Chi-Chi Earthquake In Taiwan Research Articles

Changes of mycorrhizal fungal community occurring during the natural restoration after the chi-chi earthquake in Taiwan

Arbuscular mycorrhizal (AM) fungi influence the plant establishment after disturbances, however, there were no reports on the succession of soil AM fungal communities after earthquakes. This study was carried out to monitor the changes of AM fungal species composition during plant succession after earthquakes. After a major earthquake, the ‘Chi-Chi’ event of 1999, a total of 4238 AM fungal spores belonging to 13 species were recorded. Higher AM fungal spore density was found in the crest area of the affected mountainside and the AM fungal community was significantly different between the crest and valley area. Scutellospora nigra, Acaulospora scrobiculata and Acaulospora tuberculata were dominant in the early succession stage. Glomus ambisporum, Glomus deserticola and Acaulospora mellea were more abundant in the late successional stage. These results demonstrated the dynamics of AM fungal community during succession and vegetation recovery.

Simulating the near-fault large velocity pulses of the Chi-Chi (Mw7.6) earthquake with kinematic model

The large number of pulses recorded during the 1999 Mw7.6 Chi-Chi Taiwan earthquake provided an important data for this study. The prediction of near-fault velocity pulses generated by large earthquakes can provide some reference for the Engineering anti-earthquake design. Based on the established source model and velocity structure model, this paper attempts to use the 3D finite difference method to simulate the 39 near-fault large velocity pulses. The conclusions are the following: (1) Two-segment “shovel-like” fault model constructed by 3D bending plane can better describe the characteristics of the underground real fault. (2) The seismic moment and rise time of the six asperities determine the peak and period of the velocity pulse. The asperities located at shallow low angle mainly affect the horizontal pulse components, and the asperities at high angle contribute more to the vertical pulse component. (3) The difference in sliding properties between the north and south ends of the fault causes a difference in the horizontal pulse components, reflecting the characteristics of the fling-step effect and directivity effect. (4) The characteristic period of the velocity response spectrum has the maximum near the turning point at the north end of the fault and shows a very obvious hanging wall effect in the near-fault region, resulting in the large-scale structures having severe damage because of large resonance effect. (5) Peak ground velocity (PGV) gradually increases from south to north along the fault and PGV on the hanging wall is significantly larger than PGV on the footwall, and the distribution of the pulses in front of the rupture is wider than that of the rear. Because the simulation results are basically consistent with the real records, this also verifies the feasibility of simulating pulse-like ground motions with the 3D finite difference method.

The Effects of Zoning Regulations along Fault Zone Areas on Land Development and Property Values after the 921 Chi-Chi Earthquake in Taiwan

Earthquakes are widely recognized as unpredictable and infrequent disasters that result in serious impacts on human settlements. Land use planning is one non-structural measure used to eliminate disaster risk by steering future development away from the existing built environment and enforcing particular structural engineering measures according to the disaster risk. However, arguments have arisen about applying land use planning to earthquake risk areas, as this serves as a type of disaster risk information disclosure that might impact the willingness to develop land or property value. Therefore, this study uses the spatial autocorrelation coefficient to examine the impact of land use planning on both land use and property transactions in the Chelungpu fault zone area (15 m from each side of the fault line) in Taiwan. The overall impacts with and without zoning regulation in the fault zone area are explored. The results demonstrate that parcels that changed to building use in the earlier time period (1995–2008) are located distant from those maintaining the same building use, whereas, later, building use (2008–2014) is located on or nearby the fault zone area. In addition, the most recently constructed buildings are located in or close to the fault zone area and have a relatively higher property price. The legal zoning regulation along the fault zone for building use requires lower height and less intensive building, which might help mitigate the potential impact of future earthquakes.

