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Using bathymetric and multichannel seismic (MCS) data, we explored the volcanic influence on the bathymetric and stratigraphic features of the Mianhua Terrace. The Mianhua Terrace occupies the marine counterpart of the Northern Taiwan Volcanic Zone (NTVZ) along the collapsed Taiwan orogenic wedge and is dominated by post-collisional magmatism and extensional structures. The bathymetric data showed several semicircular-shaped features near the shelf break. The MCS profiles showed that the Pleistocene unconformity buried beneath the Mianhua Terrace is partly difficult to observe due to seafloor multiples, suggesting that the seafloor is dominated by physically hard lithology, probably volcanic lavas. We interpreted the high-amplitude reflectors and their projected seafloor relief as intrusive sills and associated extrusive edifice. Similarly, we interpreted high-amplitude reflectors in the vicinity of normal faults as intrusive sills emplaced and facilitated by fault structures. A volcanic or hydrothermal mound was also recognized. We propose that the Mianhua Terrace is a breached ramp in a transfer zone between the tips of two successive normal faults along the shelf break. Once the fault tips reactivate and extend toward each other, the Mianhua Terrace may continue to collapse, leading to catastrophic volcanic or associated hydrothermal events.

In this study, we compiled recently collected (from 2005 to 2015) and previously reported (published and open access) gravity data, including land, shipborne and satellite-derived data, for Taiwan and its surrounding regions. Based on the cross-over error analysis, all data were adjusted; and, new Free-air gravity anomalies were obtained, shedding light on the tectonics of the region. To obtain the Bouguer gravity anomalies, the densities of land terrain and marine sediments were assumed to be 2.53 and 1.80 g/cm3, respectively. The updated gravity dataset was gridded with a spacing of one arc-minute. Several previously unnoticed gravity features are revealed by the new maps and can be used in a broad range of applications: (1) An isolated gravity high is located between the Shoushan and the Kaoping Canyon off southwest Taiwan. (2) Along the Luzon Arc, both Free-air and Bouguer gravity anomaly maps reveal a significant gravity discontinuity feature at the latitude of 21°20′N. (3) In the southwestern Okinawa Trough, the NE-SW trending cross-back-arc volcanic trail (CBVT) marks the low-high gravity anomaly (both Free-air and Bouguer) boundary.

The architecture and distribution of mud diapirs are shaped by tectonic activity, sediment filling and unbalanced loading characteristics. Mud diapir development also controls spatial variations of intraslope basins in slope areas and can spur upward fluid migration with diapiric intrusion. The offshore area of southwestern Taiwan is an incipient collision zone in which thick sequences of deep marine sediments filled a rapidly subsided foredeep basin during the Pliocene. Large volumes of deposited sediment serve as source materials of diapiric ridges that extend NNE-SSW, and some mud diapirs even extend to on land SW Taiwan with subsurface signatures of gas. This study examines relationships between mud diapir and intraslope basin development in convergent tectonics through seismic and bathymetry data analyses. Four types of mud diapirs are identified: (1) buried symmetrical diapirs; (2) symmetrical diapirs extruded above the seafloor; (3) asymmetric and irregular diapirs; and (4) small individual diapirs manifested as mud intrusions found in local areas. A 3-stage model is proposed as a tool for describing the development and distribution of these types of diapirs. We further examine the relationship between mud diapirs and intraslope basin development patterns by analyzing 2D and 3D seismic images to reveal structural and sedimentary processes occurring in the Lower Fangliao Basin. This basin is characterized by BSR and amplitude anomalies of seismic profiles and is a prospect of the Taiwanese gas hydrate investigation project. An 8-stage development model with six depositional units is proposed as a means to explain the evolution of diapirs, submarine canyons, and fold and fault activities in the Lower Fangliao Basin, in turn revealing the relationship between mud diapir formation and intraslope basin development offshore of southwestern Taiwan.

