The TAICRUST project is a comprehensive seismic program carried out by scientists from Taiwan, the U. S. and France to investigate the deep structure of the Taiwan arc-continent collision zone. Deep seismic reflection profile data were collected by the R/V Maurice Ewing in the area off eastern and southern Taiwan in August and September of 1995. Wide-angle reflection and refraction data have also been collected by using both ocean bottom seismometers (OBS) and onland seismic recording instruments. Data collected during the TAICRUST survey are being processed and analyzed at various participating institution in Taiwan and in the U. S. Here we present some deep seismic reflection results at the western end of the Ryukyu subduction system. T\vo deep seismic reflection profile which run perpendicular to the Ryukyu arc-trench system and parallel to the arc in the center of the forearc basin, respectively, reveal the sedimentary and cmstal structures of the western end of the Ryukyu arc-trench system. The oceanic basement of the subducting Philippine Sea plate in the Huatung Basin can be traced to extend below the toe of the Yaeyama Ridge. A deep reflection has been observed at about 1.5s below the basement reflection. Near 3 sec of sediments are observe in the Ryukyu Trench. Thick forearc basin strata are little deformed. Hie arc basement can be clearly imaged beneath the forearc basin strata and the arc-side of the accretionary wedge. Three forearc basin have been identified in the study area. An elevated basement, which is caused by the subduction of the Gagua Ridge, separates the East Nanao Basin from the Nanao Basin. Active normal faults cut the upper portion of this basement high and the thick Nanao Basin strata on top of it. However, the western half of the Nanao basin strata are almost undisturbed. Further west, elevated arc basement and deformed old arc strata form basement of the Hoping Basin. The depths of the East Nanao Basin, the Nanao Basin and the Hoping Basin are 4500m, 360()m, respectively, illustrating the step-wise elevated forearc basin structures as the Ryukyu arc extends toward the Taiwan collision zone. The Taiwan collision has affected the western end of the Ryukyu forearc region west of 122° 20'E. Introduction Taiwan is situated at the juncture between Ryukyu and the Luzon arc systems. The collision of the Luzon volcanic arc with the passive Chinese continental marigin that started about 5 million years ago has produced the present Taiwan mountain belt (Biq, 1972; Ho, 1986; Teng, 1990) and may also be responsible for the recent phase of the back-arc extension and opening of the southern Okinawa trough (Letouzey and Kimura, 1986). While the collision is

Along offshore to the east of southern Taiwan, different stages of subduction and collision occur simultaneously along strike of the convergent boundary. As a result, the evolution of the Luzon arc and its forearc basin can be studied from the younger subduction zone to the South to the collision zone to the north. Examining more than 8000 km of seismic lines, we analyzed the seismic stratigraphy of strata in a forearc basin and its successive basins in the collision zone, to study the processes related to arc collapse and forearc basin closure. The study area presents three evolutional stages: intra-oceanic subduction, initial arc-continent collision, and arc-continent collision. We divided 9 seismic sequences in the forearc basin and found older, sub-parallel basin-fill sequences (4-9) and younger, divergent sequences (1-3). Isochron maps of the sequences were used to interpret different deformation modes and their areal extends. On the arc side of the basin of the subduction and initial collision zones, we found relatively undisturbed strata, showing little arc deformation. On the trench side, the growth strata in sequences 1 through 3 are the result of recent tectonic wedging along the rear of the accretionary prism. Tectonic wedging and back-thrusts incorporate the forearc strata into the rear of the accretionary prism until they close the forearc basin at a region with a 2200 m basement relief. This relief is not caused by active deformation, as young flat forearc strata lap onto it and mark the transition from initial collision to collision where many growth strata to the north suggest abrupt increase in active arc basement deformation. The (1) deforming basement, (2) back-thrusts, and (3) other sedimentary processes affect the architecture of the successive basins in the collision zone until the arc is juxtaposed to the rear of the fold and thrust belt on land. (C) 2009 Elsevier B.V. All rights reserved.

