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The choice of stiffness profile can be crucial in a site response analysis. This research aims to study site response predictions at the large-scale seismic test site in Lotung, Taiwan, employing three different approaches to choosing the stiffness profile in nonlinear and equivalent linear analyses. These approaches consider point average, layer average, and deposit average stiffness profiles. One strong and one weak earthquake event recorded at the site are simulated with these three stiffness profile approaches. Moreover, the stiffness profiles are tested under sets of seven modified real input motions (selected from the European Strong-Motion Database) at various seismic intensity levels. The results indicate that the different stiffness profiles have a minimal effect on the nonlinear site response predictions, in particular for input motions having a PGA greater than or equal to 0.05 g. The spectral acceleration values and PGA and shear strain profiles from nonlinear site response analyses change negligibly when using different approaches to derive the stiffness profile. In the equivalent linear site response analysis, the spectral acceleration predictions are strongly influenced by the stiffness profile approach, regardless of the PGA level of the input motions. The stiffness profile has a more significant role in equivalent linear site response analysis than in nonlinear site response analysis. Therefore, the point average stiffness profile should be used in equivalent linear site response analysis. [ABSTRACT FROM AUTHOR]

Early warning systems can estimate the possible-shaking intensity of the earthquake based on the initial P-waves on-site. Researchers have used the following two indicators: the initial peak P-wave displacement ( P d ) and the ground motion characteristic period ( τ c ). In this study, we re-examine the performance of the two indicators by employing ground motion data from the P-Alert low-cost network in Taiwan. We have found that the signal-to-noise ratio of displacement ( S N R d ) is effective for data selection. In addition, we have observed the irregular behavior of τ c in the P-Alert dataset. [ABSTRACT FROM AUTHOR]

The macroseismic intensity of the February 6, 2018, Mw 6.4, Hualien earthquake, which caused extensive damage around the Hualien area of eastern Taiwan is reassessed using the Environmental Seismic Intensity (ESI-07) scale. We compiled data on earthquake environmental effects (EEEs) caused by the 2018 Hualien earthquake, which includes surface ruptures, ground cracks, liquefaction, and occasional landslides, and estimated the epicentral intensity (I 0) as well as site-specific intensities. We found that the ESI-07 epicentral intensity of the Hualien quake in 2018 is IX. We note that the epicentral area of the 2018 Hualien earthquake was the mesoseismal area of the October 22, 1951, (M w 6.6) Hualien earthquake, as reported in primary contemporary sources and historical earthquake catalogs. The 1951 Hualien earthquakes also caused prominent surface ruptures, liquefaction, and ground cracks. Consequently, we reassess the macroseismic intensities of this historical seismic event and compare it to the Hualien earthquake in 2018. The comparison suggests similar epicentral intensities for the two earthquakes (IX and X ESI-07). Moreover, we conducted a systematic comparison between intensity obtained using different scales which revealed the differences of two to three degrees between the ESI-07 and traditional intensity scales. This result reconfirms the significance of documentation and recording of earthquake environmental effects to make intensity assessments for modern seismic events consistent with the historical earthquake records. Moreover, a re-evaluation of historical earthquake intensity in eastern Taiwan could be performed in order to update the seismic hazard map. Application of the ESI-07 intensity scale of recent and historical earthquakes will be helpful in post-earthquake recovery efforts for a future earthquake. The prepared ShakeMaps from the ESI-07 values suggests completely different shapes to the previously generated ShakeMaps considering the peak ground acceleration or peak ground velocity. It suggests that the ShakeMaps prepared from the earthquake environmental effects can be complemented with the instrumental based intensity map to have a better seismic hazard prediction and future land use planning for the region. [ABSTRACT FROM AUTHOR]

This paper considers the issue related to the protection of buildings and structures against seismic influences and the prevention, exclusion, or reduction of seismic hazards. The catastrophic destruction of modern «earthquake-resistant» buildings in Turkey and Taiwan has shown that existing methods of strengthening and reinforcing structures are not perfect and require further study. Analysis of existing approaches to ensuring seismic resistance showed that seismic insulation and seismic suppression systems still do not have a scientific and technical justification for the effectiveness of their operation from the point of view of ensuring the stability of structures. The estimation-dynamic models of the «base-seismic insulation-structure» system developed to date do not always make it possible to simulate the joint work of their interaction during an earthquake and account for the transformation of the seismic impact on the structure. An alternative technique has been devised, a geotechnical seismic insulation screen, as a seismic insulation system that reduces the intensity of seismic loads on the structure and ensures its seismic resistance. In a specific example, the effectiveness of this seismic insulation system is confirmed. This seismic insulation technique in the form of damper screens is characterized by reliability and manufacturability in ensuring the seismic resistance of objects under construction. The results of computational and experimental modeling of the interaction of an earthquake-insulated structure with a ground base found that the values of axial forces and bending moments in a building with a seismic insulating screen are less than in a building without seismic insulation by 30–40 %. The geotechnical seismic insulation screen makes it possible to advance the development of new seismic insulation techniques and determine their effectiveness. This technique will also be effective when strengthening the base and seismic insulation systems of historical monuments, protecting them against seismic and dynamic influences. [ABSTRACT FROM AUTHOR]

