Earthquake Doublet Sequences: Evidence of Static Triggering in the Strong Convergent Zones of Taiwan

Three earthquake sequences, each with two main earthquakes of almost the same magnitudes (ML from 5.9 to 7.0 with differences less than 0.1), have recently been observed in Taiwan. The two largest earthquakes in each sequence occurred with a short delay time between them, were strikingly similar in terms of magnitude, location and/or focal mechanism and are referred to as doublets. They were markedly distinct from typical single mainshock sequences. Our estimated static stress field generated by the first shock in the doublet shows that the second shock and most of their aftershocks were located within a region where static stress increased substantially. Thus, a possible explanation for earthquake doublet is that seismic energy for each shock had accumulated independently within adjacent crustal volumes, separated by an asperity, and that the second shock is triggered by the increased static stress after the first one. An important implication of doublet sequence is that works by emergency response teams after the first earthquake could be made more hazardous by the second

The Volcanic Earthquake Swarm of October 20, 2009 in the Tatun Area of Northern Taiwan

On October 20, 2009, a series of felt earthquakes with local magnitudes ranging from 2.8 - 3.2 occurred in the Tatun volcanic area off the northern tip of Taiwan. Although there was no damage caused by those earthquakes, many residents in the Taipei metropolitan area, particularly for people who live near the Yangminshan National Park, felt strong ground shaking. In order to know what the possible mechanisms were that generated those earthquakes, we carefully examined seismic data recorded by a dense seismic array in the Tatun volcanic area. During the period between October 18 and 22, 2009 we detected at least 202 micro-earthquakes. Most of the earthquakes were relocated using the double-difference method and were clustered in the shallow crust beneath the Dayoukeng area, which is the strongest fumarole in the Tatun volcanic area. Among these earthquakes, 72 focal mechanisms were determined by polarizing the first P-wave motion. Most earthquakes belonged to normal faulting. An extremely high b-value of 2.17 was obtained from those earthquakes. Based on the seismic variations in both the temporary and spatial distribution as well as an extremely high b-value, we conclude that the earthquake sequence on October 20, 2009 was a typically seismic swarm associated with possible active volcanism in the Tatun volcanic area

Effect of Surface Geology on Ground Motions: The Case of Station TAP056 - Chutzuhu Site

In the Tatun mountain area of northern Taiwan are two strong motion stations approximately 2.5 km apart, TAP056 and TAP066 of the TSMIP network. The accelerometer at station TAP056 is often triggered by earthquakes, but that at TAP066 station is not. Comparisons of vertical and horizontal peak ground accelerations reveal PGA in the vertical, east-west, and north-south components at TAP056 station to be 3.89, 7.57, and 5.45 times those at station TAP066, respectively. The PGA ratio does not seem to be related to earthquake source or path. Fourier spectra of earthquake records at station TAP056 always have approximately the same dominant frequency; however, those at station TAP066 are different due to different sources and paths of different events. This shows that spectra at TAP056 station are mainly controlled by local site effects. The spectral ratios of TAP056/TAP066 show the S-wave is amplified at around 8 ~ 10 Hz. The horizontal/vertical spectral ratios of station TAP056 also show a dominant frequency at about 6 and 8 ~ 10 Hz. After dense microtremor surveying and the addition of one accelerometer just 20 meters away from the original observation station, we can confirm that the top soft soil layer upon which the observation station is constructed generates the local site response at station TAP056

The Geophysical Database Management System in Taiwan

The Geophysical Database Management System (GDMS) is an integrated and web-based open data service which has been developed by the Central Weather Bureau (CWB), Taiwan, ROC since 2005. This service went online on August 1, 2008. The GDMS provides six types of geophysical data acquired from the Short-period Seismographic System, Broadband Seismographic System, Free-field Strong-motion Station, Strong-motion Building Array, Global Positioning System, and Groundwater Observation System. When utilizing the GDMS website, users can download seismic event data and continuous geophysical data. At present, many researchers have accessed this public platform to obtain geophysical data. Clearly, the establishment of GDMS is a significant improvement in data sorting for interested researchers