Fifth generation warfare has arrived and is irreversibly changing the character and nature of human conflict. It confronts the United States with the evolving strategic dilemma of not only dealing with the War on Terror, but of simultaneously crafting strategies that look beyond military preparedness for past wars and embrace the perspective of national preparedness for the spectrum of future conflicts. This article uses four essential elements of war—the new domains of conflict, the changing nature of adversaries, the changing nature of objectives, and the changing nature of force—to build a generational typology of war and conflict that informs the characteristics of fifth generation warfare. The resultant model produces two outcomes: First, it demonstrates how recent events such as the rise of computer hackers, the 2001 anthrax and the 2003–2004 ricin attacks, the 2004 Madrid bombings, and the emergence of Al Qaeda demonstrate characteristics of fifth generation warfare. Second, it illustrates the way in which these events are unique indicators of a future in which non-state entities are increasingly able to wage war on equal footing with nation-states. The article concludes that the United States must embrace fifth generation warfare if it is to successfully confront these threats that have taken on new and heretofore unimagined forms in the postmodern era of war.

We study crustal thermal evolution by examining heat flow patterns along a convergent boundary from a young subduction zone to a more structurally mature collision zone. More than 8000 km of seismic profiles covering an offshore region of 45,000 km(2) in southern Taiwan show widespread bottom-simulating reflectors (BSRs). We derived 1107 BSR-based heat flows before combining 42 additional, published, offshore thermal probe data and 86 on-land heat flow data to document the shallow forearc thermal structures from the subduction zone to the collision zone. In the subduction zone, the geothermal gradient ranges mostly within 30-80 degrees C/km, and decreases toward the arc due to slab cooling, intensive dewatering at the toe, sediment blanketing, topographic effects, and other processes. The geothermal gradient ranges mostly from 30 to 90 degrees C/km in the collision zone, and increases, instead of decreases, toward the arc, possibly caused by exhumation, erosion, topographically induced groundwater circulation, and some upper mantle processes related to collision. Heat flow in the collision zone ranges from 80 to 250 mW/m(2). The high heat flow in the collision zone correlates with a shallower seismicity zone and high seismic attenuation, while the lower heat flow in the subduction zone might allow the earthquakes to rupture to greater depth. The heat flow increases along the topographic high from subduction to collision zone due to increasing geothermal gradients and higher thermal conductivities of the exhumed basement rocks. This heat flow variation may generate an artificial exhumation rate pattern, if a conventional 30 degrees C/km geothermal gradient was used in fission-track studies.

Methane hydrates are considered a major potential source of hydrocarbon energy and could be important in meeting natural gas demand in the future. To study the feasibility of recovering methane from the offshore southern Taiwan region and its impact on many geological processes, it is necessary to know the total amount of hydrate in the region; something that is still unclear. Here we take the first step using a bottom-simulating reflector (BSR) to estimate the total volume of the stability field that can hold hydrates in the sediments offshore of southern Taiwan. We used a dense grid of 6-channel and 120-channel reflection profiles to study the distribution and sub-bottom depth of a BSR. BSRs are marked by a reversed polarity reflector that increases in sub-bottom depth with increasing water depth, suggesting that BSRs mark the base of methane hydrate stability zones. For offshore Taiwan a BSR is located in offscraped sediments derived from the Taiwan orogen and the Chinese continental margin. These sediments may have high amounts of organic carbon, thereby providing a source for the methane. We document the areal extent and subbottom depth of BSRs covering a 45000 km(2)-wide region. The BSRs were classified into three categories based on how well they fit the seismic characteristics of the BSR associated with hydrates. Q1 BSR fits with all the expected seismic attributes to be found at the base of a hydrate boundary, while Q2 and Q3 BSRs are possible and probable reflectors resulting from such a boundary. We then estimate the volume of the hydrate stability zone bounded between the seafloor and the mapped BSRs in the offshore region. At least 1023 km(3) of the hydrate stability field is underlain by the highest quality BSRs while as much as 11522 km(3) is underlain by all mapped BSRs. We then speculated on the total amount of hydrate stored in the region using published regional porosity-depth relations and assuming a range of saturation values of hydrates in the pore spaces. Hydrate storage can be better estimated once additional porosity and saturation information becomes available.

