Taiwan Collision Research Articles

The erosional and weathering response to arc–continent collision in New Guinea

Arc–continent collision is a fundamental stage in the plate-tectonic cycle that allows the continental crust to grow and can influence global climate through chemical weathering. Collision between Australia and the oceanic North Coast Range–New Britain Arc began in the Middle Miocene, resulting in uplift of the modern New Guinea Highlands. The temporal evolution of this collision and its erosional and weathering impacts is reconstructed here using sedimentary archives from the Gulf of Papua. Sr and Nd isotopes show dominant erosion from igneous arc-ophiolite crust, accounting for c . 40–70% of the total flux in the Early Miocene, and rising to c . 80–90% at 8 Ma, before falling again to 72–83% by the present day. Greater erosion from Australia-derived units accelerated in the Pliocene, like the classic Taiwan collision but with greater erosion from arc rather than continental units. Chemical alteration of the sediment increased through time, especially since c . 5 Ma, consistent with increasing kaolinite indicative of more tropical weathering. Erosion was focused in the high topography where mafic arc units are preferentially exposed. Comparison of sediment with bedrock compositions implies that the source terrains have been more efficient at removing CO 2 from the atmosphere compared with Himalayan drainages. Supplementary material : Details of analytical conditions, analytical results and compositions compiled from the GEOROC database are available at https://doi.org/10.6084/m9.figshare.c.7168147

Record of short-lived “orogen” on Eurasian continental margin by South China Sea obduction preserved in Taiwan collision

The Taiwan mountain belt is the result of an arc-continent collision following the total subduction of the South China Sea and subsequent closure of the Luzon forearc, a process important in the accretionary growth of continents. Due to the oblique convergence, the southern tip of Taiwan Island is experiencing incipient collision, which is key to observing the oceanic-continental subduction transition. Within the monotonous turbidite extensively exposed on the Hengchun Peninsula as an uplifted Manila Trench accretionary wedge, the Shihmen Conglomerate, as a few intercalated lenses of coarse mafic pebbles, represents a dramatic change in sediment provenance and the causal tectonic event. New zircon U-Pb and amphibole 40Ar/39Ar ages are obtained from sediments, including sands and mafic pebbles that are either gabbro or foliated amphibolite. The 22–24 Ma zircon crystallization ages confirm the South China Sea origin of the mafic clasts, while the much younger 13 ± 2 Ma amphibole 40Ar/39Ar isochron ages from foliated amphibolites suggest a later thermal-tectonic event other than seafloor metamorphism. The amphibole 40Ar/39Ar ages overlap with the biostratigraphic age (∼11–14 Ma), indicating that the mafic source rocks were exhumed and eroded in a high-relief topography immediately after metamorphism. Detrital zircon U-Pb ages from a sandy layer within the conglomerate are also mostly identical to those from the mafic pebbles. Since the paleocurrent of the Shihmen Conglomerate was similar to that of the neighboring turbidites, which were derived from major rivers draining the southeastern Chinese continent, the provenance of the mafic pebbles and sands was best explained as an isolated subaerial mountain on the Eurasian continental margin with a very limited temporal and spatial extent, as the detrital products are poorly distributed. The most likely cause of the ephemeral mountain was the obduction of the South China Sea onto the Eurasian continental margin when the latter first impinged on the Philippine Sea Plate at the Manila Trench, where the gabbroic oceanic crust was uplifted and exhumed, followed by dynamic metamorphism along the basal thrust.

