Lowly amoeba may provide early warning for big quakes

Scientists say that tiny, shelled amoebas may help provide early warning for large earthquakes five to 10 years before they happen, giving communities time to plan for high-magnitude quakes that can cause tsunamis.

Evidence suggests that the type of amoebas change in certain shallow coastal areas five to 10 years before a megathrust earthquake occurs, a study in the July issue of the Geographic Society Bulletin says.

Megathrust quakes are destructive earthquakes that occur where two plates of the Earth's crust collide. One such area, the Cascadia Subduction Zone, lies off the Northwest coast where the Juan de Fuca plate dives beneath the North American plate.

A magnitude-9 megathrust earthquake in the Indian Ocean last December caused a massive tsunami that killed more than 200,000 people.

The study is based on core samples taken before and after the 9.2-magnitude Alaskan earthquake in 1964, and from Netarts Bay on the Oregon coast, where scientists have found evidence of large earthquakes and tsunamis 300 to 3,000 years ago.

The samples show a change in amoeba populations caused by slight elevation decreases along the coast in the years before a large earthquake, said David Scott, professor of Earth sciences at Dalhousie University in Halifax, Nova Scotia, and one of the study's authors.

When the elevation dropped, sometimes by just a few centimeters, the single-celled organisms that lived in seawater increasingly mixed with those in fresh water in certain locations, Scott said.

"We see the same precursor mechanisms in microorganism populations five to 10 years before a megathrust earthquake, whether it happened more recently or in the prehistoric past," he said.

Scott said there are several low-lying areas on the Washington coast where such microorganisms could be monitored.

Washington state's Emergency Management Department is working with communities such as Willapa Bay and Grays Harbor to promote public awareness and evacuation plans in areas at risk for tsunamis caused by megathrust earthquakes.

"Were making sure communities in hazard areas are developing mitigation plans," said George Crawford, technical adviser on seismic activity for the state Emergency Management Department.

In Long Beach, Pacific County, Crawford is working with community leaders to protect coastal-dune ridges that may serve as natural barriers to a tsunami wave. He also is helping Aberdeen plan evacuation drills in areas where roads may be washed out by a tsunami.

"I've got to get communities prepared, so we're making sure communities in hazard areas like Long Beach are developing mitigation plans," Crawford said. "However, a few years warning may spur legislation to fast-track more direct funding to those areas that will be most affected by earthquakes."

Scott and his co-authors recommend that tiltmeters, which measure elevation movement down to the millimeter, be placed in areas where changes in the amoeba populations are found. Or scientists could regularly monitor the populations to look for evidence of elevation change.

The organisms, called foraminefera, are barely visible, single-celled creatures with shells the size of a grain of sand. In fact, sand from many beaches is made up in part from the shells of foraminefera.

Peter Ward, professor of biology and of Earth and space sciences at the University of Washington, said using the organisms and their fossilized remains is a radically different yet simple way to understand subtle elevation changes.

Some scientists, though, are skeptical that changes in such organisms could warn of a possible earthquake.

The organisms change when the salinity of the water changes, said Ian Hutchinson, professor of physical geography at Simon Fraser University in British Columbia. And salinity can change without an elevation drop, he said.

Also, tidal records in Alaska before the 1964 earthquake show no evidence of sea-level change, Hutchinson said.

U.S. Geological Survey geologist Brian Atwater at the University of Washington also is cautious about using the organisms to warn of earthquakes. He said the location of the creatures in sediment may be the result of burrowing rather than elevation changes.

"But this is a tantalizing result that deserves to be looked into further," Atwater said.

"There are a whole range of warning systems out there. Technology has gotten a lot of attention recently, but geological history is also a warning on a different time scale."

Carina Stanton: 206-464-8349 or cstanton@seattletimes.com