The structural geometry, kinematics and density structure along the rear of the offshore Taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling. Deformation between the offshore prism and forearc basin at the point of incipient collision, and southward into the region of subduction, has been interpreted as a tectonic wedge, similar to those observed along the front of mountain ranges. This tectonic wedge is bounded by an east-dipping roof thrust and a blind, west-dipping floor thrust. An east-dipping sequence of forearc-basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge. Section restoration of the roof sequence yields an estimate of 4 km of shortening, which is small compared with that inferred in the collision area to the north, based on the variation in distance between the apex of the prism and the island arc.Previous studies propose that either high-angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the Central Range in the collision zone on land. To better constrain the initial crustal configuration, we tested 350 crustal models to fit the free-air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land. The gravity anomaly, observed in the region of subduction (20.2degreesN), can be modeled with the arc basement forming a trenchward-dipping backstop that is overlain by materials with densities in the range of sedimentary rocks. Near the point of incipient collision (20.9degreesN), however, the free-air gravity anomaly over the rear of the prism is approximately 40 mgal higher, compared with the region of subduction, and requires a significant component of high density crustal rocks within the tectonic wedge. These results suggest that the forearc basement may be deformed along the rear of the prism, associated with the onset of collision, but not in the subduction region further to the south. (C) 2003 Elsevier B.V. All rights reserved.

15 Ma ago, a major plate reorganization occurred in East Asia. Seafloor spreading ceased in the South China Sea, Japan Sea, Taiwan Sea, Sulu Sea, and Shikoku and Parece Vela basins. Simultaneously, shear motions also ceased along the Taiwan–Sinzi zone, the Gagua ridge and the Luzon–Ryukyu transform plate boundary. The complex system of thirteen plates suddenly evolved in a simple three-plate system (EU, PH and PA). Beneath the Manila accretionary prism and in the Huatung basin, we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations. These two patterns are rotated by 15°. They were formed by seafloor spreading before 15 Ma and belonged to the same ocean named the Taiwan Sea. Half-spreading rate in the Taiwan Sea was 2 cm/year from chron 23 to 20 (51 to 43 Ma) and 1 cm/year from chron 20 (43 Ma) to 5b (15 Ma). Five-plate kinematic reconstructions spanning from 15 Ma to Present show implications concerning the geodynamic evolution of East Asia. Amongst them, the 1000-km-long linear Gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the PH Sea plate; the formation of Taiwan was driven by two simple lithospheric motions: (i) the subduction of the PH Sea plate beneath Eurasia with a relative westward motion of the western end (A) of the Ryukyu subduction zone; (ii) the subduction of Eurasia beneath the Philippine Sea plate with a relative southwestward motion of the northern end (B) of the Manila subduction zone. The Luzon arc only formed south of B. The collision of the Luzon arc with Eurasia occurred between A and B. East of A, the Luzon arc probably accreted against the Ryukyu forearc.

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps-extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms-are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific-North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.

A bottom-simulating reflector (BSR) has been identified in the offshore Taiwan accretionary prism using both migrated 6-channel and 120-channel reflection profiles. The BSR is marked by a reversed polarity reflector that increases in sub-bottom depth with increasing water depth, suggesting that the BSR marks the base of the methane hydrate stability field. The BSR is located in offscraped sediments derived from the Taiwan orogen and the Chinese continental margin, which may contain high amounts of organic carbon, thereby providing a source for the methane. Gas seepage found on land north of this region also supports the presence of methane in these strata. The BSR is typically located in the crests of anticlines and mud volcanoes, implying the migration and entrapment of methane gas. Recent uplift of the seafloor in anticlines may reduce pore pressure, thereby decomposing the hydrate phase into free gas, which may enhance the acoustic impedance contrast across the BSR. BSRs are conspicuously absent beneath submarine canyons in the region. A "flat spot" was found under the BSR within an anticline, suggesting that the hydrate-filled pore-space may result in lower sediment permeability, therefore enhancing the entrapment of free gas. We document the areal extent and sub-bottom depth of the BSR over a 77000 km(2)-wide region around southern Taiwan. In particular at least 30% of the seafloor, to as much as 60%, along the trenchward slope of the accretionary prism is underlain by the BSR. The BSR is located at shallower sub-bottom depths on the trenchward (western) side of the accretionary prism than on the arcward (eastern) side, even though water depths are similar, implying enhanced fluid flow from depth, resulting in a higher geothermal gradient as sediments are accreted and dewatered along the Manila trench.