The kinematic source rupture process of the 2016 Meinong earthquake (Mw = 6.4) in Taiwan was derived from apparent source time functions retrieved from teleseismic S-waves by using a refined homomorphic deconvolution method. The total duration of the rupture process was approximately 15 s, and one slip-concentrated area can be represented as the source model based on images representing static slip distribution. The rupture process began in a down-dip direction from the fault toward Tainan City, strongly suggesting that the rupture had a unilateral northwestern direction. The asperity with an area of approximately 15 × 15 km2 and the maximum slip of approximately 2 m were centered 12.8 km northwest of the hypocenter. Coseismic vertical deformation was calculated based on the source model. Compared with the results derived from InSAR (Interferometric Synthetic Aperture Radar) data, our results demonstrated that the location with maximum uplift was accurately well detected, but our maximum value was just approximately 0.4 times of the InSAR-derived value. It reveals that there are the other mechanisms to affect the vertical deformation, rather than only depending on the source model. At different depths, areas west, east, and north of the hypocenter maintained high values of Coulomb stress changes. This explains the mechanism behind aftershocks being triggered and provides a reference for predicting aftershock locations after a large earthquake. The estimated seismic spectral intensities, including spectral acceleration and velocity intensity (SIa and SIv), were derived. Source directivity effects caused damage to buildings, and we concluded that all damaged buildings were located within a SIa value of 400 gal. Destroyed buildings taller than seven floors were located in an area with a SIv value of 30 cm/s. These observations agree with those on damages caused by the 2010 Jiasian earthquake (ML 6.4) in Tainan, Taiwan. [ABSTRACT FROM AUTHOR]

The earthquake (ML5.2) occurred at Chushan town, Nantou on Nov.11, 2017 and had caused a lot of aftershocks around the hypocenter of the mainshock. The Coulomb stress changes (ΔCFSs) by the mainshock demonstrated most of the aftershocks located within the positive parts greater than 0.1 bar, revealing the aftershocks may be induced by the mainshock. After investigating the ΔCFSs at different depths, the results showed most of positive parts of ΔCFSs under depth 15km were transferred to the southeast and southwest regions. About ten days later, there were lots of earthquakes (ML 5.2~3) with depth below 15km clustered exactly in the southeast region. The southwest region nears the Meishan fault, which began as a reverse thrust slip and caused large earthquake with ML 7.0 before 110 years ago. This means the Meishan fault may be triggered by the successive earthquakes near the fault. Based on the seismic spectrum intensities, the seismic hazards by the potential Meishan earthquake are estimated. The maximal seismic intensities will occur at Chushan town and the segment of freeway 3 connects Nantou city and Chushan town have to pay more attentions. The landslides may happen at the junctions of Nantou and Yunlin counties, which great landslides had happened, when Chi-Chi earthquake (ML7.3) occurred in 1999. [ABSTRACT FROM AUTHOR]

Earthquake waveforms are necessary for simulation, verification, and validation during the development of structural and earthquake engineering. However, due to the fact that the processes of earthquake preparation and generation are extremely complex and the human observations cover a relatively short period compared to large earthquake cycles, recorded earthquake waveforms are often limited and quite imbalanced. Consequently, the generation of artificial earthquake waveforms is meaningful and can produce useful earthquake data. In this study, a new method based on a generative approach is proposed by leveraging machine learning (ML) techniques. The generative models based on generative adversarial network (GAN) and conditional GAN (cGAN) are introduced, and the adversarial training between the generator and the discriminator is utilized to learn how to generate artificial earthquake waveforms. In addition, several criteria are exploited to terminate the adversarial training early in order to prevent modal collapse. Besides, different earthquake datasets and several earthquake features are used to verify the proposed method. The preliminary generation is carried out using the dataset recorded during the Chi-chi earthquake, and the generated samples show similar earthquake features to those extracted from the earthquake dataset. Subsequently, conditional generation is conducted using several sub-datasets recorded in different areas around Taiwan. The results demonstrate that the well-trained model can efficiently generate waveforms according to a pre-specified seismic intensity, with an overall accuracy of up to 90%. Although the model is reliable for Taiwan and in general to restricted subdomain of the probability distribution support, the proposed method shows its ability to produce new samples for a given class, even when the number of generated samples exceeds the number of training samples. • A large number of artificial earthquake waveforms are generated by using generative adversarial networks (GAN). • Several criteria based on the generated samples are used to terminate the adversarial training early to avoid modal collapse. • The conditional generation enables GANs to generate artificial earthquake waveforms according to various labels. [ABSTRACT FROM AUTHOR]

