Earthquake mitigation at Oakland City Center

Today is San Francisco Earthquake Day. Just before dawn on this day in 1906, at 5:13 local time (meaning 6:13 daylight time), a rip in the crust off Ocean Beach started tearing its way north and south along the San Andreas fault, setting in motion one of California’s greatest defining events.

At the Oakland City Center and the Clorox building, at 1221 Broadway, you’ll see this odd feature on the ground.

citycentergap

It’s a long steel ribbon that covers a pair of long sawcuts in the pavement about 3 inches apart. Between the cuts, the tile has been pulled out and replaced with a flexible gasket. One edge of the steel ribbon is anchored to the tiles, but the other edge is loose.

That’s a retrofit for big earthquakes. During a moderate-to-major event, say magnitude 5-1/2 or larger, the Clorox building will shimmy back and forth, and so will the buried BART station. Because of their different sizes and dimensions, they won’t move in unison. Without the gasket in the pavement, the tiles in the rigid pavement will buckle and shatter and fly in all directions, leaving one more mess to clean up that will probably fester for years.

The gasket promises to prevent that. If you’re here when the next sizeable earthquake hits, and you have the presence of mind (not guaranteed!), watch it work. The free side of the steel ribbon should slide over the ground while the gasket cushions the two sides of the cut beneath it.

This won’t prevent all damage, and it may not matter at during the biggest quakes we can get (magnitude 7 and maybe 7.5), but for the much more abundant moderate events it will save us some grief.

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