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Background: Few studies have explored the field experiences and risk factors related to post-traumatic stress disorder (PTSD) among disaster rescue workers.Methods: A 6.4-magnitude earthquake struck southern Taiwan on February 6, 2016. A standardized, paper-based, self-administered survey questionnaire including demographic information, field experiences and the Post-Traumatic Stress Disorder Checklist (PCL) was conducted among emergency medical technicians (EMTs) one month after the earthquake. A multivariate regression model was used to analyze the associations between risk factors and the PCL. A two-sided p value less than 0.05 was considered statistically significant.Results: The survey response rate was 86.1% (447/519). The respondents who exceeded the cut-off points for the re-experience, avoidance, or hyperarousal domains were 11.8%, 2.7%, or 4.7%, respectively. A proportion of 12.7% of respondents met partial PTSD. The personality characteristics of anxiety (p < 0.001), perfectionism (p = 0.023) and introvert tendency (p = 0.002) were significantly correlated with partial PTSD. Emergency medical services (EMS) were significantly associated with partial PTSD than other main tasks (p < 0.001). The prevalence of partial PTSD was higher but was not significantly different in the groups of lower educational level, longer EMT careers, earlier arrival date, fewer field working hours, or managing dead people. Both univariate and multivariate logistic regression analyses showed that an anxious personality and EMS as the main task during the missions were significantly associated with PTSD risk.Conclusion: Not only personality characteristics but also the task components could alter the PTSD risks in disasters. A broad realization of these risks may improve the mental outcomes of disaster rescuers. [ABSTRACT FROM AUTHOR]

It is well known that coseismic landslides are likely to occur under stronger shaking at shorter epicentral distance under the effects of topography and amplification of shaking together with such local geology as rock and soil types. However, this paper addresses a different issue that is the role of faults played in the triggering of landslides, both coseismic and non-seismic, and the long-term slope instability that lasts for decades or centuries after devastating earthquakes. Experiences during and after gigantic landslides are important to understand what happens in and around faults. Noteworthy is that there are cases in which slope instability starts after earthquakes and lasts for some time along surface manifestation of faults, whether or not they are the causative fault. Another important issue is the recovery of stability in shallow parts of slopes. Experiences in Japan, Taiwan and China suggest that a few decades is needed for this re-stabilization. Discussion is further made of geologically generated ground water pressure that is another causative mechanism of landslides. Thus, further field study is encouraged to promote slope hazard assessment. • Long-term slope instability after major earthquakes was studied by introducing examples in the past. • Compound effects of earthquake and rainfall on slope instability are presented. • Continuous slope instability along major tectonic lines is discussed. • Landslides triggered by abnormal ground water pressure are touched upon. • The concepts of process zone and geopressure should be investigated in more details. • The studied cases suggest the importance of more geological/geomorphological studies for understanding the landslide hazards in tectonically active regions of the world. [ABSTRACT FROM AUTHOR]

Abstract: Given the difficulty of earthquake forecast, Probabilistic Seismic Hazard Analysis (PSHA) has been a method to best estimate site-specific ground motion or response spectra in earthquake engineering and engineering seismology. In this paper, the first in-depth PSHA study for Taipei, the economic center of Taiwan with a six-million population, was carried out. Unlike the very recent PSHA study for Taiwan, this study includes the follow-up hazard deaggregation, response spectra, and the earthquake motion recommendations. Hazard deaggregation results show that moderate-size and near-source earthquakes are the most probable scenario for this city. Moreover, similar to the findings in a few recent studies, the earthquake risk for Taipei should be relatively high and considering this city''s importance, the high risk should not be overlooked and a potential revision of the local technical reference would be needed. In addition to the case study, some innovative Excel applications to PSHA are introduced in this paper. Such spreadsheet applications are applicable to geosciences research as those developed for data reduction or quantitative analysis with Excel''s user-friendly nature and wide accessibility. [Copyright &y& Elsevier]

Abstract: Elementary and junior high school buildings in Taiwan are designed to serve not only as places of education but also as temporary shelters in the aftermath of major earthquakes. Effective evaluation of the seismic resistance of school buildings is a critical issue that deserves further investigation. The National Center for Research on Earthquake Engineering (in Taiwan) currently employs performance-target ground acceleration (AP ) as the index to evaluate school structure compliance with seismic resistance requirements. However, computational processes are complicated, time consuming, and require the input of many experts. To address this problem, this paper developed an evolutionary support vector machine inference system (ESIS) that integrated two AI techniques, namely, the support vector machine (SVM) and fast messy genetic algorithm (fmGA). Based on training results, the developed system can predict the AP of a school building in a significantly shorter time base, thus increasing evaluation efficiency significantly. The validity of ESIS was tested using the 10-Fold Cross-Validation method. Another aim of this paper is to retain and apply expert knowledge and relevant experience to the solution of similar problems in the future. [Copyright &y& Elsevier]

