We Can't Predict Earthquakes

It's Thursday, June twenty fifth. Yesterday a 7.1 magnitude earthquake hit Venezuela. Buildings collapsed in Caracas. And I live in the Bay Area, which sits on the San Andreas Fault, which means this is not an abstract topic for me. I ride my scooter to the Caltrain every morning on ground that could, at any moment, shift underneath me. So I started looking into earthquakes, and I realized I couldn't actually explain what one is. Like, I know "the ground shakes" but I couldn't tell you why it shakes, why we can't predict when it's going to shake, why some buildings survive and others collapse, or whether a tsunami is just an earthquake that happens to be underwater. The answers to all of those questions are wilder than I expected, starting with the fact that the USGS, the agency responsible for monitoring earthquakes in the United States, says, and I'm quoting: "Neither the USGS nor any other scientists have ever predicted a major earthquake. We do not know how, and we do not expect to know how any time in the foreseeable future." We can forecast weather two weeks out. We can predict solar eclipses centuries in advance. We cannot predict an earthquake more than a few seconds before it hits. So I had to start with the basics because I realized I was embarrassingly fuzzy on them. Here's what an earthquake actually is.

The ground you're standing on right now isn't one solid piece. It's broken into about fifteen massive slabs of rock called tectonic plates, and they're all moving, constantly, driven by heat from the Earth's mantle. They move slowly, a few centimeters per year, roughly the rate your fingernails grow. Where the edges of these plates meet, they grind against each other, pull apart, or push one under the other.

The best way to think about it is a rubber band. As two plates move in opposite directions, friction along the boundary locks them together. The plates keep trying to move but the boundary won't slip. Stress builds in the rock. It bends. It stores energy. More and more and more, for years or decades or centuries. And then the stress exceeds the strength of the friction and the rock snaps, releasing all that stored energy at once as seismic waves. That's the shaking. An earthquake is a rubber band that's been stretched for a hundred years finally breaking.

Here's a number that kind of blew my mind: about 500,000 earthquakes happen every year. Five hundred thousand. There's probably one happening somewhere right now while you're listening to this. Most of them are too small to feel. Only about 100,000 are strong enough for a human to notice, and only about 100 per year cause any damage. A magnitude 8 or larger happens roughly once a year somewhere on Earth. And eighty one percent of the world's largest earthquakes occur along the Ring of Fire, a horseshoe-shaped belt of plate boundaries encircling the Pacific Ocean from New Zealand through Japan, up through Alaska, and down the western coasts of the Americas. If you live on the Pacific Rim, you live on the Ring of Fire. I ride my scooter across it every morning. This is the part that I found most unsettling. We've gotten incredibly good at predicting natural phenomena. Weather forecasts are accurate a week out. We know the exact minute of the next solar eclipse for the next thousand years. We can predict volcanic eruptions by monitoring gas and ground deformation. But earthquakes? The USGS says they've never predicted a major earthquake and don't expect to learn how in the foreseeable future. Ever. That's not a temporary limitation. That's the world's leading earthquake scientists saying this might just be a problem we can't solve.

The reason is that the process that causes earthquakes happens deep underground where we can't see it. We can't watch the rock bending. We can't measure the exact stress level on a fault. We don't know how much more pressure it can take before it breaks. Scientists have spent decades looking for warning signs, changes in groundwater, radon gas emissions, animal behavior, and none of them have proven reliable. Earthquakes don't announce themselves the way storms do.

What we do have is early warning, and the difference between prediction and early warning matters. Prediction would mean telling you days or weeks in advance. Early warning means detecting an earthquake the instant it starts and racing an electronic alert ahead of the shaking. It works because earthquakes produce two types of waves: P-waves that are fast but weak, and S-waves that are slow but destructive. Sensors pick up the P-waves first and send alerts faster than the S-waves travel through rock. In California, ShakeAlert covers over fifty million people and can give you a few seconds to about a minute of warning. Japan's system is even more advanced: it automatically brakes bullet trains, stops elevators at the nearest floor, shuts off gas lines, and interrupts every TV and radio broadcast in the country. A few seconds doesn't sound like much until you realize it's the difference between standing next to a window and being under a desk. One of the things that surprised me most in the research is that earthquakes themselves rarely kill anyone. What kills people is buildings falling on them. The USGS estimates that collapsing structures account for the vast majority of earthquake deaths worldwide. Which means the difference between a natural event and a catastrophe is almost entirely about building codes.

