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A continuous bi-weekly water isotope analysis (δ18O, δD, and d-excess) was done since 2015 from a subtropical reservoir (Feitsui Reservoir) in northern Taiwan. The Feitsui reservoir is an important national freshwater system, as it provides water for the large urban population of Taipei. The isotopic data reveals a multiyear pattern and it closely follows the rainfall isotopic composition. We made a simple mass-balance model using the rainfall isotopic composition, inflow and outflow volumes, and meteorological parameters that fit well (R2 = 0.55; p-value < 0.05) with the observed isotopic composition of the reservoir. Based on this model, we estimated reservoir isotopic composition for the previous 20 years (2001-2021). The model also well reproduced a few years of historical data reported in the literature. In the model, we noted two conspicuous patterns: (1) multiyear cyclicity in δ18O and d-excess, and (2) a long-term enriching trend in δ18O. These patterns were not so obvious in rainfall because of the strong seasonality, which gets diluted in the reservoir because of the longer water residence time (~6 months). However, these patterns became visible in rainfall isotopes after removing the seasonal cycles. The observed multiyear patterns do not resemble with the known multiyear global processes, such as ENSO, PDO, and the East Asian Monsoon Index. However, the role of these global processes cannot be ruled out completely. We believe that because of the unique geographical location of the island, multiple moisture sources (South China Sea and central/northern China), dual monsoons (summer and winter monsoons), and complex hydrometeorological processes, the signals of these multiyear global processes get modulated and modified. The long-term enriching trend in δ18O seems to be a consequence of climate change. The enriching trend is more vivid during the winters than summers. This indicates the possible role of global warming and the expansion of the tropics because the Tropics of Cancer passes through central Taiwan. There also remains a significant knowledge gap in understanding the role of winter monsoons in East Asia. This study highlights the importance and the need for rigorous climatic research in Taiwan because of its unique location which makes it highly sensitive to climate change. This study may also have implications for paleoclimatic studies because it highlights the complex hydrometeorology of the region.

Most earthquakes are considered to be caused by stress accumulating in and subsequently releasing from the crust. To extract non-linear and non-stationary earthquake-induced signals associated with stress accumulation, the Hilbert–Huang transform was utilized to filter long-term movements, short-term noise, and frequency-dependent (annual and semi-annual) variations from surface displacements measured by the global positioning system (GPS) in Taiwan. Earthquake-related surface displacements were expressed as horizontal directions (i.e., GPS azimuths) using the north–south and east–west components of residual GPS data to bypass influences resulted from the inhomogeneous nature of the crust. Analytical results showed that the relationships between earthquake occurrence and the aligned GPS azimuth passed the statistical test of the Molchan’s error diagram. Aligned GPS azimuths were in agreement with direction of earthquake-related P axes for 81% (26/32) studied events. Areas with the highest paralleling orientations of GPS azimuths appeared around epicenters several days to weeks before earthquake occurrence. Durations from aligned GPS azimuths to earthquake occurrence are roughly proportional to earthquake magnitude. Similar variations of the GPS azimuths were observed in GPS data containing or excluding co-seismic dislocation (i.e., one day before) in the temporal and spatial domain. These suggest that the aligned GPS azimuth could be a promising anomalous phenomenon for studying crustal deformation before earthquakes.

We report, for the first time, a detailed study at river water and hyporheic zone systems through collection and analyses of shallow sediments and selected source rocks, pore water, and river water from forty-two locations at the Chianan Plain (CP), SW Taiwan. The study was focused to understand the possible changes in the river water and sediment chemistry as a consequence of high arsenic (mean±SD=71.28±16.24μg/L, n=46) groundwater discharge to three major rivers in the plain. The study shows, except few locations, As concentration in river sediments corresponds to average As concentration in soil and upper crustal abundance and of source rock. Sequential extraction indicates that As is mostly bound to FeOOH. No enrichment of arsenic in river sediments or depletion of aqueous As and iron in pore water was observed down to the maximum sampling depth of 1.7m although manganese is enriched in sediments. Dissolved As concentrations in the river sediments are much lower compared to the hotspots in the CP aquifers. This suggests that no As attenuation processes are active or they cannot be detected in this zone. Mn precipitates at higher redox level compared to Fe and As and thus attenuates in the studied zone.

