Modelling temporal variation of surface creep on the Chihshang fault in eastern Taiwan with velocity-strengthening friction

Abstract

S U M M A R YThe active Chihshang fault at the boundary between the Eurasian and the Philippine Sea plates along the Longitudinal Valley in eastern Taiwan is creeping near the surface but has also produced large earthquakes at mid-crustal depth such as the 2003, M w 6.5, Chengkung earthquake. The creep rate measured at the surface shows strong seasonal fluctuations before the Chengkung earthquake, correlated with groundwater pressure variations measured at nearby wells. The Chengkung earthquake did not rupture the fault near the surface but induced a sudden increase of creep rate that decayed with time during the postseismic period. These observations suggest that the near surface fault obeys a rate-strengthening friction law. We conduct numerical simulations based upon the observed variations of creep rate with regard to a velocity-strengthening friction law and 1-D groundwater diffusion model to investigate the fault rheology behind this phenomenon. The model, which assumes a creeping fault segment extending from the surface to a depth of 5 km, yields a good fit to the creep data when the friction parameters are assumed to vary with depth or to have changed at the time of the Chengkung earthquake. Our best model suggests that the creeping zone is characterized by a rate parameter a = ∂μ/∂log (V ) of 1.3 × 10 −2 and a friction coefficient of 0.84, and a long-term slip rate of 25.9 mm yr −1 at depths less than 87 m. By contrast, the lower segment of the creeping zone exhibits a much lower friction coefficient of 0.19, a smaller a of 6.6 × 10 −3 and a higher long-term slip rate of 38.1 mm yr −1 at depths between 0.087 and 5.0 km. This change in rate parameters implies that the lithologies or physical properties of the fault rocks may vary with depth. Alternatively, a model assuming a dramatic increase in rate parameter from 5.6 × 10 −4 to 6.2 × 10 −3 by the strong ground shaking of the Chengkung earthquake can also yield a fair agreement with the observed data. The lack of a notable deceleration in fault creep rate during the dry period from 2002 to mid-2003 suggests that the real recharging system for the fault zone may be more complicated than what we assumed in this study.

Rate‐and‐state friction properties of the Longitudinal Valley Fault from kinematic and dynamic modeling of seismic and aseismic slip

“…It accommodates a reverse left‐lateral motion, and it is known to display both seismic and aseismic behavior at seismogenic depth. The LVF creeps near the surface [e.g., Angelier et al , ; Chang et al , ; Thomas et al , ], but it has also produced M w >6.8 earthquakes, including four events in 1951 [ Shyu et al , ] and the M w 6.8 Chengkung earthquake of 2003 [e.g., Wu et al , ; Hsu et al , ]. The spatiotemporal evolution of fault slip over the 1992–2010 period [ Thomas et al , ] suggests a patchwork of velocity‐weakening patches, where the earthquakes can nucleate, and velocity‐strengthening patches, which produce mostly aseismic creep in the interseismic period or during postseismic transients (Figures c–e).…”

The Burst‐Like Behavior of Aseismic Slip on a Rough Fault: The Creeping Section of the Haiyuan Fault, China

“…Along strike-slip faults, the seismogenic zone can remain locked during the interseismic period or interseismic creep can occur from the surface to the transition zone at depth, affecting as a consequence the total budget of slip where it occurs (e.g., Ryder and Bürgmann, 2008;Jolivet et al, 2012). An increasing number of observations reveals a wide variety of aseismic slip behaviors, from constant creep to episodic slow-slip events (e.g., Çakir et al, 2003;Murray and Segall, 2005;Titus et al, 2006;Chang et al, 2009), often collocated with a variety of seismic events (e.g., Johanson and Burgmann, 2005;Shelly et al, 2009), which raises the debate on the physical relationships between seismic and aseismic slip (Ide et al, 2007;Peng and Gomberg, 2010). The behavior of creeping faults has often been interpreted in terms of effective frictional properties, with creeping sections corresponding to velocity-strengthening domains, whereas seismic faults would have velocity-weakening properties (Chang et al, 2009;Barbot et al, 2012).…”

“…An increasing number of observations reveals a wide variety of aseismic slip behaviors, from constant creep to episodic slow-slip events (e.g., Çakir et al, 2003;Murray and Segall, 2005;Titus et al, 2006;Chang et al, 2009), often collocated with a variety of seismic events (e.g., Johanson and Burgmann, 2005;Shelly et al, 2009), which raises the debate on the physical relationships between seismic and aseismic slip (Ide et al, 2007;Peng and Gomberg, 2010). The behavior of creeping faults has often been interpreted in terms of effective frictional properties, with creeping sections corresponding to velocity-strengthening domains, whereas seismic faults would have velocity-weakening properties (Chang et al, 2009;Barbot et al, 2012). In the following, we will discuss a possible physical interpretation of the slip behavior of faults, where the rough geometry of a fault produces a heterogeneous stress field and creates long-range elastic interactions that may control the rich dynamics of creep, as it has been proposed by Schmittbuhl et al (2006).…”

Faulting and Mud Volcano Eruptions Inside of the Coastal Range During the 2003 Mw = 6.8 Chengkung Earthquake in Eastern Taiwan

“…The total displacements, including co-seismic and 4-month post-seismic displacements, obtained from measurements of the geodetic networks across the Chihshang Fault zone were 7 -12 and 6 -11 cm, for horizontal shortening and vertical offset respectively (Lee et al 2006). Lee et al (2006) and Chang et al (2009) interpreted that the fault had undergone strongly elastic coupling or partial locking at shallow depths according to velocity-strengthening friction behavior, which impeded dynamic rupturing of the Chengkung earthquake from propagating up to the surface.…”

“…However, the co-seismic displacement decreased dramatically near the surface trace of the Chihshang Fault. Close to the fault and near the surface level, the Chengkung earthquake produced a relatively small co-seismic slip and a relatively larger post-seismic slip along the Chihshang Fault (Lee et al 2006;Chang et al 2009;Cheng et al 2009;Hsu et al 2009). For instance, the creep meters at the Chinyuan site exhibited less than 1 cm of co-seismic shortening during the main shock (Lee et al 2006).…”