Shuei-Huei You - Academia.edu (original) (raw)

Papers by Shuei-Huei You

Frontiers in Public Health, 2021

In response to the COVID-19 pandemic, Taiwan has been one of the best performers in the world wit... more In response to the COVID-19 pandemic, Taiwan has been one of the best performers in the world with extremely low infections and deaths. This success can be attributed to the long experiences dealing with natural disasters and communicable diseases. However, with different disastrous characteristics, the disaster management systems for communicable diseases and natural disasters are very different in terms of laws, plans, frameworks, and emergency operations. Taking the response to COVID-19 pandemic as a study subject, we found that disaster management for communicable diseases can be improved through a comparison with natural disasters, and vice versa. First, having wider and longer impacts than natural disasters, the plans and framework for communicable diseases in Taiwan focus more on national and regional scales. Local governments would need more capacity support including budgets and training to conduct investigations and quarantine during the COVID-19 pandemic. Second, for quic...

We apply ambient noise surface wave analysis to the continuous waveform records acquired from the... more We apply ambient noise surface wave analysis to the continuous waveform records acquired from the seismic array sited in the Tatun Volcanic Area (TVA) from January 2004 to September 2005. The seismic array consisting of 8 seismic stations is initiated in May 2003 by Lin et al. (Lin et al., 2005). Each station is equipped with a short-period three-component sensor to enhance the understanding of the seismic characteristics of TVA. The Green’s functions of elastic waves can be retrieved by computing cross-correlations of continuous waveform records between station pair (e.g. Shapiro and Campillo, 2004). The stacked cross-correlation results are then treated as surface waves traveling between the station pairs, and their dispersion characteristics of group-velocity are analyzed. We present the dispersion curves for each path with a frequency-time analysis method in the period band from about 0.2 to 4 second. From the dispersion characteristics, we can extract the information of velocit...

ABSTRACT Retrieving empirical Green functions (EGF) between stations by cross-correlating continu... more ABSTRACT Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seismic records has quickly become a popular technique in seismology for its operational simplicity and various advantages over traditional surface wave tomography; in particular, the derived short period Green's functions of surface waves are usually inaccessible from seismic record caused by nature earthquakes. We apply this technique to three component continuous seismic data recorded at 88 short period stations in Taiwan. The data are collected from three seismic networks, including the island-wide Central Weather Bureau Seismic Network, and two temporary local seismic arrays, Tatun Volcanic Area array and Hsinchu array, for the time period from Jan, 2006 to Dec, 2006. For each station pairs, we derive Love waves from T-T (transverse) component cross-correlation functions (CCF), and Rayleigh waves from Z-Z (vertical) and R-R (radial) component CCF respectively. We measure group and phase velocities for the period range from 1 to 5 seconds. The achieved dense path coverage together with the retrieved short period EGF provide an unprecedented resolving power to the shallow crust structure of Taiwan island. With the qualified dispersion curves, we apply a multi-scale inversion technique to derive two dimensional phase, group velocity maps for both Rayleigh and Love waves, and three dimensional Vs structure of shallow crust. Besides tomographic study, we also attempt to probe the sources of ambient noise by several approaches: (1) analyzing the relative strength between the causal and acausal empirical Green's functions (EGF); (2) measuring the relative strength of CCF amplitudes with respect to their own annual average as a function of time and azimuth to determine the background energy flow; and (3) computing power spectra density of continuous record for representative costal stations. With the results, we are able to characterize the spatial and temporal variations of CCF and their possible relationship to the atmospheric perturbations and coastal bathymetry.

