Anchorage earthquake is a warning to California

One of similar magnitude hitting downtown L.A. would be devastating

LOS ANGELES— Buildings cracked. Roads collapsed. People were injured by falling debris.

But for all the ferocity of the 7.0 magnitude earthquake that struck the Anchorage area Friday, it did not cause the catastrophic damage or loss of life that have occurred from even smaller quakes around the world, including California.

Friday’s Alaska quake was larger in magnitude than the 1989 Loma Prieta quake and the 1994 Northridge quake, each of which killed more than 50 people and caused billions of dollars in damage.

Experts emphasized they are still studying the Anchorage earthquake but said several factors made it less destructive than other major quakes.

For one thing, the quake was not centred directly under Anchorage. The centre was about 13 kilometres away, said Jonathan Tytell, a geophysicist with the U.S. Geological Survey. That’s still fairly close, but doesn’t have the same effect as if it were directly under the city.

The quake was also fairly deep, 40 kilometres beneath the surface, which also resulted in less shaking at the surface, said Joann Stock, a geology and geophysics professor at California Institute of Technology.

“Earthquakes are just complex,” said Heidi Tremayne, director of the Earthquake Engineering Research Institute. “Each has its own thumbprint.”

Much of the structural damage in Anchorage was the result of liquefaction, which is when sediments and water are shaken together and act like quicksand.

Anchorage is a newer city, with fewer old buildings that are likely to collapse, Tremayne said. Building codes for newer construction are designed to allow buildings to easily withstand the shake intensity ranges seen in the Anchorage earthquake, she said.

The 9.2 magnitude 1964 Alaska quake significantly damaged many buildings, so there are few of Anchorage’s oldest structures left, Tremayne said.

But in California, for example, a Los Angeles Times analysis found that there are hundreds of old brick buildings in the Inland Empire that have been marked as dangerous but haven’t been retrofitted, de- spite decades of warning.

Across California, there are other vulnerable building types, such as apartments with parking on the ground floor, older houses with a few steps off the ground, and vulnerable concrete and steel buildings.

San Francisco’s last extremely large earthquake was in 1906, with an estimated magnitude of 7.9. Southern California’s last great one was in 1857, also an estimated 7.9 magnitude, which moved the San Andreas Fault almost 300 kilometres between Monterey County and the San Gabriel Mountains near Los Angeles.

California has a long history of large earthquakes, and experts said the Anchorage destruction should be another warning to prepare.

A similar-size earthquake around downtown L.A. would be much more destructive because the buildings are older and the area much more densely populated.

“In the Los Angeles area, there’s a much more extensive array of infrastructure throughout the city,” Tytell said.

“Up in Alaska, things are a little bit more rural, a little bit more spread out. But make no mistake, there is a city there.”