The spreading of a pure, volatile liquid on a wettable substrate has been studied in extensive detail. Here we show that the addition of a miscible, non-volatile liquid can strongly alter the contact line dynamics and the final liquid deposition pattern. We observe two distinct regimes of behavior depending on the relative strength of solutal Marangoni forces and surface wetting. Fingerlike instabilities precede the deposition of a sub-micron thick film for large Marangoni forces and small solute contact angles, whereas isolated, pearl-like drops emerge and are deposited in quasicrystalline patterns for small Marangoni forces and large solute contact angles. This behavior can be tuned by directly varying the contact angle of the solute liquid on the solid substrate.

We report on laboratory experiments designed to explore the fundamental processes that impact fluid permeability during drilling and fluid injection. Coupled ultrasonic and permeability measurements are presented for Westerly granite samples fractured in situ and used to illuminate the relationship between nonlinear dynamic stiffness and fracture permeability indexed via fracture aperture. We perturb the effective stress field using normal stress and pore pressure oscillations. The velocity of ultrasonic waves transmitted across the fracture is used to infer the evolution of elastic properties and the fracture nonlinearity. Changes in permeability are measured concurrently. We observe that relative changes in wave velocity and permeability, due to both normal stress and pore pressure oscillations, are correlated, such that larger drops in wave velocity (higher nonlinearity) correspond to larger increases in permeability. Our observations suggest that dynamic stressing is more likely to enhance the permeability of fractures that exhibit greater nonlinearity.

Slow slip events (SSEs), lasting for days to months, have been widely recognized as an important part of the continuum bridging fast, elastodynamic ruptures and stable fault creep at plate boundaries globally (Bürgmann, 2018;Ide et al., 2007;Peng & Gomberg, 2010). These types of slip modes are particularly important because of the role they play in the seismic cycle and the accommodation of plate motion, and because of the clues they provide about plate interface rheology. In some cases, SSEs are thought to trigger ordinary fast earthquakes by loading adjacent fault patches (Kato et al., 2012;Meng et al., 2015). In other cases, SSEs have been triggered (Araki et al., 2017;Wallace et al., 2017) or arrested (Wallace et al., 2014) by nearby earthquakes. Thus, the precise role played by SSEs in the overall earthquake cycle is unclear. Moreover, many SSEs at convergent margins globally have been documented at the downdip limit of the seismogenic zone, that is, at depths of 30-40 km (Schwartz & Rokosky, 2007), which makes it impossible to directly sample and study the frictional behavior of the active SSE source rocks.The northern Hikurangi margin, offshore New Zealand, is an important example of shallow and accessible SSEs. These faults host robustly documented, quasi-periodic shallow SSEs (Wallace, 2020) that rupture close to the trench (Wallace et al., 2016) and have recurrence intervals of 12-18 months. Additionally, the source region of these SSEs has hosted tsunami earthquakes which may have ruptured to the trench (Bell et al., 2014) and is hypothesized to have significant pore fluid overpressure (Bassett et al., 2014;Bell et al., 2010;Ellis et al., 2015). Thus, it is important to constrain the frictional behavior of the source material to better understand the rock properties and processes that govern fault slip behavior, and ultimately the future risk of earthquake and tsunami generation.

No abstract

No abstract