Japan Geoscience Union, 2016

菲律賓塔阿火山位於呂宋島上，馬尼拉市南方60公里處。塔阿火山是座非常活躍的活火山，基於它頻繁爆發的歷史，以及對於鄰近地區數百萬人口的高潛在危害度，塔阿火山被選為世界上15座最危險的火山之一。在2... more 菲律賓塔阿火山位於呂宋島上，馬尼拉市南方60公里處。塔阿火山是座非常活躍的活火山，基於它頻繁爆發的歷史，以及對於鄰近地區數百萬人口的高潛在危害度，塔阿火山被選為世界上15座最危險的火山之一。在2008年三月，我們在塔阿火山區域設置了一個由8個短周期地震觀測站所組成的臨時性地震觀測網，從2008年三月運行到2010年三月，記錄了超過2270個地震事件。在初期資料處理階段，我們利用周遭噪訊交互相關運算法，發現許多測站所記錄的資料具有線性偏移的誤差，並使用線性回歸方法修正所有地震事件的波相到時。地震的波相到時是經由仔細地人工挑選，並使用定位程式HYPO71，利用全球一維速度構造模型AK135測定初始的震源位置。之後我們挑選定位良好的地震，使用程式VELEST進行塔阿火山地區一維速度模型的反衍運算，並利用所得到的一維速度模型，改善地震事件的定位結果，並發現兩個地震群。一個地震群位於塔阿湖西岸呈現線性分佈的特性，另外一個地震群散佈於塔阿火山島東側，深度較淺的位置。之後我們利用改善之後地震定位結果，使用程式LOTOS進行三維速度模型的層析成像反衍計算，從反衍結果中我們發現幾個有趣的構造：在塔阿火山島的西北角，我們發現一個具有高速P波、高速S波，以及低P波-S波波速比值的構造，暗示了一個已經固化的舊有岩漿通道。而在塔阿火山島中央位置，我們發現一個低速S波以及高P波-S波波速比值的構造，可能代表一個大型的熱液儲存庫。另外我們在塔阿湖的西南角，發現一個具有低速P波、低速S波，以及高的P波-S波波值的構造，結合塔阿火山湖西側線性分佈的地震群，我們推測在塔阿火山湖西南角地底下可能存在著一個岩漿庫，並有一條岩漿通道從此處延伸到塔阿湖西北岸，如此的火山構造暗示著未來在遠離塔阿火山島上的歷史火山口的地區，可能會有新的火山口伴隨著岩漿噴出而形成。最後，我們量測地震剪力波分離的現象，藉以研究塔阿火山區域地殼中的方位非均向性，經過嚴格地篩選，我們得到40個有效的剪力波分離的量測結果，其結果顯示塔阿火山島底下的地殼方位非均向性相當複雜，可能反映著由島上眾多的歷史火山噴發口，以及反覆的岩漿入侵造成的地殼膨脹現象所形成的複雜應力非均向性，或是複雜的構造非均向性。The very active Taal Volcano is situated 60 km south of Metro Manila in the southern part of Luzon Island. Based on its frequent explosive eruptions and high potential hazards to nearby population of several million, Taal Volcano is chosen as one of the 15 most dangerous “Decade Volcanoes” in the world. We deployed a temporary seismic network consisting of 8 stations since March 2008. The temporal network was operated from late March 2008 to mid March 2010 and recorded over 2270 local earthquakes. In the early data processing stages, unexpected linear drifting of clock time was clearly identified from ambient noise cross-correlation functions for a number of stations. The drifting rates of all problematic stations were determined as references to correct timing errors prior to further processing. Initial locations of earthquakes were determined from manually picking P- and S-phases arrivals with a general velocity model based on AK135. We used travel times of 305 well-located local events to derive a minimum 1-D model using VELEST. Two major earthquake groups were noticed from refined locations. One was underneath the western shore of Taal Lake with a linear feature, and the other spread at shallower depths showing a less compact feature around the eastern flank of Taal Volcano Island. We performed seismic tomography to image the 3D structure beneath Taal Volcano using a well-established algorithm, LOTOS. Some interesting features are noted in the tomographic results, such as a probable solidified past magma conduit below the northwestern corner of Taal Volcano Island, characterized by high Vp, Vs, and low Vp/Vs ratio, and a potential large hydrothermal reservoir beneath the central of Taal Volcano Island, characterized by low Vs and high Vp/Vs ratio. Combining the results of seismicity and tomographic images, we also suggest the potential existence of a magma chamber beneath the southwestern Taal Lake, and a magma conduit or fault extending from there to the northwestern shore of Taal Lake. Such magmatic signatures have never been reported in previous studies, suggesting that new eruption centers might be forming in places away from the historical craters on Taal Volcano Island. Finally, to investigate the anisotropy beneath Taal Volcano, we conducted shear wave splitting measurements using data from local earthquakes. With strict selection criteria, 40 valid measurements are remained. The resulting patterns of azimuthal anisotropy are difficult to interpret, and such complexity might be attributed to complex stress-induced anisotropy caused by numerous past eruptions and inflating behaviors induced by episodic intrusion of magma into a shallow reservoir, or complex structural anisotropy caused by crustal media with complicated patterns of prominent structures such as layers, parallel fractures, or lineated fabrics.口試委員會審定書………………………………………………………………i 誌謝………………………………………………………………………………ii 中文摘要…………………………………………………………………………iii Abstract…………………………………………………………………………iv Table of Contents………………………………………………………………vi List of Figures……………………………………………………………………viii List of Tables……………………………………………………………………x Chapter 1 Introdution……………………………………………………………1 Chapter 2 Temporary seismic network…………………………………………8 Chapter 3 Ambient noise analysis and timing-error detection and correction………………15 3.1 Introduction………………………………………………………………... 15 3.2 Data processing of ambient noise analysis………………………………... 17 3.3 Linear drifting of CCFs………………...…………………………………. 17 3.4 Time-drifting correction…………………………………………………... 19 3.5 Conclusion………………………………………………………………… 20 Chapter 4 Minimum 1-D velocity model and local seismicity…………………30 4.1 Introduction………………………………………………………………30 4.2 Concept of VELEST………………………………………………………31 4.3 Preliminary seismic locations and data selection…………………………33 4.4 Model determination and test of model layering……………………34 4.5 Spatial and temporal distribution of earthquakes………………36 4.6 Conclusion…………………………………………………………38 Chapter 5 3D local earthquake tomography…………………………………54 5.1 Introduction………………………………………………………………54 5.2…

