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492 results on '"Wu, Yih-Min"'

106. The influence of inherited continental margin structures on the stress and strain fields of the south-central Taiwan fold-and-thrust belt

Author

Biete, Cristina, Brown, Dennis, Lund, Björn, Alvarez-Marron, Joaquina, Wu, Yih-Min, Kuo-Chen, Hao, Ho, Chun-Wei, Biete, Cristina, Brown, Dennis, Lund, Björn, Alvarez-Marron, Joaquina, Wu, Yih-Min, Kuo-Chen, Hao, and Ho, Chun-Wei

Abstract

In this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (sigma(1), sigma(2) and sigma(3)) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (S-H) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of SH from north to south across the study area, with the direction of SH remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45 degrees counter-clockwise. The direction of the horizontal maximum compression strain rate (epsilon(H)) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. We interpret the southward change in the SH, eH and the dextral maximum shear plane directions, together with that of the horizontal displacement field to be related to the reactivation of east-northeast striking faults inherited from the rifted Eurasian margin and to the shelf/slope break. Inherited faults in the basement are typically reactivated as strike-slip faults, whereas newly formed faults in the fold-and-thrust belt are commonly thrusts or oblique thrusts. Eastwards, the stress inversions and strain data show that the western flank of the Central Range is undergoing extension in the upper crust. SH in the Central Range is roughly parallel to the relative plate convergence vector, but in southwestern Taiwan it undergoes a marked

Published
2019
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111. A strong-motion hot spot of the 2016 Meinong, Taiwan, earthquake (M_w = 6.4)

Author

Kanamori, Hiroo, Ye, Lingling, Huang, Bor-Shouh, Huang, Hsin-Hua, Lee, Shiann-Jong, Liang, Wen-Tzong, Lin, Yen-Yu, Ma, Kuo-Fong, Wu, Yih-Min, and Yeh, Te-Yang

Abstract

Despite a moderate magnitude, M_w = 6.4, the 5 February 2016 Meinong, Taiwan, earthquake caused significant damage in Tainan City and the surrounding areas. Several seismograms display an impulsive S-wave velocity pulse with an amplitude of about 1 m s-1, which is similar to large S-wave pulses recorded for the past several larger damaging earthquakes, such as the 1995 Kobe, Japan, earthquake (M_w = 6.9) and the 1994 Northridge, California, earthquake (M_w = 6.7). The observed PGV in the Tainan area is about 10 times larger than the median PGV of M_w = 6.4 crustal earthquakes in Taiwan. We investigate the cause of the localized strong ground motions. The peak-to-peak ground-motion displacement at the basin sites near Tainan is about 35 times larger than that at a mountain site with a similar epicentral distance. At some frequency bands (0.9 - 1.1 Hz), the amplitude ratio is as large as 200. Using the focal mechanism of this earthquake, typical “soft” and “hard” crustal structures, and directivity inferred from the observed waveforms and the slip distribution, we show that the combined effect yields an amplitude ratio of 17 to 34. The larger amplitude ratios at higher frequency bands can be probably due to the effects of complex 3-D basin structures. The result indicates that even from a moderate event, if these effects simultaneously work together toward amplifying ground motions, the extremely large ground motions as observed in Tainan can occur. Such occurrences should be taken into consideration in hazard mitigation measures in the place with frequent moderate earthquakes.

Published
2017

134. Testing the performance of earthquake early warning system in northern India.

Author

Yang, Benjamin Ming, Mittal, Himanshu, Wu, Yih-Min, Sharma, Mukat Lal, and Gupta, Sushil

Subjects
EARTHQUAKES, NATURAL disaster warning systems, ACCURACY of measuring instruments, SEISMOGRAMS
Abstract

The main goal of present study is to test the functionality of an earthquake early warning (EEW) system (a life-saving tool), in India using synthesized data and recorded earthquake data from Taiwan. In recent time, India set up an EEW system in the central seismic gap along the Himalayan Belt, consisting of about 100 low-cost P-Alert instruments. The area, where these instruments are installed, is highly sensitive to the seismic risk with the potential of strong, major and great earthquakes. In the absence of recorded data from the Himalayas required for analysis of such system, we take advantage of recorded waveforms from Taiwan, to test the EEW system. We selected Taiwanese stations in good accordance with the Indian sensor network, to have a best fit in terms of inter station spacing. Finally, the recorded waveforms are passed through Earthworm software using tankplayer module. The system performs very well in terms of earthquake detection, P-wave picking, earthquake magnitude and location (using previously estimated regressions). Pd algorithm has been tested where the peak amplitude of vertical displacement is used for estimating magnitudes using previously regressed empirical relationship data. For the earthquakes located between Main Boundary Thrust and Main Central Thrust along with a matching instrumentation window, a good estimate of location, as well as magnitude is observed. The approach based on Pd for estimating magnitude works perfectly as compared to τc approach, which is more sensitive to signal-to-noise ratio. To make it more region specific, we generated synthetic seismograms from the epicenters of historical Chamoli (1999) and Uttarkashi (1991) earthquakes at EEW stations in India and checked the functionality of EEW. While placing these earthquakes within the instrumentation window, a good approximation of earthquake location and magnitude is obtained by passing these generated waveforms. The parameters used to judge the performance of EEW system included the time taken by the system in issuing warning after the confirmation of the occurrence of damaging earthquake and the lead time (time interval between the issuing of warning and arrival of damaging earthquake ground motion at a particular location). High lead times have been obtained for the plainer regions including thickly populated regions of Gangetic plains, such as Delhi National Capital Region according to the distance from the epicenter, which are the main target of EEW system. [ABSTRACT FROM AUTHOR]

