A government agency discovers “major monetization” | Local news stories

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Last week, the California Geological Survey released new hazard maps for San Mateo and Contra Costa counties detailing where landslides and soil liquefaction are likely to occur in the event of a major earthquake.

CGS seismic hazard zone maps found “significant” liquefaction areas in parts of San Mateo County, particularly in Half Moon Bay, Miramar and San Bruno. The state has already drawn maps of most of the peninsula, including Mount Montara, Woodside, and San Mateo. But La Honda and San Gregorio are two notable rural areas for which there is no accessible data yet.

Each map, a roughly 60-mile-wide area called the Quadrangle, represents three types of geological problems caused by earthquakes: fault rupture, landslide and liquefaction, which describes the process when seismic tremors cause soil to mix with groundwater and act like quicksand.

The state agency defines most of Half Moon Bay as being within the liquefaction area. The quadrangular area is 74 square miles, and the liquefaction area extends the entire coast of the city and more, including most neighborhoods up to Pilarcitos Creek, including El Granada and Miramar, and rural areas such as Purisima Creek Redwoods Preserve. The map also identifies fault zones on the east and west sides of Half Moon Bay Airport, and more than half of the Mount Muntara Quadrilateral is at risk for landslides caused by earthquakes.

The CGS maps were drafted in February but became official on September 23. Land and city management agencies use risk maps to identify properties that require site-specific studies before beginning new development. Under the Seismic Hazard Mapping Act of 1990, local jurisdictions can withhold permits at a site within the danger zone until geological surveys have been completed and used in development plans. The law also requires real estate agents and sellers to disclose whether their property is within a designated danger zone.

Eric Frost, CGS’ chief engineering geologist, said the maps don’t automatically mean that there is a hazard waiting to occur in every area. Rather, it indicates that more work is needed if anyone is planning to build on the land. He stressed that maps should not be a substitute for location-specific research.

“These areas are simply areas where there is a higher probability of danger being present. It’s not a 100 percent chance,” Frost said. A site-specific study says, ‘Is there really danger here? If so, how significant is the danger, and how do we engineer around it?’

The state agency’s data goes back to the 1989 Loma Prieta earthquake, when a 6.9-magnitude earthquake shook the Gulf region, killing 63 and injuring more than 3,700. CGS says earthquakes of 5.5 or more on the Richter scale can trigger landslides. or monetization. Much of the work creating these maps involved pairing data from county soil reports with GIS mapping software, including light-band-detection technology, known as lidar, which uses lasers to survey landscapes, said Max Marshall, an engineering geologist. and mapping it.

For residents looking to purchase and develop real estate within the danger zone, an earthquake can be devastating if proper insurance policies are not in place. In general, earthquake insurance does not cover landslides for homes or businesses. This means that specialized coverage, commonly referred to as a “variance of circumstances,” said Janet Ruiz, a spokeswoman for the Insurance Information Institute.

Although public data for CGS is available to insurance companies, it is not always used when selling policies. The California Seismic Authority, for example, uses standardized prediction of earthquake ruptures in California, according to CEA spokeswoman Sarah Sol.

“The release of new maps for this area has no immediate impact on CEA insurance premiums because we take a consistent statewide view of earthquake risk and rely on the best available science about California earthquake prospects as a whole when setting our rates,” Sol wrote in a review email.

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