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Because of its complex tectonic setting, the Philippines experiences vigorous seismic activity. On December 15, 2019, an Mw 6.8 earthquake struck Davao del Sur, the Philippines, severely damaging infrastructure and adversely affecting the population. In this study, we used Interferometry Synthetic Aperture Radar (InSAR) and teleseismic broadband data to explore the earthquake’s source parameters, rupture process, and tectonic characteristics through a Bayesian modeling approach and Coulomb stress analysis. An analysis of InSAR suggested that the mainshock occurred on an NW–SE oriented single plane within the Cotabato fault system, with the Makilala-Malungon fault being the causative fault. The Joint inversion revealed that the rupture initiated in the middle crust (depth: approximately 16.5 km), exhibiting a blind, left-lateral strike-slip fault rupture propagation with minimal reverse slip and no surface rupture. The slip was concentrated in a distinct asperity spanning a depth of 3–24 km, with the peak slip reaching approximately 1.8 m. The source time function of this event indicated a single pulse with a total source duration of approximately 17 s. The static stress drop value was low, which may be related to the brittle condition of the crust. Coulomb stress changes calculations suggested earthquake risk in the future.

Abstract A doublet earthquake event including two main shocks with a magnitude larger than Mw 6.0 occurred on 1 July 2022 in the Zagros fold‐and‐thrust belt, southeast Iran. The coseismic InSAR deformation field shows that this event caused significant surface uplift due to fault‐related folding in the seismic zone. The estimated preferred faulting model suggests that a higher dip angle fault (maximum slip of ∼1.1 m), and an overlying gentle dipping fault (maximum slip of ∼1.2 m) within the Bandar‐e‐Lengeh Anticline, are responsible for the first and second main shocks, respectively. The calculated Coulomb failure stress change suggests that the first main shock and its Mw 5.7 aftershock have a significantly positive triggering effect in the second main shock. The accumulated interseismic strain should have been partly released by the two main shocks. Finally, the salt diapir activity may affect the generation of the earthquake in the seismic zone.

Understanding the kinematic characteristics of the Longitudinal Valley Fault Zone (LVFZ) can help us to better understand the evolution of orogens. The 2022 Mw7.0 Taitung earthquake that occurred in Taiwan provides us with a good opportunity to understand the motion characteristics of the Central Range Fault (CRF) and the strain partitioning pattern within the Longitudinal Valley Fault (LVF). We obtained the coseismic displacement and slip distribution of the 2022 Taiwan earthquake based on the strong-motion and GPS data available. The causative fault of this earthquake is the west-dipping Central Range Fault, which is buried beneath the western boundary of the LVF. The coseismic displacement field exhibits a quadrant distribution pattern, indicating a left-lateral strike-slip mechanism with a maximum displacement exceeding 1.25 m. The joint inversion results show that the size of the main asperity is 40 km × 20 km, and the maximum slip amount of 2.6 m is located at a depth of 10 km, equivalent to an earthquake of Mw7.04. The LVFZ is composed of LVF and CRF, which accommodates nearly half of the oblique convergence rate between the Philippine Sea Plate and the Eurasian Plate. There is a phenomenon of strain partitioning in the southern segment of the Longitudinal Valley Fault Zone. The Central Mountain Range Fault is primarily responsible for accommodating strike-slip motion, while the Longitudinal Valley Fault is mainly responsible for accommodating thrust motion.

