The Next L.A. / Reinventing Our Future : PREPAREDNESS : IDEA FILE: Danger Zones

How It Works

Using detailed fault maps and seismic data to strengthen zoning and building codes on a neighborhood-by-neighborhood basis. Incorporate neighborhood seismic profiles into zoning regulations, so that buildings would be constructed to withstand the actual ground shaking a particular block might be expected to experience in a major quake.

Benefits

Most of the most severe earthquake damage experienced in Southern California during a major temblor could be prevented, or at least alleviated, by requiring stringent engineering precautions be taken in areas most prone to earthquake damage.

Short-term or Long-term Impact?

Short term. The U.S. Geological Survey is already considering updating its seismic hazard maps, but detailed block-by-block risk assessments are not yet possible.

Supporters

Many local building codes already require engineering measures designed to minimize earthquake damage, but earthquake experts say that many of the regulations are laxly enforced. The state’s 20-year-old Alquist-Priolo Act, for example, bans construction within 50 feet of active faults, but it is left largely to localities to enforce. It is now evident, based on such recent quakes as Landers, Loma Prieta, Whittier Narrows and Northridge, that faults are zones, sometimes a half mile wide, rather than lines, and that shaking intensities can affect areas very far from the faults. So, Alquist-Priolo is at least out of date and should be strengthened.

Opponents

There probably is not the political willpower to carve out large areas and rule out building there, even if scientists knew enough to do so. To accurately profile seismic risks at the neighborhood level would require more precision and understanding of the region than seismologists and geologists today can command. Nearly every big quake of recent years has come on a fault that had not been identified before, usually a thrust fault that cannot readily be seen on the surface. The Los Angeles Basin has dozens of such faults.

Any effort to assign an earthquake risk to specific neighborhoods is likely to have a profound impact on housing values.

The Costs

Unknown.

REALITY CHECK

Unlikely.