Abstract: The observation of ELF Schumann resonances in Nakatsugawa, Japan has suggested the presence of anomalous behavior in Schumann resonances (that is, the main point is the enhancement at the fourth (or the third) harmonic) at Nakatsugawa, and we have indicated that those anomalies in the Schumann resonances at Nakatsugawa are highly likely to be associated with the large earthquakes in Taiwan. This paper is intended to provide the statistical significance of those Schumann resonance anomalies in possible association with earthquakes in Taiwan on the basis of the ELF observation during the period from the beginning of 1999 to the end of 2004 (6years). With the criterion of the magnitude greater than 5.0, there were observed 33 earthquakes in and around Taiwan, and the Schumann resonance anomaly is observed for 9 earthquakes (so that the anomaly percentage will be 9/29 (because no observation for 4 earthquakes)). Twenty nine earthquakes included 7 earthquakes in the land, while other 22 earthquakes took place in the sea. It is surprising that anomalous Schumann resonances are observed prior to all the land earthquakes. Two sea earthquakes from the 22, had the anomalous Schumann resonances, but these two earthquakes had the following characteristics (one was the largest magnitude, and another, the shallowest). The paper discloses the causative link between the anomalous Schumann resonances and earthquakes in Taiwan. Especially, the land earthquakes with large magnitude are found to trigger the anomalous Schumann resonances. [Copyright &y& Elsevier]

In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in northern Taiwan. The spatial anomalies of soil gas are related to tectonic faults, while the temporal anomalies of soil gas are associated with pre-earthquake activities. Detailed soil gas sampling was systematically performed, and the analysis of the collected gas species shows that high helium and nitrogen concentrations appear in samples from specific sites, which coincide with the structural setting of the area studied. This analysis indicates the possibility of using these soil gases to determine fault zones in the studied area. Based on the soil gas data, a station (Tapingti) for automatic soil gas monitoring was constructed on an appropriate site at the fault zone. Some anomalous high radon concentrations at certain times can be identified from the dataset, which was generated by the continuous monitoring of soil gas for over a year. Notably, many of these anomalies were observed several hours to a few days before the earthquakes (M L > 3) that occurred in northern Taiwan. By combining the information of epicenters and fault plane solutions of these earthquakes, we find that the shallow earthquakes (<15 km) were mainly strike-slip and normal-type earthquakes, and concentrated within a distance of 30 km to the monitoring site (Group A). The deep earthquakes (>20 km) were mainly thrust-type earthquakes and distributed in greater distances (>45 km) east of the monitoring site (Group B). Such focal mechanisms of earthquakes suggest an extensional and compressional structural domain in the continental crust for Group A and Group B earthquakes, respectively. It is suggested that the pre-earthquake activities associated with the seismicity of Group B may be transmitted along the major decollement in the region below the Tapingti station, leading to the observed soil gas enhancements. [ABSTRACT FROM AUTHOR]

Many earthquake empirical models were developed based on the statistics in the past. However, it is commonly seen that a non-local model was applied to a local study without any adjustment. In this paper, a new algorithm using maximum likelihood estimation (MLE) to adjust a non-local model for local applications was presented, including a case study assessing the probability of major earthquake occurrences in Taipei. Specifically, considering the fault length of 36 km and slip rate of 2 mm/yr, it suggests the Sanchiao (or Shanchiao) fault could induce a major earthquake with magnitude M w 7.14±0.17, based on a non-local model integrated with limited local data using the MLE algorithms. [ABSTRACT FROM AUTHOR]

This paper presents the first whole Taiwan-scale spatial variation of the seismogenic zone using a high-quality crustal seismicity catalog. The seismicity onset and cutoff depths (i.e., seismogenic depths) are determined by the earthquake depth–moment distribution and used to define the upper and lower boundaries of the seismogenic zone, respectively. Together with the published fault geometries and fault area–moment magnitude relations, the depth difference in the onset and cutoff depths (i.e., seismogenic thickness) is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults. Results show that the largest ( Mw 7.9–8.0) potential earthquake may occur along the Changhua fault in western Taiwan, where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern. In addition, the first-motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters. For crustal earthquakes (≤ 50 km), the shallowest onset and cutoff depths are observed for normal and strike-slip events, respectively. This observation is different from the prediction of the conventional continental-rheology model, which states that thrust events have the shallowest cutoff depth. Thus, a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types. Meanwhile, for intermediate to large crustal ( Mw ≥ 4; depth ≤ 50 km) earthquakes, thrust events tend to occur at the bottom region of the seismogenic zone, but normal and strike-slip events distribute at a large depth range. [ABSTRACT FROM AUTHOR]