An obvious magnetic disturbance has been repeatedly observed by magnetometers located outside of urban areas in Yangmingshan National Park and has affected the monitoring of volcanic activity in the northern region of Taiwan. The disturbance has amplitudes of approximately 3–5 nanoteslas, and regularly appears for approximately 21 hours per day, except during the New Year period, when it is observed continuously for 45 hours. This change coincides with the annual extended operation of the Mass Rapid Transit (MRT) system. A 750-volt direct current drives the MRT trains and leaks to the ground, with a maximum value of approximately 1000 amperes measured along the routes. The disturbance is dominated by the unbalanced supply and return currents resulting from the leakage. The daily changes in the magnetic noise levels are correlated with the electricity consumption of the MRT system because the leakage is proportional to the use of electric power.

Based on global hydrological data, Taiwan has been classified as an area of water shortage. In some regions, and particularly during dry periods, groundwater is the only reliable water resource in Taiwan. This is particularly true for mountain regions. To determine the potential yield, and also to support sustainable management of groundwater resources, groundwater recharge must be estimated. The results of this study showed that there was a close relationship between measurements of the water table and the accumulated monthly precipitation in a well field close to Chien-Shih, Shinchu, NW Taiwan, which suggests that precipitation is the major source of recharge in the study area. However, the difference in the water table between the wet and dry seasons indicated that, in addition to precipitation, there is recharge from another stable source. We determined the pathway from, and the geological setting of, the recharge source areas by comparing precipitation events and temporal transformations in the water types. Out of four potential water types, the water corresponded to the Ca/Mg–SO4 2− type (III) at different points throughout the study period, indicating geochemical controls, such as dissolution–precipitation, dilution, cation exchange, silicate weathering, and mineralization. Meteoric water stored in the mountain region was another source of recharge that contributed to hydrochemical variability during the dry season. When this source was added, the mean δ18O value dropped from −15.8 to 1.4‰ in precipitation, from −9.6 to −7.8‰ in river water, from −9.1 to −6.9‰ in gully 1, from −7.4 to −5.8‰ in gully 2, and from −9.8 to −6.6‰ in groundwater. The isotopic compositions of Well C and Well W1 became lighter with additional recharge from the river, while those of Well E, Well W, and Well W2 became heavier during the rainy season. In the dry season, the isotopic composition was lighter in Well W1 and heavier in the other wells. It is worth noting that the isotopic composition of Well W1 was similar to that of the river, suggesting high connectivity between the river and Well W1, possibly through fractures.

Hydrologic responses to earthquakes and their mechanisms have been widely studied. Some responses have been attributed to increases in the vertical permeability. However, basic questions remain: How do increases in the vertical permeability occur? How frequently do they occur? Is there a quantitative measure for detecting the occurrence of aquitard breaching? We try to answer these questions by examining data from a dense network of ∼50 monitoring stations of clustered wells in a sedimentary basin near the epicenter of the 1999 M7.6 Chi-Chi earthquake in western Taiwan. While most stations show evidence that confined aquifers remained confined after the earthquake, about 10% of the stations show evidence of coseismic breaching of aquitards, creating vertical permeability as high as that of aquifers. The water levels in wells without evidence of coseismic breaching of aquitards show tidal responses similar to that of a confined aquifer before and after the earthquake. Those wells with evidence of coseismic breaching of aquitards, on the other hand, show distinctly different postseismic tidal response. Furthermore, the postseismic tidal response of different aquifers became strikingly similar, suggesting that the aquifers became hydraulically connected and the connection was maintained many months thereafter. Breaching of aquitards by large earthquakes has significant implications for a number of societal issues such as the safety of water resources, the security of underground waste repositories, and the production of oil and gas. The method demonstrated here may be used for detecting the occurrence of aquitard breaching by large earthquakes in other seismically active areas.

