Central Geological Survey, MOEA

Research Article| March 01, 2006 Temporal and spatial records of active arc-continent collision in Taiwan: A synthesis Chi-Yue Huang; Chi-Yue Huang 1Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan Search for other works by this author on: GSW Google Scholar Peter B. Yuan; Peter B. Yuan 2Institute of Marine Geology and Chemistry, National Sun Yat-Sen University, Kaohsiung, Taiwan Search for other works by this author on: GSW Google Scholar Shuh-Jung Tsao Shuh-Jung Tsao 3Central Geological Survey, MOEA, Taipei, Taiwan Search for other works by this author on: GSW Google Scholar GSA Bulletin (2006) 118 (3-4): 274–288. https://doi.org/10.1130/B25527.1 Article history received: 17 Nov 2003 rev-recd: 06 Jan 2005 accepted: 02 Feb 2005 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Chi-Yue Huang, Peter B. Yuan, Shuh-Jung Tsao; Temporal and spatial records of active arc-continent collision in Taiwan: A synthesis. GSA Bulletin 2006;; 118 (3-4): 274–288. doi: https://doi.org/10.1130/B25527.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Well-documented stratigraphy and clearly defined geodynamics in Taiwan, where some of the best records on arc-continent collision have been preserved, offer a unique example for the study of collision belts worldwide. The oblique arc-continent collision in Taiwan caused a simultaneous and sequential migration of four tectonic processes. Beginning from 16 to 15 Ma, subduction of the South China Sea oceanic crust beneath the Philippine Sea plate resulted in volcanism in the Coastal Range and formation of an accretionary prism in the Central Range. Beginning in the latest Miocene–earliest Pliocene, the subduction was followed by initial arc-continent collision, as supported by the following: unroofing and erosion of the deformed accretionary prism, and deposition of sediments thus derived in the adjacent accretionary forearc (5 Ma) and slope basins (4 Ma); waning of volcanism (north, 6–5 Ma; south, 3.3 Ma); buildup of fringing reefs on the gradually quiescent volcanoes (north, 5.2 Ma; south, 2.9 Ma); arc subsidence by strike-slip faulting and the development of pull-apart intra-arc basins (north, 5.2–3.5 Ma; south, 2.9–1.8 Ma); thrusting of forearc sequences to generate a collision complex starting from 3 Ma; and clockwise rotation of the arc-forearc sequences (north, 2.1–1.7 Ma; south, 1.4 Ma). The collision propagated southward and reached southern Taiwan by 5 Ma, as evidenced by the successive deformation of the associated accretionary wedge en route. Afterward, the advanced arc-continent collision stage appeared in the earliest Pleistocene, as marked by the westward thrusting and accretion of the Luzon arc-forearc against the accretionary wedge (north, 1.5 Ma; south, 1.1 Ma) and exhumation of the underthrust Eurasian continent rocks (north, 2.0–1.0 Ma; south, 1.0–0.5 Ma). The final stage of the tectonic process, arc collapse-subduction, began by 1 Ma off the northern Coastal Range.The geologic records compiled and presented in this study strongly support the scenario of a continuous southward migration of tectonic processes and a change in sediment source and structural style. Most importantly, the model has a broad potential for reconstructing and predicting the evolution of arc-continent collision through space and time. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| May 01, 1976 Rb-Sr ages of granitic rocks in southeastern China and their tectonic significance BOR-MING JAHN; BOR-MING JAHN 1TN7 Geochemistry Branch, National Aeronautics and Space Administration Johnson Space Center, Houston, Texas 77058 Search for other works by this author on: GSW Google Scholar P. Y. CHEN; P. Y. CHEN 2Department of Geology, National Taiwan University, Taipei, Taiwan Search for other works by this author on: GSW Google Scholar T. P. YEN T. P. YEN 3Geological Survey of Taiwan, Taichung, Taiwan Search for other works by this author on: GSW Google Scholar Author and Article Information BOR-MING JAHN 1TN7 Geochemistry Branch, National Aeronautics and Space Administration Johnson Space Center, Houston, Texas 77058 P. Y. CHEN 2Department of Geology, National Taiwan University, Taipei, Taiwan T. P. YEN 3Geological Survey of Taiwan, Taichung, Taiwan Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (5): 763–776. https://doi.org/10.1130/0016-7606(1976)87<763:RAOGRI>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation BOR-MING JAHN, P. Y. CHEN, T. P. YEN; Rb-Sr ages of granitic rocks in southeastern China and their tectonic significance. GSA Bulletin 1976;; 87 (5): 763–776. doi: https://doi.org/10.1130/0016-7606(1976)87<763:RAOGRI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Rb-Sr age data and initial Sr87/Sr86 ratios (I values) are reported for the Mesozoic granitic batholiths along the coast of southeastern China. Two major thermal episodes are recognized: 90 to 120 m.y. B.P., derived from the mineral isochrons, and 165 ± 13 (2σ) m.y. B.P., derived from a whole-rock isochron. These episodes appear to be correlative with periods of rapid spreading of the Mesozoic Pacific Ocean floor and embrace two orogenic phases of the Yenshan orogeny.The I values of granitic gneisses (0.7060 to 0.7159) vary systematically with the Rb/Sr ratios of their whole-rock samples. The high I value (0.7112) of a pegmatite dike cutting a granitic gneiss in Chinmen suggests that the pegmatite is derived from remelting of upper crustal rocks. The narrow range of I values for more mafic intrusive bodies in Matsu (0.7065 to 0.70695) suggests that they are genetically related and are probably derived from an upper mantle source and have some crustal contamination. An un-metamorphosed granitic sample from Changlo has a mineral isochron age of about 120 m.y., which is interpreted as the time of intrusion. Its rather low I value (0.70546) suggests that the magma source is likely in the upper mantle.The Yenshan orogenic belt in southeastern China may belong to the inner belt of the Pacific-type orogeny; it is characterized by polycyclic deformation, magmatism, and regional metamorphism. Unlike a classical geosynclinal regime, the magmatic activities in this region were not immediately preceded by a major marine geosynclinal subsidence. The apparent absence of marine deposits after Triassic time suggests that marine transgression is not a universal result of rapid sea-floor spreading. The extensive development of magmatic belts along the eastern margin of the Asian continent appears to require large-scale consumption of oceanic lithosphere at the edge of the continental plate. The age distribution and structural trend data of the magmatic rocks suggest that the presumed subduction zone may have dipped westward or northwestward in the western Pacific region during late Mesozoic time. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

