Coseismic fold scarps and their kinematic behavior in the 1999 Chi‐Chi earthquake Taiwan

Abstract

[1] Discrete scarps that are created or reactivated during large earthquakes are a locus of concentrated hazard. A number of the coseismic scarps activated in the 1999 Chi-Chi earthquake are actually fold scarps, which display several types of ground deformation characterized by localized folding and are distinct from classic fault scarps, which form by a fault cutting the surface. This paper documents and analyzes fold scarps that formed or reactivated in the 1999 Chi-Chi Taiwan earthquake. Our results show the Chi-Chi fold scarps can be generally divided into two types: (1) those associated with folding ahead of the tip of a blind thrust fault at shallow depths and (2) those associated with folding by kink band migration above fault bends at substantial depths ranging from $0.8 to 5 km). The previously published trishear model can be applied to model the former type, while a new curved hinge kink band migration model is provided to describe the behavior of the latter type. A key feature of fold scarps of the second type is that hinge zones are typically wide (25-100 m) relative to the displacement in a single earthquake (1-10 m), which exerts a significant control on fold scarp morphology and evolution. Because the coseismic strains of both types of fold scarps display relatively wide deformation zones (10-100 m) relative to fault scarps, wider set-back zones might be appropriate from a public policy point of view to alleviate the risk to structural damage and collapse resulting from permanent ground deformation.

The 1999 Earthquake Fault and Its Repeated Occurrence at the Earthquake Museum, Central Part of Chelungpu Fault, Taiwan

“…These data indicate that the fault plane dips eastward with a dip of 30 degree. This dip is nearly equivalent to the dips at Chushan trench site (Chen et al 2007b). B4 hole also shows that the amount of total shortening along the fault is at least 18 m and this is too large to interpret by only two faulting events, thus it is very likely that more events have occurred.…”

A paleo-seismological study of the Dauki fault at Jaflong, Sylhet, Bangladesh: Historical seismic events and an attempted rupture segmentation model

“…Instead coseismic, wide surface deformations were formed. Chen et al (2007) called these surface deformations fold scarps, distinguishing them from fault scarps. At Jaflong an active fault was not identified in the trench where the folding was identified.…”

“…At Jaflong an active fault was not identified in the trench where the folding was identified. The southern slope of T2 is estimated to be a fold scarp by Chen et al (2007). If the buried tip of the Jaflong fault was projected to the surface, it could reach the base of the folding scarp.…”

Trenching exposures of the surface rupture of 2008 Mw 7.9 Wenchuan earthquake, China: Implications for coseismic deformation and paleoseismology along the Central Longmen Shan thrust fault

“…Works on large seismic ruptures along continental reverse faults (Philip and Meghraoui, 1983;Stein and King, 1984;Angelier et al, 2003;Chen et al, 2007a) indicate that an active thrust fault commonly shows complex geometric patterns of deformation. On the other hand, paleoseismicity along a thrust fault has also been discussed by combining trench with the geomorphic observations (Philip et al, 1992;Lee et al, 2001;Chen et al, 2004Chen et al, , 2007b.…”