The gravity-type wharf is generally more vulnerable during earthquakes due to its massive gravity quay wall, especially when located in a liquefiable area. Therefore, this study aims to develop numerical analysis procedure for its seismic performance assessment and fragility analysis considering the influence of soil liquefaction. Firstly, the quantitative damage criteria for gravity-type wharves were introduced and verified by case histories. Then, the finite element (FE) modeling of a gravity quay wall founded on liquefiable ground for seismic response analysis using PLAXIS 2D was suggested. Utilizing this modeling, the earthquake-induced damage cases of two gravity-type wharves in two ports in Taiwan were simulated for validation. The seismic performance of both wharves was further assessed by comparing the analyzed response under design earthquake with the damage criteria. Finally, the procedure of seismic fragility analysis based on massive numerical analysis was proposed. Actual earthquake records were scaled to various seismic intensity levels to serve as input motions. Thus, the relationships between the seismic intensity and the damage probability of a gravity-type wharf corresponding to different damage levels, namely, the fragility curves, can be accordingly obtained. These results benefit the seismic performance design and rapid estimation of possible seismic damage of port facilities. • Existing seismic damage criteria of gravity-type wharf justified by case histories. • FE modeling for seismic performance assessment of gravity-type wharf suggested. • Fragility curves of gravity-type wharf derived using massive numerical analysis. • Case studies performed for demonstration and results compared with real situation. • Procedure of performance assessment and fragility analysis verified satisfactory. [ABSTRACT FROM AUTHOR]

An earthquake with an epicenter offshore of Hualien City in eastern Taiwan occurred at midnight on February 6, 2018. The Richter magnitude (ML) of the earthquake was 6.26 and the seismic intensity ranged up to level VII, the strongest seismic intensity level regulated in Taiwan. Almost all the major damage resulting from this seismic event was occurred near both sides of the Milun Fault, where records from nearby strong motion stations displayed the characteristics of near-fault ground motions. The main seismic damage was the collapse of four buildings with soft bottom stories, one of which resulted in fourteen of the seventeen total fatalities. Comparing the acceleration response spectra with the design response spectra sheds light on the effects of near-fault ground motions on the collapsed buildings. Based on the eventual forms of collapsed buildings, building collapses that have generally led to major casualties in past seismic events around the world can be classified into sit-down, knee-down and lie-down types. In addition to the four collapsed buildings, seismic reconnaissance on other buildings, bridges, ports, and non-structural components have also been conducted. This study explores the issues and challenges arising from the reconnaissance results and thereby enhances learning from the seismic event. [ABSTRACT FROM AUTHOR]

Real-time probabilistic seismic hazard assessment (PSHA) was developed in this study in consideration of its practicability for daily life and the rate of seismic activity with time. Real-time PSHA follows the traditional PSHA framework, but the statistic occurrence rate is substituted by time-dependent seismic source probability. Over the last decade, the pattern informatics (PI) method has been developed as a time-dependent probability model of seismic source. We employed this method as a function of time-dependent seismic source probability, and we selected two major earthquakes in Taiwan as examples to explore real-time PSHA. These are the Meinong earthquake (ML 6.6) of 5 February 2016 and the Hualien earthquake (ML 6.2) of 6 February 2018. The seismic intensity maps produced by the real-time PSHA method facilitated the forecast of the maximum expected seismic intensity for the following 90 d. Compared with real ground motion data from the P-alert network, our seismic intensity forecasting maps showed considerable effectiveness. This result indicated that real-time PSHA is practicable and provides useful information that could be employed in the prevention of earthquake disasters. [ABSTRACT FROM AUTHOR]

Floor acceleration plays a major role in the seismic design of nonstructural components and equipment supported by structures. Large floor acceleration may cause structural damage to or even collapse of buildings. For precision instruments in high-tech factories, even small floor accelerations can cause considerable damage in this study. Six P-wave parameters, namely the peak measurement of acceleration, peak measurement of velocity, peak measurement of displacement, effective predominant period, integral of squared velocity, and cumulative absolute velocity, were estimated from the first 3 s of a vertical ground acceleration time history. Subsequently, a new predictive algorithm was developed, which utilizes the aforementioned parameters with the floor height and fundamental period of the structure as the new inputs of a support vector regression model. Representative earthquakes, which were recorded by the Structure Strong Earthquake Monitoring System of the Central Weather Bureau in Taiwan from 1992 to 2016, were used to construct the support vector regression model for predicting the peak floor acceleration (PFA) of each floor. The results indicated that the accuracy of the predicted PFA, which was defined as a PFA within a one-level difference from the measured PFA on Taiwan’s seismic intensity scale, was 96.96%. The proposed system can be integrated into the existing earthquake early warning system to provide complete protection to life and the economy. [ABSTRACT FROM AUTHOR]

Proposed in the late 1980s, cumulative absolute velocity (CAV) is a new intensity measure for earthquake ground motion characterizations, followed by studies and applications such as CAV ground motion prediction equations (GMPEs). In this study, two new CAV GMPEs were developed with 24,667 strong-motion records from Taiwan, and the first CAV seismic hazard assessment for Taipei (the most important city in Taiwan) was then conducted using the local CAV models. It shows that the annual rate for the study area to encounter a ground motion with CAV >0.97 g-sec is 0.002 per year, corresponding to a 10% occurrence probability in 50 years. By contrast, the deterministic scenario-based analysis shows that the CAV seismic hazard is about 0.60 g-sec for the study area. Future studies are worth conducting to develop more sophisticated, local CAV GPMEs and to explore more applications of such CAV prediction models, such as the developments of PGA-CAV joint probability distributions for conducting PGA-CAV joint seismic hazard assessments. • First CAV GMPE for Taiwan areas. • More than 4,000 strong motion records used. • CAV-based seismic hazard analysis for Taipei. [ABSTRACT FROM AUTHOR]

