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The first 30 min of the aftershock sequence following the 2022 September 17, ML 6.4, Guanshan, Taiwan earthquake is investigated by the back-projection (BP) method. Based on the Automatic Gain Control (AGC) to process individual earthquake record and sort waveforms by epicentral distance, 80 events are identified near the Guanshan earthquake epicenter to verify its temporal variation. However, most of these events cannot clearly image by the BP method to determine its spatial locations for its small amplitude and short time separation. In total, 29 aftershocks are imaged by this study to identify its spatial locations during this time period. The relocated events are compared with the Central Weather Bureau (CWB) rapid report catalogue. Only 5 events have been reported by the CWB rapid report catalogue. These unreported hidden aftershocks are identified to distribute surrounding the epicenter and extended to the east. This extracted information of hidden aftershocks is crucial for assessing the potential for future large aftershocks and estimating the associated seismic hazards in a given region, and provide extra message to evaluate the source physics in general. Key Points: Propose and verify earthquake location using the back-projection method. Discover 29 hidden events with 30 min after the Guanshan earthquake. Provide extra information to study following large aftershocks and to estimate its associated seismic hazards. [ABSTRACT FROM AUTHOR]

This study applies the unit tsunami method and probabilistic tsunami hazard analysis to investigate the tsunami hazard for the southern region of Pingtung County in southern Taiwan. The FUNWAVE-TVD model is used to calculate the aleatory and epistemic uncertainties. The aleatory uncertainty is analyzed using a comparison of simulated and observed maximum tsunami wave heights and the epistemic uncertainty is evaluated using a scenario caused by earthquakes in the Manila and Ryukyu subduction zones according to probabilistic seismic hazard analysis in Taiwan using Senior Seismic Hazard Analysis Committee Level 3 methodology. A unit tsunami method database is established for the Manila and Ryukyu subduction zones and used to carry out a probability-based offshore tsunami wave height simulation for the southern region of Pingtung County. A hazard map for tsunamis caused by earthquakes in the Manila and Ryukyu subduction zones is also derived. [ABSTRACT FROM AUTHOR]

Interseismic deformation describes the gradual accumulation of crustal strain within the tectonic plate and along the plate boundaries before the sudden release as earthquakes. In this study, we use 5 years of high spatial and temporal geodetic measurements, including Global Navigation Satellite System and Interferometric Synthetic Aperture Radar to monitor 3‐dimension interseismic crustal deformation and horizontal strain rate in Taiwan. We find significant deformation (strain rate >8 × $\times $ 10−6 yr−1) along the plate boundary between the Philippine Sea and the Eurasian Plates in east Taiwan. The high strain rate in the southern part of the Western Foothills is distributed along a few major fault systems, which reveals the geometry of the deformation front in west Taiwan. Our results help identify active faults in southwest and north Taiwan that were not identified before. These findings can be insightful in informing future seismic hazard models. Plain Language Summary: An earthquake cycle includes three phases: interseismic, coseismic, and postseismic. Interseismic deformation refers to the continuous crustal deformation that is built up by active tectonics. Depending on the relative motion between tectonic plates, the earthquake recurrence interval could vary by a few orders between different locations. As a result, knowing the crustal deformation rate and deformation accumulated in different fault zones can be useful for investigating future earthquake hazards. Using space geodesy tools like Global Navigation Satellite System and Interferometric Synthetic Aperture Radar, we can monitor surface deformation during the interseismic period. In this study, we monitor interseismic deformation in Taiwan using geodesy. We find that east Taiwan where two tectonic plates collide has the highest rate of deformation. In southwest and north Taiwan where most of the population resides, there is also high‐level of deformation distributed across a few different faults, indicating that some of the faults have a higher risk generating future earthquakes. As a result, knowing the amount of faults slip and amount of deformation built up during this interseismic period may inform us of potential future earthquake hazards. Key Points: This study combines Interferometric Synthetic Aperture Radar and Global Navigation Satellite System and produces high‐resolution 3‐D interseismic crustal velocities and strain rate estimates in TaiwanStrain rate measurements show high surface strain cumulation along east and southwest TaiwanThe surface strain rates and the earthquake hazard models based on seismology and field study are in good agreement [ABSTRACT FROM AUTHOR]

The 2018 February 6 M w 6.3 Hualien earthquake caused severe localized damage in Hualien City, located 20 km away from the epicentre. The damage was due to strong (>70 cm s−1) and sharp (duration ∼2.5 s) velocity pulses. The observed peak ground-motion velocity in Hualien City symmetrically decays with distance from the nearby Milun fault. Waveforms observed on the opposite sides of the fault show reversed polarity on the vertical and N–S components while the E–W component is almost identical. None of the published finite-fault slip models can explain the spatially highly localized large velocity pulses. In this study, we show that an M w 5.9 strike-slip subevent on the Milun fault at 2.5 km depth, rupturing from north to south at ∼0.9 V s speed, combined with site effects caused by surficial layers with low S-wave speed, can explain the velocity pulses observed at the dense strong-motion network stations. This subevent contributes only 25 per cent of the total moment of the 2018 Hualien earthquake, suggesting that a small local slip patch near a metropolis can dominate the local hazard. Our result strongly suggests that seismic hazard assessments should consider large ground-motion variabilities caused by directivity and site effects, as observed in the 2018 Hualien earthquake. [ABSTRACT FROM AUTHOR]

To provide information towards understanding Taiwan's earthquake hazard and risk, the multi-disciplinary Taiwan Earthquake Model (TEM) project, supported by the Ministry of Sciences and Technology, had prepared and published a first version of seismic hazard assessment maps of Taiwan in 2016, together with an on-land seismogenic structure database of the island. In the years following the publication of this first version, we have constructed an updated version of this database. Seven structures were identified and added to the database. Based on additional information, we have also updated the structural parameters of four existing structures, as well as systematically updated the parameters of all structures to include more complete parameter uncertainties. This update of the database represents the most up-to-date information of seismogenic structures in Taiwan, and would provide better constraints for future seismic hazard assessment and mitigation studies. [ABSTRACT FROM AUTHOR]

In probabilistic seismic hazard analysis (PSHA), the standard practice is to select a set of appropriate ground motion prediction equations (GMPEs) and assign weights on the logic tree, especially for regions where strong motion data are sparse and where no indigenous GMPE exists. Subjectively assigning weights to a set of models usually has the disadvantage of not obtaining mutually exclusive and collectively exhaustive models because of sparse or unavailable data. Therefore, the development of logic tree weightings in PSHA remains a major challenge. In this study, a distance metric measure for GMPEs is first analyzed to show how a set of GMPE's prediction models can be partially reconciled by using high-dimensional information visualization techniques. Visualization of a large suite of GMPEs onto a 2-D graphical map provides a powerful theoretical framework that can guide the selection of a set of representative models. These models are considered mutually exclusive and collectively exhaustive, and have the ability to represent the center, body, and range of ground-motion distribution in a logic tree analysis. Second, determination a set of weights for PSHA are estimated based on the residuals, likelihood and EDR-index which are known as data - driven weight. The other weight type is non-data driven which is calculated based on the probability of a random model generated on a Sammon's map. The methods presented here, that improve consistency in the weight assignment, can help to reduce overall epistemic uncertainties and offer a way of assigning weight on the logic tree. Finally, an example for assigning the weights on the logic tree for PHSA are discussed. [ABSTRACT FROM AUTHOR]