Multi-source datasets, including the UAV-Lidar/Photogrammetry, InSAR, and field investigation data, have been used for revealing the complex surface displacement pattern and focal mechanism of the 2021 Maduo Mw 7.3 earthquake. First, a co-seismic surface deformation field was extracted from the Synthetic Aperture Radar (SAR) images captured by ALOS-2 and Sentinel-1 satellites. Second, the SAR pixel offset tracking results were adopted to detect the initial location of the seismogenic fault. Then, the Lidar digital elevation model with high spatial resolution and field investigation were employed to refine and verify the location of the seismogenic fault. It was found that bifurcated strike-slip rupture should account for the 2021 Maduo earthquake. As indicated by the estimated faulting model based on the InSAR data, the maximal fault slip was ~6.2 m, occurring in the southeast of the main seismogenic fault, and five remarkable slip concentrations controlled the surface displacement of the 2021 Maduo earthquake. Furthermore, the co- and post-seismic InSAR deformation, dilatation, shear strain, Coulomb failure stress, and aftershock sequence suggest that the co-seismic rupture of the two main seismogenic faults have triggered the aseismic slip along the Changmahe fault. Lastly, according to the Coulomb failure stress change due to the historical earthquakes and the 2021 Maduo earthquake, the 1937 M 7.8 earthquake predominantly controlled the Coulomb failure stress change along the Kunlun fault, and the Xidatan-Alake Lake and Maqin segments had a higher risk of future earthquake than the other segments.

On 6 February 2018 at 23:50 local time, a Mw 6.4 earthquake struck eastern Taiwan. We characterize the instantaneous surface ground motion and the permanent displacement induced by this event from continuous GPS data and SAR images within a short time after the mainshock. We use high-rate GPS positioning techniques to obtain epoch-by-epoch positions peak ground displacement to assess potential seismic damage. The maximum coseismic GPS horizontal displacement of about 450 mm trending to the northeast is observed at the station HUAL located on the hanging wall of the Milun fault. The PEPU located on the footwall of the Milun fault shows a coseismic horizontal displacement of 280 mm trending to the southwest and a coseismic uplift of about 70 mm. Moreover, ascending and descending tracks of ALOS-2 and Sentinel-1 SAR images are processed to estimate coseismic surface deformation along the line-of-sight (LOS) toward the satellite. Then, wide coverage from east-west and uplift components of surface deformation is fulfilled by combining the LOS displacement from ascending and descending interferograms. The main deformation area revealed by both GPS results and D-InSAR interferograms is concentrated around the Milun and Lingding faults. Significant uplift on the footwall of the northern Lingding Fault implies that the Milun fault and an unknown westdipping fault close to the Lingding fault were triggered. Both the two nodal planes of the Mw 6.4 Hualien event could be different with the kinematic behavior of the Milun fault and Lingding fault. Thus we suggest that slip on multiple faults was triggered during the 0206 event.

A slow-moving landslide on the Huafan University campus, which is located on a dip slope in northern Taiwan, has been observed since 1990. However, reliable monitoring data are difficult to acquire after 2018 due to the lack of continuous maintenance of the field measurement equipment. In this study, the multitemporal interferometry (MTI) technique is applied with Sentinel-1 SAR images to monitor the slow-moving landslide from 2014–2019. The slow-moving areas detected by persistent scatterer (PS) pixels are consistent with the range of previous studies, which are based on in situ monitoring data and field surveys. According to the time series of the PS pixels, a long period gravity-induced deformation of the slow-moving landslide can be clearly observed. Moreover, a short period seasonal surface fluctuation of the slow-moving landslide, which has seldom been discussed before, can also be detected in this study. The seasonal surface fluctuation is in-phase with precipitation, which is inferred to be related to the geological and hydrological conditions of the study area. The MTI technique can compensate for the lack of surface displacement data, in this case, the Huafan University campus, and provide information for evaluating and monitoring slow-moving landslides for possible landslide early warning in the future.

We here present an example of the 2016 Kumamoto earthquake with its coseismic surface deformation mapped by the ALOS-2 satellite both in the right- and left-looking observation modes. It provides the opportunity to reveal the coseismic surface deformation and to explore the performance of the unusual left-looking data in faulting model inversion. Firstly, three tracks (ascending and descending right-looking and descending left-looking) of ALOS PALSAR-2 images are used to extract the surface deformation fields. It suggests that the displacements measured by the descending left-looking InSAR coincide well with the ascending right-looking track observations. Then, the location and strike angle of the fault are determined from the SAR pixel offset-tracking technique. A complicated four-segment fault geometry is inferred for explaining the coseismic faulting of the Kumamoto earthquake due to the interpretation of derived deformation fields. Quantitative comparisons between models constrained by the right-looking only data and by joint right- and left-looking data suggest that left-looking InSAR could provide comparable constraints for geodetic modelling to right-looking InSAR. Furthermore, the slip model suggests that the series of events are dominated by the dextral strike-slip with some normal fault motions. The fault rupture initiates on the Hinagu fault segment and propagates from southwest to northeast along the Hinagu fault, then transforms to Futagawa fault with a slip maximum of 4.96 m, and finally ends up at ~7 km NW of the Aso caldera, with a rupture length of ~55 km. The talent of left-looking InSAR in surface deformation detection and coseismic faulting inversion indicates that left-looking InSAR can be effectively utilized in the investigation of the geologic hazards in the future, same as right-looking InSAR.