Seismic risk assessment of lifeline networks or building portfolios requires the quantification of spatial correlation of ground motion intensity over a region during an earthquake event. In this paper, the spatial correlation of vertical spectral accelerations (SAs) at single and multiple periods is studied. In the first part, the spatial correlations of vertical SAs at eight periods in the range of 0.0–3.0 s are investigated. The geostatistical analysis is performed to compute the spatial correlations of SAs using records compiled from ten earthquake events occurred in California, Japan, Taiwan, and Mexico. The results show that the spatial correlations of the vertical SAs at short periods are dependent on the regional site conditions indicated with the spatial correlation of shear wave velocity in the top of 30 m (Vs30). However, the effect of the correlation of Vs30 on the correlation of the vertical SAs decreases as the spectral period increases. A simple predictive model is proposed to quantify the correlation ranges of the vertical SAs considering regional site conditions. The proposed model is compared with the models presented for horizontal SAs. The comparison shows that the correlation ranges of horizontal SAs are generally larger than those of the vertical ones. As an illustrative example, seismic performance of a hypothetical bridge network is studied with different ranges of spatial correlations. The results indicate that ignoring spatial correlation may significantly affect the exceedance probability for spatially distributed engineering demand parameters of bridges in the network. In the second part, the multivariate spatial correlation is investigated using linear model of coregionalization (LMC) approach. Based on the correlation estimates obtained from geostatistical analysis, a predictive model is proposed to simulate vertical SAs at multiple periods and different sites. [ABSTRACT FROM AUTHOR]

The real-time Probabilistic Seismic Hazard Assessment (PSHA) is developed for considering the practicability for daily life and the rate of seismic activity with time. The real-time PSHA follows the traditional PSHA framework, but the statistic occurrence rate is substituted by time-dependent seismic source probability. Pattern Informatics method (PI) is a proper time-dependent probability model of seismic source, which have been developed over a decade. Therefore, in this research, we chose the PI method as the function of time-dependent seismic source probability and selected two big earthquakes in Taiwan, the 2016/02/05, Meinong earthquake (ML 6.6) and the 2018/02/06, Hualien earthquake (ML 6.2), as examples for the real-time PSHA. The forecasting seismic intensity maps produced by the real-time PSHA present the maximum seismic intensity for the next 90 days. Compared to real ground motion data from the P-alert network, these forecasting seismic intensity maps have considerable effectiveness in forecasting. It indicates that the real-time PSHA is practicable and can provide a useful information for the prevention of earthquake disasters. [ABSTRACT FROM AUTHOR]

Cities in seismic regions often have unknown numbers of older buildings vulnerable to strong earthquake ground motion. Simple methods are needed with urgency to screen these buildings. The problem is of immense proportions as it affects some of the largest cities in the world. Seismic vulnerability indices proposed by Hassan and Sozen (ACI Struct J 94(1):31-39, 1997), Islam et al. (Architectural Institute of Japan-Academic Lecture Collection Summary, 2017), NCREE (Chiou et al. in 16th World Conference on Earthquake Engineering, 16WCEE 2017, Santiago, 2017), and Shiga et al. (Proceedings, Tohuku District symposium, Architectural Institute of Japan, 1968) possess the required simplicity. The indices have different forms and have been calibrated through independent activities, but all imply that the key to building survival is in the relative sizes of elements resisting lateral inertial forces. Data collected after the 2016 Meinong, Taiwan, Earthquake were used to evaluate these indices. The evaluation showed that differences among indices did not lead to wide differences in the cost associated with a given benefit especially if they are used to include the effects of all lateral-load resisting elements including masonry infill. [ABSTRACT FROM AUTHOR]

This study analyzed site effects including PGA and empirical transfer functions at 15 selected surface–downhole stations by using ground motion recordings of earthquakes with M L > 4 during 2012 and 2013 in Taiwan. In addition, we used all strong motion recordings of four large earthquakes (M L > 6) to generate intensity distribution maps and assess the differences in magnitude at the surface and downhole. The site amplification factors of the PGA were calculated using the ratio between the surface and downhole recordings. The mean PGA amplification factors ranged from 2 to an exaggerated value of 20 at different stations. In addition, the power law relationships between the PGAs at the surface and downhole were evaluated to understand how amplification varies as PGA increases. Strong ground motions with and without site effects throughout Taiwan could be observed by comparing intensity distribution maps generated using the surface and downhole accelerations from four large earthquakes with magnitudes > 6. Empirical transfer functions derived using the single-station and two-station methods at the same stations showed comparable dominant frequencies and amplification factors; however, the empirical transfer function derived using the two-station method showed clearer resonance peaks, not only at fundamental frequencies but also at higher mode resonance frequencies. The HHSR and the HVSR were highly similar, particularly at medium frequencies. This finding indicates that the HVSR can be used instead of the HHSR when only the surface recording is available. Moreover, the local magnitudes calculated using surface recordings were higher than those calculated using downhole recordings. The differences are attributed to the amplification caused by the sedimentary layers and resultant in 0.36, 0.46 and 0.49 on average for events with M L of > 6, 5–6, and 4–5. Furthermore, HHSRs at 5–10 Hz and 1.1–1.7 Hz were strongly correlated with PGA amplifications and M L differences, respectively. [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]