Given the probability distribution function relating to the recurrence interval and the occurrence time of the previous occurrence of a fault, a time-dependent model of a particular fault for seismic hazard assessment was developed that takes into account the active fault rupture cyclic characteristics during a particular lifetime up to the present time. The Gutenberg and Richter (1944) exponential frequency-magnitude relation uses to describe the earthquake recurrence rate for a regional source. It is a reference for developing a composite procedure modelled the occurrence rate for the large earthquake of a fault when the activity information is shortage. The time-dependent model was used to describe the fault characteristic behavior. The seismic hazards contribution from all sources, including both time-dependent and time-independent models, were then added together to obtain the annual total lifetime hazard curves. The effects of time-dependent and time-independent models of fault [e.g., Brownian passage time (BPT) and Poisson, respectively] in hazard calculations are also discussed. The proposed fault model result shows that the seismic demands of near fault areas are lower than the current hazard estimation where the time-dependent model was used on those faults, particularly, the elapsed time since the last event of the faults (such as the Chelungpu fault) are short. [ABSTRACT FROM AUTHOR]

Taiwan is tectonically situated in a terrain resulting from the oblique collision between the Philippine Sea plate and the continental margin of the Asiatic plate, with a continuous stress causing the density of strong-moderate earthquakes and regional active faults. The continuous time series of soil radon for earthquake studies have been recorded and some significant variations associated with strong earthquakes have been observed. Earthquake prediction is not still operative but these correlations should be added to the literature about seismo-geochemical transients associated to strong earthquakes. Rain-pore pressure related variations, crustal weakness at the studied faults system is consistent with the simultaneous radon anomalies observed. During the observations, a significant increase of soil radon concentrations was observed at Chunglun-T1 (CL-T1), Hsinhua (HH), Pingtung (PT), and Chihshan (CS) stations approximately two weeks before the Meinong earthquake (ML = 6.6, 6 February 2016) in Southern Taiwan. The precursory changes in a multi-stations array may reflect the preparation stage of a large earthquake. Precursory signals are observed simultaneously and it can apply certain algorithms the approximate location and magnitude of the impending earthquake. [ABSTRACT FROM AUTHOR]

The purpose of this study is to estimate maximum ground motions in southern Taiwan as well as to assess potential human fatalities from scenario earthquakes on the Chishan active faults in this area. The resultant Shake Map patterns of maximum ground motion in a case of Mw 7.2 show the areas of PGA above 400 gals are located in the northeastern, central and northern parts of southwestern Kaohsiung as well as the southern part of central Tainan, as shown in the regions inside the yellow lines in the corresponding figure. Comparing cities with similar distances located in Tainan, Kaohsiung, and Pingtung to the Chishan fault, the cities in Tainan area have relatively greater PGA and PGV, due to large site response factors in Tainan area. Furthermore, seismic hazards in terms of PGA and PGV in the vicinity of the Chishan fault are not completely dominated by the Chishan fault. The main reason is that some areas located in the vicinity of the Chishan fault are marked with low site response amplification values from 0.55 - 1.1 and 0.67 - 1.22 for PGA and PGV, respectively. Finally, from estimation of potential human fatalities from scenario earthquakes on the Chishan active fault, it is noted that potential fatalities increase rapidly in people above age 45. Total fatalities reach a high peak in age groups of 55 - 64. Another to pay special attention is Kaohsiung City has more than 540 thousand households whose residences over 50 years old. In light of the results of this study, I urge both the municipal and central governments to take effective seismic hazard mitigation measures in the highly urbanized areas with a large number of old buildings in southern Taiwan. [ABSTRACT FROM AUTHOR]

On 6 February 2016 (UTC 19:57), the Meinong earthquake with Richter magnitude (ML) 6.6 struck southern Taiwan and caused hundreds of damaged buildings, resulting in 117 casualties. We investigated the relationship between the damaged buildings and the ground motion in the forms of peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration (SA) at 0.3 s (SA0.3), 1.0 s (SA1.0), and shaking duration to identify which ground motion parameter most represents building damage. PGV and SA1.0 present better correlation with consequent damage. The Intensity converted from PGV presents better correlation to the damage than PGA. We disaggregated the TEM PSHA2015 hazard contribution to the Meinong earthquake damage region (Southern Taiwan) from different seismic source typologies to clarify the seismic source contributing to the hazard. The hazards contributed by the Meinong earthquake were 16, 26, and 23% for PGA, SA0.3, and SA1.0, respectively. The predicted seismic hazard source areas were 38, 61, and 75% for PGA, SA0.3, and SA1.0, respectively, for the PSHA with a return period of 475 years. This result indicates that the 2016 Meinong earthquake did partially diminish the seismic hazard potential in southern Taiwan. However, more than about 80% of the seismic hazard potential, especially the fault sources were not yet released. These values suggest that the seismic hazard potential in southern Taiwan remains high regardless of the 2016 Meinong earthquake. [ABSTRACT FROM AUTHOR]

Seismic landslide hazard assessment is typically based on deterministic analysis to calculate slope displacements during an earthquake. However, deterministic analysis is unable to account for various uncertainties in the analysis process. This study focuses on utilizing the established results from probabilistic seismic hazard analysis (PSHA) and extending probabilistic seismic landslide hazard analysis (PSLHA) to account for the uncertainties of ground motions and soil strengths. Two simplified methods, being flexible and fast, are proposed and evaluated by comparing with the fully but complex probabilistic method. One of the methods that yields a better performance is applied to evaluate the probabilistic seismic landslide hazard in the Tsao-Ling area of Taiwan using information regarding the seismic hazard curve and it's deaggregation results. Lastly, seismic landslide hazard maps are constructed for different return periods and compared with the deterministic map for the 1999 Chi-Chi earthquake. • Simple method for probabilistic seismic landslide hazard analysis is proposed. • The method incorporates uncertainty of ground motions and strength parameters. • The method only requires a probabilistic seismic hazard curve and its deaggregation. • The method is validated with the full but complex probabilistic method. • The method is demonstrated by applying it to the Tsao-Ling area of Taiwan. [ABSTRACT FROM AUTHOR]

this study presents the development of a region- and -site specific ground motion model (GMM) based on ground motion data obtained from the I-lan alluvial basin in northeastern Taiwan. The development was performed by calibrating the ergodic Phung et al. (2020) (Ph20) GMM developed for Taiwan. The source of strong ground motion data includes events from shallow crustal and subduction zones with magnitudes (M W) from 4.0 to 7.6, records from distances shorter than 200 km, and focal depths up to 150 km. The resulting regional model accounts for peculiarities that are not captured by the ergodic Ph20 GMMs, such as (1) the difference in source type effects, (2) V S30 -scaling from the local site effects, and (3) enhancement of long period spectral ordinates due to the deep sedimentary basins. The standard deviations of the local model are much lower than those of the ergodic model, particularly the component of the standard deviation that corresponds to the site-to-site variability (ϕ S 2 S), indicating that better site characterization can significantly reduce the overall uncertainty in ground motion estimation. • The bilinear- Vs30 scaling is better represented by the regional data rather than the linear Vs30 -scaling of the ergodic GMM. • Regional characteristics are significantly characterized by the source-type effects and site effects. • Two way random effects model should be considered when performing a site – specific probabilisitic seismic hazard analysis. [ABSTRACT FROM AUTHOR]