Quantitative understanding of stress transfer between major fault systems can elucidate the kinematics of large-scale plate interactions. This study analyzed right-lateral strike-slip motion on the North Tabriz fault (NTF) in an area where this structure appears to transition into a thrust fault known as the North Mishu fault (NMF). These faults play an important but cryptic role in accommodating stress related to the Arabia-Eurasia plate collision. We analyzed regional velocity vectors from permanent and temporary GPS arrays to estimate changes in fault-parallel and fault-normal slip rates in the transition zone between the NTF and NMF. Independent of its compressional motion, the NMF exhibits a dextral strike-slip rate of ~2.62 mm/yr. Along the NTF, the right-lateral slip rate decreases and the vertical slip rate on increases at rates of 0.08 and 0.38 mm/yr km, respectively, as the NTF approaches the NMF. This study also used small baseline (SBAS) PS-InSAR results to reveal a NE-SW-striking reverse fault and a developing syncline hidden beneath the Tabriz Basin. Additionally, we calculated the vertical displacement rates using horizontal vectors from the GPS data and mean line-of-sight rate estimates from the SBAS data. While the study area does not express large-scale extrusion, such as that observed in the Anatolian Plate, the transformation of strike-slip motion into thrusting and crustal shortening along the NMF-NTF fault zone accommodates most of the N-S compression affecting the northwestern Iranian Plateau. In this region, small-sized, right-lateral strike-slip faults, and other folded structures form horsetail features. These dispersed structures accommodate eastward extrusion of the northwestern Iranian Plateau.

We focus herein on the location, characterization and the quantification of the most active structural feature of Taiwan: the Longitudinal Valley Fault that corresponds to the suture in between the Philippine and Eurasian Plates. In order to determine and monitor its present inter-seismic deformation, we focus on the Pingting Terraces area, situated in the South Longitudinal Valley (Eastern Taiwan). We first determine the structural geometry issued from both photo-interpretation deduced from new unmanned aerial vehicle (UAV) high-resolution Digital Terrain Model data that we acquired (34.78 km2 with 7.73 cm ground sampling distance), combined with geological field work. In order to characterize and quantify the present deformational patterns over the Pingting terraces, we used an InSAR time series Interferometry algorithm (MT-InSAR) applied to nine L-band SAR images from ALOS satellite acquired over the period 2007–2010. The unprecedented density of measurements (about 120 points per km2 for a total of 6,400 points) gives a continuous overview of the inter-seismic shallow deformation. The structural geometry combined with the mean velocity map (MT-InSAR) reveals two clear active faults situated above the scarps of the Pingting terraces and responsible for up to 7 and 20 mm/yr velocity offset along the radar line of sight. A temporal analysis of the deformation is performed with one measurement at each SAR acquisition date, giving major improvements in the characterization and quantification of the Longitudinal Valley active Fault trace.