We systematically investigated precursory seismic patterns using the pattern informatics (PI) method and suggest an operable procedure for making PI maps for all seasons, in the context of earthquake forecasting. We examined the PI patterns before several inland earthquakes with magnitudes larger than 6, which occurred between 2001 and 2010 in Taiwan. We fixed a cutoff magnitude and a change interval, which is the time span used to calculate the seismicity change. Our results show that locations with high PI anomalies are typically associated with large earthquakes when the cutoff magnitude is 3.2 and the change interval is 4 years. Therefore, the PI method can be utilized as a routine forecasting tool with regular updates, such performing the PI calculation every season. We also conducted random tests, the results of which indicate a significant difference between large events and random, hypothetical events. [ABSTRACT FROM AUTHOR]

We examined forecasting quiescence and activation models to obtain the conditional probability that a large earthquake will occur in a specific time period on different scales in Taiwan. The basic idea of the quiescence and activation models is to use earthquakes that have magnitudes larger than the completeness magnitude to compute the expected properties of large earthquakes. We calculated the probability time series for the whole Taiwan region and for three subareas of Taiwan-the western, eastern, and northeastern Taiwan regions-using 40 years of data from the Central Weather Bureau catalog. In the probability time series for the eastern and northeastern Taiwan regions, a high probability value is usually yielded in cluster events such as events with foreshocks and events that all occur in a short time period. In addition to the time series, we produced probability maps by calculating the conditional probability for every grid point at the time just before a large earthquake. The probability maps show that high probability values are yielded around the epicenter before a large earthquake. The receiver operating characteristic (ROC) curves of the probability maps demonstrate that the probability maps are not random forecasts, but also suggest that lowering the magnitude of a forecasted large earthquake may not improve the forecast method itself. From both the probability time series and probability maps, it can be observed that the probability obtained from the quiescence model increases before a large earthquake and the probability obtained from the activation model increases as the large earthquakes occur. The results lead us to conclude that the quiescence model has better forecast potential than the activation model. [ABSTRACT FROM AUTHOR]

One decade after the 1999 Chi-Chi earthquake, central Taiwan experienced more strong ground shaking [Central Weather Bureau (CWB), intensity VII] induced by a ML 6.2 earthquake on 5th November 2009. This earthquake occurred in the Mingjian Township of Nantou County, only 12 km southwest of the Chi-Chi earthquake epicenter. The broadband micro-earthquake monitoring network operated by the National Center for Research on Earthquake Engineering (NCREE) observed numerous aftershocks in the five days following the mainshock. The relocated aftershocks and the mainshock focal mechanism indicated a NE-SW striking fault dipping 60° toward the northwest. This fault plane is inside the pre-Miocene basement and the rupture extends from the lower crust to 10 km depth just beneath the basal décollement of the thin-skinned model that is generally used to explain the regional tectonics in Taiwan. The fault plane is vertically symmetrical with the Chelungpu fault by the basal décollement. The NW-SE compressive stress of plate collision in Taiwan, as well as the deep tectonic background, resulted in the seismogenic structure of the Mingjian earthquake at this location. [ABSTRACT FROM AUTHOR]

Abstract: The recent discovery of triggered tremors (TTs) and low-frequency earthquakes (LFEs) in various tectonic environments provides an opportunity for studying the fundamental properties and physical mechanisms of deep tectonic tremor. Here, we quantify the relationship between TTs and LFEs beneath the Central Range in southern Taiwan and their statistical properties during the teleseismic waves of six large distant earthquakes. Using waveforms of 11 LFEs triggered by the 2005 M w 8.6 Nias earthquake as templates, we scan through 12hours of waveform data around six mainshocks and identify a total of 783 LFEs. The LFEs were mainly located in a compact region between 12 and 36km in depth near the Chaochou–Lishan Fault. Most of LFEs occurred within TT during the passage of large-amplitude surface waves, and the increase of the LFE rate during the surface waves is statistically significant. The LFE rates do not follow an Omori's type decay, but rather abruptly return to the background rate immediately after the surface-wave passage. These findings suggest that LFEs do not trigger any additional LFEs at later times and are primarily driven by an external forcing. Our observations are consistent with the inference that TTs consist of many reoccurring LFEs. [Copyright &y& Elsevier]