In the early morning (01:47 local time) of September 21, 1999, the largest earthquake of the century in Taiwan (Mw=7.6, ML=7.3) struck the central island near the small town of Chi‐Chi. The hypocenter was located by the Central Weather Bureau Seismological Center at 23.87°N, 120.75°E, with a depth of about 7 km. There were extensive surface ruptures for about 85 km along the Chelungpu fault with vertical thrust and left lateral strike‐slip offsets. The maximum displacement of about 9.8 meters is among the largest fault movements ever measured for modern earthquakes. There was severe destruction in the towns of Chungliao, Nantou,Taichung, FengYuan, and Tungshi, with over 2300 fatalities and 8700 injuries.

A high-pressure phase of titanium dioxide (TiO(2)) with an alpha-PbO(2)-type structure has been identified in garnet of diamondiferous quartzofeldspathic rocks from the Saxonian Erzgebirge, Germany. Analytical electron microscopy indicates that this alpha-PbO(2)-type TiO(2) occurred as an epitaxial nanometer-thick slab between twinned rutile bicrystals. Given a V-shaped curve for the equilibrium phase boundary of alpha-PbO(2)-type TiO(2) to rutile, the stabilization pressure of alpha-PbO(2)-type TiO(2) should be 4 to 5 gigapascals at 900 degrees to 1000 degrees C. This suggests a burial of continental crustal rocks to depths of at least 130 kilometers. The alpha-PbO(2)-type TiO(2) may be a useful pressure and temperature indicator in the diamond stability field.