The Meinong earthquake generated up to ~10 cm surface displacement located 10 - 35 km west of the epicenter and monitored by InSAR and GPS. In addition to coseismic deformation related to the deep earthquake source, InSAR revealed three sharp surface displacement gradients. One of them is extensional and is inconsistent with the westward interseismic shortening of ~45 mm yr-1 in this region. The gradient sharpness suggests slip triggering on shallow structures, some of which were not well documented before. To characterize these shallow structures, we investigated potential surface ruptures in the field. Sets of ~NS tension cracks distributed over 25 - 300 m width, with cumulative extension in the same order as InSAR observations, were found along 5.5 km distance along the extensional gradient and are interpreted as surface rupture. We build two E-W regional balanced cross-sections, based on surface geology, subsurface data, and coseismic and interseismic geodetic data. From the Coastal Plain to the east edge of the coseismic deformation area, we propose a series of three active west-dipping backthrusts: the Houchiali fault, the Napalin-Pitou backthrust, and the Lungchuan backthrust. They all root on the 3.5 - 4.0 km deep Tainan detachment located near the base of the 3-km-thick Gutingkeng mudstone. Further east, the detachment would ramp down to ~7 km depth. Coseismic surface deformation measurements suggest that, in addition to the deeper (15 - 20 km) main rupture plane, mostly the ramp, the Lungchuan backthrust, and the Tainan detachment were activated during or right after the earthquake. Local extension is considered as transient deformation at the west edge of the shallow main slip zone.

We found some obvious abnormal strain induced by heavy rainfall from borehole strainmeters deployed in Western Taiwan. The strain induced by rainfall can be divided into two parts, one is the quick response for extra loads of rainwater on the ground, and another one is the slow response for rainwater infiltrating into the strata. The quick and slow rainfall responses of areal strain data are analyzed using the technique of recursive digital filtering. Moreover, the rainfall impact functions of the studied stations are calculated using deconvolution. We found, in most cases, the response strain will reach the maximum in half an hour after heavy rainfall, and then show an exponential decay, it might persist more than 200 h depending on the hydrogeological condition around the station. Whereas the river flowing beside the station will help accelerating the runoff dispersion and reducing rainfall decay time in the hill or mountain region. We also compare the results after calibration in term of isotropic and vertical coupling individually. We found that the response strains are smaller in vertical coupling rather than isotropic coupling. The effects of debris avalanches caused by intensive rainfall in the mountain areas can be viewed as two types of rock deformation: generated only under the influence of rainfall and generated by the increased load in the river channels due to rainfall-induced landslides or debris flow. When the cumulative rainfall exceeds a certain threshold, the strain response curves show a noticeable anomaly likely due to the effects of the debris flow events in places prone to landslides.

Frequent high seismic activities occur in Taiwan due to fast plate motions. According to the historical records the most destructive earthquakes in Taiwan were caused mainly by inland active faults. The Central Geological Survey (CGS) of Taiwan has published active fault maps in Taiwan since 1998. There are 33 active faults noted in the 2012 active fault map. After the Chi-Chi earthquake, CGS launched a series of projects to investigate the details to better understand each active fault in Taiwan. This article collected this data to develop active fault parameters and referred to certain experiences from Japan and the United States to establish a methodology for earthquake probability assessment via active faults. We consider the active faults in Central Taiwan as a good example to present the earthquake probability assessment process and results. The appropriate “probability model” was used to estimate the conditional probability where M ≥ 6.5 and M ≥ 7.0 earthquakes. Our result shows that the highest earthquake probability for M ≥ 6.5 earthquake occurring in 30, 50, and 100 years in Central Taiwan is the Tachia-Changhua fault system. Conversely, the lowest earthquake probability is the Chelungpu fault. The goal of our research is to calculate the earthquake probability of the 33 active faults in Taiwan. The active fault parameters are important information that can be applied in the following seismic hazard analysis and seismic simulation.

Balancing the demand of groundwater resources and the mitigation of land subsidence is particularly important, yet challenging, in populated alluvial fan areas. In this study, we combine multiple monitoring data derived from Multi-Temporal InSAR (MTI), GNSS (Global Navigation Satellite System), precise leveling, groundwater level, and compaction monitoring wells, in order to analyze the relationship between surface displacement and groundwater level change within the alluvial fan of the Choshui River in Taiwan. Our combined time-series analyses suggest, in a yearly time scale, that groundwater level increases with the vertical surface displacement when the effect of pore water pressure dominates. Conversely, this relationship is negative when the effect of water-mass loading predominates over pore water pressure. However, the correlation between the vertical surface displacement and the groundwater level change is consistently positive over the time scale of two decades. It is interpreted that the alluvial fan sequence in the subsurface is not fully elastic, and compaction is greater than rebound in this process. These findings were not well reported and discussed by previous studies because of insufficient monitoring data and analyses. Understanding the combined effect of groundwater level change and vertical surface displacement is very helpful for management of land subsidence and usage of groundwater resources. The spatial and temporal integration of multi-sensors can be applied to overcome the limitations associated with the single technique and provides further insights into land surface changes, particularly in highly populated alluvial fan areas.

