Chelungpu Fault Research Articles

An Electric Resistivity Study of the Chelungpu Fault in the Taichung Area, Taiwan

An Electric Resistivity Study of the Chelungpu Fault in the Taichung Area, Taiwan

Characterization of slip zone associated with the 1999 Taiwan Chi-Chi earthquake: X-ray CT image analyses and microstructural observations of the Taiwan Chelungpu fault

To characterize the fault-related rocks within the Chelungpu fault, we performed X-ray computed tomography (CT) image analyses and microstructural observations of Hole B core samples from the Taiwan Chelungpu-fault Drilling Project. We identified the slip zone associated with the 1999 Chi-Chi earthquake, within the black gouge zone in the shallowest major fault zone, by comparison with previous reports. The slip zone was characterized by low CT number, cataclastic (or ultracataclastic) texture, and high possibility to have experienced a mechanically fluidized state. Taking these characteristics and previous reports of frictional heating in the slip zone into consideration, we suggested that thermal pressurization was the most likely dynamic weakening mechanism during the earthquake.

Precise Temperature Measurements and Earthquake Heat Associated with the 1999 Chi-Chi, Taiwan Earthquake

% to 90%) of the total to 90%) of the total seismic energy budget, and geophysicists have long discussed the level of heat that should be observable (Brune et al., 1969; Lachenbruch and Sass, 1980; Scholz, 2002; Terada, 1930). Precise temperature measurements across the fault immediately after an earthquake can provide the most unambiguous answer; however, there has never been a ; however, there has never been a however, there has never been a however, there has never been a owever, there has never been a significant near-fault temperature change observed for any previous large earthquake that can be attributed to the frictional heating. This is because there has been no appropriate site for temperature measurements around a fault at depth just after an earthquake. The most promising way to reach the fault zone in order to observe the frictional heat is to drill a borehole to the area where large slip occurs. There have been several drilling projects to reach deep areas of the fault zone, such as the Taiwan Chelungpu fault Drilling Project (TCDP), San Andreas Fault Observatory at Depth (SAFOD), and the planned NanTroSEIZE project. We , and the planned NanTroSEIZE project. We and the planned NanTroSEIZE project. We reported the first successful temperature measurement of deep fault zone boreholes that was drilled by TCDP at the Chelungpu fault, Taiwan (Kano et al., 2006). An observation of a temperature increase, and thus an estimate of the heat generated, provides information about the frictional strength during faulting and the level of driving stress for an earthquake. These are key unknown values of important parameters that are necessary for understanding the physical process of earthquake ruptures. In this paper we outline the results of the precise temperature measurement in TCDP Hole A as an attempt to directly A as an attempt to directly A as an attempt to directly measure the frictional heat produced by an earthquake. an earthquake.

Core Handling and Real-Time Non-Destructive Characterization at the Kochi Core Center: An Example of Core Analysis from the Chelungpu Fault

Abstract. As an example of core analysis carried out inactive fault drilling programs, we report the procedures of core handling on the drilling site and non-destructive characterization in the laboratory. This analysis was employed onthe core samples taken from HoleBof the Taiwan Chelungpu-fault Drilling Project (TCDP), which penetrated through the active fault that slipped during the 1999 Chi-Chi, Taiwan earthquake. We show results of the non-destructive physical property measurements carried out at the Kochi Core Center (KCC), Japan. Distinct anomalies of lower bulk density and higher magnetic susceptibilitywere recognized in all three fault zones encountered in HoleB. To keep the core samples in good condition before they are used for variousanalyses is crucial. In addition, careful planning for core handlingand core analyses is necessary for successfulinvestigations. doi: 10.2204/iodp.sd.s01.35.2007

Joint IODP-ICDP Workshop Examines Challenges of Fault Zone Drilling

No abstract available. doi:10.2204/iodp.sd.s01.80.2007

Subsurface Structure, Fault Zone Characteristics, and Stress State in Scientific Drill Holes of Taiwan Chelungpu Fault Drillling Project

No abstract available. doi:10.2204/iodp.sd.s01.27.2007

Drilling of the Chelungpu Fault after the 1999 Chi-Chi, Taiwan Earthquake (Mw7.6): Understanding Physics of Faulting

. 1) in order to sample the slip zones that had large slip (>10 m) during the slip zones that had large slip (>10 m) during the that had large slip (>10 m) during the >10 m) during the m) during the earthquake. The borehole was drilled at an angle of about 50° to the west, penetrating the fault at a drilling depth of to the west, penetrating the fault at a drilling depth of , penetrating the fault at a drilling depth of penetrating the fault at a drilling depth of ing the fault at a drilling depth of the fault at a drilling depth of

