These are a subset of our research projects. You can find more on the group page or shoot me an email if you have other interesting ideas!
FAULT ZONE
We have been working on the dynamic effects of damaged fault zones on earthquake ruptures through a combination of dynamic rupture simulations and seismic imaging of fault zone structures. Faults are usually surrounded by damaged zones, which can extend several hundred meters across strike-slip faults. As earthquakes are nucleated inside the damaged fault zones, both reflected waves and head waves radiated by the earthquakes can interact profoundly with the rupture propagation, which in turn leaves characteristic damage pattern in fault zones [Huang and Ampuero, 2011; Huang et al., 2014; Pelties et al., 2014; Huang et al., 2016; Huang, 2018]. Our new earthquake cycle simulations unveil the crucial role of pre-existing fault zone structure in generating and maintaining small-scale stress heterogeneities that lead to realistic earthquake magnitude and depth distributions on simulated faults [Thakur et al., 2020]. By considering the coseismic damage and interseimic healing of fault damage zones during earthquake cycles, we demonstrate that fault zone healing has a critical control on earthquake magnitudes and recurrence intervals [Thakur and Huang, 2021].
SUBDUCTION ZONE
I’m always interested in developing seismic observations and numerical simulations to study the physics of earthquakes in subduction zones. Using the 2011 Tohoku-Oki Mw9.0 earthquake and the Cascadia megathrust scenarios as examples, our observation-based rupture simulations provide physical insights into the frequency-dependent rupture process, stress drop, the partitioning of earthquake energy, and the mechanical role of the shallow portion of the subducted slab [Huang et al., 2012; Huang et al., 2013; Lui et al., 2015; Ramos and Huang, 2019]. As part of our NSF PREEVENTS grant, my group at U-M developed for the first time 2D and 3D dynamic rupture simulations for the Cascadia subduction zone to improve our understanding of Cascadia earthquake hazards [Ramos and Huang, 2019; Ramos et al., 2021]. Our 2D rupture simulations show that Cascadia rupture can propagate through the deep transition region at fast speeds. Our 3D simulations based on geodetic coupling models indicate that the final size of simulated earthquakes strongly depends on the amount of strain build-up in the central Cascadia region and fault friction at shallow depths. Another ongoing effort of my group is to incorporate the physical understanding of earthquakes in tsunami simulations. We evaluate tsunami hazard from M7-9 Cascadia earthquakes using tsunami simulations constrained by earthquake rupture physics and geodetic coupling models [Salaree et al., 2021]. Our results highlight the importance of considering M>8.5 earthquakes for tsunami hazard mitigation, as they can create comparable coastal tsunami amplitudes due to the focusing effect of the concave coastline geometry near Oregon.
INDUCED SEISMICITY
Though injection and withdrawal of fluids are common in energy industries, the recent growing observations of injection-induced seismicity pose an urgent need to understand the mechanism of induced seismicity and the mechanical role of pore fluids. Source properties such as magnitude-frequency distribution [Huang and Beroza, 2015], earthquake stress drops [Huang et al., 2016, 2017 and 2019] and rupture directivity [Lui and Huang, 2019] can provide more insights into the relationship between seismicity and fluid injection as well as the inherent similarity and difference between tectonic and induced earthquakes. We’re interested in understanding how fluid induces earthquakes initially and then contributes to the sequences of earthquakes following afterwards. Both our seismic data analysis of microearthquakes in injection experiments and earthquake cycle models indicate aseismic deformation plays important roles in releasing fault stress and can delay subsequent earthquakes [Huang et al., 2019; Lui et al., 2021].
SITE EFFECT
Understanding the effects of sites on ground motions is extremely important for engineering applications. In particular, the alluvial basin can cause strikingly large amplification of seismic waves, but more efficient tools are needed to account for the heterogeneous medium and demanding numerical precision. The application of an indirect boundary integral equation method provides a better understanding of the 3-D wave focusing and basin-edge effect of alluvial basins [Liu et al., 2015 and 2016]. We are currently using physics-based ground motion models to characterize the respective contributions of earthquake source and site conditions to ground shaking. Our recent simulations show that smooth crustal velocity structure can cause a depletion of high-frequency ground motion on soil sites, as observed from the 2019 Mw 7.1 Ridgecrest, CA earthquake [Huang, 2021].