Bottom simulating reflector (BSR) is a key indicator for the presence of gas hydrate beneath the sea floor. Widely distributed BSRs have been observed in the area offshore of southwestern Taiwan where the active accretionary complex meets with the passive China continental margin. In order to better understand the distribution and characters of the gas hydrate in the region, closely spaced (1.86-km line spacing) multichannel seismic reflection surveys have been conducted in recent years under the support of the Central Geological Survey, ROC. Over 10000 km of multichannel seismic reflection profiles have been collected that cover an area of about 10000 km 2 offshore of southwestern Taiwan. BSRs can be identified along 50% of the seismic profiles that we collected. A newly compiled BSR distribution map suggests that gas hydrates are distributed both in the passive margin of the China continental slope as well as in the submarine Taiwan accretionary wedge, from water depths of 500 to over 3000 m. Gas hydrates are most concentrated underneath anticlinal ridges in the accretionary wedge, and underneath the slope ridges of the passive continental margin that were formed due to sedimentary processes. Active fluid activities are evident from various features observed on seismic reflection and chirp sonar profiles, such as mud volcanoes, gas plumes and gas charged shallow sedimentary layers. Fluid migration model has been established from a set of pseudo 3D seismic reflection data. The predicted locations of high fluid flux correlate well with those interpreted from geochemical analyses that show very high methane concentrations and very shallow sulfate-methane interfaces (SMI). This demonstrates the importance of structural control over gas hydrate emplacement. From the observed gas hydrate distribution and characters, the area offshore of southwestern Taiwan provides an ideal place to study and compare the formation and migration of gas hydrates under different tectonic settings.

Objectives: To explore three questions: 1) Do chronic stressors predict physiological dysregulation? 2) Is that relationship moderated by characteristics of the individual and his or her social environment? and 3) Do perceived levels of stress mediate the relationship between stressors and dysregulation? Methods: Data come from a nationally representative, longitudinal study of older Taiwanese (n = 916). Regression models are used to examine the relationship between the number of life challenges (i.e., stressors) during 1996 to 2000 and physiological dysregulation (in 2000) based on 16 biomarkers that reflect neuroendocrine function, immune system, cardiovascular function, and metabolic pathways. We include interaction terms to test whether psychosocial vulnerability moderates the impact of stressors. Additional models evaluate the mediating effects of perceived stress. Results: We find a positive association between the number of stressors and physiological dysregulation. The results indicate that this relationship is stronger for persons with greater psychosocial vulnerability, but even so, the magnitude of the effect remains modest. We find some evidence that the level of perceived stress mediates the relationship between chronic stressors and physiological dysregulation. Conclusions: Our results provide some support for the theory of allostatic load, although the relationship between life challenges and physiological dysregulation is weak. The evidence also supports the stress-buffering hypothesis: the combination of low social position, weak social networks, and poor coping ability is associated with greater physiological consequences of life challenges. BMI = body mass index; DHEAS = dehydroepiandrosterone sulfate; HDL = high-density lipoprotein; HPA = hypothalamic-pituitary-adrenal; IGF-1 = insulin-like growth factor 1; IL-6 = interleukin-6; SD = standard deviation; SEBAS = Social Environment and Biomarkers of Aging Study; SEI = socioeconomic index; SNS = sympathetic nervous system; UCL = Union Clinical Laboratories.

To examine the tectonic history of the Taiwan segment of the eastern margin of South China, six rock samples from the Tailuko belt, the metamorphic basement of Taiwan, were selected for zircon SHRIMP dating. The aim was to identify evidence shedding light on the timing of the change from passive to active tectonics for this part of the continental margin since South China separated from the supercontinent of Rodinia. The results lead to two age groups, 190–200 and 88–90 Ma. These age groups, augmented by the previously published age data, suggest that they could have resulted from two Mesozoic accretion/subduction events. In addition, this mid‐late Mesozoic Tailuko belt might have also been reactivated and structurally complicated by the late Cenozoic collision/accretion of the Luzon arc with the Eurasian continent. Records of older tectonic events, such as those derived from the Japanese Islands, are absent in this metamorphic basement. An important finding of this study is the existence of the 191±10 Ma Talun metagranite, the oldest granitic intrusion ever reported in the Taiwan region and along the eastern coast area of South China. In spite of a large age uncertainty, the occurrence of this metagranite is not consistent with the apparent younging trend of Jurassic‐Cretaceous igneous activity toward the coastline in South China, and should be taken into consideration by future studies.

