Active fault creep variations at Chihshang, Taiwan, revealed by creep meter monitoring, 1998–2001

Abstract

[1] The daily creep meter data recorded at Chihshang in 1998-2001 are presented. The Chihshang creep meter experiment was set up across the Chihshang thrust fault, the most active segment of the Longitudinal Valley Fault, which is the present-day plate suture between the Eurasian and the Philippine Sea plates in eastern Taiwan. Near-continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates: 16.2 mm at the Tapo site (comprising two connected creep meters) and 15.0 mm at the Chinyuan site (three creep meters straddling parallel fault branches). Four of the five creep meters showed a seasonal variation, with the fault moving steadily during the rainy season from April to October, and remaining quiescent during the rest of the year. The only exception was recorded by the creep meter located on a mélange-composed hillslope, where local gravitational landsliding played an additional role other than tectonic faulting. Through comparison with daily precipitation data, we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault, during the transition period of the dry/wet season. During the observation period from 1998 to 2001, the subsurface seismicity exhibited clusters of microearthquakes on the Chihshang Fault at depths of 10-25 km. Recurrent earthquakes occurred regardless of whether the season was wet or dry, indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface. The accumulated strain on the Chihshang Fault at shallow surface levels was released through creep during the wet season. In addition to these short-term seasonal variations, an apparent decrease in the annual slipping rate on the Chihshang Fault during the last few years deserves further investigation in order to mitigate against seismic hazard.

Campaigned GPS on Present-Day Crustal Deformation in Northernmost Longitudinal Valley Preliminary Results, Hualien Taiwan

“…The Coastal Range is attached to and thrust over the late Quaternary alluvial deposits of the Longitudinal Valley along the LVF. The earthquakes distribution and focal mechanisms indicate that the average fault plane strike of the central-southern part of the LVF is N20° -25°E with a listric-shaped dip of 25° -70° (Lee et al 2003;Kuochen et al 2004;Lee et al 2006). The seismicity from Hualien to Taitung in Eastern Taiwan can be grouped into north and south portions, separated near the middle of the Coastal Range.…”

“…The 180-km-long Longitudinal Valley in Eastern Taiwan represents the plate suture along which active left-lateral oblique thrusting of the Longitudinal Valley Fault (LVF in Fig. 1a) accommodates the present surface horizontal shortening of 2 -3 cm yr -1 , which is about one-third of the 8.2 cm yr -1 tectonic contraction across the whole Taiwan mountain belt (Biq 1965;Ho 1986;Yu et al 1990; Lee and Angelier 1993;Angelier et al 1997;Yu et al 1997;Lee et al 2003). On the northern and southern tips of the NNE-trending Taiwan mountain belt, the Ilan and Pingtung plains, show both lateral tectonic escape and/or horizontal strata bending with a rather complex combination of deformation features, such as block rotation, strike-slip faulting (i.e., shearing) and normal faulting (i.e., extension) (Angelier et al 1990;Lu et al 1995;Rau et al 2008;Angelier et al 2009;Ching et al 2011).…”

Coseismic and postseismic surface displacements of the 10 December 2003 (MW 6.5) Chengkung, eastern Taiwan, earthquake

“…Horizontal velocity field derived from the GPS measurements indicated a distinct discontinuity across the LVF with a difference of velocity of about 30 mm/yr (Yu and Kuo, 2001). This horizontal shortening is principally revealed by shallow aseismic slips on the LVF (Yu and Liu, 1989;Yu et al, 1990;Lee et al, 2003). The creeping behavior of the LVF is prominent, especially in its southern part from Juisui to Taitung (Fig.…”

Coseismic displacements and slip distribution from GPS and leveling observations for the 2006 Peinan earthquake (Mw 6.1) in southeastern Taiwan

“…During the past decades, scientists have carried out a variety of quantitative and qualitative analyses to better understand the processes of the plate suture zone in this arc-continent collision (Hsu, 1962;Barrier et al, 1982;Ho, 1986;Yu and Liu, 1989;Yu et al, 1992;Lee and Angelier, 1993;Angelier et al, 1997;Lee et al, 1998;Hu et al, 2001;Yu and Kuo, 2001;Shyu et al, 2008). Efforts from previous studies indicated a rapid shortening of about 30 mm/year in the middle and southern segments of the Longitudinal Valley Fault (LVF), which is the major fault of the plate suture in the valley (Yu et al, 1992;Yu and Kuo, 2001;Lee et al, 2003). However, a more complex architecture of the fault system and tectonic context with at least two branches (i.e., the Luyeh fault to the west and the Lichi fault to the east) and a few secondary strike-slip faults have been reported in the southern end of the LVF ( Fig.…”