Earthquake early warning (EEW) has been implemented in several regions around the world. However, because of natural randomness and uncertainty, false alarm and missed alarm can be expected in EEW. The key scope of this study is to evaluate the reliability of an on-site EEW in Taiwan, by testing the system's algorithm with 17,836 earthquake data from 1999 to 2013. The analysis shows that the on-site EEW system, empirically speaking, should have a false-alarm probability of 2.5%, and a missed-alarm probability of 14.1%. Considering missed alarm should be more critical to EEW, a new algorithm that could reduce the system's missed-alarm occurrences to 6% is also discussed in this paper. [ABSTRACT FROM AUTHOR]

For more than 13 years a multi-temporal data-analysis method, named Robust Satellite Techniques (RST), has been being applied to satellite Thermal InfraRed (TIR) monitoring of seismically active regions. It gives a clear definition of a TIR anomaly within a validation/confutation scheme devoted to verify if detected anomalies can be associated or not to the time and location of the occurrence of major earthquakes. In this scheme, the confutation part ( i.e. verifying if similar anomalies do not occur in the absence of a significant seismic activity) assumes a role even much important than the usual validation component devoted to verify the presence of anomalous signal transients before (or in association with) specific seismic events. Since 2001, RST approach has been being used to study tens of earthquakes with a wide range of magnitudes (from 4.0 to 7.9) occurred in different continents and in various geo-tectonic settings. In this paper such a long term experience is exploited in order to give a quantitative definition of a significant sequence of TIR anomalies ( SSTA ) in terms of the required space–time continuity constraints ( persistence ), identifying also the different typologies of known spurious sequences of TIR anomalies that have to be excluded from the following validation steps. On the same basis, taking also into account for the physical models proposed for justifying the existence of a correlation between TIR anomalies and earthquakes occurrence, specific validation rules (in line with the ones used by the Collaboratory for the Study of Earthquake Predictability – CSEP – Project) have been defined to drive the validation process. In this work, such an approach is applied for the first time to a long-term dataset of night-time GMS-5/VISSR (Geostationary Meteorological Satellite/Visible and Infrared Spin-Scan Radiometer) TIR measurements, comparing SSTAs and earthquakes with M > 4 which occurred in a wide area around Taiwan, in the month of September of different years (from 1995 to 2002). In this dataset the Chi-Chi earthquake ( M W = 7.6) which occurred on September 20, 1999 represents the major, but not unique, event. The analysis shows that all identified SSTAs occur in the pre-fixed space–time window around (in terms of time and location) earthquakes with M > 4. The false positive rate remains zero even if only earthquakes with M > 4.5 are considered. In the case of the Chi-Chi earthquake, 3 SSTAs were identified (all within the established space–time correlation window), one of them appearing about 2 weeks before and very close to the epicentre of the earthquake just along the associated tectonic lineaments. The wide considered space–time window, together with the high seismicity of the considered area, surely positively conditioned the achieved results, so that further analyses should be carried out by using longer datasets and different geographic areas. However, also considering the coincidence with other (possible) precursor phenomena, independently reported (particularly within the iSTEP project) at the time of the Chi Chi earthquake, achieved results seem already sufficient (at least) to qualify TIR anomalies (identified by RST) among the parameters to be considered in the framework of a multi-parametric approach to a time-Dependent Assessment of Seismic Hazard ( t-DASH ). [ABSTRACT FROM AUTHOR]

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 × 10 6 m 3 , 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. [ABSTRACT FROM AUTHOR]

Taiwan is located in the circum-Pacific seismic belt. Berms served as protections of riverbanks were all designed without taking seismic bearing capacity into account in the past. Therefore failures of berms occurred frequently even the magnitude of an earthquake was not large enough. For the long term stability of berms, an equation of seismic bearing capacity is presented in this paper. Such an equation has been proved to be able to capture seismic bearing capacity failure of berms in Taiwan. [ABSTRACT FROM AUTHOR]

Ionospheric variability observed prior to mayor earthquakes has been studied for decades. In particular, in many such studies the identification of ionospheric precursors of large earthquakes has been regarded as a specific goal. This paper analyses the observations of the maximum electron concentration (NmF2) over Concepción (36.8°S;73.0°W) and of the total electron content (TEC) for an area covering the rupture zone corresponding to the very large Chile earthquake of 27 February 2010. The analyses used here are similar to those published before for many earthquakes in Taiwan, Japan and Russia. Possible NmF2 and TEC precursors are compared with other precursors proposed for the same earthquake using different TEC determinations and satellite observations of electron/ion concentration, energetic particle bursts and electromagnetic emissions. Some possible precursors derived from the various observations are consistent with each other. However, none can be unambiguously associated to the Chilean earthquake. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of modeling the ionospheric effect of the seismogenic electrostatic field (SEF) seen at the earth’s surface as a perturbation of the vertical atmospheric electrostatic field in the earthquake preparation zone. The SEF distribution at ionospheric altitudes is obtained as an analytical solution of the continuity equation for the electric current density. It is shown that at night, the horizontally large scale SEF can efficiently penetrate into the ionosphere and produce noticeable changes in the horizontal distribution of the F region electron density. The results suggest that the seismogenic electrostatic field could be a possible source for the ionospheric variations observed over Taiwan before the strong Chi Chi earthquake of September 21, 1999. [Copyright &y& Elsevier]