The association between volcanic fluid variations and seismic events in the Tatun Volcano Group, northern Taiwan

International audienceTaiwan is located at the western edge of the circum-Pacific volcanic belt. Hydrothermal activity is still common inthe Tatun Volcano Group, and it is one of the major geothermal areas in Taiwan. Before developing the geothermalresources, monitoring volcanic activities and further evaluating volcanic hazards are essential measures. Geochemistryplays an important role in investigating geothermal reservoirs. In the past decade, researchers in Taiwanhave accomplished several studies in this area. Our group collected volcanic gas and water samples to analyzetheir chemical compositions and isotopic ratios.Integrating our observations with seismic and gravity data, we can associate fluid variations with two mechanisms.Firstly, the variations of fluid concentration, seismic events and gravity fluctuations occurred in a time series.SO2/H2S ratios from Da-you-keng varied from 0 to 3 since 2005 to 2007. Meanwhile, HCl concentrations alsoincreased dramatically. Then large gravity variations and volcanic earthquake swarms took place subsequently.Same process happened again in 2010. We infer that magma chamber disturbance and/or deep fluid transportationmight be the major cause. The other case, unlike the former one having multiple proxy variations, we only observedHCl concentration increasing rapidly after big earthquakes. The variations are reckoned as the consequenceof hydrothermal reservoir disturbed by earthquakes, and the responding time is short and rapi

Seismic Detection of a Magma Reservoir beneath Turtle Island of Taiwan by S-Wave Shadows and Reflections

Abstract Although surface geology, eruption information and clustering seismicity all suggest Turtle Island (Kueishantao) of northern Taiwan is an active volcano, there was no direct evidence to conclude that magma reservoirs exist beneath it. Even less evidence is available to determine their spatial configuration. If the magma reservoirs are filled by liquids and melt, S-waves are totally reflected and leave behind a shadow, like when passing through the Earth’s outer core. We detect both these S-wave shadows and strong reflections from the surface using earthquakes at different depths and azimuths. These observations identify a km-scale molten-filled volume located beneath Turtle Island. The magmatic nature of the reservoir is supported by the onset of non-double-couple earthquakes with strong CLVD (Compensated Linear Vector Dipole) and ISO (Isotropic) components, which show a tensor crack compatible with some volume changes within the reservoir. Combining these results with two independent 3-D velocity models and aeromagnetic anomalies recorded in Taiwan, a partially-molten ~19% low-velocity volume is estimated in the mid-crust (13–23 km), with spatial uncertainties of ~3 km. The elongated direction approximately follows the strike of the Okinawa trough, indicating that the source of the magma reservoir might be a back-arc opening

A Low Velocity Zone along the Chaochou Fault in Southern Taiwan: Seismic Image Revealed by a Linear Seismic Array

The Chaochou fault is one of the major boundary faults in southern Taiwan where strong convergence has taken place between the Eurasian and Philippine Sea plates. The surface fault trace between the Pingtung plain and the Central Range follows a nearly N-S direction and stretches to 80 km in length. In order to examine the subsurface structures along the Chaochou fault, a linear seismic array with 14 short-period stations was deployed across the fault to record seismic data between August and December 2001. Detailed examination of seismic data generated by 10 local earthquakes and recorded by the linear array has shown that the incidence angles of the first P-waves recorded by several seismic stations at the fault zone were significantly larger than those located farther away from the fault zone. This difference might reflect the lateral variation of velocity structures across the Chaochou fault. Further examination of ray-paths of seismic wave propagation indicates that a low-velocity zone along the Chaochou fault is needed to explain the significant change in incidence angles across the fault zone. Although we do not have adequate information to calculate the exact geometry of the fault zone well, the variation in incidence angles across the fault can be explained by the existence of a low-velocity zone that is about 3 km in width on the surface and extends downward to a depth of 5 km. The low-velocity zone along the Chaochou fault might imply that the fault system consists of several splay faults on the hanging wall in the Central Range

Oncological outcomes of high-risk prostate cancer patients between robot-assisted laparoscopic radical prostatectomy and laparoscopic radical prostatectomy in Taiwan