Neotectonics of the volcanic Kuei-Shan Tao island, and geodynamic implications (NE Taiwan - SW Okinawa Trough)

What are the geodynamic processes during the transition from the onshore NE Taiwan collision to the offshore southwest Okinawa back-arc basin opening associated to the Ryu-Kyu subduction? What is the local neotectonic scheme of this transition (e.g.: structural sketch map of the outcropping volcanic edifice highlighting major faults and their associated earthquakes)? These are some of the fundamental questions adressed to the Kuei-Shan Tao volcanic island (KST hereafter) which is the unique emerged volcanic outcrops situated within this geodynamic transition area.Several incompatible KST geological mappings had been published without any faults, nor dykes, nor feeders (Ichikawa, 1934; Hsu, 1963; and Chiu et al., 2010) that needed to be updated and completed on the structural point of view. In order to do so, we acquired a new high resolution UAS-drone topography (Digital Surface Model) through photogrammetric processing, with a ground resolution <10 cm. We analyse and interprete it in detail using morphostructural photo-interpretation methods. Field works on KST is restricted due to technical and administrative reasons, so we compare our morphostructural map to the shoreline outcrops observed from a boat survey. Then, we have updated the Kuei-Shan Tao geological mapping (lava flows and pyroclastic falls), and the structural scheme as well as the major erosionnal landslide processes. Taking into account the re-interpretation of surroundings offshore bathymetry, old and new seismic profiles, the different drillings done in the Kuei-Chia northern flank, previous geophysical works, the existing massive andesite datings), as well as the inferred stress regimes deduced from the earthquake's focal mechanisms, we propose a KST neotectonic map. We propose also a new scenario for the recent KST volcanic evolution. Kuei-Shan Tao geology and geodynamics may have a so great importance for the 0.5 millions citizens of the so close flat lying Ilan Plain in terms of natural hazards (eruptions, tsunamis, earthquakes…).

A new interpretation of the metamorphic core in the Taiwan orogen: A regional-scale, left-lateral shear zone that accommodated highly oblique plate convergence in the Plio-Pleistocene

In the past decades, the arc-continent collision in Taiwan was commonly interpreted as a relatively continuous process with an invariant plate convergence vector for at least the last 6–5 Ma. This steady convergence, including the rate and the obliquity, between the subducting continental margin and the plate boundary suggest a propagating collision with a space-time equivalence along the developing orogen. More recently, detailed low-temperature geochronologic and plate reconstructions suggest that the plate convergence changed from highly oblique to nearly orthogonal in the last 2 to 1 Ma. This early phase of oblique convergence, driven primarily by the northward motion of the Philippine Sea Plate wrt the Eurasian Plate, implies a significant ‘fossil’ component of left-lateral, strike-slip motion along the presumably north-trending plate boundary. A synthesis of available data compiled in this study suggests that previously uncharacterized zones of strike-slip deformation exist in the Tailuko Belt, and here we document: 1) the distribution of horizontal shear, 2) the kinematics of deformation, 3) the age of deformation, and 4) regional consistency between geologic studies and plate reconstructions. Horizontal shear may also be recorded at shallow structural levels in southern Taiwan by brittle faults and block rotations. Integration of these new data with previously published kinematic data across strike also suggests plate convergence was partitioned with strike-slip motion in the retrowedge (i.e., the Tailuko Belt) and shortening in the prowedge (i.e., the Slate Belt).

The legal complex fractured: Legal professional coalition and collision in Taiwan's judicial reform

AbstractSociolegal studies have identified a collectivity of legal actors—the legal complex—and its association with political liberalism in varying power settings. However, little attention has been paid to how such a collectivity evolves with regime change, or if and when such a collectivity might dissolve. Studying the case of Taiwan, this article demonstrates how various legal professions—lawyers, judges, and prosecutors—unite and divide during and after state transition. Democratization had an unsettling effect that brought out the internal dynamics of the legal professions, which initially aligned with one another to defend judicial autonomy from authoritarian control, but then confronted one another in judicial policy making during democratic times. Each legal profession bases its policy orientations on a normative commitment, which leads to three lines of confrontation: the ways in which the judiciary is held accountable, the extent to which the procuracy enjoys investigative power, and the institutional division between the judiciary and procuracy.