Abstract: Variations in the fractal dimension of earthquakes have been suggested to be a precursor of a large earthquake. However, the physical characteristics and seismicity are always different along a large fault system, and it is difficult to segment a large fault for further investigating. Therefore, the fractal dimension of earthquakes on a given fault only reflects the average seismic characteristics of the area and may be unrelated to precursory activity. In this paper, the evolution of the temporal generalized fractal dimension (Dq) of a seismic cluster within a small fault system associated with the Chiayi earthquake (ML =6.4), Taiwan, is investigated. The earthquakes of this sequence are confined in small source volume and reflect the behavior of the local fault system. Our results show that the Dq curve of the background stage is smooth with a low multifractal degree (0.36) and the seismicity is nearly monofractal in the Chiayi region. During the foreshock stage, the seismicity becomes active such that not only the Dq curve exhibits greater variability especially for the steep slope of Dq curve at q=0 but also the temporal fractal dimension changes from nearly monofractal to multifractal. In the aftershock stage, the fluctuation of Dq is large and the multifractal degree is up to 1.0. The temporal multifractal property becomes more pronounced as well. Finally, when the seismicity returns to the background stage, the Dq curve becomes smooth and nearly monofractal again. Therefore, the fluctuations in the Dq spectrum of an earthquake cluster associated with a large earthquake not only give a clear picture of the temporal alterations in the seismogenic regimes but also illustrate their variability through time for a large earthquake. In addition, the variation of the slope of Dq curve at q=0 in the foreshocks may be used as a precursor of a large earthquake. [Copyright &y& Elsevier]

Abstract: This paper investigates velocity structure of the active plate boundary in southern Taiwan by joint analysis of gravity anomaly and seismic arrival time data. P and S–P arrival time data from 3238 earthquakes were used. In addition to CWBSN permanent networks, seismic data include the Central Weather Bureau permanent networks and a temporary network consisting of 11 ocean bottom seismometers (OBSs) that was deployed to detect the aftershocks of the 2006 (ML7.1) Henchun earthquake occurred beneath southern Taiwan. The total available OBS data set consists of ~700 detected earthquakes, from which around 500 could be well located where about 450 events have been used in simultaneous inversion for hypocenters, three-dimensional Vp and Vp/Vs models for the study area. The main objective of incorporating gravity analysis is used to improve the velocity model for the offshore area, where it is poorly sampled by local earthquakes. This study found a low-velocity zone existing above the subducting South China Sea slab in the mantle wedge. Based on gravity modeling and our resulting velocity and Poisson''s ratio models suggest that the subduction complex, which is characterized with a low P-wave velocity and low Poisson''s ratios beneath the southern Taiwan. This duplex structure is characterized by a zone of low P-wave velocities in the range of 6.2–6.8km/s between 25 and 40km depth. It also shows that earthquake hypocenters do not fall within this low velocity zone. We have also used seismic tomography velocities to estimate the volume percentage of serpentinite and silica concentrations in southern Taiwan. The calculated serpentinite is about 30% and the volume percentage of quartz estimated is about 20% at the base of the forearc lower crust. [Copyright &y& Elsevier]

Abstract: The region around Taiwan is well known for its unique geological setting which has resulted in a high seismicity. The Central Geological Survey, Taiwan (CGST), has launched a series of investigation on characterizing the active faults on the island. The CGST revealed that there are 33 active faults and their fault parameters are suggested in the latest publication in 2010. However, the uncertainties of return period and earthquake magnitude are not provided. The main objective of the paper is to study the impact of “unspecified” parameter uncertainties on recurrence earthquake probabilities. In addition, a numerical approach involving the use of Monte Carlo simulation was proposed to estimate the exceedance probabilities in which the parameter uncertainties were taken into account. The Meishan fault in Central Taiwan with the best-estimate return period of 162years and earthquake magnitude of 7.1 was used as an example. The analyses verified the impact of parameter uncertainties on the exceedance probability in fault-induced earthquake recurrence. When uncertainty is high, the exceedance probability associated with large magnitudes is high. It was also observed that the probabilistic analysis in this study can generate a realistic, continuous distribution of exceedance probabilities that cannot be obtained by a deterministic approach. The best-estimate distribution of exceedance probability was established by enveloping the curves estimated by both deterministic and probabilistic approaches. Accordingly, the best-estimate exceedance probability for a 7.5-magnitude earthquake recurring in 2011–2060 induced by the Meishan fault in Central Taiwan was estimated as 11%. [Copyright &y& Elsevier]