The 2016 Meinong Taiwan earthquake

The Mw 6.4 Meinong earthquake occurred on 6 February 2016 in the southern region of Taiwan. The earthquake caused significant damage in and around Tainan city, with a number of collapsed and severely damaged buildings and 117 deaths. A five-member Learning from Earthquakes (LFE) team visited Taiwan approximately one month after the earthquake, with particular focus on learning from changes to design practice and seismic mitigation efforts following the 1999 Chi-Chi earthquake in Taiwan. Land damage was generally modest with liquefaction and slope-failures observed in a limited number of locations. Some notable instances of liquefaction-related foundation settlement and tilting occurred in areas associated with historical filling. Following the earthquake, the Taiwanese government publically released liquefaction hazard maps that will have a significant impact on public awareness and land values. The observed structural damage was characteristic of non-ductile and poorly configured buildings. The collapsed buildings all contained irregularities and soft-storeys. The majority of older mixed-use buildings performed adequately, but severe column failures were observed in several taller apartment buildings constructed in the 1990s. The performance of schools and district offices provided valuable insight into the successful implementation of seismic assessment and strengthening programmes. A comparison of existing and strengthened buildings showed that efficient retrofit solutions can reduce the risk posed by critical structural weaknesses and improve the safety and resilience of these buildings. A similar strategy could be implemented for common critical structural weaknesses in New Zealand buildings.

Seismic responses of super-span cable-stayed bridges induced by ground motions in different sites relative to fault rupture considering soil-structure interaction

The focus of this paper is to evaluate the seismic response of a cable-stayed bridge built in fault zones considering soil-structure interaction (SSI) effects. Bridges crossing fault-rupture zones may be built in the Forward Region (FR), Middle Region (MR) and Backward Region (BR) relative to the possible position of the fault. Three groups of ground motions (51 records in two orthogonal directions) in above regions are selected as the input from the 1999 Taiwan Chi-Chi earthquake based on the sites relative to the fault rupture. The Sutong Cable-stayed Bridge (SCB) is taken as an example. Two models are used in this study, i.e. the fixed-base bridge and the bridge with SSI effects where four different orientation angles (0°, 30°, 60°, and 90°) have been considered compared to the fault direction. Systematic lumped-parameter models are utilized to represent the dynamic behavior of the foundation supported on soil. The results reveal that the seismic behavior of the SCB in those 3 regions shows significant differences. The SSI effects affect the bridge response through a systematic decrease of all modal frequencies and a substantial change in nature of dominant shapes especially for the higher modes of vibrations. The displacement of such bridges may be underestimated if the SSI effects are ignored. The orientation of the bridge axis relative to fault trace influences the seismic responses of the bridges in fault regions. The bridge located in MR experiences larger responses than that in FR and BR. Due to the high values of velocity spectra, velocity-related intensity measures i.e. peak ground velocity (PGV) and the ratio of PGV to peak ground acceleration (PGA) show strong correlation with the seismic responses of the bridge located in FR. Since the records in MR and BR have high acceleration spectra, PGV and PGA correlate well with the responses of the bridge located in MR and BR.

Site correction of a high-frequency strong-ground-motion simulation based on an empirical transfer function

In this study, an empirical transfer function (ETF), which is the spectrum difference in Fourier amplitude spectra between observed strong ground motion and synthetic motion obtained by a stochastic point-source simulation technique, is constructed for the Taipei Basin, Taiwan. The basis stochastic point-source simulations can be treated as reference rock site conditions in order to consider site effects. The parameters of the stochastic point-source approach related to source and path effects are collected from previous well-verified studies. A database of shallow, small-magnitude earthquakes is selected to construct the ETFs so that the point-source approach for synthetic motions might be more widely applicable. The high-frequency synthetic motion obtained from the ETF procedure is site-corrected in the strong site-response area of the Taipei Basin. The site-response characteristics of the ETF show similar responses as in previous studies, which indicates that the base synthetic model is suitable for the reference rock conditions in the Taipei Basin. The dominant frequency contour corresponds to the shape of the bottom of the geological basement (the top of the Tertiary period), which is the Sungshan formation. Two clear high-amplification areas are identified in the deepest region of the Sungshan formation, as shown by an amplification contour of 0.5Hz. Meanwhile, a high-amplification area was shifted to the basin’s edge, as shown by an amplification contour of 2.0Hz. Three target earthquakes with different kinds of source conditions, including shallow small-magnitude events, shallow and relatively large-magnitude events, and deep small-magnitude events relative to the ETF database, are tested to verify site correction. The results indicate that ETF-based site correction is effective for shallow earthquakes, even those with higher magnitudes, but is not suitable for deep earthquakes. Finally, one of the most significant shallow large-magnitude earthquakes (the 1999 Chi-Chi earthquake in Taiwan) is verified in this study. A finite fault stochastic simulation technique is applied, owing to the complexity of the fault rupture process for the Chi-Chi earthquake, and the ETF-based site-correction function is multiplied to obtain a precise simulation of high-frequency (up to 10Hz) strong motions. The high-frequency prediction has good agreement in both time and frequency domain in this study, and the prediction level is the same as that predicted by the site-corrected ground motion prediction equation.

