Coseismic deformation of the 2002 Denali Fault earthquake: Insights from GPS measurements

Abstract

We estimate coseismic displacements from the 2002 Mw7.9 Denali Fault earthquake at 232 GPS sites in Alaska and Canada. Displacements along a N‐S profile crossing the fault indicate right‐lateral slip on a near‐vertical fault with a significant component of vertical motion, north‐side up. We invert both GPS displacements and geologic surface offsets for slip on a three‐dimensional (3‐D) fault model in an elastic half‐space. We restrict the motion to right‐lateral slip and north‐side‐up dip slip. Allowing for oblique slip along the Denali and Totschunda faults improves the model fit to the GPS data by about 30%. We see mostly right‐lateral strike‐slip motion on the Denali and Totschunda faults, but in a few areas we see a significant component of dip slip. The slip model shows increasing slip from west to east along the Denali Fault, with four localized higher‐slip patches, three near the Trans‐Alaska pipeline crossing and a large slip patch corresponding to a Mw7.5 subevent about 40 km west of the Denali‐Totschunda junction. Slip of 1–3 m was estimated along the Totschunda Fault with the majority of slip being at shallower than 9 km depth. We have limited resolution on the Susitna Glacier Fault, but the estimated slip along the fault is consistent with a Mw7.2 thrust subevent. Total estimated moment in the Denali Fault earthquake is equivalent to Mw7.89. The estimated slip distribution along the surface is in very good agreement with geological surface offsets, but we find that surface offsets measured on glaciers are biased toward lower values.