Abstract: We study the interoccurrence time distributions of events by analyzing synthetic catalogues and three natural catalogues of the Japan Meteorological Agency (JMA), the Southern California Earthquake Data Center (SCEDC) and the Taiwan Central Weather Bureau (TCWB). We find a universal feature, i.e. the Weibull–log Weibull transition, in the interoccurrence time statistics. This transition demonstrates that the interoccurrence time statistics of earthquakes possess the hybrid Weibull and log Weibull statistics. We further find that the crossover magnitude m c ⁎⁎ from the superposition regime to the pure Weibull regime is averagely proportional to the plate velocity. In the end of this paper we summarize a region-independent relation, i.e. m c ⁎⁎/m max =0.54±0.06, which represents a novel empirical relation related to the Weibull–log Weibull transition for earthquake processes. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to present data on the occurrence of landslides triggered by typhoon and earthquake events, and to discuss the basic earthquake triggering mechanisms involved. Four events of typhoon and earthquake triggered landslides in the Chenyoulan River catchment of central Taiwan during 1996 to 2004 were studied in order to identify their controlling factors. The landslides areas were measured by comparing aerial photos taken over the past 18 years, and sediment discharge was counted at hydrometric stations. Investigation results demonstrate that hillslope geomaterials that had been disturbed by strong seismic shaking induced expansion of landslide areas during subsequent events. Analysis of Normalized Difference Vegetation Index (NDVI) also registered the changes of uncovered conditions on the hillslope caused by landsliding. When flow discharge is lower than 100 m3 s−1, post-seismic sediment concentration is roughly four times higher than pre-seismic concentration with the same flow discharge. This fate indicates that the amount of sediment discharge at normal flow discharge is affected by supplied sediment volume, which tends to increase with seismic activity. [Copyright &y& Elsevier]

Abstract: Wide-band magnetotelluric (MT) data were collected on an east–west profile, approximately perpendicular to the local strike of the Chelungpu thrust, through the hypocentral area of the Chi-Chi earthquake for imaging the seismogenic structure. MT data were then inverted for two-dimensional resistivity models plus best-fitting static shift parameters using a nonlinear conjugate gradient algorithm that minimizes the sum of the normalized data misfits and the smoothness of the model. As shown in the inverted 2D resistivity models presented in this paper, an electrical conductor beside the hypocenter of the Chi-Chi earthquake indicates that deep-crustal fluids may participate in the rupture process of the Chi-Chi earthquake. A striking spatial correlation between the crustal conductor and occurrence of aftershocks beneath the Chelungpu fault suggests a postseismic pore pressure adjustment ongoing after the mainshock. Additionally, the hypocenter exhibits an electrical resistive zone, consistent very well with a predicted compact zone from a crustal deformation and transient fluid flow modeling. [Copyright &y& Elsevier]

Abstract: The destructive 1999 Chi–Chi earthquake (Mw 7.5) was the largest inland earthquake in Taiwan in the 20th century. Several observations witness the non-linear seismic soil response in sediments during the earthquake. In fact, large settlements as well as evidence of liquefaction attested by sand boils and unusual wet ground surface were observed at some sites. In this paper, we present a seismic response simulation performed with CyberQuake software on a site located within the Chang-Hwa Coastal Industrial Park during the 1999 Chi–Chi earthquake in Taiwan. A non-linear multi-kinematic dynamic constitutive model is implemented in the software. Computed NS, EW and UP ground accelerations obtained with this model under undrained and two-phase assumptions, are in good agreement with the corresponding accelerations recorded at seismic station TCU117, either for peak location, amplitudes or frequency content. In these simulations, liquefaction occurs between depths 1.3 and 11.3m, which correspond to the observed range attested by in place penetration tests and other liquefaction analyses. Moreover, the computed shear wave velocity profile is very close to post-earthquake shear wave velocity profile derived from correlations with CPT and SPT data. Finally, it is shown that in non-linear computations, even though a 1D geometry is considered, it is necessary to take into account the three components of the input motion. [Copyright &y& Elsevier]

