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The Taiwan–Ryukyu arc–trench junction area is a seismic active region and has high potential to generate large earthquakes. However, the detailed deep structures are not fully revealed because of data resolution problems. The Taiwan Integrated Geodynamic Research (TAIGER) project collected two wide‐angle and multichannel seismic profiles across the Taiwan mountain belt (T5) and the western end of the Ryukyu arc–trench system (T6). In this study, we perform 2‐D gravity modelling for T5 and T6 by taking advantage of well‐constrained P‐wave velocity models, which helps to reduce the nonunique problem. To better fit the observed gravity anomaly, a block with relatively high‐density must exist beneath eastern Taiwan. This high‐density material could be serpentinised mantle, which may be resulted from the dehydration of the subducting Eurasian plate. Also, our result indicates that the subducting Gagua Ridge has a deep crustal root and extends northward to the Ryukyu forearc area. [ABSTRACT FROM AUTHOR]

Zofenopril as an ACE inhibitor expired recently was found to have a favourable safety profile in comparison with other ACE inhibitors in treating high blood pressure, congestive heart failure, and acute myocardial infarction. It can be synthesised from the key building blocks of (S)-3-benzoylthio-2-methylpropanoic acid and (4S)-phenylthio-L-proline. In this report, an efficient hydrolytic resolution via Candida antarctic lipase B (CALB) for preparing the former block in isopropyl ether (IPE) containing (RS)-3-benzoylthio-2-methylpropyl pyrazolide (1) and water was developed. Quantitative improvements of the enzyme activity and enantioselectivity in terms of k2SKmS−1 = 5.726 L h−1 g−1 and E = 217 at 45 °C were found from the kinetic analysis. Insights into the CALB performance via thermodynamic analysis were then addressed and compared with those by using (RS)-3-benzoylthio-2-methylpropyl 1,2,4-triazolide (2) as the substrate. A putative thermodynamic model was moreover hypothesised for elucidating the more enthalpy reduction of 68.92-70.86 kJ mol−1 from the acyl part of (S)-1 and (S)-2 as well as that of 23.69-25.63 kJ mol−1 from the triad imidazolium to Ser105 and leaving 1,2,4-triazole moiety of (R)-2 and (S)-2 on stabilising the corresponding transition states. [ABSTRACT FROM AUTHOR]

The Tatun Volcanic Group (TVG) in northern Taiwan is the sole volcanic region on the island, with its last eruptive episode around 5,500 years ago. It has been suggested that the TVG retains the capacity for volcanic explosivity which has the potential to devastate the nearby Taipei metropolitan area of 7 million inhabitants. Though the probability of future eruption is low by probabilistic estimation, the vulnerability to volcanic hazards is high for Taipei given that it is the centre of population, industry, and government for the island. An assessment of any activity precursors is thus vital but also particularly challenging. Here, we perform an eruption-potential assessment based on the analysis of a sixteen-year Land Surface Temperature (LST) time series of data derived from satellite-retrieved thermal imagery. A Hilbert-Huang Transform (HHT) is applied to decompose oscillatory components of various timescales within the LST time series. The annual-period components are compared with those from two active volcanoes in the Philippines to assess the potential of eruption cycles in the TVG. Results from the Philippine volcanoes show that annual-period components of LST tend to lose their regularity following an eruption. By contrast, the regular annual period component of LST of the TVG Taiwan suggests a quiet and resting status with no sign of an imminent eruption. [ABSTRACT FROM AUTHOR]

The distribution of historic earthquakes in the Sumatra subduction zone reveals, in the forearc region, the intense seismic activity and frequent occurrences of M w > 8 earthquakes throughout the whole area. In contrast, the neighbouring region has less dense seismicity and no large earthquake greater than M w8 has been observed in the Java subduction zone. Such different seismic behaviours may be due to distinct degrees of the stress accumulation and release. In this study, the strength of plate coupling inferred from mantle lithosphere buoyancy (H m) estimation is used to explain the seismogenic behaviour in the Sunda–Andaman subduction zone. Strong and weak plate coupling status are obtained in the Sumatra and Java subduction zones, respectively. These results can explain the significant differences in seismogenic behaviours in the Sunda–Andaman subduction zone. In assessing the global implications of this finding, we observe that uplifted serpentinized forearc mantle peridotite is the critical phenomenon in weak plate coupling cases and leads to a limit on the width of the coupling zone. Strong plate coupling can cause a relatively low gravity anomaly as well as a negative trench-parallel gravity anomaly (TPGA) in the forearc regions and correlates well with the occurrence of large earthquakes, whereas weak plate coupling can cause a positive TPGA and constrain the potential occurrence of large earthquakes. [ABSTRACT FROM AUTHOR]