The daily creep meter data recorded at Chihshang in 1998–2001 are presented. The Chihshang creep meter experiment was set up across the Chihshang thrust fault, the most active segment of the Longitudinal Valley Fault, which is the present‐day plate suture between the Eurasian and the Philippine Sea plates in eastern Taiwan. Near‐continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates: 16.2 mm at the Tapo site (comprising two connected creep meters) and 15.0 mm at the Chinyuan site (three creep meters straddling parallel fault branches). Four of the five creep meters showed a seasonal variation, with the fault moving steadily during the rainy season from April to October, and remaining quiescent during the rest of the year. The only exception was recorded by the creep meter located on a mélange‐composed hillslope, where local gravitational landsliding played an additional role other than tectonic faulting. Through comparison with daily precipitation data, we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault, during the transition period of the dry/wet season. During the observation period from 1998 to 2001, the subsurface seismicity exhibited clusters of microearthquakes on the Chihshang Fault at depths of 10–25 km. Recurrent earthquakes occurred regardless of whether the season was wet or dry, indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface. The accumulated strain on the Chihshang Fault at shallow surface levels was released through creep during the wet season. In addition to these short‐term seasonal variations, an apparent decrease in the annual slipping rate on the Chihshang Fault during the last few years deserves further investigation in order to mitigate against seismic hazard.

In this study, six different periods of digital terrain model (DTM) data obtained from various flight vehicles by using the techniques of aerial photogrammetry, airborne LiDAR (ALS), and unmanned aerial vehicles (UAV) were adopted to discuss the errors and applications of these techniques. Error estimation provides critical information for DTM data users. This study conducted error estimation from the perspective of general users for mountain/forest areas with poor traffic accessibility using limited information, including error reports obtained from the data generation process and comparison errors of terrain elevations. Our results suggested that the precision of the DTM data generated in this work using different aircrafts and generation techniques is suitable for landslide analysis. Especially in mountainous and densely vegetated areas, data generated by ALS can be used as a benchmark to solve the problem of insufficient control points. Based on DEM differencing of multiple periods, this study suggests that sediment delivery rate decreased each year and was affected by heavy rainfall during each period for the Meiyuan Shan landslide area. Multi-period aerial photogrammetry and ALS can be effectively applied after the landslide disaster for monitoring the terrain changes of the downstream river channel and their potential impacts.

The 2003 Chengkung earthquake ( Mw 6.8) provided diagnostic evidence for a source model showing the deformation process of the seismogenic Chihshang fault in eastern Taiwan. The aftershocks show a fault‐bend at a depth of 18 km. Coseismic ground displacements recorded by strong‐motion records allow us to deduce instant rupturing of this event. Our resulting model shows a fault length of ∼33 km and dip‐slip dominant rupture on fault‐plane deeper than 18 km. Estimated coseismic displacements constrain two fault planes: one at 5–18 km depth dipping 60°E and 18–36 km depth dipping 45°E. The uppermost fault‐plane of the Chihshang Fault (0–5 km) did not break immediately after the main shock; however, it may have a major role in after‐slip and even interseismic ground deformation. The Taiyuan basin developed in the hanging wall is a geomorphic feature consistent with and adequately explained by coseismic ground displacements.