This study examines the relationships between seismo-deformation and seismo-conductivity anomalies during two M6 earthquakes that occurred on March 27th and June 2nd, 2013 in Taiwan. The Hilbert–Huang Transform is applied on surface displacement data to remove the effects of noise, semi-annual and annual cycles, and the long-term plate movements. The residual displacements have similar orientations when earthquake-related stress accumulates in the crust. Once the accumulated stress approaches the threshold for fault rupture, the orientations of the residual displacements generally become random, except in a small region near the epicenter. Interestingly, high-conductivity anomalies, which can be detected from the 3-component magnetic data via the magnetic transfer function, exist in places very close to this small region near the epicenter. Spatial and temporal correlations between the high-conductivity anomalies and the small region of seismo-deformation anomalies suggest that electric charges may migrate and become trapped in the region during seismogenic processes due to differential stress accumulation. These electric charges form a high-conductivity material that affects the Parkinson vector of the geomagnetic field.

Anomalous decreases on water levels were observed in 78 % of wells in central Taiwan about 250 days before the Chi-Chi earthquake whose magnitude is 7.6 on 20 September 1999. Variations in groundwater levels measured on anomalous wells from 1 August 1997 to 19 September 1999, were transferred into the frequency domain to unveil frequency characteristics. Analytical results show that amplitudes at the frequency band between 0.02 and 0.04 day−1 generally maintained at low stage and were apparently enhanced a few weeks before the Chi-Chi earthquake. Variations of amplitude at this particular frequency band were further examined along with other Taiwan earthquakes whose magnitude is larger than 6 from 1 August 1997 to 31 December 2009. Features of the enhanced amplitudes at the frequency band are consistently observed prior to the other two earthquakes during the 12.5-year study period. Result confirms that abnormal rise and fall changes in groundwater level yield an agreement with forward and backward surface displacements around epicenter prior to the Chi-Chi earthquake.

High arsenic concentration in groundwater is influenced by redox reactions in As-bearing iron (oxy)hydroxide minerals and elevated total organic carbon, resulting in arsenic contamination and enrichment in groundwater after introduction of seawater into an aquifer. In this study, hydrochemical and isotopic (S, O and C) techniques were used to relate arsenic contamination and seawater flooding/intrusion in groundwater aquifers in the Chianan Plain, southwestern Taiwan. Thirty-three samples (30 from groundwater and 3 from river water) were collected from April–June of 2014. Most of the groundwater samples collected from the Chianan Plain were dominated by As(III), indicating that reducing conditions prevailed within the aquifers. The δ18O-δD plots of most of the groundwater samples from the Chianan Plain are generally lined on the global meteoric water line (GMWL), but the δ18O and δD isotopic compositions of the river water samples show enriched signals. Salinity and sulfate concentrations of river water and shallow groundwater have been found to increase after seawater flooding/intrusion. The δ18O and δD isotopic compositions of the river water showed a gradual trend toward those of seawater. The trend in the isotopic compositions of the river and groundwater samples indicated a mixing of seawater and meteoric water. Up to the present, the groundwater levels in the coastal areas of the Chianan Plain have dropped to zero meters in elevation parallel to sea level due to excessive groundwater withdrawal, resulting in seawater intrusion into the aquifers in Budai, Yichu, and Beimen in the Plain. Moreover, high salinity (48.1‰) occurred only in the Beimen 2B shallow groundwater at a depth of 60 m is a result of seawater flooding infiltration from the nearby salinized Pachang River. The δ34S[SO4]/δ18O[SO4] isotopic ratios (2.63–2.82) of low-As (concentration

Summary The coupling of pre-earthquake anomalous phenomena between long-term groundwater levels recorded at 42 monitoring stations and time-varying surface strain derived from 16 GPS stations was found in the Choshuichi Alluvial Fan before the 1999 M w 7.6 Chi-Chi earthquake in Taiwan. The noise-free groundwater-level anomalies consistently comprised by a sequence of decrease, rise and flat phases, which agree very well with changes in strain rates computed from the GPS stations. These coupling agreements show that in addition to compression, tension can be generated before a thrust earthquake occurrence as well. This case demonstrates that short-term surface deformation as signals against noise and accuracy of pre-earthquake anomalous phenomena can be simultaneously examined by using multiple-parameter crosscheck for significantly reducing the uncertainty of earthquake precursory evaluation.

