Report sounds alarm on L.A. earthquake danger

A 5.1 magnitude earthquake that struck California’s Orange County produced minimal damage but prompted a look by Karen Clark & Company at the potential disaster that could befall the Los Angeles area with a more powerful tremor.

“Although the event was relatively small by California standards, it serves as a reminder that it is only a matter of time before a major earthquake impacts the Los Angeles region,” stated Karen Clark & Company in the report.

The March 28 earthquake produced damage including broken chimneys and building cracks in single family homes, foundation cracks in apartment buildings and broken water lines. It occurred along the Puente Hills faultline and researchers estimated that a more violent quake, of 6.1 or 7.1, could create losses of up to $300 billion in the Los Angeles region.

KCC reported that a 6.1 magnitude event would shake the ground from Los Angeles to Laguna Beach, producing losses of over $20 billion. It would affect the cities of La Habra, La Mirada and Brea.

However, a 7.1 earthquake stands the chance of rupturing the full 40-kilometer length of the Puente Hills fault, affecting more than 1,000 square kilometers. Ranging from Ventura through downtown L.A. to Riverside, Calif., KCC estimated that this hypothetical scenario could result in total losses over $300 billion.

From a risk management perspective, past earthquakes have shown that unreinforced masonry construction have proven highly vulnerable to earthquakes.

“Masonry materials such as bricks and concrete blocks have historically been used in construction because they are easy to assemble and relatively strong under normal gravity loads. In URM construction the mortar is the “glue” used to hold the masonry together, and the strength of the mortar deteriorates over time. When an unreinforced masonry wall is exposed to an earthquake, the mortar can easily crack and fail if the ground motion results in shaking either perpendicular or parallel to the wall,” explained KCC. While many URM buildings have been retrofitted, the potential danger warrants attention by businesses, consumers and policymakers.