Geologists dissect massive quake

Sunday's magnitude 7.9 quake in central Alaska left cracks in the ground that run the length of the Denali fault system but caused minimal damage to property and, amazingly, few injuries and no deaths.

The famous Trans-Alaskan oil pipeline also appeared to stand up very well to the shaking - just as its designers and engineers had predicted.

The ground disturbance has now been surveyed by scientists from the US Geological Survey and their photographs provide a remarkable record of one of the largest tremors ever recorded in North America.

Denali is a so-called strike-slip system, which means the two blocks of rock on either side of the fault grind horizontally past each other. In this case, the northern side moved from the west to the east.

A maximum shift of nearly seven metres (22 feet) occurred across the Tok Highway, a road that goes from Tok to Glenallen and intersects with the Alaska Highway.

Scientists now say that the main shock started at the western end of the rupture zone and then travelled eastward along the fault, where most of the seismic energy was released.

All the data gathered on the quake will help improve models of how faults slip during earthquakes, and give researchers a better understanding of the earthquake hazards associated with large faults.