Magnitude 7.9 CENTRAL ALASKA

This high-altitude view shows the approximate locations of the epicenters of the two large earthquakes that occurred recently along the Denali fault. The view is eastward along the main strand of the Denali fault, which is marked here by a prominent linear valley along the southern edge of the Alaska Range. The magnitude 7.9 earthquake that occurred in the afternoon of November 3, 2002 was preceded by a magnitude 6.7 earthquake in the early morning of October 23, 2002. The earlier earthquake and its zone of associated aftershocks were located slightly to the west of the later, larger earthquake.

The Denali fault is a major fault that follows an arcuate trace across southern Alaska, following the Alaska Range for much of its length. The eastern part of the fault shows about 300 km (180 miles) of right-lateral strike-slip displacement since early Tertiary time. Offset surficial deposits and seismicity indicate that the fault has remained active to the present, but the November 3 earthquake is the largest seismic event so far recorded on the fault. In the left foreground, the Nenana River marks the eastern boundary of Denali National Park. The Parks Highway, which connects Anchorage and Fairbanks, lies immediately east of the river north of the fault, but diverges from the river to the south. The epicenter of the November 3 earthquake was approximately 42 miles (68 km) east of the highway. In the distance, the rugged peaks of Mts. Deborah and Hess rise to about 12,000 feet (3650 m) just north of the epicenters and the bend in the Denali fault.

(Photo and interpretation by Wesley K. Wallace, Geophysical Institute, University of Alaska Fairbanks)