Abstract: The Jiufengershan rock avalanche was one of the largest and most damaging landslides triggered by the Chi-Chi earthquake (M L =7.3, M W =7.6) of 21 September 1999. The rock avalanche transported a mass of sedimentary rock 50 m thick and 1.5 km long, located on the western limb of the Taanshan syncline. The surface of rupture coincides with the bedding plane and dips moderately toward the Jiutsaihu valley. This paper is mainly devoted to the study of post-seismic surface processes that affected the sliding surface as well as the debris deposit, from September 1999 to February 2003. Large fractured blocks and a debris layer observed on the surface of rupture were subjected to mass wasting processes and denudation. The quantification of erosion was made using two different approaches. First, the subpixel correlation method was used to determine the horizontal displacement field from aerial photographs taken, respectively, 2 and 3.5 months after the earthquake. Displacements ranging from 1 to 6 m were observed around unstable blocks located at the western flank of the surface of rupture. Second, the co-seismic and post-seismic volume distributions in the sliding zone were determined from three digital elevation models, including a LiDAR image taken in 2002. Post-seismic erosion and deposition from September 1999 to April 2002 were mainly associated with mass wasting and denudation at the surface of rupture, deposition in small basins and lakes located in the debris deposit, and evacuation of materials from the debris deposit along natural and artificial drainage channels. The vertical compaction is 1% of the initial height of the deposit. [Copyright &y& Elsevier]

Abstract: In this paper, a relationship between M ⩾5.0 earthquakes and diurnal variations of the total geomagnetic field recorded at eight magnetometers in Taiwan during 1988–2001 are examined. One magnetometer station was setup in a seismic quiet area as a reference, while the others were located in areas of high seismicity or crustal activity observing earthquake effects. We compute the distribution of diurnal range ratios between the reference and each observation station for the entire thirteen years as a background and compare it with the monitored distributions during five different time periods before and after an M ⩾5.0 earthquake occurring within a distance of 50km from the observation station. Three specific earthquakes with different magnitudes, including the M =7.3 Chi–Chi earthquake show that the monitored distributions one month before and during the month of the earthquakes significantly depart from the associated background. It is found that changes of underground conductivities and currents around the forthcoming epicenter significantly affect the near-by geomagnetic field on the ground during the earthquake preparation period. The statistical results demonstrate that the monitored distributions of geomagnetic anomalies are highly related to the focal mechanism. [Copyright &y& Elsevier]

Abstract: This paper reviews the research on active and earthquake faults in Taiwan conducted prior and after the 1999 Chichi earthquake. The Chichi earthquake plays as a turning point of the relevant studies, since the 1999 coseismic surface rupture exactly follows preexisting fault scarps, created in turn by previous seismic events along the Chelungpu Fault. This fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes. Since 1999, many trenching studies have been carried out along the Chichi earthquake fault. A few of them demonstrates that the penultimate event is as young as probably only 200–430 years old; however, some others show a rather old age of several hundreds years or even older for the last faulting event before 1999. More trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length. In addition, we further discuss the offshore faulting associated with seismic event along the eastern coast of Taiwan, where the multiple Holocene terraces are well known. [Copyright &y& Elsevier]

The current simplified methods for assessing soil liquefaction potential use a deterministic safety factor in order to judge whether liquefaction will occur or not. However, these methods are unable to determine the liquefaction probability related to a safety factor. An answer to this problem can be found by reliability analysis. This paper presents a reliability analysis method based on the popular Seed''85 liquefaction analysis method. This reliability method uses the empirical acceleration attenuation law in the Taiwan area to derive the probability density distribution function (PDF) and the statistics for the earthquake-induced cyclic shear stress ratio (CSR). The PDF and the statistics for the cyclic resistance ratio (CRR) can be deduced from some probabilistic cyclic resistance curves. These curves are produced by the regression of the liquefaction and non-liquefaction data from the Chi-Chi earthquake and others around the world, using, with minor modifications, the logistic model proposed by Liao [J. Geotech. Eng. 114 (1988) 389]. The CSR and CRR statistics are used in conjunction with the first order and second moment method, to calculate the relation between the liquefaction probability, the safety factor and the reliability index. Based on the proposed method, the liquefaction probability related to a safety factor can be easily calculated. The influence of some of the soil parameters on the liquefaction probability can be quantitatively evaluated. [Copyright &y& Elsevier]

The Chi-chi earthquake that occurred on 21 September 1999 was triggered by the Che-lung-pu active fault. It caused a great deal of land deformation and damaged much of central Taiwan. Although a series of reports on surface ruptures have been published by the Central Geological Survey and earth science researchers, few papers have ever discussed the deformation before the 1999 earthquake or its activities. Therefore, this study seeks to understand the deformation and occurrence of the Che-lung-pu Fault before the Chi-chi earthquake. Aerial photograph interpretation and field observation are the methods used to identify the fault scarp, flexure scarp and range-facing scarp. The fault can be traced along the foothills between the alluvial plains and the hills which stretch from Tung-tou in the south to Cho-lan in the north.By comparing two fault traces between the inferred active Che-lung-pu Fault and the 1999 Che-lung-pu earthquake fault defined by the Central Geological Survey, we found that among the inferred active faults from aerial photographs, 67% coincide with the 1999 earthquake rupture, and about 76% of certainty I faults have ruptured during the 1999 earthquake. The estimation of paleoseismic occurrence in the area south of Ta-li River seems higher than that in the area of the north. However, the land deformation is less severe. All the reactivation and cumulation of active faults and the high percentage of occurrence at the pre-existing location provide useful information for the mitigation of seismic disasters. [Copyright &y& Elsevier]

