A Study of the 2002 Denali Co-seismic Displacement Using SPOT Horizontal Offsets, Field Measurements, and Aerial Photographs

We use SPOT image pairs to determine horizontal offsets associated with the M 7.9 November 2002 Denali earthquake in the vicinity of Slate Creek, AK. Field measurements and aerial photographs are used to further characterize the geometry of the surface rupture. The surface displacement field is generated using a sub-pixel cross correlation technique between SPOT images taken before and after the earthquake. The displacement field shows a signal that can be well-explained by an along-strike variation in dextral shear. We estimate a maximum of ~10 m of dextral shear in the east near 145° 30'W. Dextral slip then decreases to 4-5 m to the west near 144° 52'W. Locally, the fault parallel displacement that we estimate from the SPOT images is up to a factor of two larger than field measurements. We suggest the discrepancy between field and geodetic measurements can be well-explained by fault slip being distributed over a fault zone up to several hundred meters wide. If the November 2002 earthquake is a characteristic event, it implies a westward decrease in the long-term slip rate of the Denali fault. A possible mechanism to accommodate the westward decreasing fault slip on the Denali is to transfer slip to adjacent east-trending contractional structures in the west.