Summary Taiwan is an island located in the western Pacific, and falls under the influence of tropical to sub-tropical climate with two monsoons during summer and winter. This makes it an ideal location to study water vapor dynamics and its influence on the rainfall. The tropical convection/cyclones and south-west monsoon dominate the rainfall in summer while in winter, north-east monsoon overwhelms. To investigate the influence of moisture source variation, recycling and rain–vapor interaction, continuous measurements of the concentration and oxygen and hydrogen isotopic compositions (δ 18 O and δD) of the near surface atmospheric water vapor have been carried out in Taipei, Taiwan, using a commercial cavity ring down spectrometer. The water vapor mixing ratio varies between 15,000 and 38,000 ppmv, with maximum in the summer months and minimum in the winter. The isotopic composition of water vapor varies between −11‰ to −21‰ for δ 18 O and −75‰ to −150‰ for δD, but no clear seasonal variation is observed unlike that in the monthly rainwater. Therefore, the usual assumption that the monthly composite samples of rainfall reflect the isotopic variability of near surface water vapor is not valid here. Variation in δ 18 O, δD and deuterium excess (d-excess) in vapor reflects its interaction with rainwater superimposed by temperature variation and moisture recycling. To study how rainwater interacts with water vapor, two events are selected: a mei-yu event and typhoon Saola, the later affected Taiwan in 2012. Annual rainfall is dominantly contributed by these two types of meteorological phenomena in Taiwan. We find that the vapor and the rainwater are nearly in isotopic equilibrium during typhoon while they are deviated significantly during the mei-yu. A significant contribution of the vapor from recycling of surface water is observed in winter assessed using d-excess in the vapor isotopes.

Summary We present here major ion, trace element, stable and radioisotope data based on forty-six groundwater samples collected from various locations along few selected profiles across the Chianan Plain, southwestern Taiwan including the area affected by well known Blackfoot disease manifested by peripheral vascular gangrene. The objective of the study was to understand the role of local hydrogeology in terms of spatial variation of arsenic concentration in groundwater wells of the entire Chianan Plain and the foothill belt of the Central Mountain Range. An attempt has also been made to assess the contribution of nearby geothermal sources to the arsenic budget in groundwater of the Chianan Plain. Our study shows a gradual increase in all major and trace ion concentrations including total arsenic from foothill belt (arsenic: median = 4 μg/L, range = 0–667.6 μg/L, sample number n = 16) to coastal zones (arsenic: median = 42.74 μg/L, range = 0.14–348.6 μg/L, n = 15) of the plain. Inverse geochemical modeling shows that Ca may be exchanged on clays, and that the degree of the exchange increases from the foothill to the coastal zones. Inverse geochemical modeling further suggests that the oxidation of organic matter (CH2O) required in various east-west profiles across the plain to balance the total bicarbonate concentration and CO2 input from organic matters significantly increases from the foothill to the coastal zones with transfer coefficients ranging from 1.55 × 10−2 to 1.69 × 10−5 mol/L. High concentrations of tritium (mean = 1.33 ± 0.11 TU; n = 4) in foothill groundwater and low concentration of tritium in groundwater of central zone suggest gradually increasing water–rock interaction from the foothill to the coastal part. Few elevated arsenic (median = 171.8 μg/L, maximum = 667.60 μg/L, minimum = 24 μg/L; n = 6) hotspots are identified in the foothill belt. Available lithologs and aquifer test data suggest that the presence of impermeable clay around those pockets possibly inhibits vertical and lateral flushing of the aquifer and aids strong water–rock interactions subsequently leading to release of arsenic into groundwater. Using oxygen isotope and chloride mass balance method, we estimated that geothermal sources can recharge a maximum of 4% of groundwater in proximal aquifers and contribute