The deadliest earthquake in recorded history hit Shensi (SHEN-see) province in China in 1556 and killed roughly 830,000 people, many of whom lived in yaodong (yow-DONG), cave dwellings carved into soft loess cliffs that collapsed during the shaking. The 1976 Tangshan (TAHNG-shahn) earthquake in China killed between 250,000 and 300,000 people, largely because the buildings were unreinforced masonry that crumbled instantly. The 2010 earthquake in Haiti, magnitude 7.0, killed over 200,000 people in a country with almost no seismic building codes. That same year, Chile was hit by an 8.8 magnitude earthquake. Five hundred times more powerful than Haiti's. Five hundred times. And 525 people died. Same planet. Same year. The only difference was the buildings. Chile has some of the strictest seismic codes in the world. Haiti had almost none. That comparison tells you everything you need to know about earthquake survival: it's not about geology. It's about engineering.

Japan is the global leader in earthquake engineering, and they approach it with three strategies that each work differently. The first is taishin (TIE-shin), resistance: making the structure strong enough to withstand shaking without cracking. Reinforced concrete, steel frames, cross-bracing. The second is seishin (SAY-shin), damping: installing devices inside the building that absorb seismic energy the way shock absorbers in a car absorb bumps in the road. The building still moves, but the movement is controlled. The third is menshin (MEN-shin), base isolation: the building literally sits on rubber pads that allow the foundation to move horizontally while the structure above stays relatively still. During an earthquake, the ground shifts underneath the building but the building itself barely moves. It's the most expensive approach but also the most effective for large structures.

Japan's earthquake resistance rate, the percentage of buildings that meet modern seismic standards, reached roughly ninety percent in 2023. The country experiences about twenty percent of the world's strongest earthquakes. The death toll from earthquakes in Japan has dropped dramatically over the past fifty years, not because there are fewer earthquakes, but because the buildings got better. And yes, I looked into the tsunami question, because I always assumed a tsunami was basically an underwater earthquake, and that's close but not quite right.

A tsunami happens when an earthquake displaces the seafloor vertically. When a fault beneath the ocean shifts in a way that pushes a section of the seafloor up or drops it down, it displaces the water above it. That displacement creates a wave that travels outward in every direction across the ocean at speeds up to 500 miles per hour, roughly as fast as a commercial jet. In the open ocean, the wave might be only a foot or two tall and you'd never notice it from a boat. But as it approaches shallow water near a coastline, it slows down and the energy compresses, pushing the wave higher and higher. By the time it reaches shore, it can be over a hundred feet tall.

Not all underwater earthquakes cause tsunamis. The fault has to move vertically, displacing the water above. The San Andreas Fault, which runs through California, moves mostly horizontally, plates sliding past each other sideways. So a major San Andreas earthquake wouldn't generate a large tsunami, which is one less thing for me to worry about on my scooter. The 2004 Indian Ocean earthquake, magnitude 9.1, triggered a tsunami that killed roughly 230,000 people across fourteen countries. It remains one of the deadliest natural disasters in recorded history, and most of those deaths were from the wave, not the shaking itself. So if this comes up in conversation, here's how to think about it. An earthquake is what happens when tectonic plates that have been locked together by friction finally snap, releasing stored energy as seismic waves. About 500,000 happen every year. Only about 100 cause damage. Eighty one percent of the world's largest ones occur along the Ring of Fire. We cannot predict earthquakes and the USGS says they don't expect to be able to in the foreseeable future. What we can do is detect them the instant they start and send warnings seconds before the strongest shaking arrives. Earthquakes don't kill people. Buildings do. Chile survived an earthquake five hundred times more powerful than Haiti's with a fraction of the casualties because their buildings were designed for it. Japan leads the world in earthquake engineering with buildings that resist, absorb, or float above the shaking. A tsunami is caused by vertical displacement of the seafloor during an underwater earthquake, and the resulting wave can cross an ocean at the speed of a jet. Venezuela got hit yesterday with a 7.1. I live on the San Andreas Fault. The ground under all of us is moving right now. It's just a question of when it snaps.

Stay informed, stay curious, and we'll see you tomorrow.