SEATTLE -- The devastation of earthquake-generated tsunami waves is well known. Take the Magnitude 9 tsunami that wiped out portions of the northeast Japanese coastline in 2011.
Seismologists and other scientists have long warned that a tsunami and Magnitude 9-plus earthquake will hit the Northwest coast. It has been recorded in the geological record as recently as January 1700. But only the recently completed Ocosta School in Westport, Wash., is built to withstand one.
The American Society of Civil Engineers in Portland Wednesday revealed building standards for tsunami-vulnerable states including Washington, Oregon, California, Alaska, and Hawaii.
ASCE also unveiled a series of inundation maps for three sections of the west coast including Grays Harbor, Wash. In a snapshot of the map, Westport and Ocean Shores are underwater, and even areas located up adjacent waterways see levels of inundation reaching up to 15 feet.
The final ASCE standards would be published in early 2017.
"Many people can be saved in multi-story buildings, and many structures can be designed to withstand tsunami effects," reads a presentation from Yong Wei of the University of Washington's Joint Institute for the Study of the Atmosphere and Ocean and the NOAA Pacific Marine Environmental Laboratory. Along with him was Dan Cox, Professor of Civil and Construction Engineering at Oregon State University.
"The Maximum Considered Tsunami is the design basis event," they write. "Characterized by the inundation depths and flow velocities..."
They consider the maximum tsunami as having a two percent probability in a 50-year period or, a worst case scenario, hitting on an average of every 2,500 years.
But tsunamis of varying intensities are recorded in layers of peat found in mud banks along the Washington coast showing with intervals from a few hundred years to 500 years apart. Much of that based on research pioneered Brian Atwater with the U.S. Geological Survey.
ASCE proposes four risk categories ranging from low to high. A Category 1 would be "Buildings and other structures that represent a low risk to humans." A Category 4 would be defined as "Buildings and other structures designated as essential facilities" and "buildings and other structures, the failure of which could pose a substantial hazard to the community."
The consequences of inaction are also documented. For Washington, ASCE says 45,000 residents and 20,000 tourists would be at immediate risk along some 160 miles of coastline. Post-tsunami impacts could impact 900,000 people and create $4.5 billion in damage and threaten seven ports. In California, 275,000 residents and up to 2 million tourists would be vulnerable along with $200 million in damage.
The cause of the most damaging coastal tsunamis for the Northwest coast is the Cascadia Subduction Zone, which runs from Cape Mendicino, Calif., to north of Vancouver Island, B.C. They point out that Cascadia is longer than the zone that ruptured in the 2011 Tohoku quake in Japan.
But tsunamis are more than just water height and water force. They also push debris ahead and in them, ranging from logs to boats and even ships. Tsunami's propel floating vehicles, shipping containers and large pieces of buildings, even boulders. And the faster the water moves the worst the battering ram effects.