Sediment samples (213 sites) collected from the tectonic-active continental margin, offshore southwestern Taiwan were analyzed for grain sizes, organic carbon, nitrogen and carbon isotopic composition to obtain mass accumulation rate of terrestrial organic carbon and carbon budget to evaluate fate of terrestrial organic carbon from small mountainous rivers on the continental margin offshore southwestern Taiwan. Terrestrial organic carbon accumulation rates range from 0.29 to 45.6 g C m −2 yr −1 with a total accumulation budget of 0.063 Mt yr −1 , which accounts for less than 13% of total river particulate organic carbon loads exported from the adjacent rivers, the Gaoping (a.k.a., Kaoping), Erhjen and Tsengwen rivers. This low burial efficiency of terrestrial organic carbon demonstrated that a majority of river-borne particles together with organic materials was moved away from the study area. For the river-borne particles from the Gaoping river, a pair of depocenters in the upper slope flanking the Gaoping submarine canyon are the locations where the maximum TC org accumulation rate were observed which hold up to 45% (0.016 Mt yr −1 ) of the calculated accumulation found in the study region. On the other hand, the occurrence of higher-fraction terrestrial organic carbon in the upper and middle Gaoping submarine canyon suggests that a majority of particulate organic carbon of the Gaoping river was transported directly into the deep-sea basin through the Gaoping submarine canyon. Our results demonstrated that active margin with narrow shelf and slope is not an efficient sink for the large amount of terrigenous organic carbon supplied by the small rivers, but, a transient environment for these river derived particles.

Daily resolution data retrieved from the 1243 ground-based Global Positioning System (GPS) stations in Japan are utilized to expose surface displacements before the destructive M9 Tohoku-Oki earthquake (March 11, 2011). Variations in the residual GPS data, in which effects of the long-term plate movements, short-term noise and frequency-dependent variations have been removed through a band-pass filter via the Hilbert–Huang transform, are compared with parameters of the focal mechanism associated with the Tohoku-Oki earthquake for validation. Analytical results show that the southward movements, which were deduced from the residual displacements and agree with the strike of the rupture fault, became evident on the 65th day before the Tohoku-Oki earthquake. This observation suggests that the shear stress played an important role in the seismic incubation period. The westward movements, which are consistent with the angle of the maximum horizontal compressive stress, covered entire Japan and formed an impeded area (142°E, 42°N) about 75 km away from the epicenter on the 47th day prior to the earthquake. The horizontal displacements integrated with the vertical movements from the residual GPS data are very useful to construct comprehensive images in diagnosing the surface deformation from destructive earthquakes along the subduction zone.

Lakes and reservoirs play an important role in the carbon cycle, and therefore monitoring their metabolic rates is essential. The triple oxygen-isotope anomaly of dissolved O2 [17Δ = ln(1+δ17O) − 0.518 × ln(1 + δ18O)] offers a new, in situ, perspective on primary production, yet little is known about 17Δ from freshwater systems. We investigated the 17Δ together with the oxygen : argon ratio [Δ(O2 ∕ Ar)] in the subtropical Feitsui Reservoir in Taiwan from June 2014 to July 2015. Here, we present the seasonal variations in 17Δ, GP (gross production), NP (net production) and the NP ∕ GP (net to gross ratio) in association with environmental parameters. The 17Δ varied with depth and season, with values ranging between 26 and 205 per meg. The GP rates were observed to be higher (702 ± 107 mg C m−2 d−1) in winter than those (303 ± 66 mg C m−2 d−1) recorded during the summer. The overall averaged GP was 220 g C m−2 yr−1 and NP was −3 g C m−2 yr−1, implying the reservoir was net heterotrophic on an annual basis. This is due to negative NP rates from October to February (−198 ± 78 mg C m−2 d−1). Comparisons between GP rates obtained from the isotope mass balance approach and 14C bottle incubation method (14C–GP) showed consistent values on the same order of magnitude with a GP ∕ 14C–GP ratio of 1.2 ± 1.1. Finally we noted that, although typhoon occurrences were scarce, higher than average 17Δ values and GP rates were recorded after typhoon events.

