No Losses This Time, Except for Pride
The Gilroy Earthquake of May 13, 2002

Wednesday, May 15, 2002

(FREMONT)--A moderate earthquake, centered on a little-known fault a few miles west of Gilroy, rumbled across a 400-mile stretch of the central California Monday night. The jolt was felt in Ukiah to the north and San Luis Obispo to the south, and even in the Sierra foothills town of Pollock Pines.

The only confirmed losses, primarily, were the Sharks and the Braves.

For many Bay Area residents, the quake announced itself as the top story on the 10:00 news--arriving less than a minute past the hour. Early reports gave little indication of damage, other than isolated telephone and power outages.

Fortunately, later reports confirmed that this was a "non-event" as earthquakes go. Aside from some emptied shelves in few Gilroy businesses, and a bit of broken glass, china, and plaster in local residences, the region got off lightly this time.

The temblor's magnitudes were 5.2 on the "Richter Scale" and 4.9 on the "Moment Magnitude Scale" according to the US Geological Survey. In the fall of 2000, the Napa earthquake--of the same magnitude--shook the ground there five times more

Quake "downgraded"? Earth scientists use different magnitude scales these days, to measure different aspects of the shaking. The Richter magnitude represents only certain frequencies of the earthquake's vibrations; the Moment magnitude accounts for all of the frequencies. So, contrary to media reports, the 5.2 magnitude was not "downgraded" to 4.9 after the earthquake--both magnitudes still apply, in the proper context.

forcefully than Monday's quake did in Gilroy, a USGS scientist noted. The Napa shock was a bona fide disaster, injuring dozens and leaving behind $60 million in property damage.

The Gilroy quake sent waves rippling beneath the ice of San Jose's Compaq Center 30 miles to the north, where the hometown Sharks battled into overtime against their playoff foes, the Colorado Avalanche. Some twenty seconds later, as the waves reached San Francisco's waterfront 40 miles farther north, Pac Bell Park bobbed perceptibly as the Giants and Braves dueled into extra innings in the bottom of the ninth.

The Giants won. The Sharks were not so lucky--losing this game and, two days later, the playoff. They can't blame it on the quake, though, as the shaking was apparently felt only in the stands, not by the players.

In San Jose a house fire, reported moments after the earthquake, resulted in the total loss of the Silicon Valley home. Although early news reports indicated the cause to be related to a water heater toppled by the earthquake, the actual cause remains under investigation by fire officials.

A Valuable Lesson At A Bargain Price

According to the USGS, the earthquake struck along the Castro fault, an obscure break in the network of crustal fractures alongside the well-known San Andreas fault in the southern Santa Cruz Mountains. The Castro fault is a branch of the Sargent fault, known to Realtors® in southern Santa Clara County as one of the Alquist-Priolo Fault Zones the State Geologist has mandated for disclosure in real estate transactions.

Several smaller quakes have struck on the Castro fault in the previous six months. A few miles to the northwest, along the San Andreas, is the fault segment that ruptured in the disastrous 1989 Loma Prieta earthquake of Moment Magnitude 6.9.

Whether Monday's shock is merely an isolated incident--or the latest in an ongoing sequence of earthquakes that will become larger still, is unknown. Nevertheless, scientists are quick to add the obvious: damaging earthquakes, of one size or another, are a certainty in the Bay region over the life of a 30-year home mortgage--so, why wait for another costly disaster before preparing your home for the next "big one"?

This week's alarming--but harmless--shaker is a forceful reminder for Bay Area residents to get prepared. Here are a few steps a homeowner can take in order to control the damage from future earthquakes:

1. strap the water heater to nearby wall studs so it won't topple in the shaking
2. bolt and brace your home on its foundation to keep it from sliding off when the ground jerks back and forth beneath it
3. strengthen the roof adjacent to brick chimneys with thick plywood to keep the bricks outside if the chimney falls
4. gather and store emergency supplies, such as fire extinguishers, water, flash lights, and first aid supplies
5. consider purchasing earthquake insurance