By Ali Sahabi

When we think about earthquake preparedness, we often focus on the strength of the building itself. But what is underneath a building can be just as important. Across the San Diego region, some properties are located in areas susceptible to liquefaction, landslides and other forms of ground instability that can intensify damage during a major earthquake.

The City of San Diego’s Seismic Safety Study identifies areas affected by known and potential geologic hazards, including faults, liquefaction and landslides. For rental housing providers, understanding these conditions is an important part of evaluating a property’s overall seismic risk.

When Solid Ground Loses Its Strength

Liquefaction occurs when loose, water-saturated soil loses strength during strong earthquake shaking. The U.S. Geological Survey explains that when this happens, soil that normally supports buildings and infrastructure can begin behaving more like a liquid.

This hazard is particularly associated with areas containing loose, saturated sediments, including some locations near bays, rivers and areas of filled or reclaimed land. The consequences can include settlement, ground movement and damage to foundations and other structures.

California has seen these effects before. During the 1989 Loma Prieta earthquake, liquefaction contributed to significant damage in San Francisco’s Marina District, an area partly developed on artificial fill.

Earthquakes Can Also Trigger Landslides

Hillside properties face another potential hazard. Strong earthquake shaking can destabilize slopes and trigger landslides, rockfalls and other ground movement.

This is particularly relevant in Southern California, where rental properties can be located on or near hillsides, canyons and steep terrain. According to the USGS, earthquake-triggered landslides can occur when shaking reduces the stability of a slope, potentially threatening buildings, roads and utilities.

The risk is not the same for every property. Soil conditions, slope, groundwater, earthquake intensity and the design and condition of the building all influence how a property may perform.

Know Your Property’s Risk

The good news is that property owners have more information available today than ever before. The City of San Diego provides seismic safety maps that allow the public to review mapped geologic hazards throughout the city.

For properties located in areas of concern, a map should be viewed as a starting point rather than a diagnosis of an individual building. Qualified geotechnical and structural professionals can help property owners better understand site-specific conditions and whether additional evaluation is warranted.

Earthquake preparedness should ultimately look at the whole property, from the soil and foundation to the structural system above it. Understanding potential vulnerabilities before an earthquake gives rental housing providers an opportunity to make informed decisions about maintenance, improvements and seismic retrofitting.

We cannot control where or when the next earthquake will strike. But we can understand our risks and take reasonable steps to prepare. Stronger buildings and better-informed property owners help create safer, more resilient Southern California communities.

About Optimum Seismic, Inc.

The Optimum Seismic team has been making California cities safer since 1984 by providing full-service earthquake engineering, steel fabrication and construction services for multifamily residential, commercial and industrial buildings. With more than 4,000 earthquake retrofit and renovation projects completed, Optimum Seismic’s work includes soft-story multifamily apartments, tilt-up, non-ductile concrete, steel moment frame and unreinforced masonry (URM) buildings. To arrange a complimentary assessment of your building’s earthquake resilience, contact Optimum Seismic at (833) 978-7664 or visit optimumseismic.com.