Seismological Research Letters, 2018

Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Isl... more Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Islands and caused extensive damage, which motivated us to establish a temporary seismic network around the rupture zones of these earthquakes. With the available continuous seismic data recorded from eight seismic stations, we cross correlate the vertical component of ambient-noise records and calculate Rayleigh-wave group velocity dispersion curves for interstation pairs. A genetic algorithm is adopted to fit the averaged dispersion curve and invert a 1D crustal velocity model, which constitutes two layers (upper and lower crust) and a half-space (uppermost mantle). The resulting thickness values for the upper and lower crust are 6.9 and 13.5 km, respectively. The shear-wave velocities (V S) of the upper crust, lower crust, and uppermost mantle are 2.62, 3.54, and 4:10 km=s with V P =V S ratios of 1.745, 1.749, and 1.766, respectively. The differences between the predicted and observed travel times show that our 1D model (WSOLOCrust) has average 0.85-and 0.16-s improvements in travel-time residuals compared with the global iasp91 and local CRUST 1.0 models, respectively. This layered crustal velocity model for the western Solomon Islands can be further used as a referenced velocity model to locate earthquake and tremor sources as well as to perform 3D seismic tomography in this region. Electronic Supplement: Figures showing the misfit of inversion process and the comparison between observed and synthetics and the location of experiments in previous studies and tables listing information about the seismic network, parameters of the genetic algorithm (GA), information of earthquakes used in this study, and results obtained from different 1D models.

Journal of Seismology, 2017

Based on its numerous historical explosive eruptions and high potential hazards to nearby populat... more Based on its numerous historical explosive eruptions and high potential hazards to nearby population of millions, Taal Volcano is one of the most dangerous BDecade Volcanoes^in the world. To provide better investigation on local seismicity and seismic structure beneath Taal Volcano, we deployed a temporary seismic network consisting of eight stations from March 2008 to March 2010. In the preliminary data processing stage, three periods showing linear time-drifting of internal clock were clearly identified from noise-derived empirical Green's functions. The time-drifting errors were corrected prior to further data analyses. By using VELEST, 2274 local earthquakes were manually picked and located. Two major earthquake groups are noticed, with one lying beneath the western shore of Taal Lake showing a linear feature, and the other spreading around the eastern flank of Taal Volcano Island at shallower depths. We performed seismic tomography to image the 3D structure beneath Taal Volcano using the LOTOS algorithm. Some interesting features are revealed from the tomographic results, including a solidified magma conduit below the northwestern corner of Taal Volcano Island, indicated by high Vp, Vs, and low Vp/ Vs ratio, and a large potential hydrothermal reservoir beneath the center of Taal Volcano Island, suggested by low Vs and high Vp/Vs ratio. Furthermore, combining earthquake distributions and tomographic images, we suggest potential existence of a hydrothermal reservoir beneath the southwestern corner of Taal Lake, and a fluid conduit extending to the northwest. These seismic features have never been proposed in previous studies, implying that new hydrothermal activity might be formed in places away from the historical craters on Taal Volcano Island.

Terrestrial, Atmospheric and Oceanic Sciences, 2005

To enhance our understanding of the seismic characteristics of the Tatun volcanic area, a small a... more To enhance our understanding of the seismic characteristics of the Tatun volcanic area, a small aperture seismic array consisting of 5 seismic stations has been deployed in the area since May 2003. Each of the seismic stations was installed with both short-period and broadband sensors to record micro-earthquakes as well as long-period volcanic tremors. The preliminary results of the seismic monitoring of the Tatun volcanic area show a large number of shallow micro-earthquakes clustered beneath the Chihsingshan volcano and Tayoikeng areas. Among these, some swarms were also detected. Intensifying the issue further, some complex seismograms with harmonic codas and seismic tremors have been identified. Considerable crustal heterogeneity in the Tatun volcanic area is indicated by the presence of strong coda waves. Combining our findings with other geological and geochemical observations, we postulate that volcanic activities might not be totally extinct in the Tatun volcanic area. Thus, further investigations of Tatun volcanic area ought be conducted to examine the possibility of such potential volcanic activity.

This is the first time to report several types of volcanic signals such as Tornillos (screws), ha... more This is the first time to report several types of volcanic signals such as Tornillos (screws), harmonic signals (drops) and continuously short-period volcanic tremors at the Tatun volcanic group (Taiwan), which was usually considered as extinct because there was no any historical eruption. These volcanic signals are often reported in the active volcanoes in the earth. In particular, the tornillos have been considered as the potential precursor for volcanic eruption at Galeras volcano, Colombia. Combining all of these volcanic signals with the presviously geochemical analyses from the Helium isotop ratio, we strongly suggest that volcanic activities in the Tatun volcanic area might not be totally extinct yet and further investigations have to been done for evaluation of potential volcanic activities because the Tatun volcano group is not only just nearby two nuclear power plants but also about 15 km north to Taipei, the capital of Taiwan, in which more than seven million people live on.