On 2016 February 6 the South Taiwan earthquake (Mw 6.4) occurred in the Meinong District of Kaohsiung, southern Taiwan, at a depth of 17 km. It caused 117 fatalities and widespread damage to infrastructures, especially in the Tainan city. To clarify the generating mechanism of this damaging earthquake, we determined high-resolution 3-D images of P- and S-wave velocity (VP, VS) and Poisson's ratio (s) in the epicentral area. We used 105 712 P- and 61 250 S-wave arrival times of 8279 local earthquakes (1.5 = M = 6.4) recorded at 41 seismic stations in South Taiwan during 2000-2011. In the upper crust (depth = 10 km), the most remarkable feature is low-VP, low-VS and high-s anomalies in areas with known active faults in the southwestern and easternmost parts of Taiwan. In contrast, high-VP, high-VS and low-s anomalies become dominant in the lower crust. The hypocentre of the 2016 South Taiwan earthquake is located in a boundary zone where seismic velocity and Poisson's ratio change drastically in both the horizontal and vertical directions. Furthermore, the hypocentre is underlain by a vertically elongated high-s anomaly at depths of 23-40 km, which may reflect ascending fluids from the upper (or uppermost) mantle. The low-V and high-s anomalies in the upper crust coincide with areas of low heat flow, negative Bouguer gravity anomaly, and low magnetotelluric resistivity, which may reflect crustal fluids contained in the young foldand- thrust belt. These results suggest that the 2016 South Taiwan earthquake was triggered by ascending fluids from dehydration of the subducting Eurasian slab, invading into active faults with a high loading rate. [ABSTRACT FROM AUTHOR]

In historical earthquakes, fault ruptures have caused significant ground deformation and infrastructure damage. Because the occurrences of earthquakes are hard to predict, it is critical to assess the area influenced by fault propagation for disaster resistance. Based on trench excavations in active fault zones, earthquake faults propagated through the composite strata with gravel deposits are common. However, the stratigraphy change of the overburden strata and the non-spherical granular particles of the gravel deposit are rarely considered in most case studies. This study proposes a procedure that utilizes digital image analysis and discrete element modeling to estimate the composite strata deformation induced by thrust faulting. The procedure is demonstrated through a series of small-scale sandbox modeling and a case study of the Chushan excavation site in Taiwan. The gravel fabric, including gravel volumetric content, aspect ratio and initial long-axis orientation, are considered in the parametric study as well as the configuration of the strata composition. Simulations show that fault propagation restricts in the overburden because the faulting-induced kinematic energy is mostly dissipated by clast rotation, resulting in a lower fault extended distance and a wider tri-shear zone. The rotation of the gravels shows good agreement with the range of the tri-shear zone, indicating that the long-axis orientations of gravels can be an indicator to interpret the faulting history. Overall, it is feasible to construct a reasonable numerical model for assessing fault rupture-composite strata interaction (FR-CSI) once the outcrop photo data are available. The proposed procedure is useful for efficient and reliable scenario modeling regarding earthquake hazard mitigation. • In-situ gravel fabric is characterized by digital orthogonal imagery analysis. • The characterized gravel fabric is implemented into 3D DEM model to study the ground deformation under thrust faulting. • Influences of gravel volumetric content, aspect ratio, initial long-axis orientation, and strata composition are evaluated. • Trench modeling shows the evolution of transitional structural geometries within composite strata in seismic history. [ABSTRACT FROM AUTHOR]

The main goal of this study was to develop an updated and refined catalog of earthquakes in Taiwan (1900-2014) with homogenized M magnitudes that are compatible with the Harvard M. We hope that such a catalog of earthquakes will provide a fundamental database for definitive studies of the distribution of earthquakes in Taiwan as a function of space, time, and magnitude, as well as for realistic assessments of seismic hazards in Taiwan. In this study, for completeness and consistency, we start with a previously published catalog of earthquakes from 1900 to 2006 with homogenized M magnitudes. We update the earthquake data through 2014 and supplement the database with 188 additional events for the time period of 1900-1935 that were found in the literature. The additional data resulted in a lower magnitude from M 5.5-5.0. The broadband-based Harvard M, United States Geological Survey (USGS) M, and Broadband Array in Taiwan for Seismology (BATS) M are preferred in this study. Accordingly, we use empirical relationships with the Harvard M to transform our old converted M values to new converted M values and to transform the original BATS M values to converted BATS M values. For individual events, the adopted M is chosen in the following order: Harvard M > USGS M > converted BATS M > new converted M. Finally, we discover that use of the adopted M removes a data gap at magnitudes greater than or equal to 5.0 in the original catalog during 1985-1991. The new catalog is now complete for M ≥ 5.0 and significantly improves the quality of data for definitive study of seismicity patterns, as well as for realistic assessment of seismic hazards in Taiwan. [ABSTRACT FROM AUTHOR]

On 18 December 1867 a disastrous earthquake struck off northern Taiwan and generated a tsunami that caused hundreds of deaths. At that time, with little information available, people could not be expected to identify the mechanism of the1867 Keelung earthquake or the subsequent tsunami. To reconstruct the earthquake and tsunami available historical documents and references were reviewed and verified. The data were then evaluated for its' credibility. The historical place names were correlated with the present locations and GIS tools were used to reconstruct the earthquake and tsunami and identify the distribution of the resulting damage. Excluding the damage recorded in the Keelung area, there is evidence that shows that the 1867 Keelung earthquake and tsunami killed more than 580 people. The coastal area from Jinshan to Keelung Harbor was the main affected area. With a recorded tsunami wave height of 6 m occurring in Huanggang and Shueiwei, the run-up height in Jinbaoli Old Street and the Badouzi area is estimated to have been 15 m high. The tsunami wave height was observed to be 205 cm at Keelung Harbor Bay. The attenuation law was adopted to simulate the earthquake intensity distribution. The source parameters reasonableness and validity were considered by comparing the earthquake intensity distribution and the resulting damage. Our results show that the 1867 Keelung earthquake was highly correlated with the offshore Shanchiao Fault extension. The length the fault is about 40 km, with the epicenter located at 25.34°N, 121.91°E and focal depth of 10 km. The moment magnitude was 7.0. [ABSTRACT FROM AUTHOR]

The 2013 ML 6.4 Ruisui earthquake struck a seismic gap around the northern part of the Longitudinal Valley where rare earthquakes have occurred for at least two decades. Seismic data with different frequency bands connote a diverse scale of source characteristics. The slip model derived by a previous study using long-period seismic data provided us with the preliminary earthquake source properties in low-frequency energy radiation. However, the high-frequency part of the seismic energy needs to be considered for the strong motions in the comprehensive frequency band. As a case study, we carried out broadband strong motion simulations through the hybrid scheme, which simulated waveforms combining the low-frequency motions (frequency-wavenumber integration method) and high-frequency motions (empirical Green's function method) to reveal the strong ground motion and source characteristics of the 2013 Ruisui earthquake. The results show that even though the local structure is complicated this hybrid simulation can effectively rebuild the overall broadband strong ground motion characteristics for the 2013 Ruisui earthquake. Additional study issues are required to better understand the nature of localized high peak ground acceleration and the related seismic hazards for future earthquakes. [ABSTRACT FROM AUTHOR]