Subsurface structure, physical properties, fault-zone characteristics and stress state in scientific drill holes of Taiwan Chelungpu Fault Drilling Project

Continuous cores and a suit of geophysical measurements were collected in two scientific drill holes to understand physical mechanisms involved in the large displacements during the 1999 Chi-Chi earthquake. Physical properties obtained from wire-line logs including P- and S-wave sonic velocity, gamma ray, electrical resistivity, density and temperature, are primarily dependent on parameters such as lithology, depth and fault zones. The average dip of bedding, identified from both cores and FMI (or FMS) logs, is about 30° towards SE. Nevertheless, local azimuthal variations and increasing or decreasing bedding dips appear across fault zones. A prominent increase of structural dip to 60°–80° below 1856 m could be due to deformation associated with propagation of the Sanyi fault. A total of 12 fault zones identified in hole-A are located in the Plio-Pleistocene Cholan Formation, Pliocene Chinshui Shale and Miocene Kueichulin Formation. The shallowest fault zone occurs at 1111 m depth (FZ1111). It is a 1 m gouge zone including 12 cm of thick indurate black material. We interpreted this zone as the slip zone during Chi-Chi earthquake. FZ1111 is characterized by: 1) bedding-parallel thrust fault with 30-degree dip; 2) the lowest resistivity; 3) low density, V p and V s, 4) high V p/ V s ratio and Poisson's ratio; 5) low energy and velocity anisotropy, and low permeability within the homogeneous 1 m gouge zone; 6) increasing gas (CO 2 and CH 4) emissions, and 7) appearance of smectite within the primary slip zone. In situ stresses at the drill site were inferred from leak-off tests, borehole breakouts and drilling-induced tensile fractures from borehole FMS/FMI logs, and shear seismic wave anisotropy from DSI logs. The dominant fast shear-wave polarization direction is in good agreement with regional maximum horizontal stress axis, particularly within the strongly anisotropic Kueichulin Formation. A conjugate set of secondary directions are parallel to microcrack orientations. A drastic change of orientation of fast shear-wave polarization across the Sanyi thrust fault at the depth of 1712 m reflects the change of stratigraphy, physical properties and structural geometry.

Core Handling and Real-Time Non-Destructive Characterization at the Kochi Core Center: An Example of Core Analysis from the Chelungpu Fault

As an example of core analysis carried out inactive fault drilling programs, we report the procedures of core handling on the drilling site and non-destructive characterization in the laboratory. This analysis was employed onthe core samples taken from HoleBof the Taiwan Chelungpu-fault Drilling Project (TCDP), which penetrated through the active fault that slipped during the 1999 Chi-Chi, Taiwan earthquake. We show results of the non-destructive physical property measurements carried out at the Kochi Core Center (KCC), Japan. Distinct anomalies of lower bulk density and higher magnetic susceptibilitywere recognized in all three fault zones encountered in HoleB. To keep the core samples in good condition before they are used for variousanalyses is crucial. In addition, careful planning for core handlingand core analyses is necessary for successfulinvestigations. <br><br> doi:<a href="http://dx.doi.org/:10.2204/iodp.sd.s01.35.2007" target="_blank">:10.2204/iodp.sd.s01.35.2007</a>

Subsurface Structure, Fault Zone Characteristicsand Stress State in Scientific Drill Holes of Taiwan Chelungpu Fault Drilling Project

No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.s01.27.2007" target="_blank">10.2204/iodp.sd.s01.27.2007</a>

Drilling of the Chelungpu Fault after the 1999 Chi-Chi, Taiwan Earthquake (Mw7.6): Understanding Physics of Faulting

No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.s01.10.2007" target="_blank">10.2204/iodp.sd.s01.10.2007</a>

Determining fault slip distribution of the Chi-Chi Taiwan earthquake with GPS and InSAR data using triangular dislocation elements

The reactivation of the Chelungpu fault triggered the 20 September 1999 Chi-Chi Taiwan earthquake (M-w = 7.6) which caused a 100-km long surface rupture that trends north-south. We reconstruct the fault geometry using 1068 planar triangular dislocation elements that approximate more realistically the curved three-dimensional fault surface. The fault slip distribution is then determined with the observed GPS coseismic displacements as well as interferometric synthetic aperture radar (InSAR) data. The results show that our smooth 31) fault slip model has improved the fit to the geodetic data by 44% compared with the previously published inversions. The slip distribution obtained both by inversion of GPS data only and by joint inversion of GPS and InSAR data indicates that notable slips occur on the sub-horizontal decollement at the depth of 6.1-8.9 km. (C) 2007 Elsevier Ltd. All rights reserved.

