Volcano Watch — Massive Alaskan earthquake rocks the mainland

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On November 3, one of the largest recorded earthquakes to strike the U.S. mainland rocked the interior of Alaska. The quake caused countless landslides, opened 1.8 meter (6-foot) cracks in highways, shook homes and damaged supports to the Trans-Alaska pipeline.

Effects of the 5 km (3 miles) deep magnitude-7.9 quake extended for thousands of miles. It triggered microearthquakes at the Geysers geothermal area in northern California and at Yellowstone National Park in Wyoming. From Seattle to New Orleans, boats were tossed about and even torn from moorings. As far east as Pennsylvania and Florida, USGS instruments recorded significant changes in ground-water levels immediately following the earthquake.

Amazingly, very few injuries and no deaths resulted from the quake, at least in part due to its remote location: 75 miles south of Fairbanks and 175 miles north of Anchorage. Long-term research and a commitment to hazard preparedness and mitigation also played key roles.

For example, USGS scientists were instrumental in ensuring that the Trans-Alaska oil pipeline was designed and built to withstand the effects of a magnitude-8.0 earthquake with up to 20 feet of movement at the pipeline. These standards were considered to be excessively conservative at the time, but proved to be on target. The earthquake ruptured across the pipeline and, although some supports were knocked out, it did not break. The resilience of the pipeline to the fault rupture is a testament to the importance of hazard mitigation in engineering design.

The earthquake resulted from slip on the Denali fault, one of the longest continental faults in the world, stretching over 700 km (435 miles) across Alaska and southeastward into Canada. The extent of the Denali fault rivals that of California's San Andreas fault system. Like the San Andreas, it is a strike-slip fault, meaning that rocks on either side of the fault grind past each other in a mostly horizontal manner.

The November 3 earthquake ruptured at least 300 km (190 miles) along the Denali fault as the north side of the fault moved to the east and up relative to the south side, by as much as 7 meters (22 feet)!

This was the second major earthquake along this fault in less than two weeks; a magnitude 6.7 earthquake occurred a few miles to the west on October 23 and is now believed to be a foreshock of the November 3 massive quake. And the area is still rocking. As of this writing, five aftershocks larger than magnitude 5 have occurred. Frequent aftershocks are expected to occur for the next few months. They will eventually taper off in frequency and magnitude, but will continue to occur for at least a year.

While this was the largest earthquake recorded on the Denali fault, Alaska has experienced even stronger quakes in the recent past, and indeed, is the most seismically active area in the United States. Many of the intense Alaskan earthquakes have generated tsunami that caused serious damage in the Hawaiian Islands, especially on the Big Island. The recent Denali earthquake did not generate a tsunami because the fault that ruptured was on land, rather than beneath the ocean.

Geologists and seismologists world-wide are working on the data being gathered on the earthquake. These data will help improve models of how faults slip and give us a better understanding of the hazards associated with large faults. To find out more about the Denali earthquake, its effects, and what we are learning from it, check out http://earthquake.usgs.gov/.

Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. Lava flows through a tube system from the vent to the sea. Occasional breakouts from the tube system feed surface flows visible on the pali and in the coastal flats. Lava continues to enter the ocean at the Wilipe`a and West Highcastle lava deltas. An eastern arm of the flow is poised to enter the ocean east of Highcastle. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary and onto the lava deltas and benches.

Two earthquakes were reported felt in the week ending November 14. A magnitude-3.2 earthquake was felt in Volcano and Hawai`i Volcanoes National Park at 6:37 a.m. on November 12. The earthquake was located 4 km (2.4 mi) southeast of the summit of Kilauea Volcano at a shallow depth. A resident of Hilo felt an earthquake at 10:26 p.m. on November 13. The magnitude-3.0 earthquake was located 9 km (5.4 mi) southeast of Pu`u `O`o at a depth of 9.9 km (5.9 mi).

Mauna Loa is not erupting. The summit region continues to inflate. The earthquake activity is low with only 3 earthquakes located in the summit area during the last seven days.