Objective: To compare pathological and oncological outcomes between robotic-assisted laparoscopic radical prostatectomy (RaLRP) and laparoscopic radical prostatectomy (LRP) among high-risk prostate cancer patient in a tertiary center in Taiwan. Materials and methods: From November 2003 to October 2013, 129 high-risk prostate cancer patients receiving minimally-invasive radical prostatectomy were included. The Kaplan–Meier analysis was used for measuring biochemical recurrence-free survival (BFS). Multivariate logistic regression models and Cox proportional hazards regression models were used to determine predictors of positive surgical margin and BFS. Results: Among the 129 high-risk prostate cancer patients included, 80 (62%) patients received LRP and 49 (38%) patients received RaLRP. There was no significant difference of positive surgical margin and biochemical recurrence rate between RaLRP and LRP group (P = 0.802 and 0.292). Higher pathological T stage predicted an increased likelihood of positive margins (OR = 3.44, 95% CI [1.45, 8.18], P = 0.005). Higher initial PSA level (HR = 2.88, 95% CI [1.04, 7.94], P = 0.041) and positive surgical margin (HR = 2.55, 95% CI [1.20, 5.44], P = 0.015) were poor prognostic factors for BFS. Conclusion: RaLRP can be considered among high-risk prostate cancer in Asian people with comparable oncological outcomes to LRP. Higher pathological T stage was associated with increased likelihood of positive margins, patients with higher iPSA level and positive surgical margin had worsen biochemical recurrence-free survival

Interface geometry of potential mega-thrust earthquakes beneath the westernmost Ryukyu subduction system

The interface geometry at the subduction boundary plays one of the most important roles on evaluation of both seismic and tsunami impacts as the mega-thrust earthquakes occur between two plates. Although the general feature of the subducted slab at the mantle depth is clearly delineated from the seismicity in the Wadati-Benioff zone, the exact interface geometry at the crustal depth is hardly obtained from abundant earthquakes scattering in and around the interface between the two plates. Examination of seismic data recorded at the dense seismic array in the Tatun volcano group of northern Taiwan shows two unambiguous P-waves generated by shallow earthquakes offshore the Hualien area in eastern Taiwan. The detailed analyses of travel-times of both P-waves show that the 1st P-wave was the direct wave propagating within the upper crust while the 2nd P-waves were reflected from the subducted slab dipping northward ~23 degrees. This observation reveals the general interface geometry between the subducted Philippine Sea and the overlaid Eurasian plates at the crustal depth, where is often considered as the locked zone and accumulated a lot of seismic energy for release. Thus, the interface geometry obtained here provides important parameters for estimating the possible rupture plane along the mega-thrust fault between two plates in the westernmost Ryukyu subduction system in the future

Ursolic Acid Triggers Apoptosis in Human Osteosarcoma Cells via Caspase Activation and the ERK1/2 MAPK Pathway

Ursolic acid (UA), a naturally occurring pentacyclic triterpene acid found in many medicinal herbs and edible plants, has been shown to trigger apoptosis in several lines of tumor cells in vitro. We found that treatment with UA suppressed the viability of human osteosarcoma MG-63 cells and induced cell cycle arrest at sub-G1 and G2/M phases. Furthermore, exposure to UA induced intracellular oxidative stress and collapse of mitochondrial membrane permeability, resulting in the subsequent activation of apoptotic caspases 8, 9, and 3 as well as PARP cleavage, and ultimately apoptosis in MG-63 cells. Moreover, protein analysis of mitogen-activated protein kinase (MAPK)-related protein expression showed an increase in activated ERK1/2, JNK, and p38 MAPK in UA-treated MG-63 cells. In addition, UA-induced apoptosis was significantly abolished in MG-63 cells that had been pretreated with inhibitors of caspase 3, 8, and 9 and ERK1/2. Furthermore, UA-treated MG-63 cells also exhibited an enhancement in Bax/Bcl-2 ratio, whereas anti-apoptotic XIAP and survivin were down-regulated. Taken together, we provide evidence demonstrating that UA mediates caspase-dependent and ERK1/2 MAPK-associated apoptosis in osteosarcoma MG-63 cells