Strain Partitioning and Exhumation in Oblique Taiwan Collision: Role of Rift Architecture and Plate Kinematics

AbstractTaiwan is an archetypal example of continental accretionary wedges. Yet the generally poor knowledge of three‐dimensional strain distribution over time and role of architecture of the rifted margin shed doubt on the cylindrical two‐dimensional kinematic models of Taiwan collision. Here we provide new field‐based constraints on strain distribution, new Raman Spectroscopy on Carbonaceous Materials temperatures and apply mica‐chlorite multiequilibrium approach to determine pressure‐temperature in the Central Range of Taiwan. We identify three distinct structural domains that define zones of orthogonal shortening in the western Backbone Range and left‐lateral ductile shearing overprinted by left‐lateral transtensional brittle deformation in eastern Central Range. Field surveys show the lack of nappe stacking in the Backbone Range. Combining new temperature estimates with existing thermochronological constraints we emphasize that western Taiwan mostly inherited preorogenic thermal history. We show that metamorphic peak conditions of 5–6 kbar and 330–400 °C in the eastern Backbone Range and HP rocks of the Yuli Belt exhumed along the P‐T paths related to transcurrent deformation. We propose a three‐dimensional kinematic model of Taiwan accounting for the oblique motion of the Philippine Sea Plate relative to the plate boundary and the reactivation of a NS striking transform fault in the South China Sea rifted margin. Recent and ongoing strain partitioning in the Taiwan accretionary wedge is reflected by the coexistence of brittle left‐lateral shear, oblique extension, and contraction. Our results have impact on orogen‐based plate kinematic reconstructions that consider two‐dimensional kinematic evolution of orogens.

Seismotectonic characteristics of the Taiwan collision-Manila subduction transition: The effect of pre-existing structures

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 ML 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 ML 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.

Stratigraphic modeling of the Western Taiwan foreland basin: Sediment flux from a growing mountain range and tectonic implications

Abstract Sediment flux signals from source to sink in foreland basins preserve a record of tectonics, sea level and climate through erosion and sedimentation. However, longitudinal sediment transport often occurs in foreland basins, thus removing part of the orogenic material flux from foreland basin records. Here we use mass balance calculation and stratigraphic simulations of sediment fluxes for the Taiwan orogen to provide an order of magnitude estimate of how much orogenic material may bypass a foreland basin. Our results indicate a significant, potentially more than 50%, mismatch between sediment volume currently preserved in the basin and the amount of material presumably eroded from the orogen since the onset of collision in Taiwan. This suggests either a significant overestimation of average erosion rates over the period concerned with orogenic development of Taiwan, or it supports previous paleogeographic work suggesting that longitudinal sediment transport in the paleo-Taiwan Strait served as a major bypass conduit of importance for the establishment of a steady state orogen. We identify candidate submarine topography in the South China Sea that may preserve Taiwan's missing erosional mass.

Terrane‐controlled crustal shear wave splitting in Taiwan

AbstractTaiwan is the result of arc‐continent collision associated with the convergence of the Philippine Sea plate with the eastern Eurasian plate continental margin. The locus of deformation is found in eastern Taiwan in the form of mountain building (Central Range) with underlying thickened lithosphere. Rapid tectonic exhumation in the Central Range has uncovered low‐to‐high‐grade metamorphic rocks marked by steep cleavage. We carried out a crustal seismic anisotropy study across Taiwan, producing a database of over 27,000 local earthquake shear wave splitting measurements. Additionally, we carried out rock physics measurements of metamorphic outcrop samples to quantify shear wave rock anisotropy. We produced a map of station‐averaged splitting measurements across Taiwan. Patterns of fast shear wave directions correlate with tectonic terranes produced by plate convergence. Deformation‐related mineral‐preferred orientation in the metamorphic rocks produces a significant amount of the crustal anisotropy in the Taiwan collision zone.