We apply ambient noise surface wave analysis to the continuous waveform records acquired from the... more We apply ambient noise surface wave analysis to the continuous waveform records acquired from the seismic array sited in th e Tatun Volcanic Area (TVA) from January 2004 to September 2005. The seismic array consisting of 8 seismic stations is initiated in May 2003 by Lin et al. (Lin et al., 20 05). Each station is equipped with a short-period three-component sensor to enhance the understanding of the seismic characteristics of TVA. The Green's functions of el astic waves can be retrieved by computing cross-correlations of continuous waveform records between station pair (e.g. Shapiro and Campillo, 2004). The stacked cros s-correlation results are then treated as surface waves traveling between the stat ion pairs, and their dispersion characteristics of group-velocity are analyzed. We present the dispersion curves for each path with a frequency-time analysis method in the period band from about 0.2 to 4 second. From the dispersion characteristics, we c an extract the information ...

Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seism... more Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seismic records has quickly become a popular technique in seismology for its operational simplicity and various advantages over traditional surface wave tomography; in particular, the derived short period Green's functions of surface waves are usually inaccessible from seismic record caused by nature earthquakes. We apply this technique to three component continuous seismic data recorded at 88 short period stations in Taiwan. The data are collected from three seismic networks, including the island-wide Central Weather Bureau Seismic Network, and two temporary local seismic arrays, Tatun Volcanic Area array and Hsinchu array, for the time period from Jan, 2006 to Dec, 2006. For each station pairs, we derive Love waves from T-T (transverse) component cross-correlation functions (CCF), and Rayleigh waves from Z-Z (vertical) and R-R (radial) component CCF respectively. We measure group and ph...

We derive a three dimensional velocity model of seismic waves beneath Taal Volcano, Philippines, ... more We derive a three dimensional velocity model of seismic waves beneath Taal Volcano, Philippines, from about 2300 local earthquakes recorded by the Taal Volcano seismic network during the time period from March 2008 to March 2010. In the early data processing stage, with the cross-correlation functions of continuous record of station pairs, unexpected linear drifting of clock time was clearly identified. The drifting rates of each problematic station were determined and the errors were corrected before further processing. With the corrected data, we first determined initial locations by using the program HYPO71 and the reference 1-D global model ak135. 749 well-located events with 3381 P-wave and 2896 S-wave arrivals were used to derive the 'minimum 1-D velocity model' with the program VELEST developed by Kissling to further improve the 1-D velocity model and event locations. With the robust 1-D velocity model and improved event locations, we inverted a high-resolution 3-D ve...

Geophysical Research Letters, 2005

The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei... more The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei. A seismic array consisting of 5 stations equipped with both broadband and short-period sensors was installed in 2003 in order to monitor the seismic activity of the area. It recorded a variety of events including common volcano-tectonic earthquakes and volcanoseismic signals like tornillos, short duration monochromatic events (10-15 s) and long duration spasmodic bursts ($15 min). An analysis of the complex frequencies of the tornillo/monochromatic signals shows that Q-values are of the order of several hundreds. Based on the model of a fluid-filled crack, such Q-values can result from the oscillations of a crack containing a misty or dusty gas. These observations put into doubt the long-standing suggestion that the Tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area.

Bulletin of the Seismological Society of America, 2010

Journal of Asian Earth Sciences, 2013

ABSTRACT The very active Taal Volcano lies in the southern part of Luzon Island only 60 km from M... more ABSTRACT The very active Taal Volcano lies in the southern part of Luzon Island only 60 km from Manila, the capital of the Philippines. In March 2008 we deployed a temporary seismic network around Taal that consisted of 8 three-component short period seismometers. This network recorded during the period from March to November 2008 about 1050 local events. In the early data processing stages, unexpected linear drifting of clock time was clearly identified for a number of stations. The drifting rates of each problematic station were determined and the errors were corrected before further processing. Initial location of each event was derived by manually picked P-/S-phases arrival times using HYPO71 and a general velocity model based on AK135. Since the velocity structure beneath Taal is essentially unknown, we used travel times of 338 well-located events in order to derive a minimum 1D velocity model using VELEST. The resulting locations show that most events occurred at the shallow depth beneath the Taal Volcano, and two major earthquake groups were noticed, with one lying underneath the western shore of Taal lake and the other one spread around the eastern flank of the Taal Volcano. Since there is no reported volcano activities during the operation period of our seismic array, we are still not confident to interpret these findings in terms of other natures of volcano at the current stage. However, our work represents an important pioneer step towards other more advanced seismic studies in Taal Volcano.

