A tsunami is not a single wave but a series of waves, with crests arriving five minutes to an hour apart, that can persist for many hours. In today's Mexico event, the waves lasted 12 minutes in Puerto Madero and 28 minutes in Chiapas, reaching 0.3 meters above tide level — enough to be dangerous near shore but, by good fortune, not catastrophic. The process that detected and communicated this threat is a remarkable piece of planetary-scale engineering.
The warning system begins with seismometers. When the US Geological Survey detected the 15.2-kilometer-deep rupture near the Middle America Trench — where the Cocos tectonic plate slides beneath the North American plate — computers instantly calculated its location, depth and magnitude. Earthquakes above magnitude 7.0 with shallow focal depths and thrust-fault mechanisms are the primary triggers for tsunami alerts, because they displace the seafloor vertically, shoving an entire column of water upward.
Once triggered, the National Oceanic and Atmospheric Administration's two Tsunami Warning Centers — one in Hawaii and one in Alaska — take over. They rely on a network of DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys. These buoys consist of a bottom pressure recorder sitting on the seafloor and a surface buoy that communicates via satellite. When a tsunami wave passes overhead, the pressure change at the ocean floor is detected in real time. The data travels from the seafloor to the buoy to a satellite and back to the warning center in under three minutes.
With earthquake parameters and DART data in hand, forecasters run high-resolution models that simulate how the wave energy will travel across the ocean basin. The models factor in bathymetry — the shape of the seafloor — because shallow ridges and underwater canyons can focus or scatter wave energy. The result is a detailed impact forecast that tells authorities along which coasts waves will arrive, at what height and for how long. In today's case, the models successfully forecast waves below 0.3 meters for Colombia, Costa Rica, Ecuador, El Salvador, Honduras, Nicaragua, Panama and Peru, allowing those countries to avoid unnecessary evacuations while keeping their populations alert.
Knowledge takeaway: tsunami warnings rely on seismometers for rapid earthquake detection, DART seafloor pressure sensors for direct wave measurement, and bathymetry-informed computer models for impact forecasting; the entire chain — from quake to public alert — takes minutes; the Middle America Trench subduction zone that produced today's 7.3 quake is one of the most seismically active regions on Earth, making the warning network there especially critical.