In this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (σ1, σ2 and σ3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (S H) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of S H from north to south across the study area, with the direction of S H remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The direction of the horizontal maximum compression strain rate (εH) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. We interpret the southward change in the S H, εH and the dextral maximum shear plane directions, together with that of the horizontal displacement field to be related to the reactivation of east–northeast striking faults inherited from the rifted Eurasian margin and to the shelf/slope break. Inherited faults in the basement are typically reactivated as strike-slip faults, whereas newly formed faults in the fold-and-thrust belt are commonly thrusts or oblique thrusts. Eastwards, the stress inversions and strain data show that the western flank of the Central Range is undergoing extension in the upper crust. S H in the Central Range is roughly parallel to the relative plate convergence vector, but in southwestern Taiwan it undergoes a marked counter-clockwise rotation westwards across the Chaochou fault. Farther north, however, there is no significant change across the Lishan fault. This north to south difference is likely due to different margin structures, although local topographic effects may also play a role. [ABSTRACT FROM AUTHOR]

The Taiwan Strait, along with the southeastern continental margin of the Eurasian plate, Fujian in SE China, is not far from the convergent boundary between the Eurasian plate and the Philippine Sea plate. Although this region is considered tectonically relatively inactive, many small earthquakes still occur, and normal faults are well developed in the strait. To better understand the geological processes in this region, we use 2 years of ambient noise data from more than 100 stations in Fujian and Taiwan to obtain a 3‐D crustal shear‐wave velocity model using a direct surface‐wave inversion method. Our results show that the low‐velocity zone beneath the Zhenghe‐Dapu suture zone plays an important role in the tectonic evolution of the Fujian area. The relatively high velocity in the eastern part of the suture zone and low velocity in the west correspond to the Mesozoic magmatic zone and the Wuyi‐Yunkai orogenic belt in Fujian, respectively. The coastline of Fujian presents a high‐velocity anomaly in the upper crust, which is related to the Mesozoic Pingtan‐Dongshan metamorphic belt. The long strip‐like high‐velocity zone through the rift basins in the strait is interpreted as igneous rocks due to extension of the lithosphere in the Cenozoic. Two‐stage extension with different extensive centers in the strait may be the reason for the high‐ and low‐velocity anomalies in the middle to lower crust and uppermost mantle of the strait. Key Points: A 3‐D crustal shear‐wave velocity model of Taiwan Strait and Fujian, SE China, was obtained from ambient noise tomographyGeological units were influenced by older to younger tectonic events from northwest to southeast in the study regionTwo‐stage extension with different centers occurring in the early and late Cenozoic may account for the structural pattern in the strait [ABSTRACT FROM AUTHOR]

Abstract: The southwest Taiwan fold‐and‐thrust belt is forming on the outer shelf and slope of the Eurasian continental margin. It comprises a roughly N‐S striking, west verging imbricate thrust system that has been developing since the Late Miocene. Here we present the results of new surface geological mapping from which we construct balanced and restored cross sections and along‐strike sections. From these we compile maps of the basal thrust, thrust branch lines and, where possible, stratigraphic cutoffs. To interpret the structure in the subsurface and beneath the basal thrust, we use a P wave velocity of 5.2 km/s as a proxy for the top of the Mesozoic basement. We divide the southwest Taiwan fold‐and‐thrust belt into a number of thrust sheets that form the basis of our description and interpretations. From these data we interpret the 3‐D structure of the fold‐and‐thrust belt and the influence that the structure and morphology of the continental margin is having on its development. We show that there is a significant along‐strike change in the structure. This change takes place across a transverse zone that is composed of a suite of structures at the surface. We suggest that this transverse zone has a causal relationship with variations in the geometry of the basal thrust which in turn is related to (possibly fault bounded) basement highs and lows that are inherited from the continental margin. [ABSTRACT FROM AUTHOR]