Geophysical Research Letters, 2011

Frontiers in Public Health, 2021

In response to the COVID-19 pandemic, Taiwan has been one of the best performers in the world wit... more In response to the COVID-19 pandemic, Taiwan has been one of the best performers in the world with extremely low infections and deaths. This success can be attributed to the long experiences dealing with natural disasters and communicable diseases. However, with different disastrous characteristics, the disaster management systems for communicable diseases and natural disasters are very different in terms of laws, plans, frameworks, and emergency operations. Taking the response to COVID-19 pandemic as a study subject, we found that disaster management for communicable diseases can be improved through a comparison with natural disasters, and vice versa. First, having wider and longer impacts than natural disasters, the plans and framework for communicable diseases in Taiwan focus more on national and regional scales. Local governments would need more capacity support including budgets and training to conduct investigations and quarantine during the COVID-19 pandemic. Second, for quic...

We apply ambient noise surface wave analysis to the continuous waveform records acquired from the... more We apply ambient noise surface wave analysis to the continuous waveform records acquired from the seismic array sited in the Tatun Volcanic Area (TVA) from January 2004 to September 2005. The seismic array consisting of 8 seismic stations is initiated in May 2003 by Lin et al. (Lin et al., 2005). Each station is equipped with a short-period three-component sensor to enhance the understanding of the seismic characteristics of TVA. The Green’s functions of elastic waves can be retrieved by computing cross-correlations of continuous waveform records between station pair (e.g. Shapiro and Campillo, 2004). The stacked cross-correlation results are then treated as surface waves traveling between the station pairs, and their dispersion characteristics of group-velocity are analyzed. We present the dispersion curves for each path with a frequency-time analysis method in the period band from about 0.2 to 4 second. From the dispersion characteristics, we can extract the information of velocit...

ABSTRACT Retrieving empirical Green functions (EGF) between stations by cross-correlating continu... more ABSTRACT Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seismic records has quickly become a popular technique in seismology for its operational simplicity and various advantages over traditional surface wave tomography; in particular, the derived short period Green's functions of surface waves are usually inaccessible from seismic record caused by nature earthquakes. We apply this technique to three component continuous seismic data recorded at 88 short period stations in Taiwan. The data are collected from three seismic networks, including the island-wide Central Weather Bureau Seismic Network, and two temporary local seismic arrays, Tatun Volcanic Area array and Hsinchu array, for the time period from Jan, 2006 to Dec, 2006. For each station pairs, we derive Love waves from T-T (transverse) component cross-correlation functions (CCF), and Rayleigh waves from Z-Z (vertical) and R-R (radial) component CCF respectively. We measure group and phase velocities for the period range from 1 to 5 seconds. The achieved dense path coverage together with the retrieved short period EGF provide an unprecedented resolving power to the shallow crust structure of Taiwan island. With the qualified dispersion curves, we apply a multi-scale inversion technique to derive two dimensional phase, group velocity maps for both Rayleigh and Love waves, and three dimensional Vs structure of shallow crust. Besides tomographic study, we also attempt to probe the sources of ambient noise by several approaches: (1) analyzing the relative strength between the causal and acausal empirical Green's functions (EGF); (2) measuring the relative strength of CCF amplitudes with respect to their own annual average as a function of time and azimuth to determine the background energy flow; and (3) computing power spectra density of continuous record for representative costal stations. With the results, we are able to characterize the spatial and temporal variations of CCF and their possible relationship to the atmospheric perturbations and coastal bathymetry.

