Deformation rates estimated from earthquakes in the northern Cordillera of Canada and eastern Alaska

Abstract

We estimate deformation rates from earthquake catalog statistics to investigate current strain distribution resulting from the collision of the Yakutat block with North America. The collision is accommodated over a broad region of Alaska and NW Canada in a variety of tectonic regimes. Our estimates have significant uncertainties, but the results are generally in agreement with other deformation rate estimates (GPS and geological data) and provide useful first‐order constraints on local long‐term tectonic deformation and seismic hazard. We estimate that 50–75% of relative plate motion is taken up by earthquakes on the Yakutat/North America boundaries, with lateral crustal extrusion, other far‐field strain, and possibly aseismic creep accommodating the remainder. We calculate dextral strike slip of 4.5–10.2 mm/a on the Denali fault system in Alaska, remarkably similar to late Pleistocene/Holocene rates from geomorphic offsets. Right‐lateral motion essentially bypasses the Denali fault in easternmost Alaska and westernmost Yukon, passing instead along the Totschunda and Duke River fault systems. Right‐lateral transpression of 5–10 mm/a suggests that the Alaskan fore arc does not have fully block‐like behavior. Between the Denali and Tintina‐Kaltag faults in Alaska, 10–20 mm/a of dextral shear is accommodated by several NE trending “bookshelf” faults. Significant seismic deformation (in cases higher than expected from GPS data) is indicated in the NE Cordillera, where preexisting faults have a strong control on the pattern and mechanisms of current deformation.