The relationship between earthquakes and fluid pressure variations remains debated, particularly regarding whether surface fluid anomalies reflect pore pressure changes at seismogenic depth. Anomalous fluid emissions at the Chung-lun mud pool in southwestern Taiwan were continuously monitored between 2008 and 2010, with quantitative analyses focusing on periods of stable observations from mid-2009 to late 2010 using water level sensors and a digital camera system. Long-term anomalies were characterized by sustained variations in water levels and changes in degassing behavior that were independent of precipitation. In four out of five cases, these anomalies occurred in close temporal association with nearby earthquakes, indicating a systematic temporal relationship rather than a simple random coincidence. Short-term variations were linked primarily to rainfall events, while long-term discharge anomalies are interpreted as being consistent with pore pressure perturbations at depth, based on indirect surface observations and the exclusion of meteorological and shallow hydrological controls, rather than direct measurements within the seismogenic zone. The results hypothesize that pore fluid overpressure at depth can modulate both fault stability and surface fluid discharge, consistent with the concept of fault valve behavior. Some anomalies were recorded prior to seismic events, suggesting that gradual increases in pore pressure may contribute to stress evolution in critically stressed thrust faults, although the coupling is not deterministic. The integration of instrumental and photographic observations at Chung-lun demonstrates the potential of mud pools as natural observatories for geodynamically induced interactions between tectonic activity and fluid transport and emission. It highlights their important role as valuable components in regional earthquake monitoring networks.

The island of Mindoro forms the northeastern part of the Palawan Continental Terrane, a terrane that is considered to have formed at the southwestern margin of SE China and subsequently drifted into its present position as a consequence of the opening of the South China Sea. Using U-Pb age determinations of detrital zircon in sedimentary rocks and of current river sediments, this study aims to establish the relationships between the various geological units exposed on this island. The results indicate that some established units have left no trace in the current river sediments. On the other hand, some ages found in the age distributions of river sediments have no known source in the studied units. The data presented support the concept that the Northeast Mindoro Block is distinct from the Southwest Mindoro Block. Both blocks contain units that may be correlated with units exposed in northern and southern Palawan, and thus both appear to be related to the SE China margin of the South China block.

Dissolved organic carbon (DOC) and volatile fatty acids (VFAs) play key roles in the carbon cycling of marine sediment. Both microbially or thermally activated cracking of organic matter often produces high quantities of DOC and VFAs. To uncover the distribution pattern of DOC and VFAs in sediments under both impacts, a submarine mud volcano (SMV), was chosen to denote a model system that could witness how microbial activities react under the mixing of seawater and deeply-sourced fluids in a subsurface environment. We examined the concentration profiles of DOC and several VFAs (lactate, formate, acetate, propionate, and butyrate) in pore water, covering both sulfate reduction and methanogenesis zones, and further numerically modeled six porewater species (DOC, bromide, calcium, magnesium, ammonium, and total alkalinity) to quantify their fluxes from depth as well as the rates of in-situ microbial processes. Apparently, bulk DOC concentrations fluctuated with depths, probably primarily controlled by in situ microbial processes. Lactate was detectable in some samples, while propionate and butyrate were under detection limit. Acetate and formate concentrations were consistently and uniformly low throughout all biogeochemical zones, with a slightly increasing trend with depth at the center of the SMV, suggesting active utilization and turnover by the terminal steps of organic matter mineralization. The numerical modeling suggests that most DOC patterns were primarily influenced by in-situ organic matter degradation, while the impact of upward migrating fluid become more significant at center sites. The calculation of the Gibbs energy of metabolic redox reactions reveals that acetoclastic sulfate reduction yields the highest energy throughout sediment columns and may co-exist with methanogenesis below sulfate reduction zone. In contrast, acetoclastic methanogenesis yields higher energy within sulfate reduction zone than below that region, suggesting it is thermodynamically feasible to co-occur with sulfate reduction in dynamic SMV environments.

