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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. 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

On 18 September 2022, the MW6.9 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 MW6.5 Guanshan foreshock, the MW6.9 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.

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 Pwave 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. The southwest Taiwan fold‐and‐thrust belt comprises a roughly N‐S striking, west verging imbricate thrust system that has been developing since the Late Miocene. We present the results of new surface geological mapping from which we construct balanced and restored cross sections and along‐strike sections. We compile maps of the basal thrust, thrust branch lines, and stratigraphic cutoffs. 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 inherited from the continental margin. Structure of the fold‐and‐trust belt in southwest TaiwanDevelopment of a fold‐and‐thrust belt on the outer continental margin and slopeAlong‐strike changes in structure that have a causal relationship with variations in the basal thrust that, in turn, is related to basement

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, Pwave 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. We present newly mapped surface geology, which is integrated with Pwave velocity maps and sections, with an accurately relocated seismicity data set, and with high‐resolution topography to test the hypothesis of whether or not the regional‐scale features of the margin are contributing to along‐strike changes in structural style, seismicity, and topography of the south central Taiwan fold‐and‐thrust belt. As a corollary to this hypothesis, we also investigate whether or not there are differences in structural architecture, seismicity, and topography between the margin shelf and its necking zone. Taiwan provides insight into how a margin structure contributes to along‐strike changes in a fold‐and‐thrust beltStructural inheritance of basement faults is a key component in producing along‐strike changes in structure, seismicity, and topographyThese along‐strike changes vary depending on which morphological part of the margin is involved in the deformation

The Taiwan Integrated Geodynamic Research program (TAIGER) collected two wide‐angle and reflection seismic transects across the northern Manila subduction zone that provide constraints on the seismic velocity structure of the crust. Two‐dimensional gravity modeling along these two transects shows a significant, relatively high density (3.12 and 3.02 g/cm3) in the fore‐arc region, at the interface between the subducting Eurasian Plate and the accretionary prism in front of the Luzon arc on the overriding Philippine Sea Plate. The anomalous density in this zone is higher than that in the fore‐arc crust and the accretionary prism but lower than that in mantle. Numerous geophysical and geological data, together with numerical models, have indicated that serpentinization of the fore‐arc mantle is both expected and observed. Serpentinization of mantle rocks can dramatically reduce their seismic velocity and therefore their seismic velocity in a density to velocity conversion. Therefore, the source of the high‐density material could be serpentinized fore‐arc mantle, with serpentinization caused by the dehydration of the subducting Eurasian Plate. We interpret that positive buoyancy combined with weak plate coupling forces in the northern Manila subduction zone is resulting in this serpentinized fore‐arc mantle peridotite being exhumed. Two‐dimensional gravity modeling shows a significant high‐density structure in the fore‐arc regionPositive buoyancy and weak plate coupling result in serpentinized peridotite exhumedExhumed serpentinized materials in the northern Manila subduction zone are found

The interaction between two flipping subduction systems shapes the complicated lithospheric structures and dynamics around the Taiwan region. Whether and in what form the Eurasian Plate subducts/deforms under Taiwan Island is critical to the debate of tectonic models. Although an east dipping high‐velocity anomaly down to a depth below 200 km has been reported previously, its detailed morphology remains uncertain and leads to different interpretations. With a two‐step strategy of nonlinear joint inversion, the slab images of the Eurasian Plate were retrieved in a geometry that is hyperthin in the south, becoming massive and steeper in the central, and severely deformed in the north. The possible depth and dimension of a slab break were also investigated through synthetic tests of whether the slab had torn. Moreover, the slab deflection found at ~23.2°N latitude seems to correspond to where the nonvolcanic tremors and recent NW‐SE striking structures have occurred in southern Taiwan. High‐resolution lithospheric images are retrieved by a two‐step joint inversionThree‐dimensional geometry of the east subducting slab under Taiwan is establishedA possible slab deflection is observed at around latitude 23.2°N