Dr. Ming-Che Hsieh works in the fields of earthquake physics and seismic wave propagation. His researches focus on scattering theory (i.e., sensitivity or Fréchet kernel of finite-frequency approach), rupture process of earthquakes, physics-based ground motion simulation, epidemic-type aftershock sequence (ETAS), and seismic hazard assessment. In the past few years, Dr. Hsieh has developed an efficient earthquake-rupture-process determination scheme to capture source characteristics within a few minutes. This earthquake-source determination scheme has been set up for regions of Taiwan, China, and India. Dr. Hsieh has also developed a hybrid and physics-based ground motion simulator with the assistance of recent 3D subsurface velocity structure and topography models. By taking advantage of these algorithms, Dr. Hsieh is working on the safety of infrastructures and disaster prevention of metropolis and industry.
Full-waveform ground-motion simulation of scenario earthquakes
We carried out full-waveform ground-motion simulation using a 3D finite-difference algorithm. Recent-developed 3D structure and topography models were considered in a physics-based sense. We also accounted for a series of characteristic source models considering earthquake magnitude, rupture dimension, rupture speed, and asperity distribution to capture ground shaking level and range in the target region. These simulations were performed in high-performance computation (HPC) environments. The example shows the source-rupture scenario of the Shachiao Fault. In this simulation case, we delicately modeled the Taipei Basin geometry in our simulations. The ground-shaking movie shows strong resonances and amplification in the Taipei metropolitan area due to the basin. This ground motion simulation technique is effective for seismic hazard assessment and even dynamic testing of buildings and structures.
Two-step finite-rupture determination for moderate earthquakes
We develop an efficient and effective approach to determining the average finite-rupture models of moderate earthquakes by fitting synthetic and recorded broadband waveforms. A Green’s tensor database is established using 3D structural model with surface topography to enable rapid evaluations of accurate synthetic seismograms needed for source parameter inversions without the need for high-performance computing. We take a two-step strategy: In the first step, a point-source model is determined by a grid search for the best fault-plane solution. Then, taking the two nodal planes in the point-source model as candidates of the actual fault plane, a second grid search is carried out over a suite of simplified finite-rupture models to determine the optimal direction and speed of the integrated rupture of the finite source. We applied our method to four moderate events (MW ≈ 6) in southeastern Taiwan. Results show that our technique provides an effective choice in semi-automatic, near real-time determinations of finite-source parameters for earthquake hazard assessment and mitigation purposes (Hsieh et al., 2014).
Slip-distribution inversion using 3D strain Green tensor (SGT)
We develop a source inversion technique that combines a well-established slip distribution inversion method and an efficient algorithm for computing accurate synthetics in 3D structures based on a preestablished strain Green tensor database. This new technique makes it practical for slip-distribution inversion in 3D structures, which not only enhances the capability of resolving source slip distributions of moderate earthquakes through better accounting of the effects of lateral structural heterogeneities but also provides an effective tool for the development of automatic systems for near-real-time inversions of earthquake source slip distributions for seismic-hazard mitigation purposes (Hsieh et al., 2016).