[1] Large earthquakes are known to cause widespread changes in groundwater flow, yet their relation to subsurface transport is unknown. Here we report systematic changes in groundwater temperature after the 1999 Mw7.6 Chi-Chi earthquake in central Taiwan, documented by a dense network of monitoring wells over a large (17,000 km2) alluvial fan near the epicenter. Analysis of the data reveals a hitherto unknown system of earthquake-triggered basin-wide groundwater flow, which scavenges geothermal heat from depths, changing groundwater temperature across the basin. The newly identified earthquake-triggered groundwater flow may have significant implications on postseismic groundwater supply and quality, contaminant transport, underground repository safety, and hydrocarbon production.

This work addresses a new probabilistic observation model for a stereo simultaneous localization and mapping (SLAM) system within the standard Extended-Kalman filter (EKF) framework. The observation modal was derived by using the inverse depth parameterization as the landmark modal, and contributes to both bearing and range information into the EKF estimation. In this way the inherently non-linear problem cause by the projection equations is resolved and real depth uncertainty distribution of landmarks features can be accurately estimated. The system was demonstrated with real-world outdoor data. Analysis results show landmark feature depth estimation is more stable and the uncertainty noise converges faster than the traditional approach.

Unusual decreases of water levels were consistently observed in 78% (= 42/54) of wells in the Choshuichi Alluvial Fan of central Taiwan about 250 days before the Chi-Chi earthquake (M = 7.6 on 20 September 1999) while possible factors of barometric pressure, earth tides, precipitation as well as artificial pumping were removed. Variations in groundwater levels measured on anomalous wells from 1 August 1997 to 19 September 1999, which covers the 250 day unusual decreases, were transferred into the frequency domain to unveil frequency characteristics associated with the Chi-Chi earthquake. Analytical results show that amplitudes at the frequency band between 0.02 day−1 and 0.04 day−1 generally maintained at the low stage and were apparently enhanced a few weeks before the Chi-Chi earthquake. Variations of amplitude at this particular frequency band were further examined along with other Taiwan earthquakes (M > 6) from 1 August 1997 to 31 December 2009. Features of the enhanced amplitudes at the frequency band are consistently observed prior to the other two earthquakes (the Rei-Li and Ming-Jian earthquakes) during the 12.5 yr study period. In addition, surface displacements recorded from GPS, which provides insights into understanding stress status in subsurface during the Chi-Chi earthquake, are also inspected. The result confirms that abnormal rise and fall changes in groundwater level yield an agreement with forward and backward surface displacements around the epicentre prior to the Chi-Chi earthquake.

The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ≥ 5.5) in Taiwan during a period of 2002–2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event.

Summary In this study, we estimate small-scale temporal variations in groundwater pumpage and recharge in alluvial fan topography. We study these variations on a monthly scale using groundwater storage hydrograph and isotope analysis along with area rainfall hydrographs and data of historical irrigation pumpage variations. We consider multiple irrigation practices whose effect was measured only on an annual basis in mostly previous studies. In previous studies, pumpage for non-irrigation or irrigation purposes was regarded as known but illegal pumping was not accounted for. Also, recharge sources include rainfall, rivers, boundary inflow, and groundwater-irrigation, which have not been individually accounted for in previous studies. Pumpage can be estimated from the pumping rate and the number of pumping days. In alluvial fan topography, the actual pumping rate, including that because of illegal wells, can be deduced from the recession slope of the groundwater hydrograph. The annual pumping rate of non-irrigation pumping is assumed to be constant, and can be estimated as the slope of the groundwater hydrograph over consecutive non-rainy days during the non-irrigation periods of the dry season. For cases where there are multiple irrigation practices, the temporal distribution of the irrigation pumping rate can be estimated from the slope of the groundwater hydrograph and also from records provided by the Irrigation Association. In this study, we regard recharge as the difference between inflow and loss. Different types of inflow can be inferred from the storage hydrograph in rainy or non-rainy days, and the loss can then be obtained by using the groundwater balance equation. The isotope mass balance equation is then used to quantify various sources of recharge. In this study, we apply the proposed methodology to the Cho-Shui River alluvial fan, Taiwan. The results show that the proposed methodology can overcome previous restrictions of groundwater hydrograph and isotope analyses to effectively and rationally estimate monthly variations in pumpage and recharge, thus making it possible to research fine flow mechanisms within a multi-layer groundwater system.