Studies of mountain belts worldwide show that along-strike changes are common in their foreland fold-and-thrust belts. These are typically caused by processes related to fault reactivation and/or fault focusing along changes in sedimentary sequences. The study of active orogens, like Taiwan, can also provide insights into how these processes influence transient features such as seismicity and topography. In this paper, we trace regional-scale features from the Eurasian continental margin in the Taiwan Strait into the south central Taiwan fold-and-thrust belt. We then present newly mapped surface geology, P wave velocity maps and sections, seismicity, and topography data to test the hypothesis of whether or not these regional-scale features of the margin are contributing to along-strike changes in structural style, and the distribution of seismicity and topography in this part of the Taiwan fold-and-thrust belt. These data show that the most important along-strike change takes place at the eastward prolongation of the upper part of the margin necking zone, where there is a causal link between fault reactivation, involvement of basement in the thrusting, concentration of seismicity, and the formation of high topography. On the area correlated with the necking zone, the strike-slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones. Here basement is not involved in the thrusting; there is weak focusing of seismicity and localized development of topography. We also show that there are important differences in structure, seismicity, and topography between the margin shelf and its necking zone. [ABSTRACT FROM AUTHOR]

Serpentinized peridotite in the fore-arc has been observed in a number of subduction zones, including the northern Manila subduction zone which terminates northward in the Taiwan arc-continent collision. How this zone of serpentinization changes northward from the subduction of thinned continental lithosphere to full arc-continent collision in the Taiwan orogeny is not well known. In this paper we present 2-D gravity modeling along three P-wave (Vp) transects across the Taiwan orogeny. Two of these transects were collected with ocean-bottom seismometers. These two transects provide good constraints on the velocity structure to the west of, and on land, southern Taiwan. Conversion of Vp to density in this area allows us to model the gravity anomaly with very little misfit. Along the subduction zone, however, the velocity models are poorly constrained in the upper mantle, where an anomalous density unit has to be used in order to model the short wavelength gravity anomaly in this area. A third transect across central Taiwan that is derived from the TAIGER local tomography data, provides good control on the crust and upper mantle Vp structure that we use to place provide density constraints for modeling the gravity anomaly in this part of the collision zone. In order to model the short wavelength gravity anomaly across the Longitudinal Valley and the southern Longitudinal trough, an anomalous density block is required beneath the fore-arc region. We interpret that the source of this anomalous density material could be serpentinized fore-arc mantle, similar to what is interpreted for the northern Manila subduction zone farther south. Water released from the subduction of the extended crust of the continental margin results in the serpentinization of the fore-arc area and may be driving the uplifting of the high-pressure rocks. [ABSTRACT FROM AUTHOR]

Rifting along southeastern Eurasia in the Late Cenozoic led to the formation of a magma-poor rifted margin facing the South China Sea to the southeast and the Philippine Sea to the east. Further rifting along the outer part of the margin during the middle to late Miocene was accompanied by an extensive episode of intraplate flood volcanism that formed the Penghu Archipelago. Previous geophysical studies in the area of the strait have focused primarily on the shallow structures of the rift basins and the depth to the Moho. In this study we present the regional-scale 3-D S wave structure of the Taiwan Strait that is derived from a joint Chinese and Taiwanese 3-D ambient noise tomography study. The S wave model shows a thinning of the crust beneath the rift basins where, locally, thin high-velocity layers suggest the presence of intrusive bodies. The rift basin and the foreland basin along the west coast of Taiwan are imaged as low-velocity zones with thicknesses between 5 and 10 km and extending eastward beneath the Taiwan mountain belt. In the upper 10 km of the crust, the basaltic rocks of the Penghu Archipelago are imaged as a high-velocity zone that, with depth, becomes a relatively low-velocity zone. We interpret this low-velocity zone in the lower crust and upper mantle beneath the Penghu Archipelago to image a thermal anomaly related to the still cooling magma feeding system and the melt reservoir area that fed the flood basalts at the surface. [ABSTRACT FROM AUTHOR]