A chemical kinetic approach to estimate dynamic shear stress during the 1999 Taiwan Chi‐Chi earthquake

Estimation of the dynamic shear stress on a fault during an earthquake is important for understanding the earthquake itself. Using a chemical kinetic approach, we examined the thermal decomposition of carbonate minerals to estimate the shear stress on the Taiwan Chelungpu fault, which slipped during the 1999 Chi‐Chi earthquake. The reaction rate of the decomposition was related to temperature by using the Arrhenius equation, and the chemical kinetics, taking into account the temperature change over time caused by frictional heating and heat conduction, was solved by the finite difference method. The dynamic shear stress during the Chi‐Chi earthquake was deduced to be 1.31 MPa, and the frictional coefficient to be 0.04–0.05. This estimated value agrees with the hypothesis that friction along the Chelungpu fault was low.

Current stress state and principal stress rotations in the vicinity of the Chelungpu fault induced by the 1999 Chi‐Chi, Taiwan, earthquake

We carried out various stress measurements in boreholes penetrating the northern segment of the Chelungpu fault, drilled about 5 years after the 1999 Chi‐Chi, Taiwan, earthquake. In the possible depth range of the Chelungpu fault, three major fault zones were encountered. Clearly recognizable principal stress rotations in the vicinity of the shallowest major fault zone, at 1133 m depth in hole B, suggest that this fault zone ruptured during the 1999 earthquake. Moreover, the fault's rupturing altered the stress state in the area surrounding this fault zone. In this paper, we constrain the possible magnitudes of the current principal horizontal stresses around the fault zone and show that the current stress state belongs to a normal or strike‐slip fault regime. Therefore, the stress state was changed from that of a reverse fault regime by the rupturing.

High magnetic susceptibility produced in high‐velocity frictional tests on core samples from the Chelungpu fault in Taiwan

We carried out high‐velocity frictional tests on crushed fault gouge from core samples from Hole B of the Taiwan Chelungpu‐fault Drilling Project to investigate the cause of high magnetic susceptibilities in the fault core. Black ultracataclasite resembling that observed in Hole B formed during the experiments, even under low axial stress of 0.5 to 1.5 MPa. The bulk magnetic susceptibility of the tested samples was proportional to the frictional work applied and increased as slip increased. Thermomagnetic analysis of the samples before frictional testing revealed that magnetization increased at temperatures above 400 °C, probably because of thermal decomposition of paramagnetic minerals. Both the thermally and mechanically induced formation of ferrimagnetic minerals by high‐velocity friction might have caused a magnetic susceptibility anomaly. Our experimental results support the assumption that heat generation of short duration, even if it is below the melting point, can increase magnetic susceptibility.

A Dynamic Study of Frictional and Viscous Effects on Earthquake Rupture: A Case Study of the 1999 Chi-Chi, Taiwan, Earthquake

Friction is commonly considered an important factor in controlling earthquake rupture. In this work, it is assumed that viscosity is also a significant factor. A strike-slip-type, two-body spring-slider model in the presence of both friction and viscosity is applied to approximate the rupture processes of an earthquake along the fault-striking direction. Results show that in addition to friction, viscosity is also an important factor in controlling rupture. The M s 7.6 Chi-Chi earthquake which struck central Taiwan on 20 September 1999, ruptured a 100-km-long east- dipping transpressive fault (the Chelungpu fault). Measured and inferred results show that there are differences in physical properties between the northern and southern segments of the fault. Simulation results from a two-body model can explain the differences in displacement, velocity, acceleration, and predominant period between the two fault segments.