A new downhole sampler, GTFSampler, is designed to collect in-situ geothermal fluids and preserve the conditions of the sampling depth. The GTFSampler is mainly composed of a stainless sampling cylinder and a gas driven shut-in valve, which are hosted in an equipment protector. The sampler assembly connects to a stainless tube for hoisting in a borehole and switching the shut-in valve by changing the inner pressure of the stainless tube on surface. Selected gas (e.g., N-2 or noble gas) is pre-filled to the sampling cylinder at a fixed pressure before sampling. The GTFSampler is also equipped with a traditional mercury maximum thermometer. The comparison between the measured temperature and calculated thermodynamic equilibrium temperature from saturation degree of minerals is used to verify the representativeness of downhole sample collection, on-site sample separation and laboratory analysis. In the borehole IC-19 deployment in Chingshui geothermal field, Ilan, Taiwan, the measured temperature at 800 m are ca. 190 similar to 198 degrees C. Three downhole samplings were conducted in this study, i.e., the first and second samplings were deployed in discharged borehole condition and the third sampling in closed borehole condition. The first and second samplings showed that the theoretical equilibrium temperature calculated by geochemical modeling from fluid composition is very close to the measured temperature at the sampling depth. However, no convergence solution for equilibrium temperature is obtained for the third sampling, indicating certain interference in geothermal water quality by the natural convection inside the borehole as the control valve is closed. In summary, the GTFSampler and its corresponding sampling procedures successfully collect the downhole geothermal fluids.

Previous studies have revealed that gas compositions of fluid samples collected from southwestern Taiwan, where many hot springs and mud volcanoes are distributed along with tectonic structures, show significant variation before and after some disaster seismic events. Such variations, including radon activity, CH4/CO2, and 3He/4He ratios of gas compositions, are considered precursors of earthquakes in this area. An automatic system for continuous on-line gas monitoring and groundwater sampling was established at Yun-Shui (YS), where an artesian well located at an active fault zone in SW Taiwan, to validate the relationship between fluid compositions and seismicity. It is equipped with a quadrupole mass spectrometer (QMS) and a radon detector for in-situ measurement of the dissolved gas composition. Variations of dissolved gas compositions are transmitted to the laboratory through the internet. Furthermore, a syringe pump apparatus for the retrieval and temporal analysis of helium (SPARTAH) is also installed for off-line laboratory analysis for obtaining the detailed time-series records of helium, hydrogen, oxygen, and dissolved inorganic carbon (DIC) isotopic compositions as well as dissolved inorganic carbon and chloride concentration of water samples at this station. After continuous monitoring for several months, two substantial anomalies of multiparameter were observed prior to the significant earthquakes. This automated system has been demonstrated to be feasible for long-term continuous seismo-geochemical research in this area.

Qualitative and quantitative assessments of fluid cycling are essential to address the role and transport of deeply sourced fluids in subduction systems. In this study, sediment cores distributed across a submarine mud volcano (SMV) offshore southwestern Taiwan were investigated to determine the characteristics of fluids generated through the convergence between the Eurasian and Phillippine Sea Plates. The low dissolved chloride concentration combined with the enrichment of 18 O, and depletion of 2 H of pore fluids suggest the discharge of deep freshwater formed by smectite dehydration at an equilibrium temperature of 100 to 150 °C. The upward fluid velocities, decreasing from 2.0 to 5.0 cm yr −1 at the center to a negligible value at margin sites, varied with the rate and efficiency of anaerobic methanotrophy, demonstrating the impact of fluid migration on biogeochemical processes and carbon cycling. By extrapolating the velocity pattern, the flux of fluids exported from 13 SMVs into seawater amounted up to 1.3–2.5 × 10 7 kg yr −1 , a quantity accounting for 1.1–28.6% of the smectite-bound water originally stored in the incoming sediments. Our results imply that SMVs could act as a conduit to channel the fluids produced from great depth/temperature into seafloor environments in a subduction system of the western Pacific Ocean.

We report new noble gas signatures of groundwaters, hot springs, and bedrock samples from two major fault systems that form the plate boundary suture between the Eurasian Plate and the Philippines ...

