Abstract
Several tectonic processes combine to produce the crustal deformation observed across the Cascadia margin: (1) Cascadia subduction, (2) the northward propagation of the Mendocino Triple Junction (MTJ), (3) the translation of the Sierra Nevada–Great Valley (SNGV) block along the Eastern California Shear Zone–Walker Lane and, (3) extension in the northwestern Basin and Range, east of the Cascade Arc. The superposition of deformation associated with these processes produces the present-day GPS velocity field. North of ~ 45° N observed crustal displacements are consistent with inter-seismic subduction coupling. South of ~ 45° N, NNW-directed crustal shortening produced by the Mendocino crustal conveyor (MCC) and deformation associated with SNGV-block motion overprint the NE-directed Cascadia subduction coupling signal. Embedded in this overall pattern of crustal deformation is the rigid translation of the Klamath terrane, bounded on its north and west by localized zones of deformation. Since the MCC and SNGV processes migrate northward, their impact on the crustal deformation in southern Cascadia is a relatively recent phenomenon, since ~ 2 –3 Ma.
Highlights
The development of dense, continuous Global Positioning System (GPS) networks in subduction zones has provided key upper-plate displacement data that can be used to infer the nature of plate coupling along the megathrust interface
*Correspondence: kam724@psu.edu Department of Geosciences, The Pennsylvania State University, University Park, PA, USA. The effects of these non-subduction tectonic processes (LaFemina et al 2009; Morell et al 2012). Such a hybrid signal occurs along the Cascadia subduction zone (Fig. 1), where subduction coupling is overprinted by non-subduction tectonic processes, especially in southern Cascadia
Rigid versus deformable upper plate Our results show that the upper-plate displacements/ velocities in Cascadia can be described by the combination of an ephemeral subduction coupling signal and NNW-directed deformation produced by non-subduction tectonic processes (Figs. 3 and 4)—the advance of the Mendocino crustal conveyor (MCC) (Furlong and Govers 1999) and the Sierra Nevada–Great Valley (SNGV) block (Dixon et al 2000)
Summary
The development of dense, continuous GPS networks in subduction zones has provided key upper-plate displacement data that can be used to infer the nature of plate coupling along the megathrust interface. Associated with the NNW migration of the Mendocino Triple Junction (MTJ), the Mendocino crustal conveyor (MCC) produces crustal shortening, and associated crustal thickening and uplift in advance of the MTJ (Furlong and Govers 1999; Lock et al 2006). This crustal deformation is geologically long-lived and, based on modeling, should extend several 100s of km beyond the MTJ.
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