Fluid pressure and temperature transients detected at the Nankai Trough Megasplay Fault: Results from the SmartPlug borehole observatory

Changes in Physical Properties of the Nankai Trough Megasplay Fault Induced by Earthquakes, Detected by Continuous Pressure Monitoring

“…Moreover, the stronger correlation between dynamic strain (or PED as a proxy) and the observed changes shown in Figure provides additional support for the interpretation that the perturbations we observe reflect responses to dynamic strains associated with surface wave passage (e.g., Hammerschmidt, Davis, & Kopf, ). This interpretation is also consistent with global observations indicating that dynamic strain is a primary driver for triggering of earthquakes and mud volcano eruptions, and to changes in groundwater level (e.g., Kilb et al, ; Kitagawa et al, ; Manga & Wang, ).…”

“…This instrument package was recovered in 2010 as part of IODP Expedition 332 and replaced with a “GeniusPlug” having fluid sampling capabilities (Expedition 332 Scientists, ). Analysis of the SmartPlug deployment records has provided initial information about formation pressure and temperature responses to earthquakes, as well as preliminary estimates of formation properties (Hammerschmidt, Davis, & Kopf, ; Hammerschmidt, Davis, Hüpers, et al, ). However, these analyses are limited by the short duration of the deployment and by partial decoupling of the reference pressure sensor from the overlying ocean by a cap at the wellhead, which led to incomplete accounting for oceanographic and tidal signals (Hammerschmidt, Davis, & Kopf, ; Hammerschmidt, Davis, Hüpers, et al, ).…”

“…Like the Smartplug, the GeniusPlug included two pressure sensors, a “downward looking” sensor to record formation pore pressure in the screened interval and an “upward looking” sensor to measure an oceanographic reference pressure, both with a sampling interval of 30 s (Figure b). In addition, the observatory was equipped with three temperature sensors, primarily for compensation of the pressure transducers (e.g., Expedition 332 Scientists, ; Hammerschmidt, Davis, & Kopf, ), and an ~30 cm long extension at its lower end housing a fluid sampling and in situ microbiological experiment designed to collect a time series of samples for geochemical and microbiological research (Expedition 332 Scientists, ). Here we restrict our analysis to the pressure time series.…”

Anomalous Concentration of Methane Emissions at the Continental Shelf Edge of the Northern Cascadia Margin

“…Sharp slope inflections of the seafloor have been recognized previously as localized areas that produce enhanced fluid emissions (Kukowski et al, ; Orange et al, ). Local geologic structures and surface topography are also known to amplify seismic waves from distant sources, and as a result, enhance sediment permeability in both the terrestrial environment (Roeloffs, ) and on accretionary prisms (Hammerschmidt et al, ). A recent study of the seismic site response of ocean bottom seismometers on the Cascadia accretionary wedge demonstrated that seismic shaking at low excitation frequencies that occur near the continental shelf break are both amplified in intensity by 2 orders of magnitude and substantially prolonged in duration by the presence of a substantial change of slope (Gomberg, ).…”

Expedition 372B/375 summary

“…Core samples from Site U1519 acquired during Expedition 375 will also enable measurements of rock elastic and other physical properties needed to confidently interpret observatory data (e.g., Wang and Davis, 1996;Sawyer et al, 2008;Hammerschmidt et al, 2013), to assess the role of upper plate properties in possible triggering of SSEs (e.g., Wallace et al, 2017), and to define realistic rock properties to inform models of SSE slip (e.g., Williams and Wallace, 2018). Analysis of pore fluid chemistry allows identification of the source region of fluids in the hanging wall above and surrounding the SSE region to assess whether fluids from depth flow upward and escape through the fractured and structurally disrupted hanging wall and to quantify flow pathways, rates, and driving forces (e.g., Kopf et al, 2003;Hensen et al, 2004;Ranero et al, 2008;Kastner et al, 2014).…”