The method by Iwasaki et al. [Iwasaki, T., Arakawa, T., Tokida, K., 1982. Simplified procedures for assessing soil liquefaction during earthquakes. Proceedings of the Conference on Soil Dynamics and Earthquake Engineering, Southampton, UK, pp. 925–939] for evaluating the liquefaction failure potential is widely used in Japan, Taiwan, and other countries due to its ease of use and general applicability. In this method, an index, called the Liquefaction Potential Index (IL), is calculated based on an integration of the calculated factor of safety (Fs) over depth with a weighting function. Iwasaki et al. (1982) provided a set of criteria to interpret the calculated index IL based on a calibration with his dataset of field performance cases. However, in their method, the factor of safety (Fs) is based on the liquefaction evaluation method adopted in the Japanese Highway Bridge Design Code [JSHE, 1990. Highway Bridge Design Guide Book. Japan Society of Highway Engineering, in Japanese]. Whether other liquefaction evaluation methods can be used in conjunction with the index IL or not needs further investigation. In this paper, the Cone Penetration Test (CPT) data from Yuanlin, Taiwan, the area that suffered the most from liquefaction in the 1999 Chi-Chi, Taiwan, earthquake, are analyzed. Three CPT-based methods are used for the calculation of the factor of safety for these cases derived from the Chi-Chi earthquake. These factors of safety are used to define the liquefaction potential and risk indexes. The calculated indexes are then used to construct the failure potential maps, and these maps are checked with the field observations. The study shows that the Liquefaction Risk Index (IR) defined in conjunction with the Juang et al. [Juang, C.H., Yuan, H., Lee, D.H., Lin, P.S., 2003. Simplified CPT-based method for evaluating liquefaction potential of soils. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, vol. 129, no. 1, pp. 66–80] method yields the best result in interpreting field observations. [Copyright &y& Elsevier]

The 1999 Chi-Chi, Taiwan earthquake caused great destruction to buildings, bridges, and other facilities, and a death toll of more than 2400. Lessons should be learned from this event, which, albeit disastrous, represents a rare full-scale experimentation in geotechnical engineering and related fields. Of particular interest to geotechnical engineers is the phenomenon of soil liquefaction that caused significant damage to buildings, lifelines and harbor facilities. These liquefaction phenomena, in the forms of sand boils, lateral spreads, tilting and settlement of buildings, and ground settlement, were observed in the Chi-Chi event. Shortly after the earthquake, an extensive field investigation in the Yuanlin area, including in situ tests and laboratory tests, was conducted by Moh and Associates and other parties. These in situ and laboratory tests along with ground performance observations form the basis for the present study.In this paper, 24 cases of ground performance in the areas that suffered the most from liquefaction are studied. The ground performance in selected cases of the 24 cases is accounted for through a series of liquefaction analyses. The analysis of the potential of liquefaction and ground failure is performed using Cone Penetration Test (CPT) data. The results of the analyses show that the field observations of ground performance in the Yuanlin area in the Chi-Chi event can be accounted for satisfactorily using the evaluation procedure by Ishihara (Ishihara, K., 1985. Stability of natural deposits during earthquakes. Proc., 11th Int. Conf. on Soil Mechanics and Foundation Engineering, San Francisco, CA, vol. 1, pp. 321–376.). [Copyright &y& Elsevier]

This paper focuses on the stress and strain rate field of the Taiwan area. The strain rate field in the Taiwan region is studied qualitatively and quantitatively, based on the GPS observation in 1990–1995. It reflects the accommodation of the ongoing lithospheric deformation within the seismogenic portion of lithosphere and exhibits zones with contrasting deformation modes and amounts. We then compare the obtained strain rate field with the tectonic information provided by studies of borehole breakouts and earthquake focal mechanisms for the Present, and by fault slip data analyses for the Quaternary period. In the first approximation, the stress and strain rate fields show spatial similarity. The orientation of principal shortening is generally consistent with the compressive stress orientation that reflects the oblique indentation of the Luzon Arc into the Eurasian continental margin. In more detail, significant anomalies in the deformation pattern deserve consideration in that they may reveal ongoing stress accumulation. Despite the short-term variations related to the earthquake cycle, some major features of the strain rate field, including the distribution of extension and compression, highlight the long-term tectonic behavior of the mountain belt at the lithospheric scale. The time and space variations of strain should be a function of local heterogeneity and be transferred between interseismic and coseismic periods. [Copyright &y& Elsevier]

