Spatiotemporal evolution of seismic and aseismic slip on the Longitudinal Valley Fault, Taiwan

Abstract

The Longitudinal Valley Fault (LVF) in eastern Taiwan is a high slip rate fault (about 5 cm/yr), which exhibits both seismic and aseismic slip. Deformation of anthropogenic features shows that aseismic creep accounts for a significant fraction of fault slip near the surface, whereas a fraction of the slip is also seismic, since this fault has produced large earthquakes with five Mw>6.8 events in 1951 and 2003. In this study, we analyze a dense set of geodetic and seismological data around the LVF, including campaign mode Global Positioning System(GPS) measurements, time series of daily solutions for continuous GPS stations (cGPS), leveling data, and accelerometric records of the 2003 Chenkung earthquake. To enhance the spatial resolution provided by these data, we complement them with interferometric synthetic aperture radar (InSAR) measurements produced from a series of Advanced Land Observing Satellite images processed using a persistent scatterer technique. The combined data set covers the entire LVF and spans the period from 1992 to 2010. We invert this data to infer the temporal evolution of fault slip at depth using the Principal Component Analysis‐based Inversion Method. This technique allows the joint inversion of diverse data, taking the advantage of the spatial resolution given by the InSAR measurements and the temporal resolution afforded by the cGPS data. We find that (1) seismic slip during the 2003 Chengkung earthquake occurred on a fault patch which had remained partially locked in the interseismic period, (2) the seismic rupture propagated partially into a zone of shallow aseismic interseismic creep but failed to reach the surface, and (3) that aseismic afterslip occurred around the area that ruptured seismically. We find consistency between geodetic and seismological constraints on the partitioning between seismic and aseismic creep. About 80–90% of slip on the southern section of LVF in the 0–26 km, seismogenic depth range, is actually aseismic. We infer that the clay‐rich Lichi Mélange is the key factor promoting aseismic creep at shallow depth.

Testing the Influence of Static and Dynamic Stress Perturbations On the Occurrence of a Shallow, Slow Slip Event in Eastern Taiwan

“…Since we do not have sufficient data to perform a nonlinear source inversion, we search for a source compatible with the LVF or with the CRF (see section for details). We adopt the fault geometry defined by M. Y. Thomas et al () for the LVF, that is, a dip angle decreasing gradually from about 60° at 0–14 km to about 45° at 14–22 km and to 30° at 22–27 km. The fault strike is set to 30°NE and the geologic rake to 60° which corresponds to the slip vector direction estimated at the surface in the Ruisui region (around latitude 23°26 ′ ; Peyret et al, ).…”

“…The fault also displays aseismic slip at seismogenic depths, as evidenced by moderate to large frictional afterslip (Canitano, Godano, et al, ; Y. J. Hsu et al, ). Based on the analysis of 18 years of geodetic data (1992–2010) for the LVF which includes the large postseismic slip following the 2003 Chengkung earthquake (e.g., Y. J. Hsu et al, ), M. Y. Thomas et al () inferred that a major fraction (>80%) of the long‐term slip budget on the southern section of the LVF is the result of aseismic slip. The CRF, located on the western side of the valley, is a high‐angle reverse west‐dipping structure (Shyu et al, ), also capable of producing large earthquakes such as the October 2013 M w 6.2 Ruisui event (Canitano et al, , ).…”

Shallow Creep Along the 1999 Izmit Earthquake Rupture (Turkey) From GPS and High Temporal Resolution Interferometric Synthetic Aperture Radar Data (2011–2017)

“…The clay gouges associated with the aseismic slip on this fault section (Figure c) are rich in weak minerals, such as saponite and other smectites (Kaduri et al, ). These low friction minerals have been observed as well along the creeping segments of the San Andreas Fault in California, and the Long Valley Fault in Taiwan (Moore & Rymer, ; Thomas et al, ). Along the Izmit creeping section, similar detailed analysis of rocks compositions in the fault zone remain to be done.…”

Fault mechanics and post-seismic deformation at Bam, SE Iran

“…Fault zones that show the opposite behaviour, in which M ps /M cs is 80 per cent, are consistently located near parts of the fault surface that have interseismic creep rates similar to the far-field loading rate (e.g. the Parkfield section of the San Andreas Fault ) and the Longitudinal Valley Fault in Taiwan (Thomas et al 2014)). For the high M ps /M cs events there is limited locking around the co-seismic rupture, therefore post-seismic creep is not limited by the elastic resistance caused by adjacent locked zones.…”

“…Recent studies suggest faults that creep extensively during the interseismic period also experience large amounts of post-seismic afterslip relative to co-seismic slip (Heki et al 1997;Furuya & Satyabala 2008;Barbot et al 2009; Thomas et al 2014). This observation implies that the amount of afterslip is related to the degree of locking of the fault zone around the co-seismic slip patch, and the magnitude of the co-seismic stress changes.…”