ABSTRACT Sediments produced by landslides are crucial in the sediment yield of a catchment, debris flow forecasting, and related hazard assessment. On a regional scale, however, it is difficult and time consuming to measure the volumes of such sediment. This paper uses a LiDAR‐derived digital terrain model (DTM) taken in 2005 and 2010 (at 2 m resolution) to accurately obtain landslide‐induced sediment volumes that resulted from a single catastrophic typhoon event in a heavily forested mountainous area of Taiwan. The landslides induced by Typhoon Morakot are mapped by comparison of 25 cm resolution aerial photographs taken before and after the typhoon in an 83.6 km 2 study area. Each landslide volume is calculated by subtraction of the 2005 DTM from the 2010 DTM, and the scaling relationship between landslide area and its volume are further regressed. The relationship between volume and area are also determined for all the disturbed areas ( V L = 0.452 A L 1.242 ) and for the crown areas of the landslides ( V L = 2.510 A L 1.206 ). The uncertainty in estimated volume caused by use of the LiDAR DTMs is discussed, and the error in absolute volume estimation for landslides with an area &gt;10 5 m 2 is within 20%. The volume–area relationship obtained in this study is also validated in 11 small to medium‐sized catchments located outside the study area, and there is good agreement between the calculation from DTMs and the regression formula. By comparison of debris volumes estimated in this study with previous work, it is found that a wider volume variation exists that is directly proportional to the landslide area, especially under a higher scaling exponent. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Geochemical data (CH 4 , SO 4 2− , I − , Cl − , particulate organic carbon (POC), δ 13 C‐CH 4 , and δ 13 C‐CO 2 ) are presented from the upper 30 m of marine sediment on a tectonic submarine accretionary wedge offshore southwest Taiwan. The sampling stations covered three ridges (Tai‐Nan, Yung‐An, and Good Weather), each characterized by bottom simulating reflectors, acoustic turbidity, and different types of faulting and anticlines. Sulfate and iodide concentrations varied little from seawater‐like values in the upper 1–3 m of sediment at all stations; a feature that is consistent with irrigation of seawater by gas bubbles rising through the soft surface sediments. Below this depth, sulfate was rapidly consumed within 5–10 m by anaerobic oxidation of methane (AOM) at the sulfate‐methane transition. Carbon isotopic data imply a mainly biogenic methane source. A numerical transport‐reaction model was used to identify the supply pathways of methane and estimate depth‐integrated turnover rates at the three ridges. Methane gas ascending from deep layers, facilitated by thrusts and faults, was by far the dominant term in the methane budget at all sites. Differences in the proximity of the sampling sites to the faults and anticlines mainly accounted for the variability in gas fluxes and depth‐integrated AOM rates. By comparison, methane produced in situ by POC degradation within the modeled sediment column was unimportant. This study demonstrates that the geochemical trends in the continental margins offshore SW Taiwan are closely related to the different geological settings.

We detected 12 landquakes in Taiwan with collapse areas between 0.27 and 2.48 km2 associated with rock collapse, rockslide and debris and/or rock avalanche during the passage of Typhoon Morakot in 2009. These events were recorded by seismic stations of the Broadband Array in Taiwan for Seismology. Their locations were determined by a cross-correlation technique that maximizes the coherency of horizontal envelope function among seismic stations with a mean location error of 1.92 km. We applied time-frequency analysis to estimate the bandwidth of seismic energy generated by the landquakes. The predominant frequency ranges from 0.5 to 5.0 Hz, with higher-frequency signals likely caused by block impact. We extracted signal duration (SD), peak ground velocity, rise time (TR), area of velocity envelope function (AE) from the closest station and estimated the collapse area (AC) and run-out distance (DR) by mapping satellite images. Based on aforementioned seismic and geometrical parameters, we defined the potential of initial impact (PI), the frequency of rock impact signal (fI) and the mean quasi-front velocity (Vf) as indicators of landquake types, especially for events with dam formation (dam-formation-type events). We also derived an empirical linear relationship between the envelope area (AE) and collapse area (AC) with a high correlation coefficient of 0.83. Our automatic approach is very effective for rapid determination of landquake centroid location and collapse area, and for identifying dam-formation event using records from existing real-time broad-band seismic networks, thus providing an important alternative for landquake hazard mitigation.