Seismogenic strain across the transition from fore‐arc slivering to collision in southern Taiwan

AbstractTectonic slivers have profound implications on the mechanical behavior of fore arcs and subduction zones. Southern Taiwan is characterized by precollision fore‐arc slivering that likely exerts important controls on the evolution of collision. Inversion of focal mechanism solutions for seismogenic strain reveals spatially partitioned plate motion south of Taiwan, with dip‐slip faulting nearer the Manila trench and strike‐slip faulting nearer the Luzon arc. To the north these kinematics are less clearly segregated, and both types of faults appear to occur in the same volume of crust. Further north deformation is dominated by oblique slip on potentially reactivated steep reverse faults in the collision zone. Existing work on the active fault zones in Taiwan suggests that the subduction‐to‐collision transition is marked by a releasing step between the strike‐slip fault that bounds the fore‐arc sliver and the oblique thrusts of the collision zone. This configuration may help to explain the lack of fore‐arc basement and cover exposed in the suture zone marked by the Longitudinal Valley.

The linkage between longitudinal sediment routing systems and basin types in the northern South China Sea in perspective of source-to-sink

Using bathymetric and seismic data, this study describes the morpho-sedimentary features in Qiongdongnan basin and southwest Taiwan collision basin, northern South China Sea and reveals the linkages between sediment routing system and basin types. The modern Central Canyon in the Qiongdongnan basin is located along the rift margin, and subparallel to the shelf-break southeast of Hainan Island. The modern Central Canyon develops along the basin axis (i.e., Xisha Trough) and longitudinally transports sediments eastward which are mainly supplied by northern continental slope. The Penghu Canyon in the southwest Taiwan collision basin is located along the collision boundary parallel to the strike of the adjacent uplifted Taiwan orogen. The Penghu Canyon develops along the tilting basin axis transporting sediments longitudinally southward to the deep-sea basin and Manila Trench. The Penghu Canyon is supplied with sediments from both flank Kaoping and South China Sea slopes where tributary canyons and channels transport sediments down-slope and feed the axial canyon.The certain basin types may be occupied by particular styles of sediment routing system. By comparing the morpho-sedimentary features and basin characteristics associated with the modern Central Canyon to that of the Valencia Channel in NW Mediterranean Sea, the longitudinal sediment routing system in rift basin type can be determined. In contrast, the longitudinal sediment routing systems in collision setting can be represented by the comparable examples of Penghu Canyon in southwest Taiwan collision basin and Markham Canyon in western Solomon Sea. The rift type sediment routing system is characterized by an axial canyon with a single sediment supply from land drainage margin. In contrast, sediment routing system in collision type basins consists of an axial canyon and dual sediment supplies from flank adjacent slopes. The axial canyons in collision basins are more active than that of the rift basin due to abundant sediment supply and active tectonics. The results demonstrate the role of longitudinal sediment transport in delivering terrestrial sediments for a long distance from land drainages (source) to far-field deep-sea basin (sink). This study has implication for better understanding of the linkages between basin mechanics, sediment routing systems and sedimentary processes.

Simultaneous mountain building in the Taiwan orogenic belt

The obliquity of the arc-continent collision in Taiwan is thought to have produced a southward-propagating orogenic system starting as early as 8 Ma. We combine 62 new zircon fission-track ages with timing of rapid subsidence in the foreland basin to identify the timing of the onset of exhumation and orogenesis. The oldest completely reset zircon fission-track ages and the onset of rapid tectonic subsidence in both the northern and southern parts of the foreland basin are ca. 5–6 Ma. We propose that north-south rifting in the South China Sea created a north-trending continental margin before the collision rather than the commonly assumed northeast-trending margin. Consequently, both this north-trending continental margin and the Luzon arc of the Philippine Sea plate were subparallel, resulting in an initial collision that was simultaneous along strike.