Fujian, Southeastern China, has experienced multistage tectonic activities since the Neoproterozoic Era and is currently influenced by collision between the Eurasian and Philippine Sea plates. Topography, fault zones, and patterns of seismicity are the imprints of tectonic evolution. Historically, there have been several catastrophic earthquakes in the southeastern part of Fujian. To understand the crustal structure related to the fault zones, we performed Vp, Vs, and Vp/Vs travel-time tomography using joint inversion of active and passive sources. A total of 75,827 and 31,044 arrivals of P and S waves, respectively, from 33 explosions and 2543 earthquakes are used in our study. As a result, seismicity has indicated that two NE strike seismogenic zones, the Zhenghe–Dapu and Changle–Zhaoan fault zones, are currently active. Low Vp/Vs ratios in inland Fujian imply that the crust is mainly composed of felsic rocks as part of the Eurasian continental crust, which is consistent with geological observations at the surface. Based on Vp tomography, the thickness of the crust along the coastline is shallower than that on land, which is related to higher heat flow and the Bouguer anomaly. This shallow crust phenomenon near the coastline could be related to the regional extensional stress: the remaining structure of the back-arc extension that stretched the continental crust during the Mesozoic Era or/and the Cenozoic extension due to South China sea opening in Taiwan Strait. [ABSTRACT FROM AUTHOR]

The Lishan fault has been characterized alternately as a major discontinuity in stratigraphy, structures and metamorphism, a ductile shear zone, a tectonic suture or non-existent. In addition to being a geological boundary, it also marks transitions in subsurface structures. Thus, the seismicity to the west of the fault permeates through the upper and mid-crust while beneath the Central Range it is noticeably less and largely concentrated in the upper 12 km. A prominent west-dipping conductive zone extends upward to meet the Lishan fault. Also, the eastward increase of crust thickness from ~ 30 km in the Taiwan Strait quickens under the Lishan fault to form a root of over 50 km under the Central Range. In the past, the small magnitude seismicity along the Lishan fault has been noticed but is too diffuse for definitive association with the fault. Recent processing of aftershock records of the 1999 Mw 7.6 Chi-Chi earthquake using Central Weather Bureau data and, especially, data from three post-Chi-Chi deployments of seismic stations across central Taiwan yielded hypocenters that appear to link directly to the Lishan structure. The presence of a near 4-km-long vertical seismic zone directly under the surface trace of the Lishan fault indicates that it is an active structure from the surface down to about 35 km, and the variety of focal mechanisms indicates that the fault motion can be complex and depth-dependent. [ABSTRACT FROM AUTHOR]

Time-sampling measurements are used in this paper to build time dependent LTPS TFT current model. The device model that considers bias and time dependent threshold voltage (Vth) shift and mobility degradation is implemented in Eldo through GUDM for simulating a pixel circuit as an indicator of panel performance. [ABSTRACT FROM AUTHOR]

The Alishan area of Taiwan spans the transition from the platform with full thickness of the Eurasian continental margin in the north to the thinning crust of its slope in the south. This part of the foreland thrust and fold belt includes important along-strike changes in structure, stratigraphy, and seismic velocities. In this paper we present the results of new geological mapping from which we build geological cross sections both across and along the regional structural trend. Fault contour, stratigraphic cutoff, and branch line maps provide 3-D consistency between the cross sections. Minimum shortening is estimated to be ~15 km with displacement overall to the northwest. A P wave velocity model helps constrain the structure at depth by providing insight into the possible rock units that are present there. P wave velocities of ≥ 5.2 km/s point toward the presence of basement rocks in the shallow subsurface throughout much of the southeastern part of the area, forming a basement culmination. The changes in strike of thrusts and fold axial traces, the changing elevation of thrusts and stratigraphic contacts, and the growing importance of Middle Miocene sediments that take place from north to south are interpreted to be associated with a roughly northeast striking lateral structure coincident with the northern flank of this basement culmination. These transverse structures appear to be associated with the inversion of Eocene- and Miocene-age extensional faults along what was the shelf-slope transition in the Early Oligocene, uplifting the margin sediments and their higher P wave velocity basement during Pliocene-Pleistocene thrusting. [ABSTRACT FROM AUTHOR]