Seismic Performance Investigation on Out-Of-Code High-Rise Building Under Near-Fault and Far-Field Ground Motion

7 suits of near-fault ground motion without velocity pulses, 7 suits of near-fault ground motion pulse with velocity pulses and 7 suits of far-field ground motion respectively, which were all based on the Taiwan Chi-Chi earthquake ground motion record, were selected. The characteristics of frequency content about these ground motion records were discussed. Furthermore, an out-of-code high-rise building was taken as case study. These suites of ground motion records were taken as inputs to carry out elastic time-history analysis under the frequent earthquake and elastic-plastic time-history analysis under the rare earthquake of the seismic fortification intensity zone 8. The seismic response of structure were obtained and also compared with the results under the corresponding El-Centro ground motion input cases. Comparison of the results shows that seismic responses of structure under above three suits ground motion are apparently higher than the seismic responses under normal ground motion. Especially the seismic responses such as story drift and maximum horizontal displacement under far-field ground motion has been far more than the limitation as described in the specification.

Direct Measurements of Bedrock Incision Rates on the Surface of a Large Dip-slope Landslide by Multi-Period Airborne Laser Scanning DEMs

This study uses three periods of airborne laser scanning (ALS) digital elevation model (DEM) data to analyze the short-term erosional features of the Tsaoling landslide triggered by the 1999 Chi-Chi earthquake in Taiwan. Two methods for calculating the bedrock incision rate, the equal-interval cross section selection method and the continuous swath profiles selection method, were used in the study after nearly ten years of gully incision following the earthquake-triggered dip-slope landslide. Multi-temporal gully incision rates were obtained using the continuous swath profiles selection method, which is considered a practical and convenient approach in terrain change studies. After error estimation and comparison of the multi-period ALS DEMs, the terrain change in different periods can be directly calculated, reducing time-consuming fieldwork such as installation of erosion pins and measurement of topographic cross sections on site. The gully bedrock incision rate calculated by the three periods of ALS DEMs on the surface of the Tsaoling landslide ranged from 0.23 m/year to 3.98 m/year. The local gully incision rate in the lower part of the landslide surface was found to be remarkably faster than that of the other regions, suggesting that the fast incision of the toe area possibly contributes to the occurrence of repeated landslides in the Tsaoling area.

Synthesis of Near-Fault Ground Motion Using a Hybrid Method of Stochastic and Theoretical Green’s Functions

The effect of near-fault ground displacement is a significant factor when structures straddle a fault, because the fault produces both static step-like deformations and dynamic pulse-like ground motions. It has been observed that the static displacements measured up to 10 m and strong ground motion velocity pulses exceed 100 cm/s. As there is no concrete method for the seismic design of near-fault structures based on earthquake-induced fault displacement, the numerical simulation of near-fault ground motions is of great significance. In this paper, we describe a hybrid method combining stochastic and theoretical Green’s functions for synthesizing near-fault ground motions. Our approach considers the complete waveforms (far-, intermediate-, and near-field terms) of both the dynamic and static terms. To demonstrate the hybrid method, two simple examples of strike-slip and dip-slip fault models are simulated. The results exhibited dynamic displacement with the fling-step of near-fault movement. Furthermore, the 1999 Chi-Chi earthquake in Taiwan is also simulated, and the results showed good agreement with the observed recordings. Thus, the proposed method is a useful tool for evaluating near-fault ground motions for designing bridges and other structures.

