Joint Vp and Vs tomography of Taiwan: Implications for subduction-collision orogeny

By analyzing the data from 28 seismic borehole stations deployed by the Central Weather Bureau Seismic Network throughout Taiwan from 2007 to 2014, we estimated the near-surface velocity (Vp and Vs) and attenuation (Qp and Qs) structures from surface to depths of approximately 300 m. To ensure that the deeper recordings were on the ray path between the seismic source and upper receiver, only events with an incidence angle of less than 35° were selected. Local magnitudes of analyzed events were between 1.1 and 6.6. The subsurface Qp and Qs were well modeled in the 5 -40 Hz frequency band using the spectral ratio of direct P-and S-waves, respectively, at each station, under frequency-independent Q and ω 2 source model assumptions. The estimated Vp in the Coastal Plain, the Western Foothills, the Longitudinal Valley, and the Yilan Plain were approximately 1000 -2000 m s -1 , which was lower than the Vp of 2500 -4000 m s -1 in the Central Mountain Range. In addition, the Vs in the plain areas were lower than that in the Central Mountain Range. The low Vp and Vs and high Vp/Vs ratio in the Coastal Plain and the Western Foothills can be attributed to the unconsolidated soil and high pore-fluid content of subsurface sediments in the plain areas. In contrast to the velocity distribution, low Qp and Qs were observed in the Central Mountain Range. The low Qp and Qs with low Vp/Vs and low Qs/Qp ratios in the Central Mountain Range was consistent with the high thermal temperature observed in the field investigation. The obtained velocity and attenuation structures near surface could also provide important constraints in validation of the crustal structure of Taiwan.

Section: Datamentioning

confidence: 99%

Near-Surface Attenuation and Velocity Structures in Taiwan from Wellhead and Borehole Recordings Comparisons

Wang¹,

Fong²,

Wu³

et al. 2016

“…However, the 3D synthetic ground motions also revealed the problem that without the near-surface velocity structure, the amplitudes of synthetics were also insufficient to fit the observations, as discussed by Kamae et al (1998). The model of Huang et al (2014) indicates that the velocity structure beneath those stations for our study has a relatively small 3D effect. The effects of velocity structure and site might be corrected for each station to obtain better waveform fitting, however, our goal is to reproduce the main characteristics of the broadband strong motion but not to match all details of the data records.…”

Section: Application Of Broadband Waveformsmentioning

confidence: 99%

Hybrid Ground Motion Simulation for the 2013 ML 6.4 Ruisui, Taiwan Earthquake

Wen

Yen

Wen

et al. 2016

Self Cite

The 2013 M L 6.4 Ruisui earthquake struck a seismic gap around the northern part of the Longitudinal Valley where rare earthquakes have occurred for at least two decades. Seismic data with different frequency bands connote a diverse scale of source characteristics. The slip model derived by a previous study using long-period seismic data provided us with the preliminary earthquake source properties in low-frequency energy radiation. However, the high-frequency part of the seismic energy needs to be considered for the strong motions in the comprehensive frequency band. As a case study, we carried out broadband strong motion simulations through the hybrid scheme, which simulated waveforms combining the low-frequency motions (frequency-wavenumber integration method) and high-frequency motions (empirical Green's function method) to reveal the strong ground motion and source characteristics of the 2013 Ruisui earthquake. The results show that even though the local structure is complicated this hybrid simulation can effectively rebuild the overall broadband strong ground motion characteristics for the 2013 Ruisui earthquake. Additional study issues are required to better understand the nature of localized high peak ground acceleration and the related seismic hazards for future earthquakes.

“…3) for each crustal model with and without the shallow substructure in order to test and compare the simulation results. Model A is the original crustal model by Huang et al (2014), the S-wave velocity of the cubic is from 0.65 -4.26 km s -1 , P-wave velocity is from 1.9 -7.4 km s -1 . This model considered borehole logging data to improve the shallow velocity structure.…”

Section: Shallow Substructure Modelmentioning

confidence: 99%

“…The depths of the Pliocene (Pan 1967(Pan , 1968 and upper Miocene (Shaw 1996) formation tops in the deeper part were remapped as our shallow sub-layer model and the average S-wave velocities were estimated . These velocities were then used to construct a 3D velocity model with a shallow substructure and a deep crustal model (Kuo-Chen et al 2012;Huang et al 2014) for seismic wave simulation and ground motion prediction using numerical modelling. The three main depth contours of the sub-layer were determined using Engineering Bedrock.…”

Section: Shallow Substructure Modelmentioning

confidence: 99%

“…Recently, many seismic tomographic studies (Wu et al 2007(Wu et al , 2009; Kuo-Chen et al 2012;Huang et al 2014) have provided higher-resolution 3D velocity images that incorporate an increasing number of stations and records in the Taiwan region. These large-scale velocity models make it possible to include heterogeneous velocity models in numerical modelling to improve the accuracy of wave propagation modelling (Miksat et al 2010;Lee et al 2014a, b).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Simulating Shallow Soil Response Using Wave Propagation Numerical Modelling in the Western Plain of Taiwan

Chen¹,

Kuo²,

Wen³

et al. 2016

This study used the results from 45 microtremor array measurements to construct a shallow shear wave velocity structure in the western plain of Taiwan. We constructed a complete 3D velocity model based on shallow and tomography models for our numerical simulation. There are three major subsurfaces, engineering bedrock (V S = 600 m s -1 ), Pliocene formation and Miocene formation, constituted in the shallow model. The constant velocity is given in each subsurface. We employed a 3D-FD (finite-differences) method to simulate seismic wave propagation in the western plain. The aim of this study was to perform a quantitative comparison of site amplifications and durations obtained from empirical data and numerical modelling in order to obtain the shallow substructure soil response. Modelling clearly revealed that the shallow substructure plays an important role in strong ground motion prediction using 3D simulation. The results show significant improvements in effective shaking duration and the peak ground velocity (PGV) distribution in terms of the accuracy achieved by our developed model. We recommend a high-resolution shallow substructure as an essential component in future seismic hazard analyses.