Mapping fluids to subduction megathrust locking and slip behavior

Abstract

In subduction zones, high fluid content and pore pressure are thought to promote aseismic creep, whereas well‐drained conditions are thought to promote locking and failure in earthquakes. However, observations directly linking fluid content and seismic coupling remain elusive. Heise et al. (2017, https://doi.org/10.1002/2017GL074641) use a magnetotelluric survey to image the electrical resistivity structure of the northern Hikurangi subduction thrust to ~30 km depth, as an indicator of interconnected fluid content. The authors document a clear correlation between high resistivity and a distinct geodetically locked patch and between conductive areas and weak coupling. Their study, together with other recent geophysical investigations, provides new evidence for the role of fluids in governing subduction thrust locking.

Fluid and Melt Pathways in the Central Chilean Subduction Zone Near the 2010 Maule Earthquake (35–36°S) as Inferred From Magnetotelluric Data

“…Key Points: • A magnetotelluric survey was collected over the Chilean subduction zone at 36 degrees south in order to map geoelectric structure • Conductors show important dehydration reactions along plate interface as well as important zones of crustal melt beneath the volcanic arc • Correlations with previous seismic results show a possible asperity on plate interface, which may influence megathrust rupture aqueous fluids and partial melt are critical parameters in examining magma flux and magma genesis (Petrelli et al, 2018;Völker & Stipp, 2015). Furthermore, it has been widely suggested that fluids control the distribution of seismic and aseismic zones within a subduction zone and thus understanding seismicity and fluid relationships is important (Saffer, 2017).…”

“…Determining the amount of water, the depth at which it is released, and the zones of accumulation of aqueous fluids and partial melt are critical parameters in examining magma flux and magma genesis (Petrelli et al, ; Völker & Stipp, ). Furthermore, it has been widely suggested that fluids control the distribution of seismic and aseismic zones within a subduction zone and thus understanding seismicity and fluid relationships is important (Saffer, ).…”

Can the Updip Limit of Frictional Locking on Megathrusts Be Detected Geodetically? Quantifying the Effect of Stress Shadows on Near‐Trench Coupling

“…Fault properties in subduction zones may be different from those in continental collision zones, particularly due to the availability of fluids, which may alter both the mineralogy of the downgoing sediments and the seismogenic properties of the megathrust (e.g., Saffer, 2017). Seafloor geodetic observations at subduction zones are limited due to cost and logistics, and the errors in such measurements are typically an order of magnitude larger than on land, although the rates of convergence are also typically higher (DeMets et al, 2010).…”

Seismicity of the Incoming Plate and Forearc Near the Mariana Trench Recorded by Ocean Bottom Seismographs

“…However, laboratory experiments found that illite shale is velocity‐strengthening/stable (Saffer & Marone, 2003), but the fluid release during the reaction has also been considered (Lauer et al, 2017; Spinelli & Saffer, 2004). In this case, earthquakes occur downdip of peak fluid release, due to lithification and increased effective stress by reduction in fluid pressure (Heise et al, 2017; Lauer et al, 2017; Saffer, 2017). Updip of the ~150 °C isotherm, pore fluid overpressure prevents seismic slip and instead promotes creep and slow slip events (Ranero et al, 2008; Saffer & Tobin, 2011; Vannucchi et al, 2012).…”