We report noble gas signatures of groundwater, hot springs, and bedrock samples from a major fault system that separates regional-scale blocks of accreted, continental materials in southern Taiwan. Despite the continental setting, the isotopic signatures argue for the presence of mantle derived fluids, suggesting that the active fault system is deep-seated. This is consistent with deep, non-volcanic tremors identified in the same area. We speculate that the mantle fluids are escaping along a crustal-scale fault marked by clusters of non-volcanic tremors directly beneath the southern Central Range. The evidence of these tremors and electrical conductivity anomalies along the strike of the fault recognized previously correlated up dip with the surface trace of a major active fault support the hypothesis.

Taiwan is tectonically situated in an oblique collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). Continuous observations of gamma rays at the Yangmingshan (YMSG) station and soil radon at the Tapingti (TPT) station were recorded in the volcanic area and around a major fault zone, respectively, in Taiwan for seismic studies. A number of anomalous high gamma ray counts and radon concentrations at certain times were found. It is noted that significant increases of soil radon concentrations were observed and followed by the increase in gamma rays a few days to a few weeks before earthquakes that occurred in northeastern Taiwan. Earthquakes such as these are usually related to the subduction of the PSP beneath the EP to the north along the subduction zone in northern Taiwan (e.g., ML=6.4, April 20, 2015). It is suggested that the preseismic activity may be associated with slow geodynamic processes at the subduction interface, leading to the PSP movement triggering radon enhancements at the TPT station. Furthermore, the further movement of the PSP might be blocked by the EP, with the accumulated elastic stress resulting in the increase of gamma rays due to the increase in porosity and fractures below the YMSG station. The continuous monitoring of the multiple parameters can improve the understanding of the relationship between the observed radon and gamma ray variations and the regional crustal stress/strain in north and northeastern Taiwan.

Sulfate reduction could go through dissimilatory sulfate reduction and anaerobic methane oxidation couple with sulfate reduction (AOM-SR) with pyrite the end product. While ACM-SR is an important process in oxidizing methane and limiting methane entering the ocean, there is limited information available regarding pyrite formation and preservation under methane dominated environment. The purpose of this study is to report pyrite formation and preservation at a methane dominated environment, the YuanAn Ridge, where methane seeps have been observed, and to evaluate how would that differ from typical anoxic environment. Pore water methane, sulfate, dissolved sulfide, barium, and sediment pyrite, barium/Al ratio and organic carbon in sediments were analyzed from sediments collected by piston cores on board the R/V Ocean Researcher I (OR-I) from the study environment. The results showed methane flux is controlling pyrite formation in this methane dominated environment. Pyrite concentration is linearly correlated with methane flux with exceptions to shallower sulfate methane transition zone (SMTZ) sites where methane could have vent directly to the overlying water and contribute less to the pyrite formation. The more methane entering the SMTZ, the more pyrite formed and preserved in the sulfate methane transition zone sediments. Authigenic pyrite from dissimilatory sulfate reduction is a small fraction of the pyrite found in the methane dominant and low in organic carbon environment, with majority of pyrite derived from AOM-SR. Large spatial variations on rate of sulfate reduction, pyrite and methane concentrations were observed in the studied area sediments. Depth of sulfate methane transition zone varied between 1 and 14 m and is a log function of methane flux. Pore water sulfate profiles displayed three different types, linear, concave up and down, indicating methane flux have varied in time. Pyrite burial efficiency is high, approximately 50% of sulfate entering the SMTZ were preserved in sediments as pyrite. This efficiency of sulfate reduction through AOM-SR is much higher than pyrite formation from dissimilatory sulfate reduction in normal marine sediments, The AOM-SR and pyrite formation occurred at depth within the SMTZ favor a higher degree of pyrite preservation. Time require for the pyrite formation is about 4400 years in the YAR sediments, based on diffusion model calculation of barium sulfate precipitation.