This study aims to establish a bi-objective imperfect preventive maintenance (BOIPM) model in which the total maintenance cost and the mean system reliability are optimized by determining the maintenance periods and maintenance activities simultaneously. To efficiently solve the established BOIPM model, this study proposes an improved particle swarm optimization (IPSO) algorithm. The IPSO extends the practicability of the conventional PSO originally designed to solve an optimization problem with continuous decision variables. Furthermore, time-varying mechanisms associated with search parameters of the PSO are utilized to enhance the particles search capability. An adjustment mechanism addressing the issue of particles falling into the infeasible area is constructed to enhance the exploring ability of the IPSO. A case verifies the effectiveness of the proposed approach.

A blind thrust fault with a unique strike, which is orthogonal to the strike of most tectonic structures in Taiwan, triggered the Jiashian earthquake on March 4, 2010 (M = 6.4; 22.96°N, 120.70°E). This study utilizes 100 global positioning system stations to examine changes of surface displacements during the Jiashian earthquake. We mitigate effects of short-term noise and long-term plate movements from surface displacement data using a frequency dependent filter via the Hilbert–Huang transform and compute the horizontal azimuth (i.e. GPS-azimuth) using residual data at the NS component relative to residual data at the EW component. Analytical results show that orientations of horizontal azimuths were aligned and orthogonal to the strike of the blind thrust fault. Meanwhile, inverse orientations are observed before and after the earthquake that agrees well with the seismic rebound theory. As stress disturbed on strata a few days before the earthquake, an impeded region can be clearly identified by disordered orientations of horizontal azimuths for anticipating the mainshock. These results provide an additional view to explore stress disturbance associated with earthquakes and offer more information to examine diverse models of tectonic evolution in this region.

This study establishes a bi-objective imperfect preventive maintenance (BOIPM) model of a series-parallel system. The improvement factor method is used to evaluate the extent to which repairing components can restore the system reliability. The total maintenance cost and mean system reliability are optimized simultaneously through determining the most appropriate maintenance alternative. A bi-objective hybrid genetic algorithm (BOHGA) is established to optimize the BOIPM model. The BOHGA utilizes a Pareto-based technique to determine and retain the superior chromosomes as the GA chromosome evolutions are performed. Additionally, a unit-cost cumulative reliability expectation measure (UCCREM) is developed to evaluate the extent to which maintaining each individual component benefits the total maintenance cost and system reliability over the operational lifetime. This UCCREM is then incorporated into the genetic algorithm to construct a superior initial chromosome population and thereby enhance its solution efficiency. In order to obtain diverse bi-objective solutions as the Pareto-efficient frontier is approached, the closeness metric and diversity metric are employed to evaluate the superiority of the non-dominated solutions. Accordingly, decision makers can easily determine the most appropriate maintenance alternative. Three simulated cases verify the efficacy and practicality of this approach for determining an imperfect preventive maintenance strategy.

The purpose of this isotopic study is to identify groundwater sources in Taipei Basin (TPB) and their association with water of the Feitsui Reservoir (FTR), northern Taiwan. To this end, water samples including precipitation, catchment surface water, TPB groundwater, FTR water, and catchment surface water of FTR were analyzed for stable hydrogen and oxygen isotope compositions (δ 2H and δ 18O). Isotopic results support previous reports that Dahan Stream and Xindian Stream waters are the major recharge sources of TPB groundwater. These recharge regions are located along the southern border of the TPB. Further, isotopic evidence finds that water from the southern hills catchment area of the TPB also recharges TPB groundwater, and most importantly, indicates that TPB groundwater is highly related to FTR water. However, for caution’s sake, future comprehensive study is needed to confirm hydrological connectivity between the FTR water and TPB groundwater.

The dynamics of climate and runoff characteristics are studied in the territories of Kamchatka Peninsula and Taiwan Island, which are situated in the influence zone of monsoon circulation. Long-term variations in the temperature, precipitation, and runoff are examined in Kamchatka and Taiwan for the weather and gauging stations with the longest observation series to analyze new climate conditions of water resources generation.