The 1909 Taipei earthquake (M 7.3) occurred beneath the Taipei metropolitan area (TMA) causing substantial damage according to the historical literature. According to the hypocenter relocation and tectonic implications provided in a previous study, we simulated ground motions within the TMA using a hybrid simulation method involving the spectral-element method (SEM) and the empirical Green's function method (EGFM). We used the SEM for simulating low-frequency components and the EGFM for simulating high-frequency components. These high and low frequency components were subsequently combined. For the EGFM we used the records from a recent ML 4.9 earthquake (11 October 2013, depth = 143.8 km) in the Taipei area as the empirical Green's function. According to the historical literature, the observed PGA (peak ground acceleration) values are 59.2 and 67.0 gal at ancient stations TAP and KEE, with periods of 1.21 and 1.34 s, respectively. By comparing the simulated PGA values at modern stations TAPB and WFSB to the historical documented ones for 12 different models, our result suggests that the 1909 Taipei earthquake was an event with a magnitude of about Mw 7.3 and stress drop of approximately 30 bars, or a smaller equivalent magnitude between Mw 6.8 - 7.3 but with much higher average stress drop of more than 100 bars. For a deep event beneath TMA a larger vertical P-wave motion and longer period shaking wave, as addressed in the historical literature, might be expected with prolonged shaking as found in the simulation. A seismic hazard assessment is necessary for metropolitan Taipei to better understand the long period shaking from deep subduction zone intra plate events. [ABSTRACT FROM AUTHOR]

Frequent high seismic activities occur in Taiwan due to fast plate motions. According to the historical records the most destructive earthquakes in Taiwan were caused mainly by inland active faults. The Central Geological Survey (CGS) of Taiwan has published active fault maps in Taiwan since 1998. There are 33 active faults noted in the 2012 active fault map. After the Chi-Chi earthquake, CGS launched a series of projects to investigate the details to better understand each active fault in Taiwan. This article collected this data to develop active fault parameters and referred to certain experiences from Japan and the United States to establish a methodology for earthquake probability assessment via active faults. We consider the active faults in Central Taiwan as a good example to present the earthquake probability assessment process and results. The appropriate "probability model" was used to estimate the conditional probability where M ≥ 6.5 and M ≥ 7.0 earthquakes. Our result shows that the highest earthquake probability for M ≥ 6.5 earthquake occurring in 30, 50, and 100 years in Central Taiwan is the Tachia-Changhua fault system. Conversely, the lowest earthquake probability is the Chelungpu fault. The goal of our research is to calculate the earthquake probability of the 33 active faults in Taiwan. The active fault parameters are important information that can be applied in the following seismic hazard analysis and seismic simulation. [ABSTRACT FROM AUTHOR]

Taiwan is located at an active plate boundary and prone to earthquake hazards. To evaluate the island's seismic risk, the Taiwan Earthquake Model (TEM) project, supported by the Ministry of Sciences and Technology, evaluates earthquake hazard, risk, and related social and economic impact models for Taiwan through multidisciplinary collaboration. One of the major tasks of TEM is to construct a complete and updated seismogenic structure database for Taiwan to assess future seismic hazards. Toward this end, we have combined information from pre-existing databases and data obtained from new analyses to build an updated and digitized three-dimensional seismogenic structure map for Taiwan. Thirty-eight on-land active seismogenic structures are identified. For detailed information of individual structures such as their long-term slip rates and potential recurrence intervals, we collected data from existing publications, as well as calculated from results of our own field surveys and investigations. We hope this updated database would become a significant constraint for seismic hazard assessment calculations in Taiwan, and would provide important information for engineers and hazard mitigation agencies. [ABSTRACT FROM AUTHOR]

This study used the results from 45 microtremor array measurements to construct a shallow shear wave velocity structure in the western plain of Taiwan. We constructed a complete 3D velocity model based on shallow and tomography models for our numerical simulation. There are three major subsurfaces, engineering bedrock (VS = 600 m s-1), Pliocene formation and Miocene formation, constituted in the shallow model. The constant velocity is given in each subsurface. We employed a 3D-FD (finite-differences) method to simulate seismic wave propagation in the western plain. The aim of this study was to perform a quantitative comparison of site amplifications and durations obtained from empirical data and numerical modelling in order to obtain the shallow substructure soil response. Modelling clearly revealed that the shallow substructure plays an important role in strong ground motion prediction using 3D simulation. The results show significant improvements in effective shaking duration and the peak ground velocity (PGV) distribution in terms of the accuracy achieved by our developed model. We recommend a high-resolution shallow substructure as an essential component in future seismic hazard analyses. [ABSTRACT FROM AUTHOR]

The Taiwan Earthquake Model (TEM) was established to assess the seismic hazard and risk for Taiwan by considering the social and economic impacts of various components from geology, seismology, and engineering. This paper gives the first version of TEM probabilistic seismic hazard analysis for Taiwan in these aspects. We named it TEM PSHA2015. The model adopts the source parameters of 38 seismogenic structures identified by TEM geologists. In addition to specific fault source-based categorization, seismic activities are categorized as shallow, subduction intraplate, and subduction interplate events. To evaluate the potential ground-shaking resulting from each seismic source, the corresponding ground-motion prediction equations for crustal and subduction earthquakes are adopted. The highest hazard probability is evaluated to be in Southwestern Taiwan and the Longitudinal Valley of Eastern Taiwan. Among the special municipalities in the highly populated Western Taiwan region, Taichung, Tainan, and New Taipei City are evaluated to have the highest hazard. Tainan has the highest seismic hazard for peak ground acceleration in the model based on TEM fault parameters. In terms of pseudo-spectral acceleration, Tainan has higher hazard over short spectral periods, whereas Taichung has higher hazard over long spectral periods. The analysis indicates the importance of earthquake-resistant designs for low-rise buildings in Tainan and high-rise buildings in Taichung. [ABSTRACT FROM AUTHOR]

Wu, E.C.; Ma, W.H., Chen, Y.L.; Wu, H.L.; Hu, K.C.; Hsiao, S.C. and Wu, Y.C., 2016. Probabilistic Tsunami Hazard Analysis - Application to Maanshan Nuclear Power Plant in Taiwan. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1267 - 1271. Coconut Creek (Florida), ISSN 0749-0208. In the past twelve years, two earthquakes of magnitude 9.0 have occurred in the western Pacific. These earthquakes resulted in tsunamis, causing tremendous casualties, such as the nuclear disaster in Japan on March, 2011. Taiwan is an island located in the circum-Pacific belt, along which approximately 90% of the world's largest earthquakes take place. To prevent hazards, probabilistic tsunami hazard analysis (PTHA) is applied to nuclear power plants in the coastal regions of Taiwan. The approach developed here allows for the selection of reasonable tsunamis generated from distant earthquakes in the Manila Trench. Two types of uncertainty are considered: aleatory uncertainty and epistemic uncertainty. Concerning the aleatory uncertainty of modeling, a validation of prediction results is conducted against observed data. And a logic tree is introduced to help with epistemic uncertainty and set up different series of source parameters. In addition, a numerical model is used to simulate tsunami propagation and wave height. Under the assumptions of the logic tree and numerical modeling, the relationship between annual probability and maximum tsunami wave height can be obtained. Finally, tsunami hazard maps can be produced and the safety assessment of nuclear power plants can be carried out. The results provide useful information for engineering design and hazard prevention. [ABSTRACT FROM AUTHOR]