Bacteria sulfate reduction is a major pathway for organic carbon oxidation in marine sediments. Upward diffusion of methane from gas hydrate deep in the sedimentary strata might be another important source of carbon for sulfate reducing bacteria and subsequently induce higher rates of sulfate reduction in sediments. Since abundant gas may migrate upward to the surface as a result of tectonic activity occurring in the accretionary wedge, this study investigates the effect of methane migration on the sulfate reduction process in continental margin sediments offshore southwestern Taiwan. Piston and gravity core samples were taken in order to evaluate vertical and spatial variations of sulfate and methane. Pore water sulfate, sulfide, methane, sediment pyrite, and organic carbon were extracted and analyzed.

It has been found that Bottom Simulating Reflections (BSRs), which infer the existence of potential gas hydrates underneath seafloor sediments, are widely distributed in offshore southwestern Taiwan. Fluids and gases derived from dissociation of gas hydrates, which are typically methane enriched, affect the composition of seawater and sediments near venting areas. Hence, methane concentration of seawater and sediments become useful proxies for exploration of potential gas hydrates in a given area. We systematically collected bottom waters and sedimentary core samples for dissolved and pore-space gas analyses through five cruises: ORI-697, ORI-718, ORII-1207, ORII-1230, and ORI-732 from 2003 to 2005 in this study. Some sites with extremely high methane concentrations have been found in offshore southwestern Taiwan, e.g., sites G23 of ORI-697, N8 of ORI-718, and G96 of ORI-732. The methane concentrations of cored sediments display an increasing trend with depth. Furthermore, the down-core profiles of methane and sulfate reveal very shallow depths of sulfate methane interface (SMI) at some sites in this study. It implies sulfate reduction being mainly driven by the process of anaerobic methane oxidation (AMO) in sediments; thus indicating that there is a methane-enriched venting source, which may be the product of dissociation of gas hydrates in this area.

Giggenbach bottle technique is used to systematically analyze fumarolic gas composition of the Tatun Volcano Group, northern Taiwan. The area is quite active hydrothermally and is also considered volcanically active. The gas composition of fumarolic samples is predominantly steam water with CO 2 as the dominant component after de-watering. Minor components include sulfur species (mainly H S 2 and SO 2 ), N 2 and CH 4 . Interestingly, in the study area, H S 2 concentration is always much higher than SO 2 for all measured fumarolic gases. This result resembles the typical composition of low temperature fumaroles, when comparisons are made on a worldwide basis.

We relocated 6,173 shallow earthquakes and determined focal mechanism solutions of thirty-three M 5.0 L events in the eastern Taiwan region (bounded by 22.7N, 120.8E; 24.5N, 121.5E; 24.3N, 122.3E and 22.5N, 121.6E) in order to investigate their tectonic implications. Our results suggest that the distribution of the relocated earthquakes generally agrees with the fault plane determined from the focal mechanism solutions. The Longitudinal Valley (LV) is an east-dipping seismic suture zone that separates two different tectonic regions. On the left-hand side of the LV, shallow earthquakes and normal fault-type focal mechanism were found in the Central Range region. But on the right-hand side of the LV, most events that occurred in the Philippine Sea Plate (PSP) were the thrust-type, especially for the southern portion and a few normal and strike-slip focal mechanism events were observed in the northern portion. The tectonics of eastern Taiwan can be classified from south and north into two regions, and there may exist a structure or boundary at about latitude 23.5N with a strike of N110E. In the northern portion of eastern Taiwan, the plate boundary appears to be an east-dipping plane defined by the earthquake distribution. The focal mechanism solutions determined in this zone show thrust type faulting and agreed with this boundary plane (strike N20E and dip about 50). In this region, the Eurasia Plate (EP) dips to the east, and the PSP bends and dips to west. Thus, shallow earthquakes with normal and strikeslip focal mechanisms were observed in the offshore area of this region. On the other hand, the southern part of eastern Taiwan exhibits simple tectonics conditions. The EP subducts to the east under the PSP. The LV is a suture zone dipping to the east, and most events have occurred on the righthand side of the LV. Focal mechanism solutions of these events were thrust-

