Usually it’s the Cascadia Subduction Zone, the huge undersea fault that causes magnitude 9.0 earthquakes off the Northwest Coast every 300 to 500 years, that gets the most attention. But seismologist Bill Steele from the University of Washington in Seattle said even smaller quakes could cause significant damage in Cowlitz County.
Steele said the California quake caused buildings with unreinforced masonry to collapse, injuring bystanders with falling bricks and debris. Buildings with unreinforced masonry in Longview and elsewhere would be at risk of similar damage.
“I think it’s time we start thinking about how we are going to strengthen these buildings or remove some of them before an earthquake does,” Steele said.
Wet, sandy soils — like most of the lowland Longview-Kelso area — tend to magnify shock waves. This makes structures on them more prone to collapse from liquefaction — which occurs when saturated soil is shaken and turns to quicksand.
The February 2011 magnitude 6.3 quake in Christchurch, New Zealand, killed 185 people and injured thousands more and provided a valuable lesson to scientists.
“We learned from Christ Church that magnitude 6 earthquakes can be devastating. If you have poor soils and poor building types, particularly unreinforced masonry, magnitude 6 can produce … ground motion that can break and displace these bricks so that the building becomes unstable and collapses,” Steele said.
Magnitude 6 earthquakes are not a rarity in Washington and Oregon. The last one in Western Washington occurred in 2001, when a 6.8 temblor north of Olympia injured 400 people and was the most expensive natural disaster in Washington history. Even closer to home, a 5.2 earthquake along the Mount St. Helens seismic zone caused violent shaking here on Feb. 14, 1981. Seismologists believed somewhat stronger quakes are possible along the fault.
How to be earthquake-ready
• Secure ceiling fans and light fixtures using bracing wire. Anchor the bookcases, file cabinets, loose shelving and entertainment centers to walls.
• Secure china, collectibles, trophies, and other shelf items with museum putty. Install a lip or blocking device to prevent books or other articles from falling off shelves.
• Secure televisions, computers, and stereos with buckles and safety straps.
• Ensure appliances have flexible gas or electrical connections.
• Strap the top and bottom of a water heater to wall studs.
• Know how to turn off the gas supply.
• Relocate flammable liquids to a garage or outside storage location.
Source: Federal Alliance for Safe Homes