Seismic hazard evaluations require an estimate of the expected ground motion at the site of interest usually by using attenuation relationships. The mean shear-wave velocity over the top 30 m (Vs30) is incorporated in the ground motion attenuation relationships in this study. By comparing the standard deviations of the residuals between the observed and predicted values before and after incorporating the site effect term Vs30, the reduction in standard deviation for the peak ground velocity (PGV) is significantly reduced by about 11%. Clearly, the refined attenuation relationships will be more useful for engineering purposes. Analyzing the site effect term using the amplification factor (relative to a site with Vs30 = 760 m s-1), has revealed that the Changhua Plain, Chianan Plain, Pingtung Valley, Ilan Plain, and Taipei Basin have high values, implying large ground motion amplification. Following a disastrous earthquake, quick assessment and timely peak ground acceleration (PGA) and PGV map reporting will be critical for effective emergency response operations. After an earthquake we can combine the simple attenuation relationships, as determined from Model 1, to provide near real-time estimation and reporting of the PGA and PGV values for the Taiwan area. We can also use the relations between the intra-event site residual and the Vs30 to estimate the Vs30 for stations that have recorded strong motions, but do not yet have Vs30 information. Our approach including sites with estimated Vs30 has resulted in a refined Vs30 contour map that can be used for more realistic seismic hazard assessment for Taiwan. This approach is especially applicable to the foothill and mountain areas. [ABSTRACT FROM AUTHOR]

Engineering risk assessment is to estimate the structure's failure probability multiplied by its failure consequences. On the other hand, the analysis was sometimes performed on a more general basis, utilizing a few indicators to quantify relative risk levels for decision-making. On the basis of such a framework, this paper introduces a novel risk assessment on 18 active faults in Taiwan, considering the fault's location, earthquake size and return period from the literature. The result shows that the Chelungpu Fault in central Taiwan has the highest risk score among the 18 active faults, in contrast to the Hengchun Fault in southern Taiwan which has the lowest risk. Besides this, the 18 active faults in Taiwan were classified into four groups based on this risk assessment, and the classification could help the region's sustainable development against earthquake hazard. [ABSTRACT FROM AUTHOR]

The region around Taiwan is known for active seismicity, and a few studies have reported a high seismic hazard in this region, including a deterministic seismic hazard analysis (DSHA) study. Essentially, DSHA is to estimate earthquake ground motions considering the worst-case earthquake size and location, but without considering the seismic hazards from non-controlling sources. Understandably, when many non-controlling sources are present, the original DSHA framework could be insufficient. Therefore, using the extreme probability theory, this study introduces a new DSHA framework taking non-controlling seismic sources into account during DSHA calculations. The new method was applied to a seismic hazard assessment for Taiwan, showing that near the conjunctions of seismic source zones, the increase in seismic hazard could be substantial after considering a total of 19 non-controlling sources. More importantly, like other seismic hazard assessments for Taiwan, this study conveys the same alarming message that a high level of seismic hazard should be present around the region. [ABSTRACT FROM AUTHOR]

On 27 March 2013, a 6.2 ML earthquake occurred at 19 km depth in eastern Nantou, central Taiwan. Over a 2 week period it was followed by more than 680 aftershocks that ranged to 5 ML. Most events occurred below the ~10-km-deep detachment fault predicted for this part of the mountain belt, coinciding with other precisely located hypocenters that indicate that much of the crust in this area is seismically active. We combine geological data with a three-dimensional (3-D) P-wave velocity model derived from local tomography and earthquake hypocenters to determine a model for the structure of central Taiwan. Much of the surface geology of the area comprises the uplifted Eocene rocks of the Hsuehshan Basin. The 3-D P-wave velocity model shows a shallowing of higher velocities across the Hsuehshan Basin and hypocenter data indicate that its western bounding fault is clearly defined by an eastward-dipping band of events that extends to >20 km depth. The eastern bounding fault is interpreted to coincide at depth with a cluster of events between 20 and 30 km depth. These data suggest that the preexisting, rift-related extensional faults of the Hsuehshan Basin are currently being reactivated and the basin is being inverted. We present hypocenter data from the Nantou sequence that corroborate this interpretation and show the importance of choosing the correct structural model when assessing seismic risk. [ABSTRACT FROM AUTHOR]

This paper presents a new application of the Bayesian approach to objectively determine logic-tree weights for ground motion prediction equations (GMPEs) used in seismic hazard analysis. This is a considerable improvement over the current practice based on subjective judgment to determine the logic-tree weights for GMPEs. To demonstrate the feasibility of this Bayesian application, case studies at three sites in Taiwan were conducted. The results demonstrate that the logic-tree weights for three Next Generation Attenuation GMPEs can be determined in an objective and repeatable manner using this Bayesian calculation, which is based on the difference between predicted and observed peak ground accelerations. • A Bayesian application to determine logic-tree weights for PSHA • The determination based on observed earthquake ground motions • Case studies using the method also presented [ABSTRACT FROM AUTHOR]

We propose an approach to imaging earthquake source rupture process by direct back-projection of local high-frequency (0.1–2.5 Hz) P-wave displacements from strong-motion records. A series of synthetic experiments are performed which demonstrate that our approach is capable of recovering the spatial-temporal distribution of the source slip with a good station coverage and a high average coherence value between the target and template waveforms. We demonstrate the effectiveness of our approach by applying it to image the slip distribution of an earthquake occurred on 2010 March 4, in Jiasian (Mw = 6.0 and ML = 6.4) in southern Taiwan. The resulting moment-rate amplitude images show that the source rupture initiated at the vicinity of the hypocentre, followed by a moderate moment-rate release to the southeast of the hypocentre and a subsequent upward propagation, and finally propagated in the northwest direction, in agreement with the distribution of aftershocks. The majority of the slip at 17–20 km depth occurred to the west of the hypocentre, in a general agreement with the slip distributions obtained from dislocation model and finite-fault inversions. Our modified back-projection approach relies on seismic waveforms with the considerations of a recent 3-D structure model, high average coherence value, station correction factor and simplified amplitude correction. It is computationally efficient and allows for near real-time determinations of source slip distributions after earthquakes using strong-motion records. A quick result for the rupture model can be used in the calculation of strong ground-motion, providing important, useful and timely information for seismic hazard mitigation. [ABSTRACT FROM AUTHOR]

According to the Central Geological Survey Taiwan (CGST), the Meishan fault in Central Taiwan, which induced a catastrophic earthquake in 1906, is considered capable of triggering equivalent events with a return period of 162 years. Therefore, as the next event is expected around 2070, the Meishan fault poses a high level of earthquake risk in Central Taiwan, especially for those cities and townships very close to the fault. However, the best-estimate return period (162 years) and earthquake magnitude (7.1 M) reported by the CGST must be subject to some uncertainty, because such an event is very unlikely to recur every 162 years. Therefore, this study carried out a series of seismic hazard assessments for three major cities close to the Meishan fault, with the uncertainty of the best-estimate information being determined using the Rosenblueth algorithm. The results show that for Chaiyi city, which the Meishan fault passes through, the probability of the current design value (i.e., PGA = 0.33 g) being exceeded by the earthquake motion induced by the Meishan fault in the next 50 years would be as high as 55 %. Therefore, further studies should be carried out to obtain a better understanding of the Meishan fault, to develop a robust hazard mitigation plan for nearby cities. [ABSTRACT FROM AUTHOR]

