Wen-tzong Liang - Academia.edu (original) (raw)

Papers by Wen-tzong Liang

It is hoped that through the cultivation of a crew of volunteer citizen seismologists, public inv... more It is hoped that through the cultivation of a crew of volunteer citizen seismologists, public involvement could be encouraged and the discovery and inquiry into earthquake knowledge could be promoted. These volunteers can contribute to data collection, analysis, and reporting, and have the potential to greatly improve the emergency response to earthquakes. The Citizen Seismologists in Taiwan Project (CSTaiwan) is designed to elevate the quality of earthquake science education by incorporating earthquake and tsunami stories and educational earthquake games into traditional school curricula. The project aims to build a cloud-based computing service incorporating an earthquake school (i.e., a website for online learning) where teachers can easily teach their students about earthquakes and children can learn about earthquakes in a fun environment. Here we demonstrate how students perform P-and S-wave picking and measure seismic intensity through an interactive learning platform, how scientists and school teachers work together, and how we create a near-real-time earthquake games competition to facilitate continuous learning while making earthquake science fun. We also develop 49 questions associated with participants' preknowl-edge, attitude, and skills in earthquake sciences, called Citizen Seismological Literacy (CSL). The CSL model may serve as an example to quantify citizen's background in earthquake sciences and could be applied as a framework for seismologists around the world who wish to approach the public for educational purposes, while considering promoting the public's seismologic literacy.

Many researchers studied the relationships between appearances of geomagnetic anomalies and their... more Many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults. Yet, occasionally some magnetometer stations located nearby earthquake epicenters and/or faults do not observe geomagnetic anomalies. In this paper, a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988-2001 in Taiwan. The Surface Magnetic Anomaly Reference Tip (SMART) of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters. Results show that the anomalies gather along the fault and in the belt zone to the SMART. Possible mechanisms causing the anomalies in the two zones are proposed and discussed. Characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences.

Large earthquakes near active volcanoes, that exhibit non-double-couple source properties are usu... more Large earthquakes near active volcanoes, that exhibit non-double-couple source properties are usually interpreted as result the of either magma intrusion or geometrical complexity along the fault plane. Such an earthquake occurred in 1996 September 29 at Bárdarbunga volcano in central Iceland, to be followed 2 days later by a major volcanic eruption at the area between Bárdarbunga and the nearby Grimsvötn volcano. Both of these active volcanic centres lie underneath the Vatnajökull glacier, a permanent ice cap that covers a large area of central Iceland. This event was recorded by a temporary network (HOTSPOT) that consisted of 30 broad-band three-component seismometers covering most of Iceland. The waveforms of this event at all stations show an emergent, low-amplitude, high-frequency onset that is superposed on a longer-period signal. The corresponding amplitude spectra show a low-frequency content (<1 Hz) and prominent peaks around the corner frequency (~0.25 Hz) and higher frequencies. These regional waveforms were inverted in order to obtain the best-fitting deviatoric and full moment tensor using a linear, time-domain inversion method. The results for the deviatoric moment tensor indicate a large (~60 per cent) compensated linear vector dipole (CLVD) component, a hypocentral depth of 3.5 km, a moment magnitude of 5.4 and a best double-couple solution showing thrust motion in good agreement with the previously published Harvard CMT solution. The results for the full moment tensor on the other hand, indicate an implosive isotropic component of 8.5 per cent, a reduced CLVD component of 47.2 per cent and a best double-couple solution showing normal faulting. However, a statistical F-test revealed that the full moment tensor does not fit the data significantly better than the deviatoric at a confidence level of not more than 76 per cent. All of these results were found not to change substantially when a different source time function was used or when the data were weighted according to their distance from the source. The data are consistent with an earthquake of this magnitude, caused by the failure of an asperity and the formation of a tensile crack due to increasing fluid pressure. The dimensions of the crack may have been 10 × 3 km2 and 0.5 m thickness and the volume of the injected fluid was found to be 15 × 106 m3. The calculated viscosity for the fluid (0.04 Pa s) points to the possibility of water being injected rather than magma, that is also supported by the short source duration of the earthquake (~5 s). Taking into account the water saturation of the upper crust in Vatnajökull due to the presence of the glacier, this event may have been caused by increased pressure of water that was heated by magma injected through a dyke below the asperity.

