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M 7.9 (AEIC)

5.0 km (Fixed)

Huge M 7.9 Earthquake Rocks Central Alaska

Seismo-Watch Page 2
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Assorted Wirenews Photos
Special Earthquake Report Archive

November 3, 2002
Updates made as per the date below.

A powerful earthquake measuring M 7.9 rocked Central Alaska this afternoon, causing significant damage in the sparesly populated communities near the epicenter, but no serious injuries were reported and no deaths.

Seismo-Watch EQ Flash! Alert Bulletins notified subscribers of this earthquake within minutes after it happened. You should subscribe to the service too! It's FREE and Fast! NOW! Wireless EQ Flash! via pager, cell phone or PDA's! More info.

According to the Alaska Earthquake Information Center (AEIC) the earthquake measured a Local magnitude (ML) of 7.9 occurred at 1:12 p.m. AST (22:12 GMT), November 3, about 35 miles east of McKinley Park, 45 miles northeast of Cantwell, and 46 miles east-southeast of Ferry in the Central Wood River drainage - a remote region of the east-central Alaska Range. See a Topozone topographic map.

The focal depth was fixed at 5.0 km beneath the surface for quick processing. A preliminary fault plane solution indicates predominantly strike-slip motion along an east-west-trending plane. This was a complex event and the data has been describe at best as "messy".According to Stew Sipken (NEIC) "this earthquake was so big and rattled on for so long, that it is not possible to represent the body-waves as a point source", a process necessary to calculations of a moment tensor. He continued, "As far as I know, "none" of the point-source body-wave inversion techniques have come up with a reasonable solution for this event.

Surface Fault Ruptures

Preliminary information indicates the mainshock ruptured about 200 km of the Denali fault, and about 100 km of the Totschunda fault , a prominent fault splay along the southeastern portion of the Denali fault.

At Milepost 215.5 on the Richardson Highway, a horizontal offset of approximately 2.0-2.5 m (7-9 feet) was measured (see photo). The fault ruptures here trend in a NW-SE direction and show right-latteral displacement (that is as you cross cross the fault, the rocks moved to the right).

The following exerp is from a November 6 briefing by Jeff Freymueller, Geophysical Institute, University of Alaska:

There was little to no surface rupture along the western part of the fault. There was also no surface rupture associated with the foreshock [the Nenana Mountain M 6.7 earthquake] (this part of the fault was surveyed by air after the foreshock, and again after the mainshock). Surface offsets pick up a bit west of the Richardson Highway (and the pipeline). At the Richardson Highway and the pipeline, there was about 2.6 meters of offset. Offsets increased substantially to the east. At the Tok cutoff (the eastern highway crossed by the fault), there was about 6 meters of right-lateral offset. Slightly to the west of the Tok cutoff, about 10 meters was observed, and slightly to the east of if there was one spot with 13-15 meters of offset. The Totschunda fault splays off the Denali fault to the south just east of the Tok cutoff. There was no rupture on the Denali fault east of the splay, only rupture on the Totschunda fault.

Continued on Page 2...

Report update: 7:47:45 AM, Saturday, November 9, 2002

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