The major processes that determine the distribution of methane (CH4) in anoxic marine sediments are methanogenesis and the anaerobic oxidation of methane (AOM), with organoclastic sulfate reduction exerting an important secondary control. However, the factors leading to the distribution of stable carbon isotopes (δ13C) of CH4 are currently poorly understood, in particular the commonly-observed minimum in δ13C-CH4 at the sulfate-methane transition (SMT) where AOM rates reach maximum values. Conventional isotope systematics predict 13C-enrichment of CH4 in the SMT due to preferential 12CH4 consumption by AOM. Two hypotheses put forward to explain this discrepancy are the addition of 12C-enriched CH4 to porewaters by methanogenesis in close proximity to AOM, and enzymatically-mediated carbon isotope equilibrium between forward and backward AOM at low concentrations of sulfate. To examine this in more detail, field data including δ13C of CH4 and dissolved inorganic carbon (DIC) from the continental margin offshore southwestern Taiwan were simulated with a reaction-transport model. Model simulations showed that the minima in δ13C-CH4 and δ13C-DIC in the SMT could only be simulated with carbon isotope equilibrium during AOM. The potential for carbon cycling between methanogenesis and AOM in and just below the SMT was insignificant due to very low rates of methanogenesis. Backward AOM also gives rise to a pronounced kink in the δ13C-DIC profile several meters below the SMT that has been observed in previous studies. We suggest that this kink marks the true base of the SMT where forward and backward AOM are operating at very low rates, possibly sustained by cryptic sulfur cycling or barite dissolution.

The study area is close to the boundary of three tectonic plates (Anatolian, Arabian, and African plates) and is characterized by important tectonic lineaments, which consist mainly of the Dead Sea Fault (DSF), the Karasu Fault, and the East Anatolian Fault (EAF) systems. To understand the origin of soil gas emanation and its relationships with the tectonics of the Amik Basin (Hatay), a detailed soil gas sampling was systematically performed. Together with CO2 flux measurements, > 220 soil gas samples were analyzed for Rn and CO2 concentrations. The distribution of soil Rn (kBq/m3), CO2 concentration (ppm), and CO2 flux (g/m2/day) in the area appears as a point source (spot) and/or diffuses (halo) anomalies along the buried faults/fractures due to crustal leaks. The results revealed that Rn and CO2 concentrations in the soil gas show anomalous values at the specific positions in the Amik Basin. The trace of these anomalous values is coincident with the N-S trending DSF. CO2 is believed to act as a carrier for Rn gas. Based on the Rn and CO2 concentrations of soil gases, at least three gas components are required to explain the observed variations. In addition to the atmospheric component, two other gas sources can be recognized. One is the deep crust component, which exhibits high Rn and CO2 concentrations, and is considered the best indicator for the surface location of fault/fracture zones in the region. The other component is a shallower gas source with high Rn concentration and low CO2 concentration. Moreover, He isotopic compositions of representative samples vary from 0.94 to 0.99 Ra, illustrating that most samples have a soil air component and may have mixed with some crustal component, without significant input of the mantle component. Based on the repeated measurements at a few sites, soil gas concentrations at the same site were observed to be higher in 2014 than in 2013, which may be associated with the activity of the DSF in 2013–2014. This suggests that soil gas variations at fault zone are closely related to the local crustal stress, and hence are suitable for monitoring fault activities.

To systematically quantify the production, consumption, and migration of methane, 210 sediment cores were collected from offshore southwestern Taiwan and analyzed for their gas and aqueous geochemistry. These data, combined with published results, were used to calculate the diffusive methane fluxes across different geochemical transitions and to develop scenarios of mass balance and constrain deep microbial and thermogenic methane production rates within the accretionary prism. The results showed that methane diffusive fluxes ranged from 2.71 x 10(-3) to 2.78 x 10(-1) and from -1.88 x 10(-1) to 3.97 mmol m(-2) d(-1) at the sulfate-methane-transition-zone (SMTZ) and sediment-seawater interfaces, respectively. High methane fluxes tend to be associated with structural features, suggesting a strong structural control on the methane transport. A significant portion of ascending methane (>50%) is consumed by anaerobic oxidation of methane at the SMTZ at most sites, indicating effective biological filtration. Gas compositions and isotopes revealed a transition from the predominance of microbial methane in the passive margin to thermogenic methane at the upper slope of the active margin and onshore mud volcanoes. Methane production and consumption at shallow depths were nearly offset with a small fraction of residual methane discharged into seawater. The flux imbalance arose primarily due to the larger production of methane through deep microbial and thermogenic processes at a magnitude of 1512-43,096 Tg Myr(-1) and could be likely accounted for by the sequestration of methane into hydrate forms, and clay absorption.

