquake ruptures but could also be a gentle aseismic creep. In this work, we mimic this process with controlled and highly instrumented laboratory experiments using cm-sized samples. The samples are monitored by using the camera at various frame rates (from 1 frame per 5 minutes to 1 million frames per second). These images are subsequently analyzed with digital image correlations (DIC) to reveal how the samples deformed over the course of fluid injection experiments. Pocket of Quartz gouge can also be added to our setup to better represent fault zones found in nature.
Related conference presentation:
- [Invited] Sirorattanakul, K., Rubino, V., Rosakis, A. J., Lapusta, N., Injecting fluids into laboratory-scale earthquake faults, 11th James K. Knowles Lectures and Caltech Solid Mechanics Symposium, Pasadena, CA, USA, March 6, 2020.