Horizontal deformation in the Cascadia subduction zone as derived from serendipitous geodetic data
(EN)
Matsikari, T
(EN)
Snay, RA
(EN)
Data from recent Global Positioning System (GPS) surveys are combined with triangulation/trilateration data to estimate horizontal shear-strain rates for two regions in the Cascadia subduction zone. Near Bellingham, Washington, we estimate that the maximum horizontal shear rate (gamma) equals 0.116 +/- 0.089-mu-rad/yr and the direction of maximum horizontal contraction (theta) orients N71-degrees-E +/- 21-degrees for data spanning the 1905-1985 interval. The corresponding estimates for a region near Portland, Oregon, are 0.057 +/- 0.027-mu-rad/yr and N95-degrees-E +/- 14-degrees for data spanning the 1881-1988 interval. These estimates are consistent with estimates from independent geodetic data in the area. Moreover, the estimates for theta are consistent with the N68-degrees-E direction of ongoing convergence between the Juan de Fuca plate and the North American plate as predicted by the NUVEL-1 plate motion model. This consistency between theta-estimates and the direction of plate convergence supports the argument for the possibility of a great subduction earthquake occurring in the Cascadia subduction zone. The low shear rates, however, imply that the recurrence interval between such earthquakes would be several centuries long.
(EN)
