Abstract
Field investigations following the 2003 M(subscript w)=6.8 Chengkung earthquake in eastern Taiwan revealed some interesting observations of surface geological processes closely related to the co-seismic deformation. We discovered that the Tama Fault, which is about 15 km east of the causative Chihshang Fault, underwent shortening of about 15.5 mm locally in 2001-2006, particularly during the 2003 earthquake. This shows that ESE-WNW compression affects the upper crust of the Coastal Range and produces significant shortening in addition to that of the major Chihshang Fault. On the hanging wall of the Chihshang Fault, we also found vigorous activities of the two major mud volcanoes during the main shock, lasting several days. To the north, the Luoshan Mud Volcano, a large mud basin, erupted noisily with water and gases during the earthquake. To the south, in the Leikunghuo Mud Volcano, two sets of fractures, one aligned with the N16°E right-lateral fault and the other with the N80°E left-lateral fault, occurred during the earthquake. This conjugate system revealed a strike-slip stress regime with NESW compression and NW-SE extension. We interpret it to be the result of local stress permutation rather than regional tectonic stress. We conclude that deformation did occur inside of the Coastal Range, especially during the co-seismic event. Therefore, a better understanding of the internal deformation of the Coastal Range is an important target for future studies, particularly across three mapped faults: the Yungfeng, Tuluanshan and Tama faults. We also want to draw attention to the stress analysis in the mud volcanoes area, where the local stress perturbation plays an important role.
Highlights
The Coastal Range of eastern Taiwan is located at the northwestern corner of the Philippine Sea plate, representing the Luzon Arc units which were thrust over the Quaternary infill of the Longitudinal Valley and the metamor
The Longitudinal Valley Fault (LVF), located mainly along the foot of the Coastal Range adjacent to the Longitudinal Valley, is an active high-angle oblique thrust fault with a left-lateral strike slip component (Barrier et al 1982; Yu and Liu 1989; Yu et al 1990; Lee and Angelier 1993; Fig. 1. (a) Plate tectonic setting of Taiwan. (b) General geology of the Coastal Range
Much better geophysical and geological information is available from the 2003 Mw = 6.8 Chengkung earthquake (Chen et al 2006; Lee et al 2006; Wu et al 2006; Hu et al 2007; Kuochen et al 2007; Cheng et al 2009; Hsu et al 2009) (Figs. 1c and d)
Summary
We intend to present an outcrop near the Tama Fault, where we observed possible co-seismic deformation inside the Coastal Range as related to the 2003 Chengkung earthquake, it was of a relatively smaller magnitude Within this tectonic framework dominated by active collision, we address the characteristics of mud volcano behavior as it relates to active shortening and earthquake activity inside the Coastal Range. The Leikunghuo Mud Volcano, about 15 km northeast of the town of Luyeh, appears as a mud shield with dozens of big and small craters (Shih 1967; Hsieh et al 1993) This mud volcano essentially developed in the hanging wall of the Yungfeng Fault, a major backthrust of the LVF in the Lichi Mélange. We highlight the close relationships in space and time between the active shortening of an earthquake event that affects the Coastal Range, the Longitudinal Valley, and the erupting events of the mud volcanoes, taking into special consideration the major seismic event of the 2003 Chengkung earthquake
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