CLOSE UP : SEISMIC SENTINEL

From Santa Barbara Island to Topanga, from Catalina to Santa Ana, hundreds of seismometers constantly monitor every step inSouthern California’s marathon earth dance. They are secreted in graveyards and parks, outside museums and airports. There’s one even buried below the moon-white Hollywood sign.

Their job is to record L.A.’s every tickle, tremble and shudder, transmitting their data to seismographs at USC and Caltech. They must be on the job every second of every day, but they need occasional servicing and they sometimes malfunction.

It’s then that Michelle Robertson, manager of the Los Angeles Basin Seismic Network, jumps into her truck, loaded with enough electrical tools to rewire a house and “a pickax and a shovel. If the sensor is bad, I need to dig it up.” Most of the devices are on or slightly below the surface but some are many feet deep; the Baldwin Hills unit is nearly a mile deep.

The 20 L.A.-area stations she maintains complement more than 250 other permanent seismometers in various sites throughout Southern California. She alsoworks on the temporary units that are called into service after a quake.

When she’s not out in the field, Robertson, a computer and electronics wizard who has been maintaining seismic stations for more than a decade, keeps up hardware and software for USC’s Earth Sciences Department. “You can’t do science without good data,” she says, “and the data doesn’t come in unless a station is functioning.”

So she lugs her tools up and down hills and valleys, sometimes carrying two60-pound batteries. She’s stared down buffaloes on Catalina, braved thunderstorms and gotten violently ill on boats going to the island stations.

Not even “the bones in the caskets” at the cemetery sites will keep her from reviving a dead seismometer, Robertson says. “Of course,” she adds, “I’ve never been outdigging in the graveyards at night.”