Based on the multi-channel seismic (MCS) and gravity data offshore north of Taiping Island (Itu Aba Island) in the Spratly Islands (Nansha Islands), we revisited the crustal structures in the northern part of the southern margin of the Southwest (SW) Sub-basin of the South China Sea (SCS). The MCS data suggest that the basement structural highs in the southwest margin of the SCS are dominated by both fault blocks and volcanic basement structures that probably formed along with the basement faults. The gravity modeling results reveal that these volcanic basement structures were probably associated with the high velocity or density lower crust (HVDLC), suggesting that the southern margin of the SW Sub-basin serves as an intermediate margin. Based on the tectonic features in the SCS margins, including (1) the transition between the magma-poor margins of the Northwest (NW) Sub-basin and intermediate margins of the East and SW Sub-basins; (2) the cessation of the seafloor spreading in the NW Sub-basin being succeeded by a major ridge jump event, which was very likely to reflect an active mantle upwelling event; (3) the extensive distribution of the HVDLC beneath in the well-investigated northern margin of the East Sub-basin and as explored in the SW Sub-basin in this study; and (4) basement faulting and volcanism shown in this study that may be related to the HVDLC and hyper-extension, we proposed a conceptual model to interpret the origin of the HVDLC in the southern margin of the SW Sub-basin. The margin of the SCS basin was magma-poor at the time it occurred. An active mantle upwelling event caused by small-scale mantle convection, possibly related to the influence of the nascent Hainan mantle plume, was formed subsequently, resulting in a southward ridge jump and the HVDLC beneath the current margins of the East and SW Sub-basins. The East and SW Sub-basins continued to spread, latitudinally dividing their HVDLCs as the margins separated accordingly. Afterwards, the hyper-extension in the distal margins may also be responsible for a crust weakening zone wherein the subsequent volcanic events could occur.

Taiping Island, also known as Itu Aba, is the largest natural terrestrial landmass in the South China Sea and is centrally located. Using bathymetry and marine multi-channel seismic data, we explored the seismic stratigraphic features of the offshore and isolated carbonate platform north of Taiping Island. The western flank of the carbonate platform is characterized by an intercalation between high-amplitude and low-amplitude reflections, showing the landward and seaward migration of the platform foreslope deposits. In addition, there are two offshore carbonate build-ups that are underlain by normal faults. Six sequence boundaries and five depositional sequences caused by eustatic sea level cycles are identified and correlated with the eustatic sea level change chart. Although the evolution of the seismic sequences is partly controlled by local tectonics, the overall stacking pattern of the sedimentary strata in our study area reveals five third-order cycles and one second-order cycle, which is in accordance with the eustatic sea level chart. Additionally, the formations of the Western Taiping Seamount Group and the Zhenghe-Daoming Trough are preliminarily analyzed based on seismic data.

During seismic investigations, multiple and unexpected sources may cause serious interference on seismic records, and coherent noise generated by another unwanted active source could result in extremely poor data quality. Because airgun arrays have been widely used as the sound source in marine seismic surveys, the noise generated by another airgun array usually has similar characteristics to the primary signals in both frequency bands and wave forms, so the suppression of this type of coherent noise is very difficult. In practice, seismic crews try to avoid conducting multiple surveys simultaneously in a same area, so the source interference problem normally does not occur, and suppression of coherent noise from another active source has rarely been discussed and proposed before. This paper presents a dataset in which part of the records are contaminated by shot noise from another seismic vessel, and proposes a hybrid approach to suppress the coherent noise from that unwanted seismic source. Noise subtraction and primary signal preservation within different data properties are considered to begin the noise suppression. Based on different noise characteristics from various source directions and wave propagation paths, coherence noise can be separated from primary signals in frequency–wave number (F–K), frequency–time (F–T) and intercept time–slowness (tau–p) domains, respectively. This hybrid coherent noise suppression approach involves applying three different filters, F–K, F–T and tau–p, to the contaminated dataset. Our results show that most of the coherent noise generated by another seismic source could be suppressed, and seismic images could be substantially improved.