We have compiled new free-air gravity anomaly (FAA) and magnetic anomaly maps, shedding light on the tectonics in the Taiwan-Luzon region. To have a suitable datum level for both the available gravity and magnetic anomaly data, the set of data from an ACT cruise, conducted during May 27 to June 21, 1996, was chosen as a reference. Based on the cross-over error analysis, all the other data were adjusted accordingly. Some satellite-derived, airborne or land data were also added to the compilation to obtain better coverage.Several major new insights into the Taiwan-Luzon region are revealed by the new maps. (1) A prominent NE-SW trending belt of gravity and magnetic anomalies is present in the onshore and offshore areas of southwestern Taiwan. The Peikang High is located on this belt. (2) Located in the offshore region west of Taiwan and to the north of the belt described above, the Taishi Basin, in contrast, occupies a relatively low FAA area. It could be regarded as a flexural basin on account of the loading of a thrust-and-fold belt in western Taiwan. (3) A probable NW-SE trending old transform fault is well imaged off southwestern Taiwan, which separates the lithosphere (plate) of the South China Sea from a trapped piece of the Philippine Sea plate. (4) Located east of the Luzon Are, the Huatung Basin contains several E-W trending magnetic reversals and two N-S trending old fracture zones. The Huatung Basin is separated from the West Philippine Basin by the "123E Fracture Zone". Accordingly, the Gagua Ridge corresponds to a transverse ridge bounding the 123E Fracture Zone. (5) The Luzon Are is abnormally concave toward the Manila Trench and becomes wider toward the south. The internal deformation of the Luzon Are in terms of several NE-SW discontinuities could be related to its collision with eastern Taiwan, (6) Three previously proposed NW-SE trending strike-slip faults in the southern Okinawa Trough, west of 123.5 degrees E, are well imaged on both the FAA and magnetic anomaly maps. Post-collisional volcanism off northeastern Taiwan occurs along these NW-SE trending faults.

This study presents three multi-channel deep seismic reflection profiles located in the south Ryukyu margin between 122°30′E and 123°30′E, where a N-S-trending oceanic ridge, the Gagua Ridge, is entering the subduction zone, for the purpose of examining the effects of ridge subduction on structures of the forearc region. Structural features which correspond to different stages of the oblique ridge subduction are observed. East of 123°E, a short-lived sequence of indentation, tunneling, then resumption of frontal accretion occurred in the accretionary wedge (the Yaeyama Ridge) as the subducted portion of the Gagua Ridge swept the overriding Ryukyu margin from below along the northwesterly convergent direction. Under the forearc basin, the subducted portion of the Gagua Ridge is uplifting the arc basement to form the Nanao Basement Rise which separates the sedimentary strata of the Nanao and East Nanao forearc basins. Results from this study suggest that the oblique subduction of the Gagua Ridge has not only affected accretionary wedge structures but also the arc basement of the south Ryukyu margin.

A new 500-m gridded digital bathymetric data set has been produced by compiling available shipboard bathymetric data supplemented by global bathymetric data sets in the area between 18 degrees N and 27 degrees N, and from 117 degrees E to 125 degrees E. Combined with topographic data from GTOPO30, a global land data set in 30 are-second grid spacing, this new digital elevation model (DEM) reveals the regional as well as local morphology of Taiwan and its offshore area. Spatial resolution of 1 km is achieved in the area off eastern and southern Taiwan where swath bathymetric data are available, In other areas where ship tracks are sparse, a spatial resolution of 4 are-minute is retained. This DEM provides the best topographic information at present on a regional scale, which helps to reveal many of the morphotectonic features related to the active tectonic processes of subduction and are-continent collision in this region.Using 2-D shaded topographic maps and 3-D physiographic diagrams generated from the DEM, the major morphologic features in each tectonic province of the region are presented. The Taiwan Strait is characterized by low relief sea floor with two NE-SW trending depressions and a shallow bank in the center of the strait, Submarine canyons mark the continental slope. In the area off southern Taiwan, N-S trending ridges and troughs are the major morphological features, however, several NE-SW trending lineaments have been identified in the Luzon forearc region. Off eastern Taiwan, submarine canyons and topographic features related to sedimentary processes along the eastern flank of the Luzon Are are revealed in detail. A prominent N-S trending linear ridge, the Gagua Ridge, located along 123 degrees E on the West Philippine Basin floor is entering the Ryukyu Trench and has produced a big re-entrant at the frontal portion of the Yaeyama Ridge. E-W to NW-SE trending linear shear zones are observed over the Yaeyama Ridge. These linear faults are the results of westward migration of the frontal portion of the accretionary wedge due to oblique convergence. A series of four forearc basins have been identified, Different depths of the forearc basins reflect lateral variation of the forearc region from oblique subduction to collision. Along the northern wall of the Southern Okinawa Trough, faulted slope and subsided shelf blocks suggest that this region is under post-collisional extension, and the active extension of the Southern Okinawa Trough is advancing westward toward Taiwan.