The Mw 7.6 Chi-Chi earthquake struck central western Taiwan in 1999. The rupture was complex with several dislocations along the 100-km long Chelungpu thrust fault. Revisiting this earthquake is a challenge, as the precision and coverage of the data sets available are quite poor. Furthermore, the topographic and vegetation coverage complexity of the area prevents coherent radar images. In this paper, radar and optical images, and terrestrial geodetic measurements, were utilised to study the fault. The Particle Swarm Optimization and Okada Inversion (PSOKINV) geodetic inversion package was used with the generalized Akaike’s Bayesian Information Criterion (gABIC) to precisely determine the slip distribution and relative weighting of datasets. Differences in results using the data sets jointly or separately (e.g., under-estimation due to InSAR, inconsistencies in SPOT offsets, smoother slip distribution with gABIC weighting) are observable. Most of the energy was released in the northern part of the fault, where the strike veers toward the east, and mainly at depths less than 4 km. The PSOKINV-gABIC approach is viable for the study of complicated cases such as the Chi-Chi earthquake and can significantly benefit the weight determination and physical realism of the fault geometry.

The ascending and descending InSAR deformations derived from ALOS-2 and Sentinel-1 satellite SAR images and GPS displacements are used to estimate the fault model of the 2018 Mw 6.4 Hualien earthquake. The sinistral strike-slip fault dipping to the west with a high dip angle of 89.4° and a rake angle of 201.7° is considered as the seismogenic fault of this event. This seismogenic fault also triggered the ruptures of the Milun fault, which dips to the east with a dip angle of ~72°, and an unknown west-dipping fault with a dip angle of 85.2°. Two predicted faulting models indicate that the InSAR deformation fields include more postseismic slip than those of the GPS data. The north segment of the Milun fault and west-dipping fault have been triggered by the rupture of the seismogenic fault, but the postseismic slip occurred only in the south segment of the Milun fault. The InSAR-derived co-seismic and postseismic faulting model suggests that the significant slip concentrates at depths of 2.4–15.0 km of the main fault, 0.0–14.0 km of the Milun fault. Only minor slip is detected on the west-dipping fault. The maximum fault slip of ca. 2.1 m is located at the depth of ca. 2.4 km under the Meilun Tableland. The Coulomb failure stress (CFS) change calculated by the co-seismic and postseismic faulting model shows that there is a significant CFS increase in the east of the south segment of the Milun fault, but few of the aftershocks occur in this area, which indicates a high risk of future seismic hazard.

This study uses three periods of airborne laser scanning (ALS) digital elevation model (DEM) data to analyze the short-term erosional features of the Tsaoling landslide triggered by the 1999 Chi-Chi earthquake in Taiwan. Two methods for calculating the bedrock incision rate, the equal-interval cross section selection method and the continuous swath profiles selection method, were used in the study after nearly ten years of gully incision following the earthquake-triggered dip-slope landslide. Multi-temporal gully incision rates were obtained using the continuous swath profiles selection method, which is considered a practical and convenient approach in terrain change studies. After error estimation and comparison of the multi-period ALS DEMs, the terrain change in different periods can be directly calculated, reducing time-consuming fieldwork such as installation of erosion pins and measurement of topographic cross sections on site. The gully bedrock incision rate calculated by the three periods of ALS DEMs on the surface of the Tsaoling landslide ranged from 0.23 m/year to 3.98 m/year. The local gully incision rate in the lower part of the landslide surface was found to be remarkably faster than that of the other regions, suggesting that the fast incision of the toe area possibly contributes to the occurrence of repeated landslides in the Tsaoling area.

