Heat flow bounds over the Cascadia margin derived from bottom simulating reflectors and implications for thermal models of subduction

Abstract

Understanding the thermal structure of the Cascadia subduction zone is important for understanding megathrust earthquake processes and seismogenic potential. Currently our understanding of the thermal structure of Cascadia is limited by a lack of high spatial resolution heat flow data and by poor understanding of thermal processes such as hydrothermal fluid circulation in the subducting basement, sediment thickening and dewatering, and frictional heat generation on the plate boundary. Here, using a data set of publically available seismic lines combined with new interpretations of bottom simulating reflector (BSR) distributions, we derive heat flow estimates across the Cascadia margin. Thermal models that account for hydrothermal circulation predict BSR‐derived heat flow bounds better than purely conductive models, but still over‐predict surface heat flows. We show that when the thermal effects of in‐situ sedimentation and of sediment thickening and dewatering due to accretion are included, models with hydrothermal circulation become consistent with our BSR‐derived heat flow bounds.

On Shear Stresses, Temperatures, and the Maximum Magnitudes of Earthquakes at Convergent Plate Boundaries

“…Hutnak et al () argued that there is significant (perhaps 20% regionally) hydrothermal heat transfer through places where basement is exposed. Furthermore, Phrampus et al () show that the heat flux inferred from bottom‐simulating reflectors along their Profile A (close to the profile of Figure ) is consistently lower than would be predicted for a purely conductive lower plate (see also Cozzens & Spinelli, ). The maximum heat flux near the deformation front is about 120 mW/m 2 (Phrampus et al, ).…”

“…Furthermore, Phrampus et al (2017) show that the heat flux inferred from bottom-simulating reflectors along their Profile A (close to the profile of Figure 4) is consistently lower than would be predicted for a purely conductive lower plate (see also Cozzens & Spinelli, 2012). The maximum heat flux near the deformation front is about 120 mW/m 2 (Phrampus et al, 2017). Figure 4c displays the mean misfits to the heat flux values (calculated using equation (16) with unit weights) that are obtained by systematically varying Q 0 between zero and 140 mW/m 2 and finding the best fitting value of ′ corresponding to each value of Q 0 .…”

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

“…These reflectors appear widely distributed both across‐ and along‐strike of the accretionary wedge, extending from Mendocino in northern California to Vancouver Island. A recent compilation by Phrampus et al () found that there is a significant gap in the distribution of BSRs along‐strike of Cascadia upper margin occurs within the Washington segment, between the latitudes 47°N and 48°N, although many of the MCS profiles examined do not extend to the accretionary toe. This is a region where methane bubble stream emissions are particularly abundant on the upper margin and at the continental shelf edge (Figures and S1 in the supporting information).…”

Diagenetic, metamorphic, and hydrogeologic consequences of hydrothermal circulation in subducting crust

“…The simulation with hydrothermal circulation is more consistent with the observations. However, along much of the transect, the scatter in the surface heat-flux observations (e.g., Phrampus et al, 2017) spans the predicted differences in surface heat flux between the two models, thus making it difficult to definitively identify a preferred thermal model for this system based on the surface heat-flux distribution alone.…”