Fault strength during earthquakes is much weaker than inter-seismic strength. Such dynamic weakening process is essential for earthquakes. My Ph.D. research focused on the mechanisms of dynamic weakening, specifically the micro- to nano-scale processes. Here are some amazing discoveries for high-speed rock friction tests:

1. The extensive smoothing process of the fault surface can lead to strong dynamic weakening (Chen et al., 2013 in Geology).

2. Micro-sized roll "bearings" can form spontaneously to lubricate the faults (Chen et al., 2017 in AGU Monograph).

3. Concentrated friction heat can melt the localized fault zones, causing strengthening and weakening variations (Chen et al., 2017 in JGR Solid Earth).

4. Talc, the softest mineral on earth, is frictionally extremely weak with the aid of water, whereas dry talc can be strong with prolonged slip (Chen et al., 2017 in JGR Solid Earth).

5. With in-situ monitoring of fault zone fluid properties, dynamic weakening of natural gouge samples from active Alpine fault zone is believed to be caused by perssurization due to strong CO2 emission (Chen et al., 2019 in JGR Solid Earth).

6. Stick-slips can be linked to fault surface roughness, and the asperity failure may control the stick-slips (Chen et al. (2020), Pure and Applied Geophysics)

7. Dynamic rupture processes weaken the fault more efficiently than frictional processes and are responsible for earthquake initiation (Chen et al. (2021), Earth and Planetary Science Letters).

The coupled effects between fluid-rock interaction and rock deformation have wide geological implications. One of the most prominent effects is chemically assisted fracture growth. My postdoc research at UT Austin dealt specifically with subcritical fracture growth of shales under reactive conditions related to subsurface carbon sequestration. Experiments revealed strong water-enhanced fracture growth for clay-rich shales, whereas carbonate-rich shale show little water effect (Chen et al., 2017, 2019 in JGR Solid Earth). Not only rock composition, subcritical fracture grwoth is also strongly related to fluid salinity, pH level, and temperature (Chen et al., 2019 in Geomechanics for Energy and the Environment). These experimental results have direct implications for carbon sequestration such as site selection, and subsurface geomechnics characterizations.

Collaborating with other geoscientists, I extend experimental fracture mechanics to applications such as surface erosion (Eppes et al., 2018 in Geology), hydrocarbon systems (Liao et al., 2019 in Marine and Petroleum Geology and Liao et al., 2019 in Interpretation), and induced earthquakes.