Sedimentation in remnant ocean basin off SW Taiwan with implication for closing northeastern South China Sea

Taiwan is one of the most cited examples of modern mountain building in an oblique arc–continent collision. However, the recognition and significance of the Taiwan remnant ocean basin in the final stages of the collision of Luzon with the Chinese margin have long been ignored. This paper emphasizes the Taiwan remnant ocean basin as the main sink for sediments from the uplifted Taiwan suture zone and as a record of clues to the suturing history of the Taiwan collision zone. A part of the palaeo South China Sea has been closed by oblique collision of the Luzon Arc with the Chinese margin in the Taiwan region since about 4 Ma. As collision continued southward along the Taiwan–Luzon convergent zone the remaining South China Sea off SW Taiwan became the Taiwan remnant ocean basin. Beginning about 1.6 Ma much sediment from the longitudinal drainage of the Taiwan orogen was fed into this remaining basin and trapped in the intra-slope basins of the Kaoping slope, with some sediment bypassing via the Kaoping Canyon to the lower reach of the Penghu Canyon. This basin is characteristic of an axial canyon–deep-sea channel–oceanic trench system without significant sediment accumulation in submarine fans. Excess sediments from the Penghu Canyon mainly spill over out of the closing basin to the South China Sea and Manila Trench via the deep-sea Penghu Channel. The Taiwan–Luzon convergent zone continues along the NE South China Sea where the Taiwan remnant ocean basin exists. The implication of the convergence is that the Taiwan remnant ocean basin will keep shrinking in the next few million years southward to the northern end of the Manila Trench at around 20°N, where collision is replaced by subduction. The remnant ocean basin would be closed and deformed, and sediments would be accreted to uplifted collisional terranes north of the Manila Trench.

Crustal accretion in the Manila trench accretionary wedge at the transition from subduction to mountain-building in Taiwan

New marine seismic reflection and coincident wide-angle ocean-bottom seismometer data acquired offshore Taiwan provide high-resolution constraints on the crustal structure of an incipient mountain belt during the earliest stage of arc–continent collision. The new seismic reflection image and travel-time tomography velocity model show evidence for crust of the distal southern Chinese continental margin being subducted eastward beneath the Manila trench and underplated to the accretionary wedge before collision with the southern Chinese continental shelf. The distal margin crust consists of highly extended continental crust interspersed with volcanic bodies and a high-velocity lower crustal layer of likely magmatic intrusions. The distal margin crust is 10–14km thick outboard of the trench, but thins to 6km thick beneath the lower slope of the Manila trench accretionary wedge. Along the lower slope of the accretionary prism, we image westward-verging imbricate thrusts and folded strata up to 10km thick. A sharp decrease in bathymetry marks the transition from lower to upper slope, where we observe a fast (>6.0km/s) seismic velocity anomaly at the base of the wedge that we interpret as structurally underplated crust from the distal continental margin. Our results support a model of arc–continent collision in Taiwan where the accretionary wedge is first thickened by structural underplating of distal margin crust prior to collision with the continental shelf. The crustal rocks exposed throughout the Central Range in Taiwan may be similarly derived from subducted and structurally underplated crust from the highly extended distal continental margin.

Tectonic implications of nonparallel topographic and structural curvature in the higher elevations of an active collision zone, Taiwan

Curves in the topographic grain of active orogenic belts typically parallel faults and lithologic contacts in part because of linkages between uplift rates and the structural development of the overriding plate. However, in the Taiwan collision zone, the topographic grain trends nonparallel to mapped faults and folds in the central portion of the belt along the southwest flank of the Hsuehshan Range. Here, the northern side of the Puli topographic embayment trends ∼345°, forming a topographic break that lies at a high angle to the structural grain but is nearly parallel to an underlying continental margin fracture zone in the downgoing plate. We analyzed fault-slip and other structural data, extracted normalized steepness indices from streams within the Tachia, Peikang, and Mei River basins, and integrated the results with recently published precise leveling data in order to understand the spatial and temporal variation in uplift and the structures that accommodated that uplift. Stress inversion reveals a NW-SE–trending maximum compression direction for an early-stage fault population and an ENE-WSW–trending maximum compression direction for a late-stage fault population. River steepness indices delineate a NW-trending boundary in incision rate that coincides with an increase in rock uplift rates derived from independent geodetic measurements. This NW-trending boundary is consistent with the late-stage maximum compression direction, suggesting that uplift of the Hsuehshan Range relative to the Puli topographic embayment has been accommodated by the late-stage faults. Our results suggest that a continental margin promontory has slowed underplating beneath the Puli topographic embayment and that the topographic grain of active collision zones is closely linked with the architecture of the downgoing plate.