SUMMARY The 1909 April 14 Taiwan earthquake caused significant damage in Taipei. Most of the information on this earthquake available until now is from the written reports on its macro-seismic effects and from seismic station bulletins. In view of the importance of this event for assessing the shaking hazard in the present-day Taipei, we collected historical seismograms and station bulletins of this event and investigated them in conjunction with other seismological data. We compared the observed seismograms with those from recent earthquakes in similar tectonic environments to characterize the 1909 earthquake. Despite the inevitably large uncertainties associated with old data, we conclude that the 1909 Taipei earthquake is a relatively deep (50-100 km) intraplate earthquake that occurred within the subducting Philippine Sea Plate beneath Taipei with an estimated MW of 7 ± 0.3. Some intraplate events elsewhere in the world are enriched in high-frequency energy and the resulting ground motions can be very strong. Thus, despite its relatively large depth and a moderately large magnitude, it would be prudent to review the safety of the existing structures in Taipei against large intraplate earthquakes like the 1909 Taipei earthquake. [ABSTRACT FROM AUTHOR]

Abstract: Fragility curves can be developed using analytical or empirical methods. When the actual building damage records and the associated ground motion data are available, empirical methods are often adopted. Traditionally, district-based records of building damage are analyzed for developing such fragility curves. In this paper, a new procedure based on the concept of “isointensity-isoexposure” is developed. The new procedure is demonstrated through a case study of the building damage records collected from the 1999 Chi-Chi, Taiwan earthquake. The results show that the fragility curves developed with the proposed procedure are more in-line with observations than with the traditional district-based procedure. The developed fragility model may be used for earthquake loss estimation and future emergency planning in the study area. The limitations of the proposed approach include: (1) the developed fragility curves are area-specific and may not be readily applicable to other regions, and (2) ground motion intensity data may not be available at every location in an area of interest. [Copyright &y& Elsevier]

Abstract: From 1996 through 2007, several heavy typhoons and earthquakes precipitated landslide hazards in southeast Taiwan. In the present study, we analyze the impact of topography, lithology, rainfall and earthquakes on landsliding and sediment transport by quantifying the landslide ratio (ratio of landslide area to catchment area) and the sediment discharge for the Sinwulu and Luye upstream catchments of the Peinan River. The steep topography in these two catchments causes a large proportion of landslide ratios on slopes to exceeding 50°, a condition which accelerates the delivery of landslide debris to the downslope channel. The landslide ratios of 0.84%–2.30% are obviously related to the rock strength and discontinuity density of the terrain, but we find the magnitude of landsliding and sediment discharge to vary with the occurrence of earthquakes. Typhoon-induced rainstorms generate the bulk of sediment discharge in the study catchments, though the landslide debris is transported by the huge amounts of runoff produced by rainstorms. A contributing factor is the recent occurrence of severe earthquakes which weakened the geomaterial, leading in turn to further increases of fluvial sediment during subsequent typhoons. Additionally, the finding that eventual reduction of unit sediment concentration after high magnitude earthquake events reveals that the downslope transport of landslide debris associated with earthquake activity and subsequent typhoon events precipitates a relatively short term, 1–3year, increase of erosion rates in these two study areas in southeastern Taiwan. [Copyright &y& Elsevier]

Abstract: In this study, a local set of response spectral attenuation equations, developed for seismic hazard analysis in Taiwan, are introduced as an example for determining the local strong motion attenuation relationship for a region. Strong ground-motion data for shallow crustal earthquakes are obtained from the Taiwan Strong-motion Instrumentation Program (TSMIP). These data are used to establish peak ground acceleration (PGA) and response spectral acceleration (SA) attenuation equations taking into consideration both hanging-wall effects and site conditions. The obtained results show that the local set of attenuation equations gives significantly lower values of PGA and SA for structural periods shorter than 0.3s as compared to a set of global relations obtained from international data. The SAs obtained for structural periods longer than 0.3s are similar to those obtained for global sets. This indicates that developing a local set of ground-motion attenuation equations is necessary for more accurate prediction of ground motion values. [Copyright &y& Elsevier]

Abstract: In this paper the results of a case study of the annual probability and return period of soil liquefaction in Yuanlin, Taiwan, the town that suffered significant liquefaction damage in the 1999 Chi-Chi earthquake, are presented. As part of this case study, a framework for determining the average annual probability of liquefaction (AAPL) that is attributed to a known fault is developed. This framework is formulated by considering the uncertainties in both liquefaction resistance and liquefaction loading. For liquefaction loading, the seismic hazard from a known fault is considered; and for liquefaction resistance, soil parameters, characterized mainly by cone penetration test (CPT) and standard penetration test (SPT), and their uncertainties are considered. Additionally, model uncertainty of the empirically-developed liquefaction resistance models, based either on CPT or SPT, is considered in the analysis for the annual liquefaction probabilities. The results of the case study show that the proposed framework is applicable for site-specific analysis of liquefaction potential or for mapping liquefaction potential in a given town (or city). Furthermore, the AAPL and return period determined based on SPTs are found to be comparable with those determined with CPTs. The results of the case study provide some guidance for future engineering planning and regulation consideration in the Yuanlin, Taiwan area. [Copyright &y& Elsevier]

Earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes, yet little work has focused on understanding how a bedrock river responds to a single large earthquake. Data from the 1999 Mw = 7.6 Chi-Chi earthquake in central Taiwan show dramatic differences in river response that depend on the proximity to the rupture zone. Near the fault scarp, vertical ground deformation intensifies river incision on a time scale of years to decades, while distal to the fault, landslides induced by the earthquake mantle bedrock on the river bed with sediment, impeding incision for decades to centuries as the material is evacuated. This surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes. [ABSTRACT FROM AUTHOR]

The Shanchiao fault, located to the west of the Taipei Basin in northern Taiwan, is a highly active normal fault that has a left-slip component and fault length of over 40 km. We suggest that the Shanchiao fault still has the ability to induce coseismic subsidence in the Taipei Basin under present extensional regime of northern Taiwan. In order to characterize the coseismic ground deformation and assess the potential inundation hazards in Taipei Basin, we estimate surface displacements using elastic dislocation models. The largest slip is assumed to be located underneath the Kuandu area due to the observation of deepest Tertiary basement in this area. Based on the topography changes due to coseismic deformation in a potential magnitude 7 event induced by reactivation of the Shanchiao fault, a 2D inundation model was adopted to simulate several inundation scenarios, including potential flood inundation below high tide condition and under various return-period design rainfall events. The predicted inundation maps based on various return-period flood events can provide information to assess potential earthquake-induced inundation hazards. [ABSTRACT FROM AUTHOR]