Abstract: Three-dimensional (3-D) attenuation structures were determined for Taiwan region by inversion of earthquake intensity data set. The seismic intensity which is assumed to be a measure of the maximum acceleration of the S-wave at the seismic station is used to estimate the attenuation structure. The intensity data set consists of about 5500 intensity readings for 1410 earthquakes reported by the Central Weather Bureau of Taiwan from 1987 to 2010. The 3-D attenuation maps consisting of five layers were constructed to a depth of 74km. The obtained model reveals the following features: first, a high absorption zone exists in the westernmost Okinawa trough. These high-attenuation anomalies seem to extend from upper crust to mantle beneath the Yilan Plain and Kueishantao Island. We interpret the high absorption zone as the presence of the relatively hot lower crust and uppermost mantle in response to the local opening of the Okinawa trough. Second, strong lateral variation of seismic attenuation is observed from the source region of the Chi–Chi earthquake in the central Taiwan. Most aftershocks were occurred beneath the Western Foothills which is characterized by a transition from high attenuation to low attenuation between the Chelungpu fault and Chuchih fault. However, the region east to the Chuchih fault is relatively quiescent. This study suggests that the high Vp/Vs and lateral variation of attenuation features existing beneath the Western Foothills could be associated with porous materials containing fluid which might affect the generation of the Chi–Chi earthquake. [Copyright &y& Elsevier]

Spatially correlated strong ground motions can cause severe seismic damage to spatially-distributed buildings and infrastructure. Empirical spatial correlation models for ground-motion measures such as peak ground acceleration and spectral acceleration have been developed using strong ground-motion records from California, Taiwan, and Japan. In this paper, we compare an empirical spatial correlation model for the 1999 Chi-Chi, Taiwan, earthquake with that obtained from stochastic finite-fault simulations; the stochastic finite-fault method is a widely used technique to generate synthetic ground-motion records for engineering applications and hazard assessment. We show that the stochastic records do not reproduce the observed intraevent spatial correlation characteristics and comment on what would be required to make them do so. [ABSTRACT FROM AUTHOR]

About half of the 8 cm/yr of oblique convergence across the active convergent plate boundaries of Taiwan occurs in eastern Taiwan, across the Longitudinal Valley. Significant shortening and left-lateral slip occurs across the Longitudinal Valley fault there, both as shallow fault creep and as seismogenic fault slip. The southernmost Longitudinal Valley fault comprises an eastern Peinan strand and a western Luyeh strand. We derive an interseismic block model for these two strands using data from a small-aperture Global Positioning System (GPS) campaign and leveling. The model provides estimates of fault slip rates and quantifies slip partitioning between the two strands. A 45 mm/yr dip-slip rate on the northern Peinan strand diminishes southward, whereas the left-lateral component increases. In contrast, nearly pure dip-slip motion of about 20 mm/yr on the southern Luyeh strand diminishes northward to about 8 mm/yr and picks up a component of left-lateral motion of about 15 mm/yr before it dies out altogether at its northern terminus. The Luyeh and the northern Peinan strands record near-surface creep, but the southern Peinan strand appears locked. The potential earthquake magnitude for the two strands may be as high as Mw 6.5. We anticipate seismic rupture mainly on the locked portion of the Peinan strand. [ABSTRACT FROM AUTHOR]

The Arias intensity is a measure of earthquake intensity arrived at through the integration of a square of the acceleration time history. It has been demonstrated to be an effective predictor of earthquake damage potential in relation to short-period structures, liquefaction, and seismic slope stability, and has begun to be considered as a ground-motion measure suitable for use in probabilistic seismic hazard analysis (PSHA), as well as earthquake loss estimation. A new empirical Arias intensity attenuation relationship for shallow crustal earthquakes is developed where both fault type and a continuous site variable V~30 are considered. The relationship is based on a large number of strong-motion records (6570) from a wide range of earthquake magnitudes (3.9-7.6) from the Taiwan Strong Motion Instrument Program (TSMIP) network. Its functional form is modified from that of Travasarou et at. (2003), which is derived from a point-source model, and the coefficients are determined through nonlinear regression analyses using a mixed-effects model. The results show that the incorporation of V~30 can significantly reduce regression error. The Arias intensity value predicted in the present study is generally similar to that obtained by Travasarou et at. (2003), but is different in detail, being more suitable for usage in PSHA for a tectonically young orogenic belt like that in Taiwan or New Zealand. [ABSTRACT FROM AUTHOR]

Relationships between collapse ratios (CRs) of buildings and characteristics of strong ground motions during the 2008 Wenchuan earthquake was founded. Vulnerability functions of buildings were established in relation to PGA, PGV, PSA, and PPSv. Damage criteria for CR<10% corresponding to 'minor and moderate damage' were PGA<250 gal, PGV<25 cm/s, PSA<900 gal, and PPSv<50 cm/s. For CR>50%, corresponding to the 'extremely serious damage' were PGA>600 gal, PGV>55 cm/s, PSA>2200 gal, and PPSv>120 cm/s. Seismic damage during the Wenchuan earthquake was heavier than that of the 1995 Kobe and 1999 Chi-Chi earthquakes for the same levels of ground motion. [ABSTRACT FROM AUTHOR]

