Description: Complex fault geometry can strongly affect earthquake rupture processes and slip sequences. I will first present our recent work on modeling earthquake and slow slip sequences on 3D fault surfaces, with applications to the Yingxiu-Beichuan fault (YBF) which hosted the 2008 Mw 7.9 Wenchuan earthquake in China and the Cascadia subduction zone. In the rate-and-state friction computational framework, earthquake and aseismic slip nucleate and propagate spontaneously under the influence of long-term tectonic loading and heterogeneous frictional properties. In particular, fault dip angle has a primary control on the along-strike segmentation of simulated earthquake and slow slip, in general agreement with observations from YBF and Cascadia. Fault local strike angle on the other hand strongly affects small-scale along-strike variations in the rupture speed and slip rate. Next, I will introduce a newly developed mixed-flux-based discontinuous Galerkin method and its application to simulate fully dynamic ruptures on complex fault geometries. The new method greatly reduces numerical dependence on mesh quality, and can accommodate complex fault properties including geometry, material heterogeneities and multi-physics mechanisms such as off-fault plasticity and thermal pressurization.

Description: Wind-blowing snow reshapes the snow patterns in high mountain areas and results in a significant impact on local energy balance and hydrological processes. High Mountain Asia, with the most abundant snow budget outside of polar regions, contributes a huge uncertainty to the estimation of terrestrial snow mass balance due to the interactions of blowing snow processes and complex terrain. In this work, we present a framework combining field observations, remote sensing, and high-resolution modeling to predict the snow cover evolution in the typical basins of High Mountain Asia. A mobile 3-D comprehensive observation system including radar systems, automatic weather station, and snow particle counters, was built to characterize the characteristics of wind – temperature – humidity – blowing snow flux profiles, as well as the resulting snow distribution patterns. Snow redistribution, blowing snow sublimation, snow cornice formation, and snow avalanche are processes considered in the framework. The field observations were compared to both remote sensing data and high-resolution modeling with CRYOWRF, a new modeling framework for atmospheric flow simulations for Cryospheric-regions, which couples the state-of-the-art and widely used atmospheric model WRF with the detailed snow cover model SNOWPACK. Our work has the potential to contribute to precise estimates of snow distribution in mountains.

Description: Snow cornices are common snow patterns in mountain ridge, which have potential to trigger snow avalanches. In this work, we present a series of wind tunnel experiments in a cold laboratory to simulate the formation processes of snow cornices. We quantitatively investigated the growth rates of snow cornice in length and in thickness, as well as the airborne particle concentration by using a COMOS camera. From a micro view, we also observed the snow particle trajectory that can stick on the edge and form the cornice through high-speed camera. Based on the experimental results, we explained the mechanism of the formation and development of snow cornices, and the effects of the environmental factors on the cornice growth such as air temperature, wind speed. A conceptual model that can predict the horizontal growth rate of snow cornice in field is established. Our predicted results are in good agreement with the field observation data from Gruvefjellet, Svalbard. Based on the physics of drifting snow, our results provide a new insight into snow cornice formation and improve the understanding of cornice processes that can influence avalanche activities. The experimental results and the conceptual model can be useful in future snow cornice simulation and prediction work for cornice-induced avalanches.

Description: In this study, a revised method for typhoon precipitation probability forecast, based on the frequencymatching method, is developed by combining the screening and the neighborhood methods. The frequency of the high-resolution precipitation forecasts is used as the reference frequency, and the frequency of the lowresolution ensemble forecasts is used as the forecast frequency. Based on frequency–matching method, the frequency of rainfall above the rainstorm magnitude increases. The forecast members are then selected by using the typhoon tracks of the short-term predictions, and the precipitation probability is calculated for each member using a combination of the neighbor and the traditional probability statistical methods. Moreover, four landfalling typhoons (i.e., STY Lekima and STS Bailu in 2019, and TY Hagupit and Higos in 2020) were chose to test the rainfall probability forecast. The results show that the method performs well with respect to the forecast rainfall area and magnitude for the four typhoons. The Brier and Brier skill scores are almost entirely positive for the probability forecast of 0.1–250 mm rainfall during Bailu, Hagupit and Higos (except for 0.1mm of Hagupit), and for 〈 100 mm rainfall (except for 25 mm) during Lekima.

Description: Saline water is a common fluid on the Earth‘s surface and in ice planets. Potassium chloride (KCl) is a common salt and is expected to be a ubiquitous solute in salt water in the Universe; however, few studies investigated the behavior of KCl-H2O system at high pressures and temperatures. In this study, powder and single-crystal X-ray diffraction (SC-XRD), Raman and Brillouin scattering combined with diamond anvil cells were used to investigate the phase relation in the KCl-H2O system for different KCl concentrations at 0–4 GPa and 298–405 K. The results of powder X-ray diffraction and Raman scattering demonstrate that a novel KCl hydrate is formed when KCl aqueous solutions transform to solid ice-VI and ice-VII at high pressure. Simultaneously, the single-crystal of KCl hydrate is synthesized from a supersaturated KCl solution at 298 K and 1.8 GPa. The structure is solved by SC-XRD, indicating a KCl monohydrate with the P21/n space group is formed. We have verified the phase stability of KCl monohydrate by using Raman spectroscopy and density functional theory. Our results indicate that KCl monohydrate is a stable phase under pressure and temperature conditions between 1.6 and 2.4 GPa and 298–359 K. By considering the thermal profile and composition of icy moons, we hypothesize that the formation and decomposition of KCl monohydrate might induce mantle convection in these moons.

Description: Hydrothermal alteration is crucial in the formation of many ore deposits, with potassium (K) mobilization and cycling being prevalent. Potassic metasomatism of wall rocks generally forms K-bearing minerals, such as hydrothermal feldspar and mica. However, determining the source and redistribution of K (and other elements transported by the same fluid) in hydrothermal systems is challenging. K isotopes offer a potential solution to this problem. This study presents new K isotope data from two K-rich alteration assemblages — K-feldspar and sericite-quartz-pyrite — in the Jiaodong gold province of China. The data covers a compositional range from unaltered granites to syn-magmatic potassic alteration (formation of K-feldspar) and post-magmatic syn-mineralization phyllic alteration (formation of sericite). Potassic alteration in granite correlates with significant K addition, whereas phyllic alteration of earlier phases of magmatic and hydrothermal K-feldspar resulted in K loss. K-feldspar altered granites display similar δ41K values (–0.55 to –0.42 ‰ for whole-rocks and –0.56 to –0.48 ‰ for K-feldspar separates) as unaltered granite (–0.52 to –0.47 ‰). The narrow δ41K range suggests that magmatic fluid exsolution and magmatic-hydrothermal alteration have a minor effect on δ41K of the altered rock. Phyllic alteration of K-feldspar altered precursor rock leads to K loss and elevated δ41K values ranging from –0.36 to –0.19 ‰ for whole-rocks and –0.34 to –0.17 ‰ for sericite mineral separates. As sericite preferentially incorporates 41K, sericite will have higher δ41K values than the precursor K-feldspar, whereas the fluids will have lower δ41K values. Our study demonstrates that hydrothermal alteration may affect the K isotope composition of altered rocks in several ways, contingent on the nature of the involved phases, making K isotopes a promising tool for studying hydrothermal alteration and associated mineralization.