Synthetic Ground-Motion Simulation Using a Spatial Stochastic Model with Slip Self-Similarity: Toward Near-Source Ground-Motion Validation

Near-fault ground motion is a key to understanding the seismic hazard along a fault and is challenged by the ground motion prediction equation approach. This paper presents a developed stochastic-slip-scaling source model, a spatial stochastic model with slipped area scaling toward the ground motion simulation. We considered the near-fault ground motion of the 1999 Chi-Chi earthquake in Taiwan, the most massive near-fault disastrous earthquake, proposed by Ma et al. (2001) as a reference for validation. Three scenario source models including the developed stochastic-slip-scaling source model, mean-slip model and characteristic-asperity model were used for the near-fault ground motion examination. We simulated synthetic ground motion through 3D waveforms and validated these simulations using observed data and the ground-motion prediction equation (GMPE) for Taiwan earthquakes. The mean slip and characteristic asperity scenario source models over-predicted the near-fault ground motion. The stochastic-slip-scaling model proposed in this paper is more accurately approximated to the near-fault motion compared with the GMPE and observations. This is the first study to incorporate slipped-area scaling in a stochastic slip model. The proposed model can generate scenario earthquakes for predicting ground motion.

An interdisciplinary perspective on social and physical determinants of seismic risk

Abstract. While disaster studies researchers usually view risk as a function of hazard, exposure, and vulnerability, few studies have systematically examined the relationships among the various physical and socioeconomic determinants underlying disasters, and fewer have done so through seismic risk analysis. In the context of the 1999 Chi-Chi earthquake in Taiwan, this study constructs three statistical models to test different determinants that affect disaster fatality at the village level, including seismic hazard, exposure of population and fragile buildings, and demographic and socioeconomic vulnerability. The Poisson regression model is used to estimate the impact of these factors on fatalities. Research results indicate that although all of the determinants have an impact on seismic fatality, some indicators of vulnerability, such as gender ratio, percentages of young and aged population, income and its standard deviation, are the important determinants deteriorating seismic risk. These findings have strong social implications for policy interventions to mitigate such disasters.

Identification of co-seismic ground motion due to fracturing and impact of the Tsaoling landslide, Taiwan

Earthquakes can generate seismic disturbances that propagate vast distances and trigger landslides that can achieve high-speeds. It remains difficult to identify the co-seismic ground motion of these landslides and their triggering earthquakes. In this paper, we report on the analysis of co-seismic ground motions generated by the initiating fracture and deposition impact of the Tsaoling landslide. The landslide, with a source volume of 125×106m3, was triggered by the 1999 Chi-Chi earthquake in Taiwan. The ground motion was recorded by a strong ground motion station, CHY080, near the scar area. The polarization of the seismic waves indicates that the peak acceleration was parallel to the dip direction. Modified ensemble empirical mode decomposition (EEMD), with additional clustering analysis, was applied to decompose the seismic signals. Two instances were found in the seismic records of a series of peculiar wave packets, with the first being associated with the landslide initiation and the second the landslide impact on the deposit valley. To confirm the first landslide breakage, the decomposed signals were compared with the predictions of the analytic elastic wave model and Newmark analysis. The landslide impact was verified with a computational fluid dynamic simulation. Comparison between the EEMD decomposed signals, elastic wave theory, Newmark rigid body analysis, and numerical simulation demonstrates the claimed landslide motion.

Groundwater–strain coupling before the 1999 Mw 7.6 Taiwan Chi-Chi earthquake

Summary The coupling of pre-earthquake anomalous phenomena between long-term groundwater levels recorded at 42 monitoring stations and time-varying surface strain derived from 16 GPS stations was found in the Choshuichi Alluvial Fan before the 1999 M w 7.6 Chi-Chi earthquake in Taiwan. The noise-free groundwater-level anomalies consistently comprised by a sequence of decrease, rise and flat phases, which agree very well with changes in strain rates computed from the GPS stations. These coupling agreements show that in addition to compression, tension can be generated before a thrust earthquake occurrence as well. This case demonstrates that short-term surface deformation as signals against noise and accuracy of pre-earthquake anomalous phenomena can be simultaneously examined by using multiple-parameter crosscheck for significantly reducing the uncertainty of earthquake precursory evaluation.

