[1] We characterize the kinematics of modern crustal deformation in Taiwan and evaluate the potential for large earthquakes by computing tectonic block motions and fault slip rates from 531 GPS horizontal velocities. These new GPS velocity field indicates that lateral extrusion in the southern transition from collision to subduction is primarily achieved by motion along several major reverse faults and internal distortion of blocks. The northern transition is characterized by asymmetric opening of the Okinawa trough and collision-induced rotation between the Ryukyu trench and Okinawa trough. We suggest that the differences in style of deformation in northern and southern Taiwan are a result of differences in trenchward motions between the overriding plate and forearc sliver. Along-strike variations in basin thickness and the presence of foreland basement obstacles in central Taiwan result in clockwise rotation with sinistral motion on faults and counterclockwise rotation with dextral motion on faults north and south of the obstacle, respectively. In eastern Taiwan, high slip rate of ∼43 mm/yr on the southern Longitudinal Valley fault (LVF) is responsible for the full collision of Taiwan orogeny. E-W syn-orogenic extension in the southern Central Range has been inferred by our model. Patches with high slip rate deficits on the LVF and the Chelungpu fault from our model, respectively, mainly correspond to the source areas of the 1951 M 7.1 Longitudinal Valley earthquake sequence and of the 1999 Mw 7.6 Chi-Chi earthquake.

Present-day kinematics of active mountain building in Taiwan from GPS observations during 1995-2005

[1] Although much work has been done on active tectonics of eastern Tibet, little is known about the Longriba fault zone and its role in strain partitioning. Whether its two sub-parallel strands (Longriqu and Maoergai faults) can rupture simultaneously in a large earthquake remains unknown. We conducted trenching combined with the interpretation of satellite imagery, field investigations, topographic surveys, and radiocarbon and Optically Stimulated Luminescence (OSL) dating to reconstruct paleoseismic history, and we used displaced terrace risers to estimate geological slip rates. Our results demonstrate that the Longriba fault zone is predominantly right-lateral with a small southeast-verging thrust component. Four surface-rupturing events occurred on the Longriqu fault at 5080 ± 90, 11,100 ± 380, 13,000 ± 260, and 17,830 ± 530 cal yr B.P. Together with our previous trenches on the Maoergai fault, we found that the last event probably ruptured both the Longriqu and Maoergai faults. Prior to the last event, the two strands of the Longriba fault zone experienced alternating earthquakes. The fault zone has a high potential for an earthquake larger than Mw 7. The slip rate of the Longriba fault zone decreases from ~7.5 mm/yr in latest Pleistocene to ~2.1 mm/yr in the Holocene, probably related to a slowing down of the eastern motion of the Tibetan Plateau. The comparison with slip rates at the Longmen Shan fault zone suggests that the Longriba fault zone has an equally important role in strain partitioning in eastern Tibet. This study is helpful to seismic hazard assessment and an understanding of deformation mechanism in eastern Tibet.

Latest Quaternary paleoseismology and slip rates of the Longriba fault zone, eastern Tibet: Implications for fault behavior and strain partitioning

[1] The structure of the Taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment. In recent years, however, a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust, suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment, imbricate thrust belt model. To address this issue, we present new geological mapping, together with earthquake focal mechanism and seismic energy release data from the central part of Taiwan. We concur with the interpretation that the foreland basin part of the Western Foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth. To the east of the foreland basin, however, in the Hsuehshan and Central Ranges, our data show the presence of two fault systems. An earlier, inactive thrust system with a well-developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more. In the Hsuehshan Range, the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal-scale positive flower structure. Eastward, in the Central Range, Mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first, now inactive, thrust system. The involvement of deep crustal levels and Mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin-bounding faults that were located on the Eurasian continental margin.

/pdf/the-structure-and-kinematics-of-the-central-taiwan-mountain-4031jpf281.pdf

The structure and kinematics of the central Taiwan mountain belt derived from geological and seismicity data

http://www.gl.ntu.edu.tw/geodesy/images/publications/paper/pa69.pdf

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

[1] About 50 mm/yr of convergence between the Philippine Sea and Eurasian plates is absorbed in eastern Taiwan, and it remains unclear how the convergence is partitioned among active faults. The Longitudinal Valley fault (LVF), the most seismically active fault in eastern Taiwan, creeps at the surface in the south and not in the north; however, it is unclear how much of the fault is locked or creeping at depth. To address these problems, we model Holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern Taiwan. Through a fully probabilistic scheme, we invert GPS, interferometric synthetic aperture radar, creepmeter, and Holocene marine terrace data for block motions, fault slip rates, and distribution of interseismic creep. The data are explained with four blocks separated by three faults, Central Range fault, LVF, and an offshore fault. The model explains the essential features of interseismic and Holocene deformation. We find that 35–55 mm/yr of slip on the offshore fault is necessary to fit marine terrace uplift rates, which is a larger fraction of the plate convergence than previously recognized. The LVF has a Holocene slip rate of 20–30 mm/yr with approximately equal magnitudes of reverse-slip and left-lateral strike-slip components. Only about half of the surface area of the Longitudinal Valley fault appears to be locked. The southern segment of the LVF creeps at a rate of 5–28 mm/yr down to a depth of 15–20 km, while the northern segment is locked from the surface to a depth of 20 km.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JB006208

Insights into active tectonics of eastern Taiwan from analyses of geodetic and geologic data

Late Holocene paleoearthquake activity in the middle part of the Longitudinal Valley fault, eastern Taiwan

This study examined the physical and biogeochemical processes that determine the spatial and summer/winter distributions of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) in the Taiwan Strait (TS). The hydrological conditions in the TS varied between early summer and winter because of differences in terrestrial input as well as input from the poleward South China Sea Water (SCSW) during the warm summer and the strong, nutrient-rich, equatorward China Coastal Water (CCW) in winter. Concentrations of dissolved organic carbon (DOC) ranged from 60 to 100 μM-C in early summer and from 70 to 144 μM-C in winter. The average stoichiometric ratio of DOC : DON:DOP was high (353:49:1) in the land-source impacted zones and low (168:21:1) in the SCSW-laden areas, both of which are higher than the Redfield ratio. The concentrations of DOC and nutrients were higher in the western TS (on the coast of China) than in the eastern TS (on the coast of Taiwan), and the highest concentrations were mostly found in the Minjiang River plume, reflecting the profound effects of freshwater input in early summer and CCW inflow in winter. The absorption and emission characteristics of the CDOM varied to a large extent with locations because of the mixing of the shelf water with different source waters. Although the absorption coefficient (aCDOM(325)) and fluorescence intensity of the terrestrial humic-like CDOM (Ft: Ex/Em= 260/400-460) were both strongly inversely correlated with salinity, as an optical tracer, Ft may be more effective than aCDOM(325) in examining the mixing among source waters, given that aCDOM(325) may be subject to various photobleaching effects in the TS. Ft was also significantly correlated with the concentrations of terrestrially derived nitrate and nitrite (N+N) and silicate. The results of factor analysis elucidated the complexity of the hydrological and biological processes that affect the distributions of DOM and CDOM in the TS. Graphical Abstract

/pdf/biophysical-controls-on-spatial-and-summer-winter-310jm8yb.pdf

Yen-Hui Lin

Papers

Late Holocene paleoearthquake activity in the middle part of the Longitudinal Valley fault, eastern Taiwan

Biophysical controls on spatial and summer/winter distributions of total and chromophoric dissolved organic matter in the Taiwan Strait