Whether the formation of the isolated sand body deposition in the forebulge area of a foreland basin system is structure- or deposition-controlled has puzzled geologists for decades, although sand body deposition is generally believed to be indicative of the position of the flexural forebulge in a foreland basin. The formation of a modern sand body in the forebulge area is thus examined by multi-scale geophysical observations based on combined reflection seismic profiles and compressed high-intensity radar pulse (CHIRP) profiles across the sand deposition along the forebulge of the Western Taiwan Foreland Basin (WTFB), which is a Late Miocene-present foreland basin in the overfilled stage. These profiles suggest that the accumulation of the sand deposits along the forebulge of the WTFB is not directly associated with forebulge faultings. The relief map of the forebulge deposit substratum shows a northwestward tilting slope, and the isopach of the forebulge sand body indicates that a large part of the sand body accumulated along the axis of the Taiwan Strait and the subdued forebulge of the WTFB. The difference between the prevailing directions of tidal currents between the Taiwan Strait and the East China Sea reflects the probable sedimentary influence of the cratonward migrating fold-thrust belt within a foreland shelf. We suggest that the formation and distribution of the sand deposits along the forebulge of the WTFB are generally controlled not only by the transverse downslope sedimentation but also longitudinal hydrodynamic processes at distal parts of the foreland basin. Our explanation provides a plausible tectono-sedimentary cause of the sand body deposition in the forebulge area in an overfilled foreland basin. The sedimentary dynamics of the sand body in the Taiwan Strait may be applicable for understanding the formation of isolated sand bodies in the distal part of the Cretaceous Western Interior Foreland Basin.

Bottom simulating reflectors (BSRs), high methane flux, shallow sulfide/methane interfaces, fluids venting from the seafloor, authigenic carbonates within sediments, methane reefs, and self-biomes are common seafloor features in the area off southwest Taiwan. The geophysical and geochemical signatures of these features suggest a high potential for gas hydrate (GH) reservoirs in the region. The BSRs are typically interpreted as the boundary between free gases and solid hydrate, whereas the upper reaches of the hydrate stability zone and the distribution of gas hydrate in shallow sediments are not well understood. This study shows the first results of a marine controlled-source electromagnetic survey, conducted in the offshore area of SW Taiwan in 2010. The survey aimed to provide electrical resistivity information of the shallow sediments. Three target areas were surveyed: (1) an area to the southeast of the Xiaoliuchiu Island (gas seep G96), (2) an area in the west of the Yung-An Ridge (YAR) and (3) an area in the northwest of the Good Weather Ridge (GWR). In total, fourteen survey lines with a total length of 72 km were completed. Our preliminary results show that relatively high resistivity anomalies occur within pockmarks and at gas seepage sites. The apparent resistivity is estimated to be about 1 Ohm-m higher than background in G96 and YAR sites, while an anomaly up to 2 Ohm-m is found in the GWR. At gas seep site G96, the high resistivity anomaly may be due to the existence of authigenic carbonates; whereas, the high resistivity anomaly in the NW of the GWR site may also be due to the existence of gas hydrate in the shallow seabed. Based on the resistivity anomaly, the gas hydrate saturation is about 16% in the shallow sediments below the pockmark area in the northwest side of the GWR site.

This book contains six chapters dealing with the investigation of seismic and sequence stratigraphy and integrated stratigraphy, including the stratigraphic unconformities, in different geological settings and using several techniques and methods, including the seismo-stratigraphic and the sequence stratigraphic analysis, the field geological survey, the well log stratigraphic interpretation and the lithologic and palaeobotanical data. Book chapters were separated into two main sections: i) Seismic and sequence stratigraphy, ii) Integrated stratigraphy. There are three chapters in the first section, including the application of sequence and seismic stratigraphy to the fine-grained shales, to the fluvial facies and depositional environments and to the Late Miocene geological structures offshore of Taiwan. In the second section, there are three chapters dealing with the integrated stratigraphic investigation of Jurassic deposits of the southern Siberian platform, with the stratigraphic unconformities, reviewing the related geological concepts and studying examples from Middle-Upper Paleozoic successions and finally, with the integrated stratigraphy of the Cenozoic deposits of the Andean foreland basin (north-western Argentina).