[ghsc-seminars] GHSC Seminar *HYBRID* - Naofumi Aso, Tokyo Institute of Technology, February 7, 2023

[Llenos, Andrea L]

Fault Mechanics in the Roots of the San Andreas Fault through Focal Mechanisms of Low-Frequency Earthquakes


Speaker: Naofumi Aso

                 Earth and Planetary Sciences

                 Tokyo Institute of Technology

Location: HYBRID (online and in-person at 1711 Illinois St, Golden, CO, Rm 204)

                  *Non-USGS visitors are welcome! Please bring a photo ID and arrive early to allow time to go through building security*

Date/Time: Tuesday, February 7, 2023 10-11am MST


Abstract: In addition to ordinary earthquakes, low-frequency earthquakes (LFEs) at depths of 15–30 km have been studied in considerable detail near Parkfield. However, their focal mechanisms, which would provide direct evidence of the fault motion, have not been determined due to low signal-to-noise ratios.

More than a million of LFEs have been classified into 88 families based on the similarity in the seismic waveforms (Shelly, 2017), and the events in the same family are considered to have the same source location and focal mechanism. We utilize the seismic energy of P- and S-waves to solve for the focal mechanism of each LFE family, based on the comparison with synthetic estimates.

As a result, most of the LFEs are consistent with strike-slip plate motion on the San Andreas Fault. However, the focal mechanisms are rotated counterclockwise for the LFEs south of Parkfield. Their minor reverse-fault components are consistent both with the compressional regime expected mechanically for the counterclockwise rotation and with their temporal correlations to compressional tidal stress.

Bio: Ph.D., University of Tokyo, 2015
Postdoctoral Scholar, California Institute of Technology, 2015–2017
Project Assistant Professor, University of Tokyo, 2017–2018
Assistant Professor, Tokyo Institute of Technology, 2018–2023
Visiting Researcher*, USGS Golden, from November 16, 2022, through March 1, 2023
*Sabbatical visit
Research area: Mainly seismic wave analysis of small earthquakes, with broad contributions in stochastic modeling of seismicity, dynamic rupture simulation on earthquake faults, and own campaign observations.

For questions, comments, or speaker suggestions, please contact the GHSC Seminar Committee: Andrea Llenos <allenos at usgs.gov>, Benjamin Murphy <bmurphy at usgs.gov>, Lauren Schaefer <lschaefer at usgs.gov>


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