In this study, we used pore water dissolved inorganic carbon (DIC), SO42-, Ca2+ and Mg2+ gradients at the sulfate-methane transition zone (SMTZ) to estimate biogeochemical fluxes for cored sediments collected offshore SW Taiwan. Net DIC flux changes (Delta(DIC-Prod)) were applied to determine the proportion of sulfate consumption by organic matter oxidation (heterotrophic sulfate reduction) and anaerobic oxidation of methane (AOM), and to determine reliable CH4 fluxes at the SMTZ. Our results show that SO42- profiles are mainly controlled by AOM rather than heterotrophic sulfate reduction. Refinement of CH4 flux estimates enhance our understanding of methane abundance from deep carbon reservoirs to the SMTZ. Concentrations of chloride (Cl-), bromide (Br-) and iodide (I-) dissolved in pore water were used to identify potential sources that control fluid compositions and the behavior of dissolved ions. Constant Cl- concentrations throughout similar to 30 m sediment suggest no influence of gas hydrates for the compositions within the core. Bromide (Br-) and Iodine (I-) concentrations increase with sediment depth. The I-/Br- ratio appears to reflect organic matter degradation. SO42- concentrations decrease with sediment depth at a constant rate, and sediment depth profiles of Br- and I- concentrations suggests diffusion as the main transport mechanism. Therefore diffusive flux calculations are reasonable. Coring sites with high CH4 fluxes are more common in the accretionary wedge, amongst thrust faults and fractures, than in the passive continental margin offshore southwestern Taiwan. AOM reactions are a major sink for CH4 passing upward through the SMTZ and prevent high methane fluxes in the water column and to the atmosphere.

Taiwan is tectonically situated in a terrain resulting from the oblique collision between the Philippine Sea plate and the continental margin of the Asiatic plate, with a continuous stress causing the density of strong-moderate earthquakes and regional active faults. The continuous time series of soil radon for earthquake studies have been recorded and some significant variations associated with strong earthquakes have been observed. Earthquake prediction is not still operative but these correlations should be added to the literature about seismo-geochemical transients associated to strong earthquakes. Rain-pore pressure related variations, crustal weakness at the studied faults system is consistent with the simultaneous radon anomalies observed. During the observations, a significant increase of soil radon concentrations was observed at Chunglun-T1 (CL-T1), Hsinhua (HH), Pingtung (PT), and Chihshan (CS) stations approximately two weeks before the Meinong earthquake (M-L = 6.6, 6 February 2016) in Southern Taiwan. The precursory changes in a multi-stations array may reflect the preparation stage of a large earthquake. Precursory signals are observed simultaneously and it can apply certain algorithms the approximate location and magnitude of the impending earthquake.