Nondestructive continuous physical property measurements of core samples recovered from hole B, Taiwan Chelungpu‐Fault Drilling Project

The Taiwan Chelungpu‐Fault Drilling Project was undertaken in 2002 to investigate the faulting mechanism of the 1999 Mw 7.6 Taiwan Chi‐Chi earthquake. Hole B penetrated the Chelungpu fault, and core samples were recovered from between 948.42‐ and 1352.60‐m depth. Three major zones, designated FZB1136 (fault zone at 1136‐m depth in hole B), FZB1194, and FZB1243, were recognized in the core samples as active fault zones within the Chelungpu fault. Nondestructive continuous physical property measurements, conducted on all core samples, revealed that the three major fault zones were characterized by low gamma ray attenuation (GRA) densities and high magnetic susceptibilities. Extensive fracturing and cracks within the fault zones and/or loss of atoms with high atomic number, but not a measurement artifact, might have caused the low GRA densities, whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating. Minor fault zones were characterized by low GRA densities and no change in magnetic susceptibility, and the latter may indicate that these minor zones experienced relatively low frictional heating. Magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault.

Measuring the heterogeneity of the coseismic stress change following the 1999 Mw7.6 Chi‐Chi earthquake

Seismicity quiescences are expected to occur in places where the stress has been decreased, in particular following large main shocks. However, such quiescences can be delayed by hours to years and be preceded by an initial phase of earthquake triggering. This can explain previous analyses arguing that seismicity shadows are rarely observed, since they can only be seen after this triggering phase is over. Such is the case of the main rupture zone, which experiences the strongest aftershock activity despite having been coseismically unloaded by up to tens of bars. The 1999 Mw7.6 Chi‐Chi, Taiwan earthquake is characterized by the existence of several such delayed quiescences, especially off the Chelungpu fault on which the earthquake took place. We here investigate whether these delays can be explained by a model of heterogeneous static‐stress transfer coupled with a rate‐and‐state friction law. We model the distribution of coseismic small‐scale stress change τ by a Gaussian law with mean and standard deviation στ. The latter measures the level of local heterogeneity of the coseismic change in stress. The model is shown to mimic the earthquake time series very well. Robust inversion of the and στ parameters can be achieved at various locations, although on‐fault seismicity has not been observed for a sufficiently long time to provide more than lower bounds on those estimates for the Chelungpu fault. Several quiescences have delays that can be well explained by local stress heterogeneity, even at relatively large distances from the Chi‐Chi earthquake.

The use of VSP techniques for fault zone characterization: An example from the San Andreas Fault

Vertical seismic profiling (VSP) technology is increasingly being used in the fields of earthquake seismology and tectonics. This is motivated in part by the growing number of oil field microseismic monitoring surveys, but more so by projects that involve drilling deep wells for monitoring crustal activity at depth. Examples of these projects are the San Andreas Fault Observatory at Depth (SAFOD), the Nankai Trough Seismogenic Zone Experiment, the Gulf of Corinth Rift Laboratory, and the Taiwan Chelungpu Fault Drilling Project, and other projects by the International Continental and Ocean Drilling Programs (ICDP and IODP). These projects require instrumentation and surveying in deep and possibly hot borehole environments. With higher resolution than surface seismic data, images from 2D and 3D VSP data contribute to better characterization and interpretation of complex reservoirs at smaller scales. The location of receivers in the low-noise borehole environment yields higher signal-to-noise ratios, higher ...

Strong ground motion simulation of the 1999 Chi‐Chi, Taiwan earthquake from a realistic three‐dimensional source and crustal structure

We simulate the strong ground motion of 1999 Chi‐Chi, Taiwan earthquake (Mw = 7.6) by considering a three‐dimensional source rupture model in a full waveform three‐dimensional wave propagation study. The strong ground motion records during the 1999 Chi‐Chi earthquake show various characteristics at different sites in Taiwan. We adopt a three‐dimensional source model derived from an inversion study with identical path effects as considered in this three‐dimensional forward study. Comparisons between the simulation results and observed waveforms from dense island‐wide strong motion stations demonstrate that the fault geometry, lateral velocity variation, and complex source rupture process greatly influence the distribution of strong ground shaking. The simulation has reproduced the heavy damage area that is mainly concentrated in the hanging wall, especially close to the surface break of the Chelungpu fault. The source directivity effect is also reproduced and shows serious shaking along the northward rupture direction. Low‐velocity material in the shallow part of the Western Plain is found to generate significantly amplified ground motions. In the Central Range, the shaking is relatively weak owing to the energy radiation characteristics of a low‐angle thrust of the Chelungpu faulting system. The wavefield is then amplified by a high‐velocity gradient under the Coastal Range. Our simulation results in the frequency range of 0.01–0.5 Hz give good agreement with the extensive strong motion observations of the Chi‐Chi earthquake. We find that adequate source representation, good three‐dimensional crustal velocity structures, and careful numerical work are necessary to make the ground motion prediction feasible.