The Guerrero seismic gap in southern Mexico is a section of a subduction zone where large earthquakes have not occurred recently, but slow fault movements and small earthquakes are common. These include tremors, low-frequency earthquakes, and tsunami earthquakes—unusual events that produce larger tsunamis than expected for their size.

We analyzed two years of seafloor seismic data and detected many slow earthquakes near the trench, where the oceanic plate descends beneath Mexico. These events cluster in areas with rugged seafloor and strong gravity signals, indicating the subduction of large underwater mountains called seamounts. When seamounts are forced under the continent, they deform and mix surrounding rocks, creating weak zones (subduction mélanges) that influence how the fault slips.

We also studied the 2002 tsunami earthquake (magnitude 6.7), which ruptured slowly and was likely triggered by a subducted seamount. Just below this zone lies a region with no earthquakes, possibly due to fluid-rich rocks that weaken the fault.

Our results show that subducting seamounts and weak rock mixtures help determine whether faults slip slowly or break suddenly, improving our understanding of earthquake and tsunami hazards in subduction zones.