Scientists study plate collisions along state’s coast

CAPE ELIZABETH – As a pair of earthquakes struck California recently, scientists from around the world were in Maine learning about quakes.

Seismologists and geophysicists from as far away as San Francisco and Tokyo examined the peaceful shore of Two Lights State Park on hands and knees.

Scientists said Maine’s coast was not always the quiet, stable place it is today.

“It was pretty active 300 million years ago,” Mark Swanson said as he stepped across the ledges and boulders just above the crashing surf.

Swanson is a professor of geology at the University of Southern Maine and has spent about 20 years examining and mapping the cracks and lines in the rocks.

He led Thursday’s field trip to give more than 100 of his peers a close-up look inside a series of earthquakes that fractured the bedrock and shook the area way back when the west coast of Africa collided with the Maine coast.

Last Thursday’s field trip marked the highlight of a weeklong conference on earthquake physics sponsored by the American Geophysical Union. It coincided with a pair of quakes that shook part of California.

A 4.9-magnitude quake struck east of Los Angeles, startling people and knocking items off shelves and desks Thursday afternoon. Later, a 6.6-magnitude temblor hit about 125 miles off the coast of Eureka, Calif., around 11:30 p.m., rattling the ocean floor.

No one was injured.

In Maine, Swanson and a group of his students pointed out major fault lines and smaller fractures that spread outward.

They showed where the movement of earth can be measured by veins of quartz that stop abruptly, then start again several inches or several feet to the left or right of the original line. And, most exciting to the visiting scientists, they pointed to thin gray or black lines in the faults where the shifting rock faces rubbed against each other, heated up and created what is called pseudotachylite, or “false volcanic glass.”

“We’re looking up the main fault zone right here,” Ashley Bates said as she stood in a small crevasse near the water’s edge and pointed to thin layers of pseudotachylite. “When the rock was sheared off, the friction was so hot it was melted.”

A geology student from Southern Utah University, Bates is one of a group of students helping Swanson map fault lines along the Maine coast this summer.

The series of earthquakes that occurred here when the continents collided were spread over millions of years and shifted the bedrock a few centimeters at a time. The entire shift, or offset, at the Cape Elizabeth site was about 5 meters, Swanson said.