We consider the problem of identifying the simulated system with the best expected performance measure when the number of alternatives is finite and small (often < 500). Recently, more research efforts in the simulation community have been directed to develop ranking and selection (R&S) procedures capable of exploiting variance reduction techniques (especially the control variates). In this article, we propose new R&S procedures that can jointly use control variates and correlation induction techniques (including antithetic variates and Latin hypercube sampling). Empirical results and a realistic illustration show that the proposed procedures outperform the conventional procedures using sample means or control variates alone. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012 [ABSTRACT FROM AUTHOR]

The 150km long Longitudinal Valley (LV) in eastern Taiwan is located at the suture zone of Eurasian and Philippine Sea Plate, connecting two subduction systems in northeastern and southern Taiwan. In this area, considerable seismicity as well as crustal deformation are accommodated by the Longitudinal Valley fault system (LVF), which is mainly composed of high angle east-dipping thrust faults. To better understand the subsurface structure and the fault geometry of the southern LV, we conducted shallow seismic reflection survey across the LVF from Donli to Luyeh in 2017. Totally, there are four 4-km-long seismic reflection profiles. We used two mini vibroseis trucks with sweeping frequencies from 35-200Hz as sources and the common-midpoint spacing is 2.5m with maximum 30 folds. A strong east-dipping reflector relative to the bedrock reflection down to 1.5km deep can be observed after noise suppression. Some low reflectivity zones in the east side of the profiles could be related to the muddy Lichi mélange. It is interesting to note that in the eastern Luyeh profile, the syncline with the east-dipping axis implies the Lichi segment of the LVF and the orientation of the tectonic deformation. As a result, the southern LV displays an asymmetric sedimentary basin pattern with a deeper bedrock to the east. [ABSTRACT FROM AUTHOR]

Picking seismic events is a time-consuming task by just relying on manpower, especially in high seismicity regions. For instance, Taiwan, on February 2018, over 4,000 aftershocks were detected within 12 days after the Hualien earthquake. Although there are lots of papers propose various deep learning models that are suitable for dealing the problem, there is still a gap between the picking routine and the AI research. Thus, we design a toolbox that can be easily integrated into the regular work flow. In this study, based on PhaseNet developed by Zhu et al. (2018), the masking arrival-time label with a Gaussian distribution is the essential part for the training methodology. In addition, we implement the neural network model UNet++, which re-designs the skip pathways for better performance comparing to the original U-Net that is used by the PhaseNet. Here, we provide an open-source framework that can be easily installed and operated. This automatic picking toolbox is built upon Obspy and Keras with Tensorflow backbone, by reading S-file catalogs from SEISAN for generating labeled datasets. Besides, a Docker image is available for fast server deployment. As a result, in our scenario, most of the temporary stations are only contained single channel and mainly focus on P arrivals. We reduce the training set from input: three-components – output: P/S/Noise categories into input: Z-component – output: P category. The testing data is successfully identified by the model trained with 90,000 traces. Moreover, minor events missed by manually picking are detected by the model. [ABSTRACT FROM AUTHOR]

Autocorrelation of the ambient noise field and the seismic wave coda theoretically provide the near zero-offset reflectivity responses of the structure beneath the recording stations. The strong reflectivity in the stacked result implies the existence of the strong impedance of the subsurface layers. In this study, we investigate the crustal reflection characteristics beneath Taiwan by autocorrelating the ambient noise data and the regional/teleseismic coda waves. The broadband data are from the permanent broadband network BATS and the temporary deployments Formosa Array which aims to provide dense spatial sampling at the northern part of Taiwan. The autocorrelations are calculated by the phase autocorrelation and the amplitude autocorrelation with an additional spectral whitening at the pre-processing stage. Then the resulting stacks are computed using the time-frequency phase weighted stacking method. Similar results at the same location but from different recording periods and instrument types indicate the consistency and robustness of the subsurface signal. For the results of permanent stations which have years of data, seasonal variations of the amplitude of the signal can be observed. The priori information from receiver functions and tomographically inferred theoretical PmP two way times can help us to identify the signal from Moho, and most of the results show good correspondence with it, although some of the stations appear no clear Moho signal that can be attributed to gradual structural transition. Besides of explaining the single station result, for the dense array dataset, we can further trace the variation of the reflectivity responses along the profile we interest, which provides more constraint for illustrating the subsurface images. [ABSTRACT FROM AUTHOR]