Published
2019
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145. Bayesian Analysis on Earthquake Magnitude Related to an Active Fault in Taiwan

Author

Wang, Jui-pin, Chang, Su-Chin, Wu, Yih-Min, Xu, Yun, Wang, Jui-pin, Chang, Su-Chin, Wu, Yih-Min, and Xu, Yun

Abstract

It is understood that sample size could be an issue in earthquake statistical studies, causing the best estimate being too deterministic or less representative derived from limited statistics from observation. Like many Bayesian analyses and estimates, this study shows another novel application of the Bayesian approach to earthquake engineering, using prior data to help compensate the limited observation for the target problem to estimate the magnitude of the recurring Meishan earthquake in central Taiwan. With the Bayesian algorithms developed, the Bayesian analysis suggests that the next major event induced by the Meishan fault in central Taiwan should be in M-w 6.44 +/- 033, based on one magnitude observation of M-w 6.4 from the last event, along with the prior data including fault length of 14 km, rupture width of 15 km, rupture area of 216 1cm2, average displacement of 0.7 m, slip rate of 6 mm/yr, and five earthquake empirical models. (C) 2015 Elsevier Ltd. All rights reserved.

Published
2015

146. Major Earthquakes Around Taipei and a Seismic Hazard Assessment with Monte Carlo Simulation

Author

Wang, Jui Pin CIVL, Wu, Yih-Min, Huang, Duruo, Wang, Jui Pin CIVL, Wu, Yih-Min, and Huang, Duruo

Abstract

The region around Taiwan is known for high seismicity. Under the circumstances, seismic hazard assessments and proper earthquake-resistant designs are essential to the region. From a well-studied earthquake catalog, this paper presents the statistics of major earthquakes (i.e., moment magnitude Mw≥5.5 and distance ≤200km) around the most important city in Taiwan (i.e., Taipei). The analysis shows that the mean annual rate of the major earthquakes is 2.79 around the city, with mean magnitude and SD equal to Mw 6.12 and 0.68, respectively, and mean source-to-site distance and SD equal to 129 and 39 km, respectively. With the earthquake statistics and local ground motion models, a seismic hazard assessment was conducted with Monte Carlo simulations (MCSs). The analysis shows the mean rate for peak ground acceleration ≥0.23g (where g is gravitational acceleration) should be around 0.013 per year, indicating that the current design peak ground acceleration in Taipei. From this paper, the current seismic design in Taipei might not be as conservative as expected, and a review and revision could be needed for assuring the city's seismic safety against high seismicity in the region.

Published
2015

147. Relationship Between Earthquake <italic>b</italic>‐Values and Crustal Stresses in a Young Orogenic Belt.

Author

Wu, Yih‐Min, Chen, Sean Kuanhsiang, Huang, Ting‐Chung, Huang, Hsin‐Hua, Chao, Wei‐An, and Koulakov, Ivan

Abstract

Abstract: It has been reported that earthquake b‐values decrease linearly with the differential stresses in the continental crust and subduction zones. Here we report a regression‐derived relation between earthquake b‐values and crustal stresses using the Anderson fault parameter (Aϕ) in a young orogenic belt of Taiwan. This regression relation is well established by using a large and complete earthquake catalog for Taiwan. The data set consists of b‐values and Aϕ values derived from relocated earthquakes and focal mechanisms, respectively. Our results show that b‐values decrease linearly with the Aϕ values at crustal depths with a high correlation coefficient of −0.9. Thus, b‐values could be used as stress indicators for orogenic belts. However, the state of stress is relatively well correlated with the surface geological setting with respect to earthquake b‐values in Taiwan. Temporal variations in the b‐value could constitute one of the main reasons for the spatial heterogeneity of b‐values. We therefore suggest that b‐values could be highly sensitive to temporal stress variations. [ABSTRACT FROM AUTHOR]

Published
2018
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