PhD Defense of Deepa Mele Veedu: Slow and fast slip events near the stability transition from laboratory experiments and numerical simulations
- Oral Defense
About the Event:
Theoretical studies establish a stability criterion for frictional instabilities. However, how the transition from slow to fast ruptures takes place is not fully understood. Here, I investigate the unique fault behaviour around the stability criterion in numerical and laboratory experiments. In the first study, I simulate sequences of alternating slow and fast ruptures on the same patch to explain the peculiar recurrence pattern of the period-doubling Parkfield tremors along the San Andreas Fault. Second, I systematically investigate the physical parameters that control the inter-event times of the slow-fast ruptures. I extend the criterion for instabilities from a simple threshold to a finite transition zone characterized by slow-slower and slow-fast events. Finally, I study the slow-fast phenomenon in a laboratory setting using granular quartz samples to compare the bifurcation pattern to that predicted numerically. Overall, these findings may provide a theoretical framework to understand slow transients propagating within the mainshock rupture area.
Oral Defense Chair: Prof. Kerry Sieh, Nanyang Technological University, Singapore
Member: Asst. Prof Aron Meltzner, Nanyang Technological University, Singapore
Member: Asst. Prof Judith Hubbard, Nanyang Technological University, Singapore
Advisor: Asst. Prof Shengji Wei, Nanyang Technological University, Singapore
Co-advisor: Asst. Prof Sylvain Barbot, University of Southern California, United States
About the Speaker:
Deepa Mele Veedu joined NTU as an ASE student in 2014 and started her first study on the Parkfield tremors with Sylvain Barbot, in which she discovered slow and fast ruptures on the same patch. After publishing that work in 2016, she wanted to produce slow-fast ruptures in a laboratory setup. With that in mind, she visited the National Institute of Geophysics & Volcanology, Italy in 2017 using the Stephen Riady fund. In Italy, she collaborated with Carolina Giorgetti, Marco Scuderi, and Cristiano Collettini. On a beautiful day, they witnessed laboratory events slipping slow and fast, one after another, in granular quartz material. Hence, they validated the numerical results. To test if another laboratory setting can reproduce the same slow-fast phenomenon, Deepa has extended her collaborations with Chris Marone, Penn State University, in 2018 using the second-time Stephen Riady funding. With the team at Penn State University, she reproduced the same slip behaviour in quartz material with six different grain sizes, once again showing that the results are robust, and it can be applied to a range of slip observations from natural faults.