Japan Geoscience Union, 2016

菲律賓塔阿火山位於呂宋島上，馬尼拉市南方60公里處。塔阿火山是座非常活躍的活火山，基於它頻繁爆發的歷史，以及對於鄰近地區數百萬人口的高潛在危害度，塔阿火山被選為世界上15座最危險的火山之一。在2... more 菲律賓塔阿火山位於呂宋島上，馬尼拉市南方60公里處。塔阿火山是座非常活躍的活火山，基於它頻繁爆發的歷史，以及對於鄰近地區數百萬人口的高潛在危害度，塔阿火山被選為世界上15座最危險的火山之一。在2008年三月，我們在塔阿火山區域設置了一個由8個短周期地震觀測站所組成的臨時性地震觀測網，從2008年三月運行到2010年三月，記錄了超過2270個地震事件。在初期資料處理階段，我們利用周遭噪訊交互相關運算法，發現許多測站所記錄的資料具有線性偏移的誤差，並使用線性回歸方法修正所有地震事件的波相到時。地震的波相到時是經由仔細地人工挑選，並使用定位程式HYPO71，利用全球一維速度構造模型AK135測定初始的震源位置。之後我們挑選定位良好的地震，使用程式VELEST進行塔阿火山地區一維速度模型的反衍運算，並利用所得到的一維速度模型，改善地震事件的定位結果，並發現兩個地震群。一個地震群位於塔阿湖西岸呈現線性分佈的特性，另外一個地震群散佈於塔阿火山島東側，深度較淺的位置。之後我們利用改善之後地震定位結果，使用程式LOTOS進行三維速度模型的層析成像反衍計算，從反衍結果中我們發現幾個有趣的構造：在塔阿火山島的西北角，我們發現一個具有高速P波、高速S波，以及低P波-S波波速比值的構造，暗示了一個已經固化的舊有岩漿通道。而在塔阿火山島中央位置，我們發現一個低速S波以及高P波-S波波速比值的構造，可能代表一個大型的熱液儲存庫。另外我們在塔阿湖的西南角，發現一個具有低速P波、低速S波，以及高的P波-S波波值的構造，結合塔阿火山湖西側線性分佈的地震群，我們推測在塔阿火山湖西南角地底下可能存在著一個岩漿庫，並有一條岩漿通道從此處延伸到塔阿湖西北岸，如此的火山構造暗示著未來在遠離塔阿火山島上的歷史火山口的地區，可能會有新的火山口伴隨著岩漿噴出而形成。最後，我們量測地震剪力波分離的現象，藉以研究塔阿火山區域地殼中的方位非均向性，經過嚴格地篩選，我們得到40個有效的剪力波分離的量測結果，其結果顯示塔阿火山島底下的地殼方位非均向性相當複雜，可能反映著由島上眾多的歷史火山噴發口，以及反覆的岩漿入侵造成的地殼膨脹現象所形成的複雜應力非均向性，或是複雜的構造非均向性。The very active Taal Volcano is situated 60 km south of Metro Manila in the southern part of Luzon Island. Based on its frequent explosive eruptions and high potential hazards to nearby population of several million, Taal Volcano is chosen as one of the 15 most dangerous “Decade Volcanoes” in the world. We deployed a temporary seismic network consisting of 8 stations since March 2008. The temporal network was operated from late March 2008 to mid March 2010 and recorded over 2270 local earthquakes. In the early data processing stages, unexpected linear drifting of clock time was clearly identified from ambient noise cross-correlation functions for a number of stations. The drifting rates of all problematic stations were determined as references to correct timing errors prior to further processing. Initial locations of earthquakes were determined from manually picking P- and S-phases arrivals with a general velocity model based on AK135. We used travel times of 305 well-located local events to derive a minimum 1-D model using VELEST. Two major earthquake groups were noticed from refined locations. One was underneath the western shore of Taal Lake with a linear feature, and the other spread at shallower depths showing a less compact feature around the eastern flank of Taal Volcano Island. We performed seismic tomography to image the 3D structure beneath Taal Volcano using a well-established algorithm, LOTOS. Some interesting features are noted in the tomographic results, such as a probable solidified past magma conduit below the northwestern corner of Taal Volcano Island, characterized by high Vp, Vs, and low Vp/Vs ratio, and a potential large hydrothermal reservoir beneath the central of Taal Volcano Island, characterized by low Vs and high Vp/Vs ratio. Combining the results of seismicity and tomographic images, we also suggest the potential existence of a magma chamber beneath the southwestern Taal Lake, and a magma conduit or fault extending from there to the northwestern shore of Taal Lake. Such magmatic signatures have never been reported in previous studies, suggesting that new eruption centers might be forming in places away from the historical craters on Taal Volcano Island. Finally, to investigate the anisotropy beneath Taal Volcano, we conducted shear wave splitting measurements using data from local earthquakes. With strict selection criteria, 40 valid measurements are remained. The resulting patterns of azimuthal anisotropy are difficult to interpret, and such complexity might be attributed to complex stress-induced anisotropy caused by numerous past eruptions and inflating behaviors induced by episodic intrusion of magma into a shallow reservoir, or complex structural anisotropy caused by crustal media with complicated patterns of prominent structures such as layers, parallel fractures, or lineated fabrics.口試委員會審定書………………………………………………………………i 誌謝………………………………………………………………………………ii 中文摘要…………………………………………………………………………iii Abstract…………………………………………………………………………iv Table of Contents………………………………………………………………vi List of Figures……………………………………………………………………viii List of Tables……………………………………………………………………x Chapter 1 Introdution……………………………………………………………1 Chapter 2 Temporary seismic network…………………………………………8 Chapter 3 Ambient noise analysis and timing-error detection and correction………………15 3.1 Introduction………………………………………………………………... 15 3.2 Data processing of ambient noise analysis………………………………... 17 3.3 Linear drifting of CCFs………………...…………………………………. 17 3.4 Time-drifting correction…………………………………………………... 19 3.5 Conclusion………………………………………………………………… 20 Chapter 4 Minimum 1-D velocity model and local seismicity…………………30 4.1 Introduction………………………………………………………………30 4.2 Concept of VELEST………………………………………………………31 4.3 Preliminary seismic locations and data selection…………………………33 4.4 Model determination and test of model layering……………………34 4.5 Spatial and temporal distribution of earthquakes………………36 4.6 Conclusion…………………………………………………………38 Chapter 5 3D local earthquake tomography…………………………………54 5.1 Introduction………………………………………………………………54 5.2…