A side-scan sonar survey was conducted of Monterey Canyon and the San Gregorio fault zone, off shore of Monterey Bay. The acoustic character and morphology of the sonar images, enhanced by SeaBeam bathymetry, show the path of the San Gregorio fault zone across the shelf, upper slope, and Monterey Canyon. High backscatter linear features a few kilometers long and 100 to 200 m wide delineate the sea-floor expression of the fault zone on the shelf. Previous studies have shown that brachiopod pavements and carbonate crusts are the source of the lineations backscatter. In Monterey Canyon, the fault zone occurs where the path of the canyon makes a sharp bend from WNW to SSW (1800 m). Here, the fault is marked by NW–SE-trending, high reflectivity lineations that cross the canyon floor between 1850 m and 1900 m. The lineations can be traced to ridges on the northwestern canyon wall where they have ∼15 m of relief. Above the low-relief ridges, bowl-shaped features have been excavated on the canyon wall contributing to the widening of the canyon. We suggest that shear along the San Gregorio fault has led to the formation of the low-relief ridges near the canyon wall and that carbonate crusts, as along the shelf, may be the source of the high backscatter features on the canyon floor. The path of the fault zone across the upper slope is marked by elongated tributary canyons with high backscatter floors and `U'-shaped cross-sectional profiles. Linear features and stepped scarps suggestive of recent crustal movement and mass-wasting, occur on the walls and floors of these canyons. Three magnitude-4 earthquakes have occurred within the last 30 years in the vicinity of the canyons that may have contributed to the observed features. As shown by others, motion along the fault zone has juxtaposed diverse lithologies that outcrop on the canyon walls. Gully morphology and the canyon's drainage patterns have been influenced by the substrate into which the gullies have formed.

The Taitung Canyon originates at the southern end of the Longitudinal Valley. It runs southward along the axis of the Taitung Trough. The canyon turns eastward into the Huatung Basin, after crossing the Luzon arc between the volcanic islands of Lanyu and Lutao. It then flows northeastward for about 170 km and merges,vith the Hualien Canyon near the Ryukyu Trench, thus forming the largest canyon in the Huatung Basin. High resolution bathymetric data, and several multi-channel seismic profiles are used to describe the structural fabric in the vicinity of the Taitung Canyon and the factors controlling its path within the Huatung Basin. Crossing the eastern slope of the Lanyu-Lutao volcanic ridge, the head of the Taitung Canyon is fan shaped and its entrenchment rapidly increases downslope. Throughout the canyon's upper and central portions, the channel depth ranges from 300 to 500 m with respect to the surrounding seafloor. The canyon's levees are generally asymmetric and turbidite overbank deposits are observed. Then, a basement high, trending parallel to the Gagua Ridge, forces the path of the Taitung Canyon to turn 90 degrees toward the northwest. As the canyon reaches the Ryukyu Trench, the width of the main channel has decreased from 14 km near the Luzon arc, to less than 200 m at the outer-slope of the Ryukyu Trench. The importance of structural controls, such as basement highs and faulting, on the canyon's development are examined. Thus, the existence of a strike-slip fault system, affecting the oceanic basement in the Huatung Basin, and its role in controlling the path of the canyon are discussed.