By JCP Geologists

Napa Suffers Moderate Damage in 5.2 Quake

NAPA, CA -- North Bay residents were shaken out of their beds -- and some out of their homes -- by a surprisingly strong magnitude 5.2 earthquake on Sunday, September 3, 2000. The quake struck at 1:36 in the morning in the middle of a Labor Day weekend, little more than a year after the region's last significant jolt, a magnitude 5.1 event on August 17, 1999, near Bolinas, in Marin County.

Initial damage estimates gauged the dollar loss at between $5 million and $15 million dollars, due mainly to damages to homes and businesses in the city of Napa. Obvious damage included hundreds of brick chimneys cracked or broken off at the roofline, cracked walls, partially collapsed porches, and household appliances, televisions and other contents scattered across rooms. In the downtown area, glass littered the sidewalks from storefront windows shattered by the early morning shaking.

That damage toll could rise significantly as inspectors and engineers check buildings in detail. City officials estimate that as many as 5,000 buildings may be damaged to one extent or another. Many of the residences and businesses initially thought to have sustained only superficial damage are being found to have suffered structural damage. In some cases, this has included damage to home foundations.

State officials indicate that the damage total may exceed $50 million -- enough that Governor Gray Davis issued a State of Emergency for the City of Napa on September 6 and began a formal damage assessment of the affected area. The formal assessment is necessary before requesting federal disaster assistance from President Clinton for homeowners in the hard-hit Napa neighborhoods and commercial building owners and merchants downtown.

Numerous residents suffered injuries, most of them minor. However, the quake caused several major injuries, one a child struck by bricks tumbling from an interior chimney.

At least one apartment building was evacuated due to structural damage, forcing its residents into Red Cross shelters. Over 70 people spent Sunday night in the shelters.

UNRECOGNIZED FAULT TO BLAME

As data flowed into the U.S. Geological Survey (USGS), however, it became clear the quake was centered about 8 miles northwest of the city, 3 miles west-southwest of Yountville, on a different fault -- one not previously recognized by geologists or represented on maps. In this area, there is no record of a previous earthquake.

The temblor was felt thoughout the Bay region, from as far north as Lake and Mendocino Counties, to as far south as Santa Clara County.

The shaking level in Napa, ranked at Modified Mercalli Intensity VII, is classified by the USGS as "Very Strong" and potentially capable of causing moderate damage.

The USGS forecasted a 1-in-5 chance of strong and possibly damaging aftershocks in the Yountville area during the week following this quake.