The aim of this study is to evaluate the probability of seismic hazard for the Taipei metropolitan area in northern Taiwan from readily available information, including the attenuation relationship of peak ground acceleration (PGA), tectonic settings, fault-slip data, and seismicity. The PGA seismic hazard mapping reveals that the hazard level in this area increases going from northwest to southeast and southwest. There are four important earthquake sources that contribute to the hazard level: (1) the plate-boundary interface (subduction zone interface) located offshore of the Ilan plain; (2) the intraslab subduction zone underneath Taipei itself; (3) the crustal areal sources in eastern Taiwan and central Taiwan; and (4) the nearby active Shanchiao fault. The slip-rate of the targeted fault is relatively low, and therefore not the most dangerous earthquake source revealed in the 475-year return period. However, there is no doubt that the target fault is the control source in the 2475-year return period. Furthermore, higher PGAs are predicted using the attenuation relationship of subduction zone earthquake sources rather than crustal earthquake sources, meaning an increase of the seismic hazard level over previous estimates. Consequently, more attention needs to be paid to subduction zone sources when considering mitigation of seismic hazards in northern Taiwan. [ABSTRACT FROM AUTHOR]

A novel approach to construct site-dependent ground-motion prediction equations (GMPEs) was implemented to build a uniform hazard response spectra (UHRS) using a reservoir site in southern Taiwan as an example. This innovation minimizes the GMPE uncertainties to avoid over-estimations in a probabilistic seismic hazard analysis (PSHA). We selected ground-motion records with similar site conditions from the stations within 70 km of the studied site to build a site-dependent ground-motion prediction model for crustal earthquakes in the region. This site-dependent GMPE set obtains a significantly smaller scattering of residuals compared with the existing regional GMPEs from the Taiwan data set. This indicates that a set of site-dependent GMPEs could provide a more accurate and reasonable prediction of ground-motion levels for the design or safety evaluation of important infrastructures. • A new site-dependent approach for ground-motion prediction equations (GMPEs). • New GMPEs implemented to build uniform hazard response spectra for a reservoir site. • New approach provides a more accurate prediction of ground-motion levels for Taiwan. [ABSTRACT FROM AUTHOR]

A strong collision between the Eurasian and Philippine Sea Plates causes high seismicity in the Taiwan region. A substantial number of cities and large towns exist on thick sediments in western Taiwan. Larger-magnitude inland earthquakes, for example the 1999 Chi-Chi earthquake, can cause serious damage in urban areas. Consequently, urban seismology is of great interest to the local seismological community. The Taipei Metropolitan Area (TMA) is the political, economic, and cultural center of Taiwan. It is situated over a region where the Philippine Sea plate subducts the Eurasian plate. Although seismicity in the TMA is lower than other areas of Taiwan, earthquakes still occur. Seismic risk mitigation is of grave concern in the TMA because of its high population, number of tall buildings, mass rapid transit system, and two nearby nuclear power plants. In this article, procedures for seismic risk mitigation, previous studies, core issues for future research and related topics are described and reviewed. [ABSTRACT FROM AUTHOR]

The 1999 Chi-Chi, Taiwan, earthquake (Mw 7.6) caused damage to 49 tunnels within 60 km of the epicenter, including the collapse of three mountain tunnels, ending the traditional perception that tunnels, and especially mountain tunnels, were earthquake-resistant. A series of studies that involved seismic damage investigation, physical model and numerical simulation experiments, numerical analyses and field monitoring have been carried out to investigate the damage mechanism, influencing factors and the seismic response of tunnels, and these are reviewed in this manuscript. The results of such studies over the last two decades demonstrate that tunnels suffer less seismic damage than surface structures. Most of seismic damage to tunnels involves failure of the adjacent ground or the movement of a fault that is crossed by the tunnel. Tunnel damage that is caused by ground motion occurs where the seismic effects are amplified, such as at the slope next to mined sections and portals, in shallow overburden tunnels, and at particular combinations of tunnel depth and geological conditions. Results of physical model-based tests using shaking tables and centrifuges reveal that tunnels exhibit rocking responses along with ovaling deformation or racking distortions under seismic excitation; also residual earth pressures remain on the tunnel side walls and internal forces of lining exist after shaking. The structural responses of a tunnel under non-uniform excitation are larger than that under uniform excitation. Beyond investigations of the damage mechanism and influencing factors, physical model-based tests provide experimental benchmarks for correcting numerical model settings and calibrating the characteristic parameters in numerical simulations, and validate the application of such models and simulations in the investigation of tunnel seismic responses. A fully dynamic analysis with complete descriptions of the topography and geological characteristics of a site, and the engineering characteristics of the tunnel and surrounding ground, is nowadays probably the most effective way for the seismic simulation of tunnels, and the design and evaluation of the same. An understanding of the state-of-the-art with respect to the seismic response of tunnels demonstrates the importance of three-dimensional geological models for tunnel seismic analysis; the evaluation of regional ground motion models that can capture the expected range of possible ground motions at tunnel site, and determinations of both the static and dynamic characteristics of geological conditions that are associated with site-scale vulnerabilities. Since residual earth pressures and internal forces remain on tunnel after an earthquake, the seismic damage to tunnels and loads and strain of the surrounding ground may accumulate. Methods for evaluating potential seismic damage to existing tunnels must be further developed, and more field monitoring of the seismic responses of tunnels is required. • Seismic response of tunnels revealed in past two decades is extensively reviewed. • Ground motion-induced tunnel damage occurs where the seismic effects are amplified. • Seismic damage to tunnels and loads and strain of surrounding ground may accumulate. • 3D geological models and more field monitoring are important for fully dynamic analyses. [ABSTRACT FROM AUTHOR]

The reactivation of the Chelungpu Fault triggered the 1999 Chi-Chi M w 7.6 earthquake, resulting in substantial ground surface ruptures and severe damage. After the earthquake, the surveys organized by the Central Geology Survey (CGS) of Taiwan and the National Center for Research on Earthquake Engineering (NCREE) immediately investigated a variety of cases related to engineering structures damaged by substantial ground deformation. The investigations gathered valuable in-situ data before human activities disturbed the local setting and altered co-seismic features of interest, providing opportunities for studying the interaction between surface rupture and engineering structures. This study outlines the reconnaissance of damaged engineering structures in Shigang District that cover three typical types of foundations and analyzes the fault geometry and fault slip at the local scale to construct a geomechanical model for numerical simulation. In addition, 3-dimensional (3D) modeling was performed for each case study to investigate the damage mechanisms of the structures subjected to the substantial ground deformations by using PFC3D (Particle Flow Code 3D), which is based on the discrete element method (DEM). The results of the DEM analyses, which have been calibrated with the in-situ data, showed the ability to evaluate the overall ground deformation, the detection of structural movement, and the critical elements of progressive collapse during faulting. This study demonstrates that the 3D DEM simulation is a reliable analysis tool for studying earthquake fault rupture-overburden layer-engineering structure interactions and can produce useful information for hazard assessment with an acceptable computation time. The 3D DEM analysis is therefore suggested to be applied to assess the potential damage scenarios for the engineering structures located in active fault zones. • Analysis of earthquake fault rupture-overburden layer-engineering structure interaction in the Chelungpu fault zone • Integrated field investigations, geomechanical analysis, and 3D DEM modeling • Damaged cases of engineering structures with different foundation types in the Shigang District were simulated. • Current abilities and limitations of the full-scale 3D DEM model are discussed. [ABSTRACT FROM AUTHOR]

Deals with a study about the development of a fully nonlinear finite-element (FE) model to investigate the impact of hysteric and viscous material behavior on the downhole motion recorded by an array at a large-scale seismic test site in Lotung, Taiwan. Design of the model; Evaluation of the fully nonlinear analysis relative to that of an equivalent linear model.