On 18 September 2022, the MW 6.9 Chihshang earthquake struck the south half of the Longitudinal Valley, Taiwan, and caused severe damage. A precise and rapid report for the distribution of aftershock sequence after a devastating earthquake provides key information for deciphering the seismogenic structure in the source region. The utilization of deep-learning methodologies for earthquake event detection offers a significant acceleration in data analysis. In this study, we use SeisBlue, a deep-learning platform/package, to extract the whole earthquake sequence from September to October 2022, including the MW 6.5 Guanshan foreshock, the MW 6.9 mainshock, over 14,000 aftershocks, and 866 foal mechanisms from two sets of broadband networks. After applying hypoDD for earthquakes, the distribution of aftershock sequence clearly depicts not only the Central Range Fault and the Longitudinal Valley Fault but also several local, shallow tectonic structures that have not been observed along the southern Longitudinal Valley. [ABSTRACT FROM AUTHOR]

The Manila subduction zone is located at the plate boundary where the Philippine Sea plate (PSP) moves northwestward toward the Eurasian plate (EU) with a high convergence rate. However, historically, no large earthquakes greater than Mw7 have been observed across the northern Manila subduction zone. The poorly understood plate interaction between these two plates in this region creates significant issues for evaluating the seismic hazard. Therefore, the variation of mantle lithospheric buoyancy is calculated to evaluate the plate coupling status across the northern Manila subduction zone, based on recently published forward gravity modeling constrained by the results of the P-wave seismic crustal structure of the TAIGER (Taiwan Integrated Geodynamic Research) project. The results indicate weak plate coupling between the PSP and EU, which could be related to the release of the overriding PSP from the descending EU’s dragging force, which was deduced from the higher elevation of the Luzon arc and the fore-arc basin northward toward the Taiwan orogen. Moreover, serpentinized peridotite is present above the plate boundary and is distributed more widely and thickly closer to offshore southern Taiwan orogen. We suggest that low plate coupling may facilitate the uplifting of serpentinized mantle material up to the plate boundary. [ABSTRACT FROM AUTHOR]

Knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern China and adjacent areas. In this study, we integrated the datasets from the TAIGER (TAiwan Integrated GEodynamic Research) and ATSEE (Across Taiwan Strait Explosion Experiment) projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Three seismic profiles were resolved, and the longest profile was 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. In total, data from 40 shots, 2 earthquakes, and approximately 1,950 stations were used; 15,612 arrivals were selected among three transects. Using these data, we determined the complex crustal evolution since the Paleozoic era , involving the closed Paleozoic rift basin in central Fujian, the Cenozoic extension due to the South China Sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen. The shape of the Moho, which also reflects the crustal evolution, can be summarized as follows: ~ 30 km deep to the west of Fujian, deepening toward central Fujian (~ 35 km), becoming shallower toward the Taiwan Strait (~ 28 km), deepening again toward the mountain belt of Taiwan (~ 42 km), and becoming shallower toward the Pacific Ocean (~ 10 km). [ABSTRACT FROM AUTHOR]

Abstract: Here we tackle a tectonically important question – the upper mantle velocity structure beneath central Taiwan – with seismically interesting observations – receiver-side slab waveform effects. We use teleseismic P waveforms of the NS broadband array deployed by the TAIGER project to examine patterns of variation in arrival time, pulse width, and amplitude – measuring the first two by Gaussian fitting – and contrast measurements of earthquakes to the southeast (SE earthquakes) with those of one Sumatra earthquake in order to focus on upper mantle heterogeneities. Overall variation patterns as a function of earthquake are compatible with ray-tracing predictions. Relative reduced arrival times and amplitudes at central Taiwan stations suggest the existence of a deep aseismic slab below. From simulations of 2-D wave propagation, we conclude that lateral heterogeneity of crust and uppermost mantle primarily contributes to variations in arrival time and only secondarily to variations in amplitude and pulse width. Furthermore, discrepancies between source-side and receiver-side waveform effects, where the latter are not always amplitude-reduced, are explained by constructive interference between the fast and slow phase. Thus, the use of full waveform information can provide independent constraints to complement results of previous studies. A future extension will be to incorporate S waves and apply waveform inversion to yield quantitative constraints. [Copyright &y& Elsevier]