Controls on fluvial evacuation of sediment from earthquake-triggered landslides

Large earthquakes in active mountain belts can trigger landslides, which mobilize large volumes of clastic sediment. Delivery of this material to river channels may result in aggradation and flooding, while sediment residing on hillslopes may increase the likelihood of subsequent landslides and debris flows. Despite recognition of these processes, the controls on the residence time of coseismic landslide sediment in river catchments remain poorly understood. Here we assess the residence time of fine-grained ( 5 mm day–1). Together with previous observations from the C.E. 1999 Chi-Chi earthquake in Taiwan, our results demonstrate the importance of landslide density and runoff intensity in setting the duration of earthquake-triggered landslide impacts on river systems.

Optimal Scheduling for Highway Emergency Repairs Under Large-Scale Supply–Demand Perturbations

In this paper, we develop a model for emergency repair problems under large-scale supply-demand perturbations. The model formulation proposed in this paper has the following key features. First, a novel time-space network flow technique is adopted to generate detailed schedules for repair teams and allow dynamic updates of the network due to perturbations. Second, the original schedules prior to the perturbations are considered by controlling the total difference between the original schedule and the adjusted schedule. Third, to reduce computational complexity, the model is formulated with different levels of detail (individual teams versus a team group). The model is also formulated as a special mixed-integer network flow problem with side constraints, which is characterized as NP-hard. An ant-colony-system-based hybrid global search algorithm is developed to efficiently solve large-scale problems. To test how well the model formulation and the heuristic algorithm may perform in actual operations, we conduct a case study using actual data from the 1999 Chi-Chi earthquake in Taiwan. The results show that the proposed model and solution algorithm perform very well and thus have great potential for assisting with the making of emergency repair decisions in the event of disasters given large-scale perturbations in supply and demand.

Initiation, movement, and run-out of the giant Tsaoling landslide — What can we learn from a simple rigid block model and a velocity–displacement dependent friction law?

Tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 Taiwan Chi-Chi earthquake. Pliocene sedimentary rocks of about 125Mm3 in volume slid along very flat bedding planes dipping by 14° with an average speed of 35–40m/s for about 1650m, before hitting the bank of the Chinshui River during the landslide. Detailed analysis of DTMs before and after the earthquake using a GIS software leads to an accurate determination of the locations of the centroids of landslide mass, revealing the horizontal and vertical displacements of the 2524m and 524m, respectively. Those displacements and landslide mass give an apparent friction coefficient of 0.21 and the release of the potential energy of 1.6×1015J. We conducted rotary-shear high-velocity friction experiments on fault gouge from bedding-parallel faults under semi-wet conditions and at 3MPa normal stress corresponding to the overburden pressure of the landslide mass. We also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions, and proposed a velocity–displacement dependent friction law that can describe most experimental data. Newmark analysis of landslide motion with six scenarios for different landslide materials and conditions, assuming a simple rigid block sliding and using measured frictional parameters, revealed that the landslide did not occur with dry frictional properties, and that the landslide occurred at 38–39s with accumulated displacements of 0.62m–1.09m and reached at the river bank at 82–87s after the generation of Chi-Chi earthquake at its epicenter. Those timings are consistent with high-frequency signals at 32–40s and at 76s recorded at a nearby seismic station and with a survivor's witness that the landslide initiated 10s after he felt strong ground motion, possible S wave arrival at 25.2s. Slip-weakening is essential in initiating the landslide and low friction coefficient (0.08–0.1) allowed high-speed of the landslide possible. The landslide was caused by a few peaks of northeast-oriented strong accelerations of the ground motion. Frictional work during the sliding of the landslide mass was estimated to be of about 23% of potential energy, and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation, heat dissipation, and spreading of the landslide deposits.

