Current tectonics of northern Cascadia from a decade of GPS measurements

Abstract

[1] Global Positioning System (GPS) measurements to study regional deformation were initiated in northern Cascadia in the late 1980s and early 1990s. On the basis of a decade of GPS data, we derive a crustal velocity field for NW Washington-SW British Columbia. The permanent and campaign GPS velocities are defined with respect to North America in the ITRF2000 reference frame. Velocity uncertainties are estimated using a model of time series noise spectra. This new velocity field is the basis for interpretation of the tectonics of the northern Cascadia subduction system. GPS velocities are interpreted in terms of interseismic loading of the megathrust using different coupling models. Our data confirm that the upper part of the megathrust is nearly fully locked. An exponential model for the downdip transition zone gives slightly better agreement with the data compared to the common linear transition. The landward decrease of forearc strain loading is smaller than predicted by any of the current subduction interseismic models. This could be a consequence of a small (0-3 mm/yr) long-term motion of the southern Vancouver Island forearc, with respect to North America, or of a concentration of interseismic strain across the elastically weaker Cascadia volcanic arc. In northern Vancouver Island, our velocity field supports the existence of an independent Explorer microplate currently underthrusting underneath North America, at least up to Brooks Peninsula. Further north, GPS velocities indicate transient and/or permanent deformation of northernmost Vancouver Island related to the interaction with the Explorer microplate and possibly with the Queen Charlotte transform margin.

Geodetic and seismic signatures of episodic tremor and slip in the northern Cascadia subduction zone

“…Analyses of GPS data from these sites have confirmed that long-term elastic deformation occurs along the northern Cascadia Margin due to the locking of converging plates across a portion of the subduction interface between the Juan de Fuca plate and the overlying North America (NA) plate (cf. Mazzotti et al, 2003). The motion vectors shown in Fig.…”

Coseismic Slip and Afterslip of the GreatMw 9.15 Sumatra–Andaman Earthquake of 2004

“…Deep afterslip has been observed for several large subduction events (Hutton et al, 2001;Melbourne et al, 2002;Zweck et al, 2002). It has been shown in some cases to coincide with the transition zone between the LFZ and the zone creeping at the long-term slip rate (Dragert et al, 1994;Mazzotti et al, 2003;Chlieh et al, 2004b). In most cases, even though some component of large-scale viscous relaxation might be present, deep afterslip seems to evolve as predicted by ratestrengthening frictional sliding (Montesi, 2004;Perfettini et al, 2005).…”

Seismic hazard in western Canada from GPS strain rates versus earthquake catalog

“…Data time spans vary from 1992 to 2008, with an average time series length of 5-6 years. Details of the regional network processing are given in Mazzotti et al [2003b] and Leonard et al [2007]. The various networks are combined, aligned to the International Terrestrial Reference Frame ITRF2000, and referenced to stable North America using the North America/ITRF2000 rigid rotation [cf.…”

“…It comprises 179 horizontal velocity vectors derived from 89 continuous and 90 campaign GPS stations throughout Alberta, British Columbia, and northern Washington [Henton et al, 2006;Leonard et al, 2007;Mazzotti et al, 2003aMazzotti et al, , 2003b] (see auxiliary material). Data time spans vary from 1992 to 2008, with an average time series length of 5-6 years.…”

“…Thus, this component of the GPS velocity field has to be removed in order to (4) and (7)): m: shear modulus; h: seismic thickness; _ ɛ G : average scalar strain rate; j: moment -magnitude asymmetry correction factor; b: slope of GR distribution (equation (1) estimate the long-term tectonic strain of the Cordillera. We use the interseismic loading models developed for the Cascadia subduction zone [Wang et al, 2003] and the Queen Charlotte transform and under-thrusting faults [Mazzotti et al, 2003b] to correct the GPS velocities. Detailed descriptions of the applied corrections are given by Mazzotti et al [2008].…”