Interplay Between Seismic and Aseismic Deformation on the Central Range Fault During the 2013 Mw 6.3 Ruisui Earthquake (Taiwan)

The 2013 Ruisui earthquake represents the first unequivocal evidence of the activity of the Central Range fault (CRF) in central Longitudinal Valley, Taiwan. Using a joint Bayesian finite-fault source inversion of Global Navigation Satellite System and strain time series, we infer that coseismic rupture occurred between 4 and 19 km depth with maximum slip of 0.5 m located near the hypocenter. We then apply a variational Bayesian independent component analysis approach to displacement signals to infer a 3-months long afterslip located in the near-source region. This observation represents the first evidence of aseismic slip on the CRF. Combining geodetic and seismological analysis with simulations based on rate-and-state friction mechanics, we analyze the interplay between seismic and aseismic deformation during the earthquake sequence. We observe that afterslip is the dominant postseismic deformation mechanism, with >95% of the moment being released aseismically in the postseismic phase and also likely represents the driving force controlling aftershock productivity. Finally, we infer the presence of a shallow velocity strengthening zone (similar to 0-4 km depth) associated with spatially heterogeneous slip during the postseismic phase with maximum slip of 0.18 m located above the zone of maximum coseismic deformation. Plain Language Summary Tectonic faults display a broad range of slip patterns, ranging from fast slip (earthquakes) to episodic or continuous aseismic slip. Aseismic transient slip events are now widely observed in active regions and play an important role in stress redistribution in the Earth's crust. The Central Range fault (CRF) is the second most active fault in the Longitudinal Valley, in eastern Taiwan. During the past 15 years, the fault hosted large to destructive earthquakes, but little is known about the presence and the role of aseismic events on the fault deformation. The 2013 Ruisui earthquake reveals for the first time the presence of transient slip regions on the CRF, capable of sustaining aseismic deformation over months. Besides, slow stress relaxation on the fault plane may have also influenced the behavior of seismicity following the mainshock. Monitoring and characterizing the sources of aseismic slip is fundamental to identify areas with high seismic hazard on the fault and to gain more knowledge about the interactions between seismic and aseismic processes.

Automated summary

The study provides evidence of aseismic slip on the Central Range fault (CRF) and observes afterslip as the dominant postseismic deformation following the 2013 Ruisui earthquake sequence.