If the 1906 earthquake happened today, San Francisco would get zero warning. Here’s why that makes the seconds everyone else gets even more important.

The SF Chronicle ran an article this week that got a lot of attention: if the 1906 San Francisco earthquake happened today, the city itself would get no advance warning from ShakeAlert. Zero seconds. The shaking would start before the system could even transmit the message.

That’s not a flaw in ShakeAlert. It’s physics. The system works by detecting P-waves (the fast, less destructive waves) and sending alerts before the S-waves (the slow, destructive ones) arrive. When you’re sitting on top of the fault, those two waves arrive almost simultaneously. There’s no gap to exploit.

Robert de Groot, ShakeAlert’s coordinator at the USGS, confirmed it directly: San Francisco, Oakland, and Berkeley would be in the no-warning zone for a San Andreas rupture. Palo Alto might get 5-10 seconds. Santa Cruz, 15-20 seconds.

The instinct is to read that and think the system doesn’t work. The opposite is true. The no-warning zone is exactly why what happens everywhere else matters so much.

The people who get 5-20 seconds aren’t just protecting themselves

When a major earthquake hits close to a population center, the first few hours are chaos. Emergency responders are overwhelmed. Hospitals are flooded with casualties. Roads are blocked. Communication systems are strained or down. Every secondary problem that piles on top of the primary disaster pulls resources away from the people who need them most.

That’s the real argument for earthquake early warning at facilities outside the immediate epicenter zone. It’s not just about protecting the people inside those buildings. It’s about keeping those buildings operational so they can serve the people in the no-warning zone who had no chance to prepare.

Think about what happens in the 20-mile radius around the epicenter when facilities farther out use their warning time well.

A hospital in San Jose that gets 10 seconds of warning can pause active surgeries, secure imaging equipment, and lock down hazmat storage. That hospital stays operational. Now it can receive trauma patients from San Francisco, where hospitals closer to the fault may be damaged or overwhelmed.

Fire stations in the South Bay that get 8 seconds can open apparatus bay doors automatically before the shaking jams them shut. Those trucks roll. They get to the epicenter zone faster instead of sitting behind doors that won’t open.

Then there are the secondary disasters that don’t happen. A manufacturing plant in the East Bay that shuts down chemical processes before shaking starts doesn’t become a hazmat incident that pulls first responders away from search and rescue. A school on the Peninsula that gets kids under desks before anything falls doesn’t tie up ambulances that should be heading into the city.

None of these scenarios involve the epicenter. They all happen in the ring outside it. And they compound. Every facility that stays operational, every injury that doesn’t happen, is capacity that flows toward the people who had no warning at all.

This is the part most people miss about earthquake early warning

The public conversation about ShakeAlert usually focuses on the phone alert — the notification from apps like MyShake that tells you to drop, cover, and hold on. That matters. But for facilities, the real value is in the automated systems that act without any human decision.

Five seconds isn’t enough time for someone to read a notification, understand what it means, and take action. It is enough time for a system to open fire station bay doors, cut gas valves, trigger PA announcements, pause surgical equipment, unlock exit doors, and send parent notifications at a school. All automatically. All before shaking starts.

Research published in Seismological Research Letters (Strauss & Allen, 2016) estimated that earthquake early warning could reduce injuries by roughly 50% in scenarios where people receive and act on a warning before shaking. For automated facility systems, that number is likely higher — the system doesn’t freeze or fumble for a phone. It just acts.

April 18 is the 120th anniversary of 1906

The 1906 earthquake killed an estimated 3,000 people and destroyed more than 28,000 buildings. It happened at 5:12 a.m., when most people were asleep. There was no warning system. There was no way to prepare.

120 years later, the technology exists to give millions of people seconds of warning before shaking starts. Not everyone — not the people sitting directly on the fault. But the ring of cities and facilities surrounding the epicenter can use those seconds to reduce injuries, stay operational, and respond faster to the people who had no chance at all.

That’s what earthquake early warning is really for. Not just the people who get the alert. The people who don’t.

Learn how EWL brings automated ShakeAlert warnings to facilities →