An index to describe the earthquake effect on subsequent landslides in Central Taiwan

Chelungpu fault reactivation produced the 1999 Chi-Chi earthquake in Central Taiwan in 1999, triggering many landslides over a broad area. The ground damage caused by the Chi-Chi earthquake still influences successive rainfall-triggered landslides. The landslide distribution triggered by heavy rainfall during typhoon Mindulle in 2004 has a high correlation to the landslide sites triggered by the previous Chi-Chi earthquake. This research calculated and ordered landslide data for both the area and distance from the Chelungpu fault. The rank correlation coefficient for measuring two covarying variables is employed to quantify the degree of correlation between the landslide distribution and the Chelungpu fault. A high rank correlation coefficient value demonstrates a highly correlated relationship between the subsequent landslides in 2004 and previous Chelungpu fault activity in 1999.

Estimation of slip parameters associated with frictional heating during the 1999 Taiwan Chi-Chi earthquake by vitrinite reflectance geothermometry

Abstract To estimate the slip parameters and understand the fault lubrication mechanism during the 1999 Taiwan Chi-Chi earthquake, we applied vitrinite reflectance geothermometry to samples retrieved from the Chelungpu fault. We found a marked reflectance anomaly of 1.30% ± 0.21% in the primary slip zone of the earthquake, whereas the reflectances in the surrounding deformed and host rocks were 0.45% to 0.77%. By applying a kinetic model of vitrinite thermal maturation together with a one-dimensional heat and thermal diffusion equation, we determined the shear stress and peak temperature in the slip zone during the earthquake to be 1.00 ± 0.04 MPa and 626°C ± 25°C, respectively. Taking into account the probable overestimation of the temperature owing to a mechanochemically enhanced reaction or flash heating at grain contacts, this temperature should be considered an upper limit. The lower limit was previously constrained to 400°C by studies of fluid-mobile trace-element concentrations and magnetic minerals. Therefore, we inferred that the peak temperature during the Chi-Chi earthquake was 400°C to 626°C, corresponding to an apparent friction coefficient of 0.01 to 0.06. Such low friction and the previous evidence of a high-temperature fluid suggest that thermal pressurization likely contributed to dynamic weakening during the Chi-Chi earthquake.

Mineral assemblage anomalies in the slip zone of the 1999 Taiwan Chi-Chi earthquake: Ultrafine particles preserved only in the latest slip zone

We determined mineral assemblages of samples from the Taiwan Chelungpu fault and from milling and heating experiments by using X-ray diffraction and scanning and transmission electron microscopy. The fault system contains three dominant fault zones, the shallowest of which slipped during the 1999 Chi-Chi earthquake. The quartz and clay mineral contents of the primary slip zone were low, and it contained partly amorphous ultrafine particles (several tens of nanometers). Up to 30 weight percent of materials in that zone could not be fit to standard diffraction patterns, whereas nearly 100 weight percent of those in surrounding samples could be. The unfitted component could be attributed to the observed ultrafine particles produced by comminution during the earthquake, because weak diffraction intensities are caused from mineral lattice distortion, granulation, and amorphous coatings. Such particles are a potential proxy for identifying the slip zone of the most recent earthquake along a fault.

Rainfall-triggered ordinary earthquakes in Taiwan: a statistical analysis

This study was carried out to investigate the role of rainfall in triggering ordinary earthquakes that occurred before and after the major Chi-Chi earthquake (7.2 ML) in central Taiwan on 21 September 1999. To test a possible mechanism, earthquake activities from January 1995 to July 2012 were examined. The Chi-square (χ2) test revealed a significant difference between the correlations of monthly accumulated rainfall values and earthquake activities before and after the Chi-Chi earthquake. This result is discussed in terms of changes in crustal conditions after the Chi-Chi earthquake. Two ordinary earthquakes that may have been associated with heavy rainfall after the Chi-Chi earthquake are identified.Editor D. Koutsoyiannis; Associate editor A. PorporatoCitation Lin, J.-W., 2014. Rainfall-triggered ordinary earthquakes in Taiwan: a statistical analysis. Hydrological Sciences Journal, 59 (5), 1074–1080.