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

Field investigations following the 2003 Mw = 6.8 Chengkung earthquake in eastern Taiwan revealed some interesting observations of surface geological processes closely related to the co-seismic deformation. We discovered that the Tama Fault, which is about 15 km east of the causative Chihshang Fault, underwent shortening of about 15.5 mm locally in 2001 - 2006, particularly during the 2003 earthquake. This shows that ESE-WNW compression affects the upper crust of the Coastal Range and produces significant shortening in addition to that of the major Chihshang Fault. On the hanging wall of the Chihshang Fault, we also found vigorous activities of the two major mud volcanoes during the main shock, lasting several days. To the north, the Luoshan Mud Volcano, a large mud basin, erupted noisily with water and gases during the earthquake. To the south, in the Leikunghuo Mud Volcano, two sets of fractures, one aligned with the N16¢XE right-lateral fault and the other with the N80¢XE left-lateral fault, occurred during the earthquake. This conjugate system revealed a strike-slip stress regime with NE-SW compression and NW-SE extension. We interpret it to be the result of local stress permutation rather than regional tectonic stress. We conclude that deformation did occur inside of the Coastal Range, especially during the co-seismic event. Therefore, a better understanding of the internal deformation of the Coastal Range is an important target for future studies, particularly across three mapped faults: the Yungfeng, Tuluanshan and Tama faults. We also want to draw attention to the stress analysis in the mud volcanoes area, where the local stress perturbation plays an important role.

The Shanchiao fault, located to the west of the Taipei Basin in northern Taiwan, is a highly active normal fault that has a left-slip component and fault length of over 40 km. We suggest that the Shanchiao fault still has the ability to induce coseismic subsidence in the Taipei Basin under present extensional regime of northern Taiwan. In order to characterize the coseismic ground deformation and assess the potential inundation hazards in Taipei Basin, we estimate surface displacements using elastic dislocation models. The largest slip is assumed to be located underneath the Kuandu area due to the observation of deepest Tertiary basement in this area. Based on the topography changes due to coseismic deformation in a potential magnitude 7 event induced by reactivation of the Shanchiao fault, a 2D inundation model was adopted to simulate several inundation scenarios, including potential flood inundation below high tide condition and under various return-period design rainfall events. The predicted inundation maps based on various return-period flood events can provide information to assess potential earthquake-induced inundation hazards.

The 2016 Mw 6.0 Hutubi earthquake occurred in the northern Tien Shan fold-and-thrust belts, China. However, the coseismic fault rupture model and the seismotectonics of the 2016 Hutubi earthquake remain uncertain up to the present due to the small magnitude, deep hypocenter, and no surface rupture caused by the seismogenic fault. Here, we show the evidence that the 2016 Hutubi earthquake occurred on a deep (15-20 km) blind-thrust fault, and the rupture of the blind fault triggers the slip of a shallow overlying fold. Ascending and descending Interferometric Synthetic Aperture Radar (InSAR) observations captured by Sentinel-1A/1B satellites are used to construct the seismogenic structure of the 2016 Hutubi earthquake. It is found that a single fault fails to provide a good fit to the observed Sentinel-1 ascending and descending InSAR deformation. A shallow fault-bend fold with strike along the surface trace of the Qigu anticline and a varying dip angle along the down-dip direction is proposed in this study based on the geodetic observations, which significantly improves the model fit to the InSAR observations. The estimated faulting model shows that the 2016 Hutubi earthquake occurred on a deep blind fault with 264.4° strike and 28.8° dip, and significant fault slip is located at the depth of 13-18 km with a peak slip of ~10.0cm. The triggered shallow fault-bend fold has a listric surface with slight predominant thrust slip. The static Coulomb stress change from the mainshock on the shallow fold structure is negative, which indicates the dynamic stress may play a more important role than the static stress in the triggering of the shallow fault-bend fold in this case. The result of this study suggests that a moderate earthquake with a deep hypocenter has the potential to trigger the rupture of the shallow overlying fault-bend fold in this zone. [ABSTRACT FROM AUTHOR]

