6.8 Washington Quake Rattles Hanford Observatory
by Stan Whitcomb
 
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Just minutes before 11:00 AM on Wednesday, February 28, a magnitude 6.8 earthquake struck near Olympia, Washington, about 35 miles southwest of Seattle. This strong, rolling quake--the most powerful to strike the Washington area in over 50 years--was reportedly felt from as far away as Vancouver, British Columbia and Portland, Oregon. It also registered strongly with those of us here at the LIGO Hanford Observatory.

Map of Washington State

The temblor was too remote to cause any significant damage to the durable LIGO facilities or vacuum system. But the delicate suspensions for the in-vacuum optics of the two LIGO interferometers were more vulnerable. These optics are suspended by fine wires and the shaking caused them to swing until they hit restraints designed to protect them from any catastrophic damage in just such an incident. The optics for the 4-km interferometer were in the midst of being installed, and for them this was a small annoyance requiring minor realignment. But the quake caused a number of the 2-km interferometer optics to become misaligned to the extent that we will have to vent the vacuum system to make corrections. This work is expected to take about two months, and we will try to turn adversity into opportunity by making other planned modifications to the 2-km hardware at the same time.

Still, this accident is a great disappointment. Besides the time needed to realign the optics, the LIGO Scientific Collaboration had scheduled the first engineering run involving interferometers at both sites for March 9-12. But neither Hanford interferometer will be operational that soon. The engineering run will still proceed but, because of the setback, the data from Hanford will be limited to environmental veto data.

Coincidentally, a visiting panel of reviewers from the National Science Foundation was on site in the Hanford control room when the earthquake struck. At the time they were getting a first hand look at the sort of natural hazards one has to prepare for when performing such sensitive measurements.