Seismological Research Letters, 2018

Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Isl... more Two earthquakes, M w 8.1 in 2007 and M w 7.1 in 2010, hit the western province of the Solomon Islands and caused extensive damage, which motivated us to establish a temporary seismic network around the rupture zones of these earthquakes. With the available continuous seismic data recorded from eight seismic stations, we cross correlate the vertical component of ambient-noise records and calculate Rayleigh-wave group velocity dispersion curves for interstation pairs. A genetic algorithm is adopted to fit the averaged dispersion curve and invert a 1D crustal velocity model, which constitutes two layers (upper and lower crust) and a half-space (uppermost mantle). The resulting thickness values for the upper and lower crust are 6.9 and 13.5 km, respectively. The shear-wave velocities (V S) of the upper crust, lower crust, and uppermost mantle are 2.62, 3.54, and 4:10 km=s with V P =V S ratios of 1.745, 1.749, and 1.766, respectively. The differences between the predicted and observed travel times show that our 1D model (WSOLOCrust) has average 0.85-and 0.16-s improvements in travel-time residuals compared with the global iasp91 and local CRUST 1.0 models, respectively. This layered crustal velocity model for the western Solomon Islands can be further used as a referenced velocity model to locate earthquake and tremor sources as well as to perform 3D seismic tomography in this region. Electronic Supplement: Figures showing the misfit of inversion process and the comparison between observed and synthetics and the location of experiments in previous studies and tables listing information about the seismic network, parameters of the genetic algorithm (GA), information of earthquakes used in this study, and results obtained from different 1D models.

Journal of Seismology, 2017

Based on its numerous historical explosive eruptions and high potential hazards to nearby populat... more Based on its numerous historical explosive eruptions and high potential hazards to nearby population of millions, Taal Volcano is one of the most dangerous BDecade Volcanoes^in the world. To provide better investigation on local seismicity and seismic structure beneath Taal Volcano, we deployed a temporary seismic network consisting of eight stations from March 2008 to March 2010. In the preliminary data processing stage, three periods showing linear time-drifting of internal clock were clearly identified from noise-derived empirical Green's functions. The time-drifting errors were corrected prior to further data analyses. By using VELEST, 2274 local earthquakes were manually picked and located. Two major earthquake groups are noticed, with one lying beneath the western shore of Taal Lake showing a linear feature, and the other spreading around the eastern flank of Taal Volcano Island at shallower depths. We performed seismic tomography to image the 3D structure beneath Taal Volcano using the LOTOS algorithm. Some interesting features are revealed from the tomographic results, including a solidified magma conduit below the northwestern corner of Taal Volcano Island, indicated by high Vp, Vs, and low Vp/ Vs ratio, and a large potential hydrothermal reservoir beneath the center of Taal Volcano Island, suggested by low Vs and high Vp/Vs ratio. Furthermore, combining earthquake distributions and tomographic images, we suggest potential existence of a hydrothermal reservoir beneath the southwestern corner of Taal Lake, and a fluid conduit extending to the northwest. These seismic features have never been proposed in previous studies, implying that new hydrothermal activity might be formed in places away from the historical craters on Taal Volcano Island.

Terrestrial, Atmospheric and Oceanic Sciences, 2005

To enhance our understanding of the seismic characteristics of the Tatun volcanic area, a small a... more To enhance our understanding of the seismic characteristics of the Tatun volcanic area, a small aperture seismic array consisting of 5 seismic stations has been deployed in the area since May 2003. Each of the seismic stations was installed with both short-period and broadband sensors to record micro-earthquakes as well as long-period volcanic tremors. The preliminary results of the seismic monitoring of the Tatun volcanic area show a large number of shallow micro-earthquakes clustered beneath the Chihsingshan volcano and Tayoikeng areas. Among these, some swarms were also detected. Intensifying the issue further, some complex seismograms with harmonic codas and seismic tremors have been identified. Considerable crustal heterogeneity in the Tatun volcanic area is indicated by the presence of strong coda waves. Combining our findings with other geological and geochemical observations, we postulate that volcanic activities might not be totally extinct in the Tatun volcanic area. Thus, further investigations of Tatun volcanic area ought be conducted to examine the possibility of such potential volcanic activity.

This is the first time to report several types of volcanic signals such as Tornillos (screws), ha... more This is the first time to report several types of volcanic signals such as Tornillos (screws), harmonic signals (drops) and continuously short-period volcanic tremors at the Tatun volcanic group (Taiwan), which was usually considered as extinct because there was no any historical eruption. These volcanic signals are often reported in the active volcanoes in the earth. In particular, the tornillos have been considered as the potential precursor for volcanic eruption at Galeras volcano, Colombia. Combining all of these volcanic signals with the presviously geochemical analyses from the Helium isotop ratio, we strongly suggest that volcanic activities in the Tatun volcanic area might not be totally extinct yet and further investigations have to been done for evaluation of potential volcanic activities because the Tatun volcano group is not only just nearby two nuclear power plants but also about 15 km north to Taipei, the capital of Taiwan, in which more than seven million people live on.

