When a 7.3 magnitude earthquake struck off the coast of southern Mexico near the town of Puerto Madero, people in nearby coastal areas were urged to stay away from beaches for six hours as a tsunami warning was issued. The quake, which struck at a depth of about 15km, was felt as far away as Guatemala and El Salvador, triggering evacuations and sending people running into the streets. Fortunately, no fatalities or serious damage were reported, and the tsunami warning was later cancelled after waves of only 0.3 metres were recorded. But the event highlights how a powerful earthquake can trigger a potentially dangerous series of ocean waves known as a tsunami.
Earthquakes are measured using the moment magnitude scale (often reported as Richter magnitude), with each whole number representing a tenfold increase in amplitude of the seismic waves. A magnitude 7.3 quake is considered a "major" seismic event—powerful enough to cause damage if close to populated areas, and capable of triggering tsunamis if it occurs under or near the ocean. The United States Geological Survey (USGS) initially recorded the quake at 7.4 before revising it down to 7.3. It was preceded by a smaller quake and followed by aftershocks ranging from 4.7 to 6.0. The epicentre was 48km southwest of Aquiles Serdán, near the coast of Chiapas, a region that sits along the Middle America Trench, where the Cocos Plate is subducting beneath the North American Plate. This type of plate boundary is responsible for many of the world's largest earthquakes and tsunamis.
“Why a 7.3 magnitude earthquake triggered a tsunami warning off Mexico's coast.”
When a large earthquake displaces the seafloor vertically, it pushes the water above, creating a series of waves called a tsunami. These waves can travel across entire ocean basins at speeds of up to 800km/h. In deep water, the wave height is small—often less than a metre—but as it approaches shallow coastal waters, the wave slows and its height increases dramatically. The US National Oceanic and Atmospheric Administration (NOAA), which operates the Pacific Tsunami Warning Center, issued a warning for coasts within 300km of the epicentre, advising that hazardous tsunami waves were possible. In this case, the waves reached only 0.3 metres, but the agency warned that waves up to 1 metre above tide level could occur. NOAA explains that people caught in tsunami water may drown, be crushed by debris, or be swept out to sea.
For UK readers, this may seem distant, but it has real-world implications. First, the UK is a global hub for travel and business; many British citizens vacation in Mexico or nearby countries, and a major tsunami could affect flights, tourism, and consular services. Second, understanding how tsunami warnings work helps people interpret news and assess risks when travelling. Third, the UK itself faces tsunami risks—though rare, the Storegga Slide off Norway around 6100 BC caused a tsunami that hit the coast of Scotland, and a potential collapse of the Cumbre Vieja volcano in the Canary Islands could generate a large tsunami affecting the UK's western shores, according to some scientific models. Knowing what to do—staying away from beaches when warnings are issued—is universally relevant.
Q: How does a tsunami warning work? Tsunami warnings are issued by regional centres like NOAA's Pacific Tsunami Warning Center when an earthquake of sufficient magnitude (usually over 7.0) occurs under or near the ocean. They assess the seismic data and, if a tsunami is likely, broadcast alerts to government agencies, which then evacuate coastal areas. The warning is often cancelled once actual wave heights are measured.
Q: Why do some earthquakes cause tsunamis and others don't? Not all undersea earthquakes produce tsunamis. The key factor is whether the earthquake displaces the seafloor vertically—this happens most commonly at subduction zones, where one tectonic plate dives beneath another. Magnitude alone isn't enough; the depth, location, and mechanism (thrust faulting) all matter. The 7.3 quake off Mexico had the right characteristics for a tsunami warning.
Q: Could a similar earthquake and tsunami affect the UK? The UK is far from active subduction zones, so it rarely experiences large earthquakes. However, tsunami waves can travel long distances. The most likely source of a significant UK tsunami is a large landslide or volcanic collapse in the Atlantic. But the warning systems and science used to monitor tsunamis globally are the same that would protect UK coasts if such an event occurred.
What happens next? In Mexico, authorities continue to monitor aftershocks and assess structural impacts. President Claudia Sheinbaum stated that protocols were activated in neighbouring states, and inspections are ongoing. The tsunami warning has been stood down, but officials advise people to remain observant near the sea. For the broader scientific community, each event provides data to refine earthquake and tsunami prediction models—improving warnings for future events.