The 1999 Taiwan Earthquake: A Proposed Stress-Focusing, Heel-Shaped Model

Abstract

Stress focusing in a proposed heel-shaped model reasonably explains the occurrence of the largest onland earthquake (M W 7.6) in Taiwan's history. The epicenter of the mainshock was located in a low-seismicity block, where, historically, large earthquakes have not been documented for the past century. Spatial variations in crustal deformation reported in Global Positioning System surveys suggest that the crustal strength in the low-seismicity block was stronger than in the surrounding area. Since the low-seismicity block, which roughly coincides with the northern part of the Peikang High, is defined by a convex curve, stress partitioning or reorientation might well have taken place along the convex boundary; it then likely stored a lot of strain energy before eventually failing. The low-seismicity block with strong crust characteristics was finally overcome by stress focusing, resulting in the generation of the 921 Chi-Chi earthquake near the focus of the low-seismicity block, where a cluster of earthquakes had occasionally occurred during the past decade. Significant surface ruptures with vertical offset ranging from 2 to 8 m, primarily along the Chelungpu fault, were restricted to within the low-seismicity block. In short, when a low-seismicity block with small velocity fields of crustal deformation is identified in an active foreland belt, there should be a greater risk of a larger earthquake to release energy that accumulates in the strong crust. This finding provides some useful insight with which to evaluate potential earthquakes in Taiwan and other convergent zones.

Quantification of Hanging-Wall Effects on Ground Motion: Some Insights from the 1999 Chi-Chi Earthquake

“…A large set of records has been acquired by one of the densest and most advanced seismic and geodetic networks in the world (e.g., Shin et al, 2000;Yu et al, 2001). The high quality and quantity of these data have led to numerous studies on mechanical and kinematical characteristics of the earthquake process (e.g., Chung and Shin, 1999;Ma et al, 2001;Oglesby and Day, 2001;Lin, 2001;Zeng and Chen, 2001;Wang et al, 2001;Yoshioka, 2001;Dalguer et al, 2001).…”

Static stress drop inferred from near-fault parameters for the 1999 Chi–Chi earthquake in Taiwan

“…In this case, Kikuchi and Fokao (1988) stated that the rupture area was to be uniform without discontinuities (i.e., barriers). This interpretation seems to give a possible explanation for the interesting patterns of aftershocks generated by the Chi-Chi earthquake (Lin, 2001;Ma et al, 1999). Both studies stated that most of the aftershocks occurred on the eastern side of the Chelungpu fault and just outside the main rupture area.…”

Tectonic implications of nonparallel topographic and structural curvature in the higher elevations of an active collision zone, Taiwan

“…In map view, the edges of the continental margin promontory are also roughly outlined by a convex high-seismicity boundary with a lowseismicity core (Lin, 2001;Wu et al, 2004).…”

“…Stress trajectories from their study were repositioned in Figure 12A toward the northeast so that the margin of the modeled indenter coincides with the Sanyi-Puli seismic zone, the heel-shaped seismogenic boundary (Lin, 2001), and the continental margin magnetic anomaly high (Byrne et al, 2011). This repositioning allows us to compare the maximum compression direction from the early-and late-stage fault populations to those simulated for a collision zone with a rigid indenter of similar geometry to the continental margin promontory.…”