hazard identification and vulnerability analysis - Mason County

Property damage estimated at upwards of $25 million resulted from a magnitude
7.0 earthquake near Olympia on April 13, 1949. Eight deaths were caused either
directly or indirectly, and many were injured. At Olympia, nearly all large buildings
were damaged, and water and gas mains were broken. Heavy property damage
was caused by falling parapet walls, toppled chimneys, and cracked walls (MM
VIII). Electric and telegraphic services were interrupted. Railroad service into
Olympia was suspended for several days; railroad bridges south of Tacoma were
thrown out of line, delaying traffic for several hours. A large portion of a sandy
spit jutting into Puget Sound north of Olympia disappeared during the
earthquake. Near Tacoma, a tremendous rockslide involving an 0.8 km section of
a 90 meter cliff toppled into Puget Sound. The felt area extended eastward to
western Montana and southward to Cape Blanco, Oregon, covering about
400,000 square km in the United States. A large portion of western Canada also
experienced the shock.
On November 5, 1962, a moderately strong earthquake caused minor damage in
the Vancouver, Washington - Portland, Oregon, area. Numerous chimneys were
cracked or shaken down (MM VII) in Portland. Several buildings had tile ceilings
fall, and other damage such as cracked plaster and broken windows were
reported. Slight damage was reported from several towns in Washington. The
tremor was felt over an area of approximately 52,000 square km of Washington
and Oregon. The magnitude was measured at 4 3/4.
A magnitude 6.5 shock on April 29, 1965, which was centered very close to the
epicenter of the 1949 earthquake, caused about $12.5 million damage. Three
persons were killed by falling debris, and the deaths of four elderly women from
heart failure were attributed to the earthquake. There were numerous injuries, but
most were minor. The shock was characterized by a relatively large intensity VII
area and small pockets of intensity VIII damage in Seattle and Issaquah.
Extensive damage to chimneys was noted in West Seattle. In 188 city blocks, it
was found that 1712 of 5005 chimneys were damaged. Two schools in West
Seattle and two brick school buildings in Issaquah were damaged considerably.
In general, damage patterns repeated those experienced during the 1949 shock.
Buildings that apparently had been damaged in 1949 often sustained additional
damage in 1965. The tremor was felt over 340,000 square km of Washington,
Oregon, northern Idaho, northwestern Montana, and part of British Columbia.
A magnitude 5.3 earthquake hit Seattle on May 2, 1996. Information about this
earthquake is available from the Pacific Northwest Seismograph Network. o
Another earthquake struck Western Washington on July 2, 1999. Information
about this earthquake is available from EQE, a consulting company. * The most
recent major earthquake, the Nisqually quake, was a magnitude 6.8 quake and
struck near Olympia, WA on February 28, 2001.
People, buildings, emergency services, hospitals, transportation, dams, and
electric, natural gas, water and sewer utilities are susceptible to an earthquake.
Effects of a major earthquake in the Puget Sound basin are catastrophic,
providing the worst-case disaster short of war. Thousands of people could be
killed and many tens of thousands injured or left homeless. An earthquake in the
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