Thermal environment of the Southern Washington region of the Cascadia subduction zone

Abstract

AbstractEleven recently collected multichannel seismic (MCS) profiles from the Cascadia Open‐Access Seismic Transects experiment offshore Washington State are used to characterize the distribution of bottom‐simulating reflectors (BSRs) from seaward of the deformation front onto the continental shelf of the Cascadia Subduction Zone. The 11 MCS lines consisted of nine lines perpendicular and two lines parallel to the Cascadia margin covering a 100 km along‐strike region of the accretionary wedge. From these MCS profiles we generated a 3‐D view of the Cascadia margin thermal structure by interpreting 40,232 individual BSR picks in terms of temperature and heat flow. Overall BSR‐derived heat flow values decrease from approximately 95 mW m−2 10 km east of the deformation front to approximately 60 mW m−2 located 60 km landward of the deformation front. Anomalously low heat flow values near 25 mW m−2 on a prominent midmargin terrace indicate recent sediment failure within the accretionary prism. Localized differences between BSR heat flow and numerical models reflect an estimated regional mean vertical fluid flow of +0.53 cm yr−1 for the survey area, with localized fluid flow approaching a maximum of +3.8 cm yr−1. Distinct finite element models for the nine MCS profiles perpendicular to the deformation front reproduce BSR heat flow values, producing an overall root‐mean‐square misfit of 10.2 mW m−2. At the deformation front, the incoming oceanic sediment/crust interface temperatures vary from 164°C to 179°C, indicating the updip limit of the Cascadia seismogenic zone.