The Ilan Plain, located in Northeast Taiwan, represents a transition zone between oblique collision (between the Luzon Arc and the Eurasian Plate) and backarc extension (the Okinawa Trough). The mechanism for this abrupt transition from arc-continent collision to backarc extension remains uncertain. We used Global Positioning System (GPS), leveling and multiinterferogram Small Baseline Persistent Scatterer Interferometry (SBAS-PSI) data to monitor the interseismic activity in the basin. A common reference site was selected for the data sets. The horizontal component of GPS and the vertical measurements of the leveling data were converted to line-of-sight (LOS) data and compared with the SBAS-PSI data. The comparison shows that the entire Ilan Plain is undergoing rapid subsidence at a maximum rate of -11 ± 2 mm yr-1 in the LOS direction. We speculate that vertical deformation and anthropogenic activity may play important roles in this deformation. We also performed a joint inversion modeling that combined both the DInSAR and strong motion data to constrain the source model of the 2005 Ilan earthquake. The best-fitting model predicts that the Sansing fault caused the 2005 Ilan earthquake. The observed transtensional deformation is dominated by the normal faulting with a minor left-lateral strike-slip motion. We compared our SBASPSI results with the short-term (2005-2009) groundwater level changes. The results indicate that although pumping-induced surface subsidence cannot be excluded, tectonic deformation, including rapid southward movement of the Ryukyu arc and backarc extension of the Okinawa Trough, characterizes the opening of the Ilan Plain. Furthermore, a series of normal and left-lateral strike-slip transtensional faults, including the Choshui and Sansing faults, form a bookshelf-like structure that accommodates the extension of the plain. Although situated in a region of complex structural interactions, the Ilan Plain is primarily controlled by extension rather than by shortening. As the massive, pre-existing Philippines-Ryukyu island arc was pierced by the Philippine Sea Plate, the Ilan Plain formed as a remnant backarc basin on the northeastern corner of Taiwan. [ABSTRACT FROM AUTHOR]

Captured CO2 could be deliberately injected into the ocean at great depth, where most of it would remain isolated from the atmosphere for centuries. CO2 can be transported via pipeline or ship for release in the ocean or on the sea floor. In Taiwan, CO2 release is preliminarily projected from 2010 to 2030 in an average amount of 6.957 Gt within this duration. If deep sea sequestration for CO2 can be the possible option in Taiwan, it seems to exists possible potential area delimited between 122.0°E to 122.5°E and 21.8°N to 22.3°N for CO2 sequestration on account of its isolated and flat topography. Apparently, the area to the southeast of Taiwan is found to reach a depth deeper than −3,000 m and can be taken as a testing area for pilot studies. This study searches the area using the contours from the depth of −4,554 to −5,500 m with 1-m interval; the area, topographic volume, maximum mean height (volume/area), and ocean volume are reported. If the emission rate is kept constantly, for 20-year storage it needs 3 m of thickness reaching the sea ridge at the depth −4,554 m using top-down style; for 100 years of storage it needs 12 m. On the other hand, if it accounts for the bottom the sea floor is taken as the reference and the accumulated CO2 is stored from the depth at −4,900 m using bottom-up style, it requires about 37 m for the 20-year storage and 61 m for one decade. [ABSTRACT FROM AUTHOR]

The 2003 Chengkung earthquake ( Mw 6.8) occurred on the east-dipping Chihshang fault of eastern Taiwan, a listric fault with dominant reverse motion. A joint inversion taking into account geodetic (GPS) and seismological (accelerometric and teleseismic) data is performed. This modelling highlights the rupture process behaviour on the fault plane at depth. The coseismic rupture developed essentially between 12 and 26 km depth, expanding laterally by about 30 km towards the SSW. Two slip patches dominated, with slip values exceeding 1.5 m. During the 30 s of the whole process, the rupture propagation decelerated with time, starting at 3.4 ± 0.3 km s–1 in the two main slip patches and ending with velocities below 1.6 ± 0.1 km s–1. The 48 hr of aftershocks that followed the main shock are distributed essentially inside the coseismic slip patches on the fault surface, except in the deepest, southern part of the fault where slip is less resolved. The results of our modelling illustrate the particular behaviour of the 2003 Chengkung earthquake where the coseismic slip rapidly diminished towards the surface, in good agreement with the observation of fast post-seismic slip followed by interseismic creep along the Chihshang fault. [ABSTRACT FROM AUTHOR]

