Spatio-temporal Slip, and Stress Level on the Faults within the Western Foothills of Taiwan: Implications for Fault Frictional Properties

Abstract

Abstract-We use preseismic, coseismic, and postseismic GPS data of the 1999 Chi-Chi earthquake to infer spatio-temporal variation of fault slip and frictional behavior on the Chelungpu fault. The geodetic data shows that coseismic slip during the Chi-Chi earthquake occurred within a patch that was locked in the period preceding the earthquake, and that afterslip occurred dominantly downdip from the ruptured area. To first-order, the observed pattern and the temporal evolution of afterslip is consistent with models of the seismic cycle based on rate-and-state friction. Comparison with the distribution of temperature on the fault derived from thermokinematic modeling shows that aseismic slip becomes dominant where temperature is estimated to exceed 200°a t depth. This inference is consistent with the temperature induced transition from velocity-weakening to velocity-strengthening friction that is observed in laboratory experiments on quartzo-feldspathic rocks. The time evolution of afterslip is consistent with afterslip being governed by velocity-strengthening frictional sliding. The dependency of friction, l, on the sliding velocity, V, is estimated to be ol=o ln V ¼ 8 Â 10 À3 : We report an azimuthal difference of about 10-20°between preseismic and postseismic GPS velocities, which we interpret to reflect the very low shear stress on the creeping portion of the décollement beneath the Central Range, of the order of 1-3 MPa, implying a very low friction of about 0.01. This study highlights the importance of temperature and pore pressure in determining fault frictional sliding.

Observation and scaling of microearthquakes from the Taiwan Chelungpu-fault borehole seismometers

“…The low shear stress on the fault explains why the lack of microearthquakes occurred on the Chelungpu-fault. The geodetic observation from inversion of the GPS data for the post-seismic slip and interseismic slip modelling on the Chelungpu-fault plane gave a coupling ratio of 1.0 in this area, suggesting the fault in this region was strongly locked (Hsu et al 2009). Our observations of microearthquakes location with no seismicity on the main fault might provide the direct evidence to the locked of the fault.…”

“…This high seismicity detachment may be associated with the decollement of the Taiwan fold-and-thrust tectonic structure (Yue et al 2005). This detachment, as shown by Hsu et al (2009), consists of low shear stresses of ∼2 MPa and a low effective friction of ∼0.01. The exceptionally low shear stress suggests the possible existence of fluid.…”

Late Cenozoic metamorphism and mountain building in Taiwan: A review

“…In addition, the details of the thermal structure in this region, as could be quantified from thermal modeling of metamorphic and thermochronological data, is of great importance for investigating the seismic cycle in western Taiwan (e.g. Dominguez et al, 2003;Hsu et al, 2009). It also comes out from the comparison between these models that metamorphic and thermochronological data alone cannot be diagnostic of mountain building processes.…”

Interseismic coupling, seismic potential, and earthquake recurrence on the southern front of the Eastern Alps (NE Italy)

“…Because examples of spontaneous creep events on locked continental faults are rare, the most likely reason for < 1 would be therefore postseismic aseismic creep (afterslip). Afterslip following the main shock on continental faults is though to be small and can typically release around 18-25% of coseismic slip [Perfettini and Avouac, 2007;Hsu et al, 2009;D'Agostino et al, 2012], then should be in the range between ∼0.7 and 1.…”