RATIONALE The oxygen isotopic composition of carbon dioxide originating at the Earth's surface is modified in the stratosphere by interaction with ozone which has anomalous oxygen isotope ratio (Δ17O = 1000 * ln(1 + δ17O/1000) – 0.522 * 1000 * ln (1 + δ18O/1000) >0). The inherited anomaly provides a powerful tracer for studying biogeochemical cycles involving CO2. However, the existing methods are either too imprecise or have difficulty in determining the small Δ17O variations found in the tropospheric CO2. In this study an earlier published CeO2 and CO2 exchange method has been modified and improved for measuring the Δ17O values of atmospheric carbon dioxide with high precision. METHODS The CO2 fraction from air samples was separated by cryogenic means and purified using gas chromatography. This CO2 was first analyzed in an isotope ratio mass spectrometer, then artificially equilibrated with hot CeO2 to alter its oxygen isotopes mass-dependently and re-analyzed. From these data the 17O/16O and 18O/16O ratios were calculated and the Δ17O value was determined. RESULTS The validity of the method was established in several tests by using artificially prepared CO2 with zero and non-zero Δ17O values. The published value of the CO2-H2O equilibrium slope was also reproduced. CONCLUSIONS The CO2-CeO2 equilibration method has been improved to measure the oxygen isotope anomaly (Δ17O value) of atmospheric CO2 with an analytical precision of ±0.12‰ (2σ). Copyright © 2012 John Wiley & Sons, Ltd.

Summary Environmental isotopes including stable hydrogen and oxygen, and radioactive tritium isotopes are employed to assess groundwater sources in the Taoyuan–Chungli Tableland (TCT), northwestern Taiwan. We evaluate the contribution to groundwater resources of copious ponds distributed throughout the TCT. Results indicate that both precipitation and pond water are the end sources of proximal shallow groundwater (P-SGw) in the TCT. Recharge of P-SGw to deep groundwater in the proximal-fan region (P-DGw) is obvious, because δ values of P-DGw are similar to those of P-SGw and no barrier restricts P-SGw entering P-DGw. However, the infiltration of precipitation or pond water to shallow groundwater in the mid- and distal-fan regions (MD-SGw) is restricted somewhere because of impermeable confining layers overlying the MD-SGw. In addition, apart from the upstream recharge of the P-SGw, MD-SGw overlying the deep groundwater in the mid/distal-fan regions (MD-DGw) contributes to MD-DGw through barrier-layer leakage between MD-SGw and MD-DGw. Overall, δ values indicate that pond-sourced moisture accounts for about 6% of precipitation in the studied tableland. This contribution fraction is larger than that in the western plains or reservoir catchments of Taiwan. The calculations also indicate that precipitation and pond water respectively contribute 51% and 49% to P-SGw. Among the 49% contribution from pond water to P-SGw, 46% is from direct infiltration and the remaining 3% is via the evaporation–precipitation process. The fractional results clearly indicate that pond water is a vital source of both local precipitation and groundwater.

Despite early optimism, pre-earthquake anomalous phenomena can be determined by using enhanced amplitude at the ultra-low-frequency range from geomagnetic data via the Fourier transform. In reality, accuracy of the enhanced amplitude in relation to earthquakes (deduced from time-varied geomagnetic data) would be damaged by magnetic storms and/or other unwanted influences resulting from solar activity and/or variations in the ionosphere, respectively. We substitute values of the cross correlation between amplitudes, summarized from the earthquake-related (0.1–0.01 Hz) and the comparable (0.01–0.001 Hz) frequency bands, for isolated amplitude enhancements as indexes of determination associated with seismo-magnetic anomalies to mitigate disturbance caused by magnetic storms. A station located about 300 km away from the others is also taken into account to further examine whether changes of the cross correlation values are caused by seismo-magnetic anomalies limited within local regions or not. Analytical results show that the values suddenly decrease near epicenters a few days before and after 67% (= 6/9) of earthquakes (M > = 5) in Taiwan between September 2010 and March 2011. Seismo-magnetic signals determined by using the values of cross correlation methods partially improve results yielded from the Fourier transform alone and provide advantageous information of earthquake locations.