The erosion of mountain belts controls their topographic and structural evolution and is the main source of sediment delivered to the oceans. Mountain erosion rates have been estimated from current relief and precipitation, but a more complete evaluation of the controls on erosion rates requires detailed measurements across a range of timescales. Here we report erosion rates in the Taiwan mountains estimated from modern river sediment loads, Holocene river incision and thermochronometry on a million-year scale. Estimated erosion rates within the actively deforming mountains are high (3-6?mm?yr-1) on all timescales, but the pattern of erosion has changed over time in response to the migration of localized tectonic deformation. Modern, decadal-scale erosion rates correlate with historical seismicity and storm-driven runoff variability. The highest erosion rates are found where rapid deformation, high storm frequency and weak substrates coincide, despite low topographic relief. [ABSTRACT FROM AUTHOR]

On 6 February 2018 at 23:50 local time, a Mw 6.4 earthquake struck eastern Taiwan. We characterize the instantaneous surface ground motion and the permanent displacement induced by this event from continuous GPS data and SAR images within a short time after the mainshock. We use high-rate GPS positioning techniques to obtain epoch-by-epoch positions peak ground displacement to assess potential seismic damage. The maximum coseismic GPS horizontal displacement of about 450 mm trending to the northeast is observed at the station HUAL located on the hanging wall of the Milun fault. The PEPU located on the footwall of the Milun fault shows a coseismic horizontal displacement of 280 mm trending to the southwest and a coseismic uplift of about 70 mm. Moreover, ascending and descending tracks of ALOS-2 and Sentinel-1 SAR images are processed to estimate coseismic surface deformation along the line-of-sight (LOS) toward the satellite. Then, wide coverage from east-west and uplift components of surface deformation is fulfilled by combining the LOS displacement from ascending and descending interferograms. The main deformation area revealed by both GPS results and D-InSAR interferograms is concentrated around the Milun and Lingding faults. Significant uplift on the footwall of the northern Lingding Fault implies that the Milun fault and an unknown westdipping fault close to the Lingding fault were triggered. Both the two nodal planes of the Mw 6.4 Hualien event could be different with the kinematic behavior of the Milun fault and Lingding fault. Thus we suggest that slip on multiple faults was triggered during the 0206 event. [ABSTRACT FROM AUTHOR]

The Meinong earthquake generated up to ~10 cm surface displacement located 10 - 35 km W of the epicenter and monitored by InSAR and GPS. In addition to coseismic deformation related to the deep earthquake source, InSAR revealed three sharp surface displacement gradients. One of them is extensional and is inconsistent with the westward interseismic shortening of ~45 mm yr-1 in this region. The gradient sharpness suggests slip triggering on shallow structures, some of which were not well documented before. To characterize these shallow structures, we investigated potential surface ruptures in the field. Sets of ~NS tension cracks distributed over 25 - 300 m width, with cumulative extension in the same order as InSAR observations, were found along 5.5 km distance along the extensional gradient and are interpreted as surface rupture. We build two EW regional balanced cross-sections, based on surface geology, subsurface data, and coseismic and interseismic geodetic data. From the Coastal Plain to the E edge of the coseismic deformation area, we propose a series of three active W-dipping back-thrusts: the Houchiali fault, the Napalin-Pitou back-thrust, and the Lungchuan back-thrust. They all root on the 3.5 - 4.0 km deep Tainan detachment located near the base of the 3-km-thick Gutingkeng mudstone. Further E, the detachment would ramp down to ~7 km depth. Coseismic surface deformation measurements suggest that, in addition to the deeper (15 - 20 km) main rupture plane, mostly the ramp, the Lungchuan back-thrust, and the Tainan detachment were activated during or right after the earthquake. Local extension is considered as transient deformation at the W edge of the shallow main slip zone. [ABSTRACT FROM AUTHOR]