Slow Motion Earthquakes: Taking the Pulse of Slow Slip with Scientific Ocean Drilling

Processes Governing Giant Subduction Earthquakes: IODP Drilling to Sample and Instrument Subduction Zone Megathrusts

“…Important avenues for future research include understanding the reasons why some megathrust earthquakes do not slip all the way to the surface, as well as understanding what governs locking vs. creeping fault systems. With recent observations suggesting that faults near the tip of a subduction system can be locked, quantifying the spatial extent of and controls on shallow locking has emerged as an urgent question for seafloor geodesy and future drilling, sampling, and observatory installation (see Wallace et al, 2019, in this issue for the first major foray into addressing this topic). Exploring how lithology controls frictional stability and slip behavior, particularly in the marine carbonates that typify deep pelagic sediments in many places, is another high-priority goal.…”

Listening Down the Pipe

“…• Subseafloor pressure recorded in wellsealed borehole observatories provides an extraordinarily sensitive proxy for plate-scale strain on timescales ranging from years to coseismic slip, with the most sensitive strain monitoring done in hydrologically isolated lowporosity formations (e.g., Davis et al, , 2013Araki et al, 2017). These measurements have led to the discovery of a range of deformation events, from small earthquakes and dike intrusions, to shallow slow slip events that may accommodate a large fraction of the plate motions in subduction zones (see Wallace et al, 2019, in this issue).…”

“…• CORK pressure records show that fault slip in shallow portions of subduction zones can occur spontaneously, be triggered by dynamic stress changes (e.g., earthquakes), and can occur with little or no seismic expression (e.g., Davis et al, 2013;Araki et al, 2017;Wallace et al, 2019, in • High-resolution borehole temperature monitoring after the 2011 Tōhokuoki earthquake at the Japan Trench enabled near-real-time estimation of the frictional shear stress and apparent friction coefficient, showing very low shear resistance to fault slip at shallow depth (Fulton et al, 2013, and, in this issue)…”

Seafloor Geodetic Positioning Models with Diversified Acoustic Delay Estimations Under Different Conditions for Detecting the Sound Speed Variation

“…This indicates that, the above positioning precision is refer to the SGO-A centroid rather than a single transponder in the array (Yokota et al 2015), and therefore it is still hard to achieve centimeter-level precision positioning in the case using a single seafloor transponder. This indicates that, currently GNSS-A technique can only resolve the tectonic motion at a time scale of more than one years' because of the positioning 5 / 35 precision limitation (Roland Bürgmann and Chadwell 2014), although a range of geophysical observations have revealed that dynamic processes of offshore subduction, seismic coupling and fault slip are inherently time-dependent over a wide range of time scales (Kato et al 2012;Bürgmann Roland 2018;Wallace et al 2019). Those abovementioned problems compel us to further advance the GNSS-A positioning model.…”