Characteristics of the outer rise seaward of the Manila Trench and implications in Taiwan–Luzon convergent belt, South China Sea

The outer rise on the distal periphery of a subduction system is caused by emplacement of an accreted load onto the flexed oceanic lithosphere. By examining the bathymetry and free-air gravity anomaly data collected by satellite observations and marine reflection seismic data collected during the TAIGER project, we demonstrate the characteristics of the flexural outer rise seaward of the Manila Trench. The region of the outer rise on the westernmost periphery of the Manila subduction system is characterized by the positive free-air gravity anomaly seaward parallel to the Manila Trench and the morphological rise at the south of the Manila subduction system. A flexure simulation is performed based on the flexural profiles along the southern Manila Trench-outer system and the resulting effective elastic thickness values may provide an alternative aspect for the spreading rates of the South China Sea basin. Since both the western periphery of the Taiwan collision belt and Manila subduction belt are dominated by the strain regime of extension of flexural origin, it appears that the strain regime of flexural extension associated with the flexural forebulge of the Western Taiwan Foreland Basin to the north, and the strain regime of flexural extension associated with the outer rise seaward of the Manila Trench to the south are meridionally interconnected. This revised understanding of the strain regime of flexural extension origin west of the Taiwan–Luzon convergent belt provides an alternative point of view on the strain regime offshore SW Taiwan.

Active extension in Taiwan's precollision zone: A new model of plate bending in continental crust

Recent multichannel seismic reflection data acquired offshore southwest Taiwan identify active extension along a deep-seated normal fault in the precollision setting of the Taiwan arc-continent collision. While ubiquitous minor flexural faulting may be observed in the Taiwan foreland, these new data image a listric, rift basin–bounding normal fault that penetrates deep into the crust and forms a significant fault scarp with ∼850 m of relief near the continental shelf break southwest of the Taiwan collision zone. These observations, along with new geodynamic models of collision between a subduction zone and a young passive margin, indicate that the recent extension may be the expression of plate bending in continental crust as thin transitional crust subducts at the Manila Trench. A similar extensional episode prior to the onset of arc-continent collision ca. 6.7 Ma has been identified in rift basins of the southern Chinese margin near Taiwan, further suggesting that collision may be preceded by bending-related extension of the continental shelf. The Lishan fault, a major structural and morphologic boundary in the Taiwan orogen, may have been a similar rift basin–bounding fault before being reactivated during the Taiwan arc-continent collision. In this scenario, the Lishan fault divides Taiwan into a western domain representing collision of the thick crust of the continental shelf and an eastern domain representing subduction and collision of thin transitional crust along the continental slope with the Manila Trench.

Monitoring of active tectonic deformations in the Longitudinal Valley (Eastern Taiwan) using Persistent Scatterer InSAR method with ALOS PALSAR data