Graphical abstract Highlights • Seismogenic characteristics near the NE rifted margin of the South China Sea are revealed. • NW-SE tensional stress controls the Taiwan collision-Manila subduction transition. • Intraslab pre-existing faults affect the seismogenic behavior of a convergent system. Abstract Based on the distribution of an earthquake swarm determined from an ocean bottom seismometer (OBS) network deployed from 20 August to 5 September 2015 in the northernmost part of the South China Sea (SCS) and data from inland seismic stations in Taiwan, we resolved a M L 4.1 earthquake occurring on 1 September 2015 as a NE-SW-trending left-lateral strike-slip event that ruptured along the pre-existing normal faults generated during the SCS opening phases. The direction of the T-axes derived from the M L 4.1 earthquake and the background seismicity off SW Taiwan present high consistency, indicating a stable dominant NW-SE tensional stress for the subducted Eurasian Plate (EUP). The distinct stress variations on the two sides of these reactivated NE-SW trending features suggest that the presence of pre-existing normal faults and other related processes may lessen the lateral resistance between the Taiwan collision and Manila subduction system, and facilitate the slab-pull process for the subducting portion, which may explain the NW-SE tensional stress environment near the transition boundary in the northernmost part of the SCS. [ABSTRACT FROM AUTHOR]

A temporary seismic network consisting of 295 land stations was deployed in 2009 in Taiwan to monitor airgun sources during an onshore-offshore experiment in Taiwan. We exploit the continuously recorded dataset to detect and map seismicity in the seismically very active Taiwan. By combining recent automatic detection and phase picking techniques, we successfully generate an initial earthquake catalog of over 8400 events. The hypoDD algorithm is used to relocate and filter these events. This network recorded smaller events than the permanent regional network because of the many stations around the high mountain ranges and the generally high station density along 6 lines. The results based on the 2009 data generally reproduce the dominant seismicity features from many years of earthquake monitoring in Taiwan. In addition, we map hitherto unknown dipping zones under the Foothills and the Central Range that may correspond to seismogenic structures. [ABSTRACT FROM AUTHOR]

Abstract: The southeastern margin of China is an ideal area to study the modern plate interactions. The previous models, however, are poorly constrained with respect to the geometry due to the sparse coverage. Here we present new observations from a temporary array with 20 stations in southeastern China. We isolated converted seismic phases in the P and S wave coda to generate receiver function from the structure of the crust and upper mantle. By using H–K stacking and common conversion point stacking, the geometry of discontinuities above was imaged along the southeastern Chinese coastline. The CCP section shows Moho dips gently northeastward with a mean depth of 30km. The 410 and 660km discontinuities are at the depth close to IASP91 model. This means that we have not seen any significant anomaly from Moho and mantle transition zone that corresponded with the geodynamics of plate subducting, instead, we found that the crust was ruptured by Min River fault to depth of the Moho. We provide a 2D map of Moho topography by combining our crustal thickness to that from permanent stations, active seismic and OBS offshore profiles. The map is consistent with previous studies and shows a crust that thins coastward and southwestward in the rate of ~1.5km per 100km. We image the lithosphere–asthenosphere boundary at a depth of 60 to 70km by using S-wave to combine with the P-wave. Our crustal structure suggests that Min River fault certainly plays an important role in adjusting regional stress field induced by plate interactions in the study area. Our lithospheric thickness is more consistent with a very strongly attenuated continental lithosphere. Given the close proximity to the coast this might suggest that the lithospheric mantle transitions to oceanic before the crust does. Alternatively, we may infer that the continental lithosphere has been thermally eroded in this region. [Copyright &y& Elsevier]