Investigations of fault zone behavior during earthquake cycles using hydrology and geodesy
This study investigates processes of three stages of the earthquake cycle: interseismic, post-seismic and coseismic periods. For the inter-seismic period, this thesis explored the inter-seismic strain accumulation on the Nicoya Peninsula, Costa Rica integrating InSAR and GPS data. This work demonstrates that the InSAR data can be used to recover small deformation signal of long wavelength with refined resolution when integrated with GPS observations. The spatial correlation between the distribution of coupling and the locations of slow slip events and low frequency events suggests that fluid and frictional heterogeneities may be the two main factors influencing coupling variations in the Nicoya, Costa Rica subduction zone. For the coseismic period, this thesis studied the coseismic friction associated with the 2008 MW 7.9 Wenchuan Earthquake using repeat measured temperature profiles across the fault slip zone, since measuring the heating signal on the fault zone after an earthquake is the most direct and efficient way to quantify the coseismic friction. The long-term temperature records following the Wenchuan Earthquake are consistent with low coseismic friction. The observed thermal anomalies above and within the fault zone cannot be the frictional transient from faulting and are likely a result of advective flow. For the post-seismic period, this thesis investigated the healing process after the Wenchuan Earthquake. The hydrogeologic properties of the fault zone can serve as a proxy for fracturing and the post-seismic recovery of fault strength, which is one of the major unconstrained elements of the earthquake cycle. We used continuous monitoring of borehole water response to tidal forcing to measure the continuous in-situ permeability properties of the Wenchuan Earthquake fault damage zone. Observed post-seismic episodically decreasing permeability over time indicates an interaction between the healing and damage in the aftermath of a major earthquake.