We apply ambient noise surface wave analysis to the continuous waveform records acquired from the... more We apply ambient noise surface wave analysis to the continuous waveform records acquired from the seismic array sited in th e Tatun Volcanic Area (TVA) from January 2004 to September 2005. The seismic array consisting of 8 seismic stations is initiated in May 2003 by Lin et al. (Lin et al., 20 05). Each station is equipped with a short-period three-component sensor to enhance the understanding of the seismic characteristics of TVA. The Green's functions of el astic waves can be retrieved by computing cross-correlations of continuous waveform records between station pair (e.g. Shapiro and Campillo, 2004). The stacked cros s-correlation results are then treated as surface waves traveling between the stat ion pairs, and their dispersion characteristics of group-velocity are analyzed. We present the dispersion curves for each path with a frequency-time analysis method in the period band from about 0.2 to 4 second. From the dispersion characteristics, we c an extract the information ...

Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seism... more Retrieving empirical Green functions (EGF) between stations by cross-correlating continuous seismic records has quickly become a popular technique in seismology for its operational simplicity and various advantages over traditional surface wave tomography; in particular, the derived short period Green's functions of surface waves are usually inaccessible from seismic record caused by nature earthquakes. We apply this technique to three component continuous seismic data recorded at 88 short period stations in Taiwan. The data are collected from three seismic networks, including the island-wide Central Weather Bureau Seismic Network, and two temporary local seismic arrays, Tatun Volcanic Area array and Hsinchu array, for the time period from Jan, 2006 to Dec, 2006. For each station pairs, we derive Love waves from T-T (transverse) component cross-correlation functions (CCF), and Rayleigh waves from Z-Z (vertical) and R-R (radial) component CCF respectively. We measure group and ph...

We derive a three dimensional velocity model of seismic waves beneath Taal Volcano, Philippines, ... more We derive a three dimensional velocity model of seismic waves beneath Taal Volcano, Philippines, from about 2300 local earthquakes recorded by the Taal Volcano seismic network during the time period from March 2008 to March 2010. In the early data processing stage, with the cross-correlation functions of continuous record of station pairs, unexpected linear drifting of clock time was clearly identified. The drifting rates of each problematic station were determined and the errors were corrected before further processing. With the corrected data, we first determined initial locations by using the program HYPO71 and the reference 1-D global model ak135. 749 well-located events with 3381 P-wave and 2896 S-wave arrivals were used to derive the 'minimum 1-D velocity model' with the program VELEST developed by Kissling to further improve the 1-D velocity model and event locations. With the robust 1-D velocity model and improved event locations, we inverted a high-resolution 3-D ve...

Geophysical Research Letters, 2005

The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei... more The Tatun Volcano Group lies at the northern tip of Taiwan only 15 km north of the capital Taipei. A seismic array consisting of 5 stations equipped with both broadband and short-period sensors was installed in 2003 in order to monitor the seismic activity of the area. It recorded a variety of events including common volcano-tectonic earthquakes and volcanoseismic signals like tornillos, short duration monochromatic events (10-15 s) and long duration spasmodic bursts ($15 min). An analysis of the complex frequencies of the tornillo/monochromatic signals shows that Q-values are of the order of several hundreds. Based on the model of a fluid-filled crack, such Q-values can result from the oscillations of a crack containing a misty or dusty gas. These observations put into doubt the long-standing suggestion that the Tatun volcanoes are extinct and prompt for a thorough assessment of the volcanic hazard for this area.

Bulletin of the Seismological Society of America, 2010

Journal of Asian Earth Sciences, 2013

ABSTRACT The very active Taal Volcano lies in the southern part of Luzon Island only 60 km from M... more ABSTRACT The very active Taal Volcano lies in the southern part of Luzon Island only 60 km from Manila, the capital of the Philippines. In March 2008 we deployed a temporary seismic network around Taal that consisted of 8 three-component short period seismometers. This network recorded during the period from March to November 2008 about 1050 local events. In the early data processing stages, unexpected linear drifting of clock time was clearly identified for a number of stations. The drifting rates of each problematic station were determined and the errors were corrected before further processing. Initial location of each event was derived by manually picked P-/S-phases arrival times using HYPO71 and a general velocity model based on AK135. Since the velocity structure beneath Taal is essentially unknown, we used travel times of 338 well-located events in order to derive a minimum 1D velocity model using VELEST. The resulting locations show that most events occurred at the shallow depth beneath the Taal Volcano, and two major earthquake groups were noticed, with one lying underneath the western shore of Taal lake and the other one spread around the eastern flank of the Taal Volcano. Since there is no reported volcano activities during the operation period of our seismic array, we are still not confident to interpret these findings in terms of other natures of volcano at the current stage. However, our work represents an important pioneer step towards other more advanced seismic studies in Taal Volcano.

Geophysical Research Letters, 2011