Subcretionary tectonics: Linking variability in the expression of subduction along the Cascadia forearc

A number of seismic and other geophysical phenomena exhibit significant lateral heterogeneity along the strike Cascadia forearc. Both overriding downgoing plate have been invoked to play dominant role in controlling along-strike correlations between seismogenic behavior, potential field measurements, morphological/tectonic characteristics, structure; however, feedbacks likely exist two. In this study, we apply a 3D velocity correction receiver function data interpret resulting discontinuity model alongside recently published shear-wave understand possible causative relationships correlative variations. Our indicates that forearc crust thickens as it approaches mantle wedge corner before progressively thinning toward magmatic arc, due basal accretion material from plate. northern southern portions forearc, “subcreted” is characterized by thick (?10 km) anomalously low zones. The thickness, high internal reflectivity, Bouguer gravity signatures associated with zones indicate subcreted composed dominantly (meta)sedimentary has emplaced through successive subcretion events over geologic timescales. Furthermore, velocities spatial correlation non-volcanic tremor (NVT) density short slow slip recurrence intervals these regions are fluid-rich. While first-order variations fluids control NVT result differences permeability slab inferred its stress state distribution intraslab seismicity, packages represent thick, vertically-impermeable lower further accentuate correlation. Variability amount explains patterns exhumation uplift margin topography timescales, controlled some combination interface geometry/rheology architecture.