Abstract: The March 04, 2010, Jiashian, Taiwan earthquake (Mw 6.4) ruptured an unknown fault at depth in southwestern Taiwan. The main shock initiated near the town of Liuquei at 23km depth and the rupture propagated westward. Measurements of coseismic displacements from Taiwan Continuous GPS Array indicate horizontal displacements of 5–27mm in the NW–SW directions to the west of the epicenter; while horizontal movements to the east of the epicenter are absent. The GPS vertical displacements show an uplift motion of about 5–25mm near the epicenter, in contrast to a small movement of about 5–10mm observed in the far-field GPS sites. We use coseismic GPS displacements and an elastic half-space dislocation model to invert for fault geometries and coseismic slip distribution associated with the Jiashian earthquake. Our preferred model exhibits 0.05–0.1m of reverse slip and ~0.04m of left-lateral slip on a N324°-trending fault with dip of 40° to NE, consistent with the earthquake focal mechanisms from BATS, USGS/NEIC, and Global CMT. The highest slip of 0.12m mainly occurs to the west of the epicenter at a depth range of 15–20km. Given the rigidity modulus of 60GPa, the geodetic moment is 4.95×1018 N-m, equivalent to a Mw 6.4 earthquake and consistent with the seismic moment estimated from seismic waveform inversion. Additionally, we notice that the mainshock rupture area is surrounded by high seismicity between 1991 and 2007, suggesting that the Jiashian earthquake may be triggered by the high stress concentration in the vicinity. The calculated Coulomb stress changes on nearby fault systems imparted by the coseismic slip suggest that the Jiashian earthquake may encourage failures on the Chukou fault and inhibit ruptures on the Hsinhua fault. However, the Coulomb stress changes are more complicated on the Chaochou fault and Chishan fault with both positive and negative stress changes. [Copyright &y& Elsevier]

Abstract: The rupture process of the disastrous Sumatra–Andaman earthquake of 26 December 2004 was analyzed by array processes for teleseismic P-waves recorded by a dense broadband seismic array in Taiwan with epicentral distances of close to 31°. The azimuthal variation from the BATS array center to both ends of the rupture fault is approximately 21°, which is larger than that reported previously for seismic arrays used to image the rupture process of this earthquake, thereby providing a high spatial resolution in studying the source rupture behavior. Two array-processing methods were used to analyze teleseismic P-wave trains. Both analyses were based on data recorded by a broadband network, covering a region of 200×400km, with the aim of evaluating the rupture behavior of the earthquake. Consistent results from both analyses indicate that the earthquake had a rupture duration exceeding 500s, with major asperities encountered at 80, 260, and 330s after the initiation of rupturing. We traced the ruptured fault for more than 1200km from the point of initial rupture. The average rupture velocity was approximately 3.0km/s and the major northward rupture propagation began at 80s after the initiation of rupturing. [ABSTRACT FROM AUTHOR]

Abstract: Probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central Taiwan is critical to understanding the local tectonics and orogeny. A linear broadband array that transects southern Taiwan, together with carefully selected teleseismic sources with the right azimuth provides useful constraints. They are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths. We implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data. The resulting patterns of the delayed times systematically vary as a function of the incident angle. Ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of Taiwan. Combining the ray tracing analysis and a pseudo-spectral method to solve the 2-D wave propagations, we determine the extent of the anomaly that best fits the observations via the forward grid search. The east-dipping fast anomaly in the upper mantle beneath the southeast of Taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc–continent collision is likely characterized by the thin-skinned style. [ABSTRACT FROM AUTHOR]

The Taipei basin, historically low in seismicity, is located in northern Taiwan. A dense broadband seismic array was deployed in the basin in June 2004 to monitor seismic activity. During the period of operation, three felt earthquakes occurred near the eastern part of the Taipei basin, about 3 km to the south of Taipei 101 then the tallest building in the world. Relocated earthquakes show a southeast-dipping distribution of hypocenters beneath the Taipei basin. The seismicity pattern and focal mechanisms of the three felt events suggest the existence of a blind normal fault whose surface projection is along the river channel in the middle of the basin. [ABSTRACT FROM AUTHOR]

We attempt at providing new insights about the earthquake behaviour in western Taiwan, based on a comparison between historical information and present-day instrumental records. We provide a consistent picture of the earthquake history during the last four centuries and draw some inferences in terms of seismic cycle. Before instrumental seismic observation in Taiwan started at the end of the 19th century, ancient written earthquake records are available from the ancient Chinese governments and the public concerning the 17th, 18th and 19th centuries. Distribution of casualties and property damage, indicating seismic intensity, can be estimated from archives. Using the Central Weather Bureau (CWB) intensity scale we calibrate the intensity–magnitude relationships from the instrumental seismicity recorded from 1995 to 2005, showing that within the range of historical uncertainties and earthquake depths in western Taiwan, 0–40 km, the depth is not critical in these relationships. With estimated intensities, the magnitudes of historical earthquakes can be evaluated based on a single average empirical relationship between ML, the local magnitude, and I0, the epicentral intensity: ML= 0.08 I02– 0.04 I0+ 3.41. Three types of diagrams are then proposed to describe the historical seismicity. The first type involves simple representation of earthquake events according to time and magnitude. The second type involves cumulative plot of the released elastic energy with time, as calculated from reconstructed magnitudes. The third type of diagram shows the evolution of cumulative seismic strain release with time, based on a Benioff's law indicating that the release of elastic strain related to an earthquake is proportional to the square root of the dissipated energy. These curves highlight inferences of historical seismicity analysis in terms of earthquake frequency and seismic cycle duration in the different segments of the front belt and foreland zones of western Taiwan, with large contrasts suggesting different levels in earthquake hazard. [ABSTRACT FROM AUTHOR]

