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SAN DIEGO — Many Californians’ first instinct in an emergency is to reach for their phone — a lifeline to loved ones, first responders and breaking news online. But when the “big one” comes, you shouldn’t count on your device working for you, experts say.

That finding is among a trove of information and predictions about a major earthquake made by a team at the U.S. Geological Survey ahead of California’s statewide “ShakeOut” drill Thursday. It’s the latest iteration on a landmark 2017 study known as The HayWired Earthquake Scenario.

That report provides a comprehensive look at the consequences of an earthquake of a magnitude greater than 7.0 in a densely populated area of the state. In the case of HayWired, that’s the East Bay Area’s Hayward fault.

“The HayWired scenario is named, in part, to recognize society’s dependence on wired and wireless information and communication technologies,” the study overview explains.

A chart from the HayWired scenario plots out the amount of time it will take to restore different amounts of service to various critical communication services after a major earthquake. (Photo: USGS)

Cell towers, the experts explain, are expected to withstand the shaking in some cases and are located at more of a distance from other hazards, though they are vulnerable to the potentially sweeping power outages that accompany major temblors. Meanwhile, cellular equipment on poles and buildings is vulnerable to the “extreme shaking, liquefaction, and fire hazards” associated with such a large quake, meaning serious disruption is likely.

In Alameda County, voice and data service was expected to drop to as low as 7% as it suffered the heaviest damage, broadest power outages and largest sudden increase in users in the scenario. As the Los Angeles Times notes, that’s equivalent to the 93% failure of cellphone calls in New York City in the moments after the 9/11 terror attacks.

The places where people need to use their phone the most will be the worst equipped to handle the load, and service will be the most spotty in the frantic moments shortly after disaster strikes.

“The percentage of demand for voice and data services that is met is at its lowest when most needed for public health and safety immediately after the earthquake,” the analysis reads.

Key problems include obvious issues — like interference with callers reaching 911 or family members to confirm they’re OK or ask for help — but also more complicated problems, such as medical systems struggling to access patients’ files.

HayWired even considers the effect that service issues — which could last to some degree for days — would have on mental health:

“For a population that is accustomed to using the internet and mobile data to manage their lives, the impact of service outages will accentuate the emotional and mental challenges of an earthquake. In a small amount of literature on the emotional aspects of limited mobile phone use, Hoffner and others (2015) found that 70 percent of people recalled loneliness, anxiousness, or vulnerability when involuntarily separated from their mobile.”

The study’s contributors suggest a series of ways that California could help mitigate the effects of earthquake damage on cell and data access, including retrofitting old buildings and infrastructure to make them more resilient overall and making telecommunication equipment less reliant on commercial electric power.

Check out the complete document here and learn more about earthquake preparedness on