A submarine mud volcano (MV) known as TY1 is one of the largest conical structures found offshore southwestern Taiwan. Active gas bubble emissions at the flat crest of the mud volcano disperse sediment particles into the water column. Changes in the mud volcanism of TY1 were revealed by radiograph and grain size analysis of the sediment cores. Pb-210 geochronology was applied to the near-seafloor sediments to reveal the detailed mud volcanism from the deposition rate. In a 58-cm long sediment core taken from the northern margin of the crest, known as TY1-N.170, the size and frequency of the mud clasts decrease upward. The clasts are smaller than 8 mm above a sediment depth of 34 cm below the sea floor (cmbsf). Sediments between 0 and 19 cmbsf are massive, and particles larger than 2 mm are absent. An enrichment of coarse, silt-sized particles in the massive sediment unit and the restricted distribution of the unit suggest that the massive unit was generated by re deposition of sediment particles that were dispersed into the water column by gas bubble emission. These characteristics suggest that during the last mud volcanism of TY1, there was a decrease in mud eruption energy, and gas bubble emission became the main activity. In core TY1-S.440, taken from the southern slope, a massive sediment unit enriched with coarse, silt-sized particles, is intercalated between mud breccia structures. This suggests repeated mud breccia flows caused by TY1. The excess 21 Pb activity present in the massive sediment unit of TY1-N.170 suggests activation of gas bubble emission. In the massive unit, a decrease in excess Pb-210 activity appears upward toward the seafloor. The highest value is 3.1 dpm/g at 19.8 cmbsf (26.4 g/cm(2) in cumulative mass); values lower than 1.0 dpm/g are distributed 2.8-6.8 cmbsf (3.6-8.8 g/cm(2)). The upwardly decreasing trend is opposite that of the reference core from which a reasonable areal sedimentation rate was obtained using a constant-flux constant-sedimentation model. The anomalous depth profile at the massive unit indicates an increasing rate of sediment deposition, which originated from the activation of gas bubble emission.

We propose an improved method for precise sulfur isotopic measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in conjunction with a membrane desolvation nebulization system. The problems of sulfur loss through the membrane desolvation apparatus are carefully quantified and resolved. The method overcomes low intrinsic sulfur transmission through the instrument, which was initially 1% when operating at a desolvation temperature of 160 degrees C. Sulfur loss through the membrane desolvation apparatus was resolved by doping with sodium. A Na/S ratio of 2 mol mol(-1) produced sulfur transmissions with 98% recovery. Samples of 3 nmol (100 ng) sulfur achieved an external precision of +/- 0.18 parts per thousand (2 SD) for delta S-34 and +/- 0.10 parts per thousand (2 SD) for Delta S-33 (uppercase delta expresses the extent of mass-independent isotopic fractionation). Measurements made on certified reference materials and in-house standards demonstrate analytical accuracy and reproducibility. We applied the method to examine microbial-induced sulfur transformation in marine sediment pore waters from the sulfate-methane transition zone. The technique is quite versatile, and can be applied to a range of materials, including natural waters and minerals. (C) 2017 Elsevier B.V. All rights reserved.

In this paper, we study (1) the spatial anomalies and (2) the temporal anomalies of soil gas in northern Taiwan. The spatial anomalies of soil gas are related to tectonic faults, while the temporal anomalies of soil gas are associated with pre-earthquake activities. Detailed soil gas sampling was systematically performed, and the analysis of the collected gas species shows that high helium and nitrogen concentrations appear in samples from specific sites, which coincide with the structural setting of the area studied. This analysis indicates the possibility of using these soil gases to determine fault zones in the studied area. Based on the soil gas data, a station (Tapingti) for automatic soil gas monitoring was constructed on an appropriate site at the fault zone. Some anomalous high radon concentrations at certain times can be identified from the dataset, which was generated by the continuous monitoring of soil gas for over a year. Notably, many of these anomalies were observed several hours to a few days before the earthquakes (M-L > 3) that occurred in northern Taiwan. By combining the information of epicenters and fault plane solutions of these earthquakes, we find that the shallow earthquakes (<15 km) were mainly strike slip and normal-type earthquakes, and concentrated within a distance of 30 km to the monitoring site (Group A). The deep earthquakes (>20 km) were mainly thrust-type earthquakes and distributed in greater distances (>45 km) east of the monitoring site (Group B). Such focal mechanisms of earthquakes suggest an extensional and compressional structural domain in the continental crust for Group A and Group B earthquakes, respectively. It is suggested that the pre-earthquake activities associated with the seismicity of Group B may be transmitted along the major decollement in the region below the Tapingti station, leading to the observed soil gas enhancements. (C) 2017 Elsevier Ltd. All rights reserved.

•The estimated total soil CO2 emission of the northern GYR is ∼1.50×107ta−1.•Fault systems act as uprising conduits for soil CO2 and mantle-derived volatiles.•An enriched mantle wedge source is proposed for origin of the GYR volatiles.•Sedimentary carbonate in the Lhasa terrane is the dominant carbon source.