The ELF observation at Moshiri (geographic coordinates: 44.29° N, 142.21° E) in Hokkaido, Japan, was used to find anomalous phenomena in the Schumann resonance band, possibly associated with a large earthquake (magnitude of 7.8) in Taiwan on 26 December 2006. The Schumann resonance signal (fundamental (n=1), 8 Hz; 2nd harmonic, 14 Hz, 3rd harmonic, 20 Hz, 4th, 26 Hz etc.) is known to be supported by electromagnetic radiation from the global thunderstorms, and the anomaly in this paper is characterized by an increase in intensity at frequencies from the third to fourth Schumann resonance modes mainly in the BEW component with a minor corresponding increase in the BNS component also. Spectral modification takes place only in the interval of 21:00 UT±1 h, which corresponds to the global lightning activity concentrated in America. While distortions were absent in other lightning-active UT intervals, in particular, around 08:00UT±1 h (Asian thunderstorms) and around 15±1 h (African lightning activity). The anomaly occurred on 23 December three days prior to the main shock. The results observed were explained in terms of ELF radio wave perturbation caused by the lower ionospheric depression around the earthquake epicenter. The difference in the path lengths between the direct radio wave from an active global thunderstorm center and the wave scattered from the non-uniformity above Taiwan causes interference at higher resonance modes, which is successful in explaining the observational data. [ABSTRACT FROM AUTHOR]

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Abstract: The Kaoping submarine canyon developed on the frontal orogenic wedge off SW Taiwan and is the largest one among others. The canyon begins at the mouth of the Kaoping River, crosses the narrow shelf and broad slope region, and finally merges into the northern Manila Trench for a distance of about 260km. Using reflection seismic sections and bathymetric mapping this paper reveals the geomorphic characteristics of the Kaoping Canyon strongly related to structural and sedimentary processes. The combined morphometry statistics analysis, seismic interpretations of structures and examinations of detailed bathymetric charts indicate that regional canyon morphology is strongly linked to intrusions of mud diapirs in the upper reach of the canyon and thrust faulting in the middle and lower reaches which produce two prominent morphological breaks of the course of the Kaoping Canyon with two sharp bends. Although excavation of floor and enlargement of the Kaoping Canyon are mainly attributed to downslope erosion of seabed, incision of this canyon is also strongly complicated by mud diapiric intrusions (upper reach), westward thrust faults (middle reach), and regional base level tilting (lower reach). The resultant cross-sectional morphology along the Kaoping Canyon changes considerably, ranging from U-shaped, broad V-shaped, to irregular troughs. The Kaoping Canyon may be served as a variant of canyon model of active margins with a distinct morphology of two sharp bends along the canyon course associated with structure deformation. [Copyright &y& Elsevier]

The shear wave velocity profile and dynamic soil properties are known to be affected by aleatory uncertainty. This paper aims to investigate the effect of a statistical variation in the initial stiffness profile, stiffness degradation and damping curves on ground response predictions by conducting stochastic analysis. The Large Scale Seismic Test site in Lotung, Taiwan, is back-analysed with a fully-coupled finite element procedure using an advanced kinematic hardening soil model. Two ground motions recorded at the site, one strong and one weak, are applied at bedrock level. The results reveal that the site response prediction is sensitive to the seismic intensity of the input motion. When the level of induced shear strain is higher, i.e. in the case of the stronger motion, the spatial variability of the stiffness degradation and damping curves has a pronounced effect on the predicted site response. In contrast, when the weaker motion is considered the prediction is particularly sensitive to the statistical variation in the initial stiffness profile. This is mainly due to the stiffness degradation at very small strains shown by the laboratory data on LSST soils, which is captured in the paper by assuming an appropriate elastic domain in the constitutive model calibration. [ABSTRACT FROM AUTHOR]

On February 6, 2018, a Mw 6.4 earthquake struck near Hualien city, in eastern Taiwan with a focal depth of 10.4 km. The earthquake caused strong shaking and severe damage to many buildings in Hualien. The maximum intensity during this earthquake reached VII (> 0.4 g) in the epicentral region, which is extreme in Taiwan, and capable of causing damage in built structures. Seventeen people died and approximately 285 were injured. Taiwan was one of the first countries to implement an earthquake early warning (EEW) system that is capable of issuing a warning prior to strong shaking. In addition to the official EEW run by the Central Weather Bureau (CWB), a low-cost EEW system (P-Alert) has been deployed by National Taiwan University (NTU). The P-Alert network is currently operational and is capable of providing on-site EEW as well as a map of expected ground shaking. In present work, we demonstrate the performance of the P-Alert network during the 2018 Hualien earthquake. The shake maps generated by the P-Alert network were available within 2 minutes and are in good agreement with the patterns of observed damage in the area. These shake maps provide insights into rupture directivity which are crucial for earthquake engineering. During this earthquake individual P-Alert stations acted as onsite EEW systems and provided 2-8 s lead-time in the blind zone around the epicenter. The co-seismic deformation (Cd) is estimated using the records of P-Alert stations. The higher Cd values (Cd > 2) in epicentral region are very helpful for authorities to respond for the purpose of damage mitigation. [ABSTRACT FROM AUTHOR]