In Central Taiwan, the destructive Chichi earthquake (Mw=7.6) of September 21st, 1999, produced a nearly 100-km-long rupture trace following the Chelungpu Fault. This paper shows how the geometry of the fault slip can locally be determined in three dimensions, based on analyses of earthquake fault in the Kuangfu stadium. The fault at this site is reverse and left-lateral. The three-dimensional geometrical analysis, done with a variety of data through independent determination modes, all applied to the deformation of the surface layer of the stadium tracks, allows complete verification of the results. Not only do these analyses constrain the fault behaviour in terms of trend, dip angle, obliquity and amount of slip, but also they reveal variations in both the horizontal and the vertical fault geometry. The comparison with relative displacements recorded at larger distances from the fault reveals that slip partitioning occurs, with nearly dip-slip thrusting along the rupture trace and distributed left-lateral shear in a deformed zone of the hanging wall, adjacent to the main fault. [Copyright &y& Elsevier]

In the early morning (1:47 Taiwan time) of September 21, 1999, the largest earthquake of the century in Taiwan (Mw=7.6, ML=7.3) struck this island country. The earthquake killed more than 2400 people and caused great destruction to buildings, bridges, dams, highways, and railways. One of the causes for heavy damages to the structures is soil liquefaction and ground settlement during the earthquake. In this paper, investigation of soil liquefaction and case histories of liquefaction are presented. Three CPT-based simplified methods, the Robertson method, the Olsen method, and the Juang method, are examined using the case histories derived from the Chi-Chi earthquake. The results of the comparison show that the Juang method is more accurate than the two methods in predicting liquefaction potential of soils based on the cases derived from the Chi-Chi earthquake, although all three methods are quite comparable in accuracy. [Copyright &y& Elsevier]

• S-wave HVSR is dependent on the variation of earthquake hypocenters. • Deep events have larger S-wave HVSR than shallow events at low frequencies (0.2–3.0 Hz). • Different S-wave incidence angles into the Taipei Basin caused variable S-wave HVSR. • A depth-dependent empirical site-correction amplification function is established to improve ground motion prediction. Techniques using horizontal-to-vertical spectral ratios (HVSR) have frequently been adopted in many studies, particularly of seismic site amplification. However, the influence of source location on the HVSR is not previously well-studied. This paper studies the variation of the S-wave HVSR in the Taipei Basin based on a variety of hypocenter locations. The earthquake records are classified into three categories, include depth, azimuth, and distance. We report the S-wave HVSR to have strong focal-depth-dependence, for which the HVSR of the deep events are larger than shallow events. Besides, the S-wave HVSR in the northern and northeastern parts of the basin also displays source azimuthal-dependence. However, there is no apparent difference in source distance-dependence. In contrast to the S-wave HVSR, the coda-wave HVSR all showed no apparent difference for various earthquake hypocenter locations. The synthetic modeling results support our idea that the cause of the variation of HVSR results for different earthquake focal depths is the different S-wave angles of incidence into the basin. Based on the dependency of the site amplification on the focal depth, a focal-depth-dependent empirical transfer function (ETF) was established. The focal-depth-dependent ETF was verified to improve the accuracy of the ground motion prediction by using the stochastic method in this study. We demonstrate that the source location effect, especially the focal depth, can significantly influence the S-wave HVSR and therefore needs to be taken into account in site response investigation. [ABSTRACT FROM AUTHOR]

The sediment fluxes to the southwesternmost Okinawa Trough (SOT) off northeast Taiwan have been measured with four sets of sediment traps. The sediment fluxes observed were much higher than those in many marginal seas and showed great variations in time and space. The fluxes exhibited a drastic seaward decline from northeastern Taiwan to the central trough and an increase with depth. Temporal variability of fluxes was in a wide range from three times to one order of magnitude for certain traps. The observed sediment fluxes had a positive correlation with river runoff from the Lanyang Hsi, a river in northeastern Taiwan. Usually, the highest fluxes could be attributed to episodic events, for example, typhoon passages, which always cause ample rainfall leading to high runoff and sediment discharge, and sediment fluxes that were observed during typhoon passages accounted for more than 50% of the long-term flux. Large earthquakes are suggested to be responsible for some sediment flux anomalies observed on the nearby steep slope because of a good match in time between sediment collection and earthquake occurrence. A conceptual model is proposed to illustrate the sources and transport of the SOT sediment. The study highlights the greater contribution of Taiwan fluvial sediments to the SOT compared to that of the Changjiang, and it provides evidence demonstrating the combined effects of river runoff and large earthquakes on the sediment fluxes observed in such a deep marginal sea. [Copyright &y& Elsevier]