Chapter 1 - The Role of Fluids in Tectonic and Earthquake Processes

Abstract

Abstract Fluids play an integral role in the geodynamical system, from consumption through serpentinization at mid-ocean ridges and outer rises, to release through dehydration and decarbonization within subduction zones and beyond. Fluids affect a number of critical elements of the tectonic cycle, including weakening plate boundaries and catalyzing mantle wedge melting for feeding volcanic arcs. This review paper summarizes the vast topic of the hydrogeological cycle of the solid earth, and how fluids affect, and are affected by, tectonic processes. Ultimately these fluids must either remain trapped in the mantle or return to the surface at high pressure via ductile processes or fracture networks. High pressure fluids returning to the surface may get trapped at the base of the brittle crust, where they can contribute to earthquake nucleation and genesis. Evidence suggests that high pressure fluids are active participants in tectonic earthquakes, and the relatively recent discovery of slow slip earthquakes and non-volcanic tremor phenomena all point to trapped, over-pressured fluids as an underlying mechanical cause. Fluids play an integral role in lithospheric geodynamics, which provides for some speculations about fluids and earthquakes in a general sense. One such speculation is that spatial aftershock patterns reflect fluid pathways taken by the release of high pressure fluids triggered by the earthquake mainshock. Some of these patterns are shown, and I introduce the term “Zen Trees” to describe them because of their aesthetic form and their resemblance to Eastern calligraphy. I hypothesize that earthquakes that do not spawn significant aftershock sequences indicate little if any trapped high pressure fluids at depth, while earthquakes producing long-lived aftershock sequences point to large reservoirs of trapped high pressure fluids. Although the viscous mantle is the ultimate geophysical fluid, the focus in this paper is limited to fluids in the lithosphere because this boundary, typically treated as a thermal boundary layer, is controlled by complex dynamical interactions between fracture, deformation, dissolution/precipitation, and fluid flow.