Exploring southwest Taiwan seismicity looking for markers of aseismic deformation related to active faults

6 months internship with possibility of pursuing a PhD Thesis

This research project focuses on active tectonics of the southwestern Taiwan fold-and-thrust belt.
This area is the place of very high strain rate (several cm/year) seen by geodesy. Yet the seismicity in this area is very low in the upper 8km. Most of the deformation is therefore aseismic. However, it is not known if most of the accumulated energy is dissipated by viscous deformation or aseismic slip, or if the fault system is capable of producing a major earthquake, with important consequences in terms of seismic hazard in this populated area.
The goal of this internship is to better characterize the low seismicity associated with the southwestern Taiwan fault system and to understand the link between seismic and aseismic deformation. To try to lower the detection threshold, we will use the new seismic stations installed in this area to detect more low magnitude earthquakes than recorded in the current catalogs of seismicity. A template-matching detection method can also be used to search in the continuous seismic data for signals similar to the earthquake signals listed in the local or national seismicity catalogs. To improve localization accuracy, "double-difference" (hypoDD) relocation methods will be used.
By lowering the detection threshold and with more accurate locations, we can look for the existence of repeaters (seismic signals that repeat on the same rupture zone), which may be markers of asismic slip on faults. We will also look for the existence of "tremor" (more or less continuous low frequency signal at 2-10 Hz) on these faults, associated with transient slow slip.
We will first look if tremors are observed after major earthquakes (remote earthquakes of magnitude M>8, or local Taiwan earthquakes M>6).
Areas where only "ambient" tremor is observed (i.e. not triggered) also often produce triggered tremor of stronger amplitude and more easily detectable.

The seismic exploration results will be interpreted using geological cross-sections and geodetic measurements (GPS and InSAR).

This internship is part of a bilateral France-Taiwan project "Active-SW" led by Erwan Pathier, which has just been funded by the French and Taiwanese research agencies (ANR and MOST). Within the framework of this project, there is funding for a PhD thesis that would be a continuation of this internship project.