2002 Denali earthquake

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File:Denali Fault surface rupture.png
Extent of surface rupture caused by faulting during the 2002 Denali earthquake

The 2002 Denali earthquake occurred at 22:12:41 UTC (1:12 PM Local Time) November 3 with an epicenter 66 km ESE of Denali National Park, Alaska, United States. This 7.9 Mw earthquake was the largest recorded in the United States in 37 years (after the 1965 Rat Islands earthquake). The shock was the strongest ever recorded in the interior of Alaska.[1] Due to the remote location, there were no fatalities and only one injury.

Due to the shallow depth, it was felt at least as far away as Seattle and it generated seiches on bodies of water as far away as Texas and New Orleans, Louisiana.[2] About 20 houseboats were damaged by a seiche on a lake in Washington State.[2]

Tectonic setting

The Denali-Totschunda fault is a major dextral (right lateral) strike-slip system, similar in scale to the San Andreas Fault system. In Alaska, moving from east to west, the plate interactions change from a transform boundary between the Pacific plate and North American plate to a collision zone with a microplate, the Yakutat terrane, which is in the process of being accreted to the North American plate, to a destructive boundary along the line of the Aleutian islands. The Denali-Totschunda fault system is one of the structures that accommodate the accretion of the Yakutat terrane.[3]

Earthquake

Foreshock

On October 23, 2002, there was a magnitude 6.7 earthquake located on the Denali fault. The event's aftershocks revealed a Script error: No such module "convert". long fault rupture along the Denali fault, but aerial reconnaissance could not locate a surface rupture. This rupture extends to Script error: No such module "convert". west of the mainshock's epicenter. Minor avalanches of snow and rockfalls were plentiful in the area as a result. Because of its location close to the November 3 event and the fact that it preceded it by only 11 days, this earthquake is regarded as a foreshock.[4] The calculated stress transfer from this foreshock indicates that it brought the Denali fault closer to failure at the location of the mainshock epicenter.[5]

Mainshock

The initial rupture on November 3, nucleating Script error: No such module "convert". east of the foreshock, was on a thrust fault segment, the previously unknown Susitna Glacier thrust,[4][3] to the south of the Denali fault. The rupture then jumped to the main Denali Fault strand propagating for a further Script error: No such module "convert". before jumping again onto the Totschunda Fault through a wide and complex transition zone, and then ruptured another Script error: No such module "convert". of fault plane.[3] The total surface rupture was ca. Script error: No such module "convert"..

Slip on the Susitna Glacier thrust peaked at Script error: No such module "convert". with an average displacement of Script error: No such module "convert". across the fault.[3] Slip on the Denali fault peaked at Script error: No such module "convert". with an average slip of Script error: No such module "convert"..[3] The transition zone between the Denali fault and the Totschunda fault which includes small normal faults had a peak displacement of Script error: No such module "convert"., while the main Totschunda fault slipped an average of Script error: No such module "convert". with a peak of Script error: No such module "convert". found.[3] Two areas of high seismic moment were observed Script error: No such module "convert". and Script error: No such module "convert". from the epicenter.[3] Three subevents were observed during the event: the first was a Template:M 7.2 primarily thrust event along the Susitna Glacier thrust with potential simultaneous Denali fault rupture.[3] The second, an Template:M 7.3 subevent, ruptured along the Denali fault, while the third, final, and largest Template:M 7.6 subevent continued past the second event along the Denali and Totschunda faults where the maximum displacements of Script error: No such module "convert". was observed.[3] The total seismic moment of this earthquake corresponds to a magnitude of Template:M 7.9.[3]

There is evidence of local supershear propagation inferred from ground motions along at least Script error: No such module "convert". of the rupture.[6]

Aftershocks

Aftershocks primarily manifested in portions of fault where surface rupture was found, and aftershocks were usually limited to very shallow depths.[3] South of Denali, aftershocks match the inferred characteristics of the Susitna Glacier thrust.[3] Many aftershocks were actually on faults nearby that are not known to have ruptured, and may just be accommodating stress changes.[3] On the Denali fault itself, there were fewer and smaller aftershocks than expected, with the largest only being a Template:M 5.8 event.[3]

Earthquake damage

File:Trans Alaska Pipeline Denali fault shift.jpg
View of Trans-Alaska Pipeline showing deliberate offsets in construction, to accommodate movement on the fault
File:Tok Cutoff USGS.jpg
The Tok Cut-Off was offset Script error: No such module "convert".

Minor damage was reported over a wide area but the only examples of severe damage were on highways that crossed the fault trace and areas that suffered liquefaction, e.g. Northway Airport.[7] Liquefaction was more severe in the eastern end of the rupture compared to the west. Sand boils were also widespread, being reported in Fairbanks, Northway, and Delta River. Massive landslides occurred in the Alaska Range, but most were within 30 kilometers of the rupture.[8] Several bridges were damaged but none so severely that they were closed to traffic.

Due to the general self-sufficiency of those living near the fault rupture, very few lifeline systems were compromised. These people tend to get water from private wells, heat their homes and cook their meals with gas furnaces and stoves, and maintain individual septic systems.[7]

The Trans-Alaska Pipeline System crosses the rupture trace; the pipeline suffered some minor damage to supports. There was no oil spillage, as the pipeline at that location was designed to move laterally along beams to withstand major movement on the Denali Fault.[9] The pipeline was shut down for three days to allow for inspections but was then reopened.

See also

References

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  7. ↑ a b Script error: No such module "citation/CS1".
  8. ↑ Script error: No such module "Citation/CS1".
  9. ↑ Sorensen, S.P. and Meyer, K.J.: Effect of the Denali Fault Rupture on the Trans-Alaska Pipeline Template:Webarchive; Sixth U.S. Conference and Workshop on Lifeline Earthquake Engineering, ASCE, August 2003.

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External links

Template:Earthquakes in 2002 Template:Earthquakes in Alaska Template:Earthquakes in the United States

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