The active Milun Fault is the northernmost segment of the suture between Philippine Seaplate and Eurasian plate on the Taiwan Island. Historically, it was linked to two destructiveearthquakes on October 22nd, 1951, and February 6th, 2018, respectively. The 1951 ML7.3earthquake and the 2018 MW6.4 earthquake both produced surface ruptures along the MilunFault, causing casualties and damage on buildings in the Hualien city, which is the mostpopulated area in eastern Taiwan. Although the Milun Fault is surely intimidating, thesubsurface configuration and history of this active fault remain little exposed. The purpose ofthis study is to uncover the fault at shallow depth, reason the activity and seismic history ofthe Milun Fault and estimate the recurrence interval. Two trenches along with four boreholeswere carried out six months after the shock at the study site, located ∼ 2.6 kmnorth of downtown Hualien, where surface ruptures were reported during the 2018earthquake. The walls of one trench revealed a high dip angle of 80˚ to the east forthe main fault of the Milun Fault and its branch faults dip 36˚, 56˚, and 70˚ tothe east, respectively. The growth strata in the footwall of the branch faults werefolded. Distinctive sedimentary features such as the colluvial-wedge deposits andsoil liquefaction were also observed on the trench walls. By compiling the resultsof restoration and stripping of strata in conjunction with the age constraints, fivepaleo-earthquake events associated with the Milun Fault are resolved: (1) the 2018 event andthe earlier ones occurred at (2) 380-0 yr BP (3) 686-380 yr BP (4) 2184-1396 yrBP (5) 3232-2630 yr BP. Although the recurrence interval was estimated as ca.70 yrs earlier, our data suggest that the recurrence interval could be longer thanpreviously expected. However, due to the limited records of stratigraphy and possibleabsence of paleo-earthquakes, further investigation will be needed to generate a moresophisticated estimate of the recurrence interval. In addition, based on the borehole data,the slip rate of the Milun fault is about 6.0 to 6.5 mm/yr within the past 5000 yrs.These new findings shall benefit the earthquake hazard assessment for the region. [ABSTRACT FROM AUTHOR]

In order to avoid the casualties caused by damaged buildings during strong earthquakes, it's important and essential to understand the seismic design specifications of buildings. The motion of a building depends on the interferometry of building and ground motion, the coupling between building and ground, and the mechanical properties of the building. We applied deconvolution to the motion recorded to separate the building response. Deconvolution interferometry is a powerful and convenient tool which allow us to extract structural parameters (e.g., shear wave velocity, resonance frequency and attenuation parameter) from seismic records. By applying deconvolution to earthquake records, it can provide a complete response of the building and understanding the motion pattern of the structure under strong motion. Therefore, we can check medium's state by tracking resonance frequency, shear wave velocity and the attenuation parameter Q to avoid damage of building in the next mega-earthquake. We deployed a seismograph array in the library of National Chung Cheng University, Taiwan, which recorded earthquakes and few months of ambient noise record. The shear wave velocity from the seismic record was calculated to be 225.26±24.29 m/s. We also used seismic record to calculate the Q value of each floor and found that the Q value for the lower floors (Q=16) was lesser on average than the higher floors (Q=23). We believe that this reflects partial energy of the wave dissipated to the surface during transfer, making the Q value of the lower floors is lesser. On the other hand, we estimated the similar shear wave velocity 289.9±7.6 m/s from ambient noise record for the entire building as well. In advance, we divided the structure into low- and high-floors to calculate the shear wave velocity from the upward and downward propagation. We found that the shear wave velocities of the low and high floors are significantly different but exhibit a stable variation. For the monitoring phase, calculating the velocity variation from ambient noise depends on stacking signal to gain better S/N ratio and more convergent result. Therefore, for ambient noise calculation, we tried different stacking time-lengths and calculated the related shear wave velocities which the results are similar to the analysis in earthquake. From the above results, we concluded that the physical parameters of the building are stable and implied that the structure is in a healthy condition. Finally, we hope these results would be helpful to build a long-term monitoring of building's healthy status and the assessment of seismic hazard. [ABSTRACT FROM AUTHOR]

The seismic source spatiotemporal rupture process of events in Japan, Taiwan and Greece are imaged by backprojection of strong motion waveforms. Normalized high frequency (>2Hz) S-waveforms from recordings on dense strong-motion networks are used to scan a predefined 3D source volume over time. Backprojection is an alternative novel approach to image the spatiotemporal earthquake rupture. The method was firstly applied for large earthquakes at teleseismic distances but is nowadays used at local distances and higher frequencies. The greatest advantage of the method is that processing is done without any a-priori constraints on the geometry, dimension and size of the source. Thus, the spatiotemporal imaging of the rupture is feasible in higher frequencies (> 1Hz) than conventional source inversion studies even when the examined fault geometry is complex. This high frequency energy emitted during an earthquake is of great importance in seismic hazard assessment for certain critical infrastructures. The actual challenge in using high frequency local records is to distinguish the local site effects from the true earthquake source content. Otherwise, mapping them incorrectly to the source area limits the resolvability of the method. The real challenge is to remove the site effect part from all available records, or at least, to distinguish quantitatively good reference stations from hard-soil and rock sites. In this study, the advantages and limitation of the method are explored using waveform data from well recorded events in Japan (Hokkaido Eastern Iburi Earthquake, 2018, Kumamoto 7.1 Mw, 2016), Taiwan (Hualien 6.4 Mw, 2018) and Greece (Zakinthos 6.8 Mw, 2018). [ABSTRACT FROM AUTHOR]

We present earthquake shaking scenarios by a physics-based ground-motion simulation scheme for seismic risk assessments. In fitting requirements of the application of loss estimations, scenarios can refer to various kinds of damage and losses to constructions (buildings, bridges, etc.), casualties, economic losses, social losses and so on. We quantitatively assess the ground motion effects by the physics-based full-waveform ground-motion simulation which is a powerful tool for earthquake-induced ground-motion prediction. The entire time history of the ground motion induced by an earthquake depends on a number of factors, including source-rupture process, subsurface velocity structure, topographic relief, and local site condition. Then, the further risk assessment can also be revealed by a combination with exposure data. As an example, we carried out simulations to model rupture scenario of the Shanchiao fault and the potential large subduction earthquake in northern Taiwan, with accounting for effects of (1) source slip distribution, (2) seismic wave propagation, (3) surface topography and (4) site amplification. Output ground-motion parameters, including peak ground acceleration (PGA), peak ground velocity (PGV), peak ground displacement (PGD), 0.3-s-period spectral acceleration (SA0.3), and 1.0-s-period spectral acceleration (SA1.0), can be adopted to further implement to loss estimation. Our results referred different shaking-level potentials of earthquake scenarios can benefit to risk management, especially for the further application of strategy making of emergency response and disaster prevention and preparations. [ABSTRACT FROM AUTHOR]