Using a two‐dimensional distinct element model, we evaluate the relationships between plate kinematics and present‐day deformation in Taiwan where active collision occurs. In particular, the distribution of velocity fields calculated in our models is compared with the actual velocity field revealed by the most recent geodetic data (GPS) obtained in Taiwan and the surrounding islands of the Philippine Sea plate and the Eurasian shelf. The main aim of this paper is to produce a mechanically consistent 2‐D model that accounts for the observed velocity field taken as whole, within the limits of acceptable rheological parameters and reasonable boundary displacement conditions. We evaluate how the active deformation of Taiwan is influenced by the presence of strong and weak zones such as the structural highs in the foreland and subduction zones with accretionary prisms, respectively, major mechanical discontinuities such as the main fault zones in the mountain belt, and the opening of the Okinawa Trough. Particular attention is paid to the role of preexisting discontinuities since the presence of mechanical decoupling along major faults strongly affects the distribution of the velocity and stress patterns. We show that despite parameter uncertainties, several tectonic factors (the presence of the strong Kuanyin and Peikang highs in contrast to the weak subduction zone to the south, the “weak” active regional shear zones, and the opening of the back arc Okinawa Trough) concur to provide an acceptable mechanical model for this regional deformation. These sources are related not only to the geometry of the plate boundary, the direction of plate convergence, and the shape of the Chinese margin but also to the presence of major zones of relative weakness and mechanical decoupling such as the Longitudinal Valley fault zone and the western thrust belt of Taiwan.

Abstract Although oriented rutile needles in garnet have been reported from several ultrahigh‐pressure (UHP) rocks and considered to be important UHP indicators, their crystallographic features including growth habit and lattice correspondences with garnet host have never been properly characterized. This paper presents a detailed analytical electron microscopic (AEM) study on evenly distributed oriented rutile needles in garnet of two eclogitic rocks from Sulu. Some garnet in one UHP diamondiferous quartzofeldspathic rock from the Saxonian Erzgebirge, and in one high‐pressure (HP) felsic granulite from Bohemia also contain a few unevenly distributed oriented rutile needles. They have also been studied for the purpose of comparison. Despite different distribution patterns, AEM revealed that all rutile needles are oriented along the 〈111〉 directions of garnet with their lateral sides surrounded by the {110} planes of garnet, and that the growth directions of most needles are close to the normal of the {101} planes of rutile. No other specific crystallographic orientation relationships between rutile and garnet host were observed, and there is no pyroxene associated with rutile, as necessitated by the precipitation reaction of rutile in garnet as previously proposed. A simple solid‐state precipitation scenario for the formation of the rutile needles in garnet in these two eclogitic rocks is not justified. Three alternative mechanisms are considered for the formation of oriented rutile needles: (i) the rutile needles may be inherited from precursor minerals; (ii) the rutile needles may be formed by a dissolution–reprecipitation mechanism; and (iii) the rutile needles may be formed by cleaving and healing of garnet with rutile deposition. None of these mechanisms can fully explain the observations, although the first one is less likely and the third one is preferred. This study presents an example where the presence of oriented/aligned inclusions in minerals does not necessarily imply a precipitation origin.

Being situated in the immediate vicinity of the 1999 Chichi earthquake epicenter, 178 automatic‐recording monitoring wells of the Choshui fan‐delta provided a very valuable data set for testing whether the coseismic water‐level changes in confined aquifers can be explained as a poroelastic response of well‐aquifer systems to coseismic volumetric strain. This study demonstrates that the polarities of the observed coseismic water‐level and river discharge changes are in good agreement with those of the static volumetric strain calculated by a dislocation model, using the well‐constrained rupture model of the seismogenic Chelungpu fault. The puzzling “bull‐eye” patterns formed by the equipotential lines of the coseismic water‐level changes in the confined aquifers in the middle parts of the fan‐delta represent pressure enhancement due to their being situated at the pinch‐out ends of conglomeratic layers.