The Tatun Volcano Group (TVG) is located at the northern tip of Taiwan, near the capital Taipei a... more The Tatun Volcano Group (TVG) is located at the northern tip of Taiwan, near the capital Taipei and close to two nuclear power plants. Because of lack of any activity in historical times it has been classified as an extinct volcano, even though more recent studies suggestthatTVGmighthavebeenactiveduringthelast20ka.InMay2003aseismicmonitoringprojectattheTVGareawasinitiated by deploying eight three-component seismic stations some of them equipped with both short-period

Located in the southeastern periphery of the Eurasian plate, eastern Taiwan marks the collional b... more Located in the southeastern periphery of the Eurasian plate, eastern Taiwan marks the collional boundary between the Eurasian plate and the Philippine Sea plate. These two plates converge at about 8 cm/yr near Taiwan and nearly half of the shortening is consumed in eastern Taiwan. There have been many studies in this area about the dynamics of the plate convergence,

Journal of Geophysical Research, 2003

We present a 2.14-Myr astronomically tuned relative geomagnetic paleointensity record from the we... more We present a 2.14-Myr astronomically tuned relative geomagnetic paleointensity record from the western Philippine Sea. Pseudosingle-domain titanomagnetite is the only magnetic mineral identified and variations in titanomagnetite concentration fall well within the accepted limits for relative paleointensity variations. No significant temporally persistent periodicities are observed in wavelet analyses of the paleointensity time series or in the rock magnetic parameters used for relative paleointensity normalization. This suggests that our paleointensity record is largely free of rock magnetic or lithological artefacts and that it represents a reliable record of geomagnetic behavior with no evidence for modulation of the field at Earth orbital periods. The paleointensity record is highly coherent with the Sint-800 global paleointensity stack for the last 800 kyr and with a coeval record from the West Caroline Basin. Our record confirms that it is normal for the geomagnetic field to un...

Tectonophysics, 2009

We compile a comprehensive list of hypocentral locations and source parameters for earthquakes oc... more We compile a comprehensive list of hypocentral locations and source parameters for earthquakes occurred in the Taiwan region. The collected database is used to construct 3D patterns of seismic deformation that are associated with various tectonic processes such as subduction and collision between the Philippine Sea plate and Eurasia. Specifically, we divide the entire Taiwan region into a 3D grid of 10km interval and the amount of seismic moment released at each point is the sum of all individual events in the vicinity. In case when the physical dimension of an earthquake is larger than 10km, the corresponding seismic moment is distributed across multiple grid points. This quantitative approach gives a better depiction on many first-order features in the region. The most intriguing one is that a significant deficit in the total amount of released seismic moment can be clearly identified around the Chi-Chi source region before the big earthquake occurred in 1999. The deficit trough is then filled by the seismic moment of the Chi-Chi earthquake sequence. This deficit-then-fill pattern in a region's seismic moment distribution can be used as an indicator to pinpoint the locations of large earthquakes in the foreseeable future. Following this argument, we suggest that disastrous earthquakes with magnitudes comparable to that of the Chi-Chi earthquake are due for the two regions adjacent to the Chi-Chi source area (i.e., the Miaoli-Hsinchu domain to the north and the Chiayi domain to the south).