This paper presents new observation of the interseismic deformation along the Longitudinal Valley (Eastern Taiwan) that represents a major tectonic boundary of the Taiwan collision zone. We investigate the southern part of the Valley from Rueisuei to Taitung (latitude 23.5°N–22.7°N), which is the part of the Valley where interseismic surface creep has already been observed at some points of the Longitudinal Valley Fault (LVF). A Persistent Scatterer SAR interferometry approach (StaMPS) is applied using ten L-band SAR images from ALOS satellite acquired over the period 2007–2010. Interferograms from L-Band data show a dramatic improvement of coherence in comparison to previous studies using C-Band ERS data. The density of measurement resulting from StaMPS processing is the highest achieved so far in the area (about 40–55 points per km2 for a total of 77,000 points) allowing a continuous view of the deformation along the Valley and also giving information on its borders (Central Range and Coastal Range). The most striking feature of the resulting mean velocity map is a clear velocity discontinuity localized in a narrow band (0.1–1km) along the LVF and responsible for up to 3cm/yr velocity offset along the radar line of sight, which is attributed to shallow interseismic creep. InSAR results are in good agreement with continuous GPS measurements over the same period (0.3cm/yrrms). The density of measurement allows us to improve fault trace map along the creeping section of the LVF (with accuracy of about 100m) and to find new field evidences of the fault activity. In some places, our trace differs significantly (hundreds of meters) from previous published traces. The creep rate shows significant variations along the fault. At the southern end of the valley the deformation is distributed on several structures, including the Luyeh Strand, and drops significantly south of the Peinanshan. However there are discrepancies with previous studies made from ERS data over the period 1993–1999 that remain to be investigated. The mean velocity for each point of measure and the improved faults' trace are provided as Supplementary data.

Multiple attenuation in crustal-scale imaging: examples from the TAIGER marine reflection data set

During summer of 2009, multi-channel marine seismic reflection data and wide-angle refraction data were acquired as part of the joint NSF and Taiwanese-funded TAIGER program with the goal of understanding the dynamics of arc-continent collision in Taiwan. One of the principle difficulties of crustal-scale imaging with marine reflection data such as these is the prevalent multiple contamination that obscures many of the deep crustal targets. Without effective treatment of multiples, many of the objectives of the TAIGER active source program may not be achieved. We present three profiles, one from each acquisition leg, that demonstrate the effectiveness of 2D surface-related multiple elimination (SRME) and radon filtering in attenuating much of this unwanted energy in broad ranges of water depths, seafloor topographies and lithologies. Two profiles from south of Taiwan image 3–4 km of sedimentary strata overlying moderately extended continental crust along the Eurasia continental shelf and a 5–6 km thick sedimentary section overlying thin crust consisting of faulted blocks and volcanic bodies along the continental slope. Our multiple attenuation efforts also reveal a seaward-dipping normal fault that penetrates into the upper mantle and separates thick crust of the continental shelf from thin crust of the continental slope. A profile from east of Taiwan reveals thin ocean crust of the Philippine Sea plate subducting beneath the Ryukyu trench that may be traced beneath the accretionary prism and Ryukyu forearc. These profiles demonstrate the success of our imaging strategy in the range of imaging environments spanned by the TAIGER marine reflection seismic data.

Subduction-continent collision in southwestern Taiwan and the 2010 Jiashian earthquake sequence

We integrated a regional tomography model, 20-year seismicity and earthquake focal mechanisms of the 4 March 2010 ML 6.4 Jiashian earthquake source region to delineate the seismogenic structure and mechanics of a relatively rare damaging inland earthquake that occurred in the southwestern fold-and-thrust belt of Taiwan. The main shock of the Jiashian earthquake occurred at a depth of 23km beneath the slate belt of the southern Central Range with a sinistral thrust mechanism. Based on seismic tomography and seismicity, the Jiashian earthquake sequence occurred in the Chishan transfer fault zone, which we interpret to be located near the transition zone between the subducted Eurasian plate to the south and the arc–continent Taiwan collision to the north. The distribution of the Jiashian aftershocks define a WNW-ESE striking fault plane that dips 30–40° NNE which is consistent with the optimal fault plane of the GPS-derived coseismic slip model. Focal mechanisms and inverted stress results of the earthquake sequence indicate both thrust and strike–slip motions with the maximum compressive stress at nearly 90° to the regional compressive stress and thus sub-parallel to the strike of the Taiwan orogen. We propose that the 2010 Jiashian earthquake resulted from rupturing of a buried oblique fault within the Chishan transfer fault zone at the subduction–collision transition zone in southern Taiwan. The orogen-parallel P-axis of the 2010 Jiashian earthquake represents collision-related lateral compression, although a local stress deviation is also possible.