SHIPS - Overview
SHIPS - (Wet) SHIPS, Dry SHIPS, Kingdome SHIPS - What's it all about?
Seismic hazards in the Puget Sound are dependent on the locations of active faults (those with earthquakes occurring on them in the recent past) and knowing how, how much, and how often slip occurs on those faults. Slip can occur without earthquakes (aseismically) but more often it occurs after enough tension builds up to suddently override the friction on the fault surface. The sudden motion on the faults is an earthquake.
Research on the ground (paleoseismology) has revealed repeated occurrences of earthquakes in the Puget Sound region. The search for the faults on which those earthquakes occurred is more difficult because of the large surface area covered by water, and also by vegetation and urban development.
The USGS spearheaded a search using oil exploration technology to 'see' into the earth and locate faults in the Puget Sound. They also need to determine the seismic velocities in the subsurface in order to predict ground shaking amplification in the region. A group of scientists from universities and government agencies (consortium) are working together to understand where these faults are, which ones can still produce earthquakes, and how often earthquakes occur.
- Environmental issues related to seismic surveying in Puget Sound center on the potential adverse impact of airgun noise on marine mammals and threatened bird species. On the basis of acoustic modeling, the survey was conducted without injury to marine life. Permits were obtained from regulatory agencies to assure compliance with environmental law. Biologists observed operations to ensure the safety of marine mammals.
(Wet) SHIPS focused on seismic reflection work in the Sound and Strait; Dry SHIPS included recordings on land across the Seattle area, and Kingdome SHIPS recorded ground shaking resulting from the demolition of the Kingdome.
The map below shows the locations of known or suspected crustal faults within a 60 mile (100 km) radius of Seattle. Large earthquakes on any of the faults within 60 miles of Seattle could produce damage in Seattle.
The uplift sites found just north of the Tacoma fault zone are too far south to have caused by the Seattle fault zone, but could have been caused by an earthquake along the Tacoma fault zone about 1100 years ago.