Journal of Geophysical Research, 2009

1] The NW moving Philippine Sea plate (PSP) collides with the Eurasian plate (EUP) in the vicinit... more 1] The NW moving Philippine Sea plate (PSP) collides with the Eurasian plate (EUP) in the vicinity of Taiwan, and at the same time, it subducts toward the north along SW Ryukyu. The Ryukyu subduction zone terminates against eastern Taiwan. While the Ryukyu Trench is a linear bathymetric low about 100 km east of Taiwan, closer to Taiwan, it cannot be clearly identified bathymetrically owing to the deformation related to the collision, making the location of the intersection of the Ryukyu with Taiwan difficult to decipher. We propose a model for this complex of boundaries on the basis of seismicity and 3-D velocity structures. In this model the intersection is placed at the latitude of about 23.7°N, placing the northern part of the Coastal Range on EUP. As PSP gets deeper along the subduction zone it collides with EUP on the Taiwan side only where they are in direct contact. Thus, the Eurasian plate on the Taiwan side is being pushed and compressed by the NW moving Philippine Sea plate, at increasing depth toward the north. Offshore of northeastern Taiwan the wedge-shaped EUP on top of the Ryukyu subducting plate is connected to the EUP on the Ryukyu side and coupled to the NW moving PSP by friction at the plate interface. The two sides of the EUP above the western end of the subduction zone are not subjected to the same forces, and a difference in motions can be expected. The deformation of Taiwan as revealed by continuous GPS measurements, geodetic movement along the east coast of Taiwan, and the formation of the Hoping Basin can be understood in terms of the proposed model. (2009), A model for the termination of the Ryukyu subduction zone against Taiwan: A junction of collision, subduction/separation, and subduction boundaries,

GEOPHYSICS, 2003

... β). The biorthogonality between the primary and dual wavelet basis functions ensures that (Ch... more ... β). The biorthogonality between the primary and dual wavelet basis functions ensures that (Chiao and Kuo, 2001). (11). This ... dz. All three of these formulations are solved using the LSQR algorithm (Paige and Saunders, 1982). Figure ...

Geophysical Research Letters, 2006

[2] In the past few years, research on earthquake early warning (EEW) has undergone a rapid devel... more [2] In the past few years, research on earthquake early warning (EEW) has undergone a rapid development [Wu and Teng, 2002; Allen and Kanamori, 2003; Kanamori, 2005; Wu and Kanamori, 2005a, 2005b; Olson and Allen,

Geophysical Research Letters, 2004

1] Turbidite layers in surficial (<0.4 m) sediments of the southern Okinawa Trough and its vicini... more 1] Turbidite layers in surficial (<0.4 m) sediments of the southern Okinawa Trough and its vicinity were dated by 210 Pb and further constrained by 137 Cs and inter-site correlation of downcore profiles of particle size and porosity. Here we show striking temporal and spatial correspondence of such episodic deposits to large (M L > 6.8) submarine earthquakes recorded in the region since the 20th century. The repeating pattern of turbidite layers reported here on decadal to centennial time scales suggests what may be the long-term rhythm of seismic activities at this tectonically active plate boundary.

Geophysical Research Letters, 2011

1] Taking advantage of a unique opportunity provided by a dense array of coastal short-period sei... more 1] Taking advantage of a unique opportunity provided by a dense array of coastal short-period seismic stations and the diverse bathymetry around Taiwan, we examine how the long-range coherent ambient noises are influenced by surrounding ocean settings using the cross-correlation functions (CCFs) between pairs of stations. The effective energy of the CCFs derived from three components of short-period seismometer data falls within the frequency range of the short period secondary microseism (SPSM). The spatial variations mapped from the amplitude asymmetry of CCFs and source migration images evidently demonstrate that the SPSM strengths are closely linked to the drastic changes in offshore ocean characteristics and result in much stronger SPSM in the shallow and narrow Taiwan Strait than in deep open seas of eastern Taiwan. The temporal variations of the CCF strengths exhibit very good correlations with the wind speeds and wave heights, explicitly indicating the observed SPSM is dominated by local sources generated from winddriven ocean waves around offshore Taiwan.

Geophysical Journal International, 2009

Skip to Main Content. Due to scheduled maintenance access to the Wiley Online Library may be disr... more Skip to Main Content. Due to scheduled maintenance access to the Wiley Online Library may be disrupted as follows: Saturday, 2 October - New York 0500 EDT to 0700 EDT; London 1000 BST to 1200 BST; Singapore 1700 SGT to 1900 SGT. ...

Geophysical Journal International, 2010

The Ryukyu subduction is known to generate very few earthquakes in its central segment contrarily... more The Ryukyu subduction is known to generate very few earthquakes in its central segment contrarily to its two extremities. We focus in this study on the southernmost part of the Ryukyu subduction zone offshore east Taiwan. Our first task was to build a homogeneous earthquake catalogue for the period 1900-2007. The new catalogue provides homogenized M W magnitudes and shows that several M W ≥ 7.0 earthquakes occurred offshore Hualien and Suao cities. We then focused on the 1920 June 5 earthquake (reported surface wave magnitude 8.1) previously located beneath the accretionary prism. The revised moment magnitude has been estimated in our catalogue at 7.7 ± 0.2. It is the biggest earthquake ever recorded in the Taiwan area but the fault that has produced this earthquake has not yet been identified with confidence. We relocated this event using regional phases (seismological bulletins archived at the Central Weather Bureau of Taiwan) about 50 km NNE and shallower of its former location, that is, within the Ryukyu Arc basement. According to earthquake bulletin information, revised magnitude, new hypocentral determination and known regional faults, we propose four potential active faults as candidates for the slip associated to this event: (1) the interplate seismogenic zone (ISZ), (2) an out-of-sequence thrust cutting through the forearc and branching on the ISZ, (3) a NS strike-slip fault cutting through the Ryukyu arc and (4) a N-S, westward dipping thrust fault, affecting the Philippine Sea Plate east of the Luzon Arc. The best compromise is to consider a rupture along the ISZ with a shallow nucleation possibly along a splay-fault followed by a downward and lateral propagation of the rupture that would explain the lack of significant seafloor motion and subsequent tsunami. We also estimate the maximum seismic coupling of the ISZ in the region east of Taiwan to about 0.4. In parallel, the evidences of aseismic slip occurring along the ISZ allow us to conclude that this region should only be affected by M < 8 earthquakes.

Geophysical Journal International, 2014

We have developed a real-time moment tensor monitoring system (RMT) which takes advantage of a gr... more We have developed a real-time moment tensor monitoring system (RMT) which takes advantage of a grid-based moment tensor inversion technique and real-time broad-band seismic recordings to automatically monitor earthquake activities in the vicinity of Taiwan. The centroid moment tensor (CMT) inversion technique and a grid search scheme are applied to obtain the information of earthquake source parameters, including the event origin time, hypocentral location, moment magnitude and focal mechanism. All of these source parameters can be determined simultaneously within 117 s after the occurrence of an earthquake. The monitoring area involves the entire Taiwan Island and the offshore region, which covers the area of 119.3 • E to 123.0 • E and 21.0 • N to 26.0 • N, with a depth from 6 to 136 km. A 3-D grid system is implemented in the monitoring area with a uniform horizontal interval of 0.1 • and a vertical interval of 10 km. The inversion procedure is based on a 1-D Green's function database calculated by the frequency-wavenumber (fk) method. We compare our results with the Central Weather Bureau (CWB) catalogue data for earthquakes occurred between 2010 and 2012. The average differences between event origin time and hypocentral location are less than 2 s and 10 km, respectively. The focal mechanisms determined by RMT are also comparable with the Broadband Array in Taiwan for Seismology (BATS) CMT solutions. These results indicate that the RMT system is realizable and efficient to monitor local seismic activities. In addition, the time needed to obtain all the point source parameters is reduced substantially compared to routine earthquake reports. By connecting RMT with a real-time online earthquake simulation (ROS) system, all the source parameters will be forwarded to the ROS to make the real-time earthquake simulation feasible. The RMT has operated offline (2010-2011) and online (since January 2012 to present) at the Institute of Earth Sciences (IES), Academia Sinica (http://rmt.earth.sinica.edu.tw). The long-term goal of this system is to provide real-time source information for rapid seismic hazard assessment during large earthquakes.