Preventing tsunami damage by developing a seafloor monitoring network off the Mexican coast and providing disaster prevention education

Like Japan, Mexico is known to be an earthquake-prone country. The Pacific coast of Mexico is located in a subduction zone, and has suffered from tsunami damage due to major earthquakes on numerous occasions during the past 250 years. The northern coast of Guerrero State, however, has not experienced an earthquake for the last 100 years. The reason is known to be the repeated occurrence of slow slip events at intervals of several years, so that some of the interplate deformation is released without earthquake movement. However, it has been shown that not all this deformation is in fact released, and as it gradually builds up, it is likely to cause a massive earthquake in the near future
Although Mexico would like to evaluate the possibility of future massive earthquakes, its earthquake monitoring mainly consists of geodetic observations on land, and it has not previously conducted seafloor monitoring. The country's tsunami preparedness and countermeasures are also inadequate.
This project therefore addressed the Guerrero seismic gap, with the goals of assessing the size of the potential future massive earthquake, and developing a disaster scenario for this massive earthquake and tsunami and a disaster-mitigation education program.

Earthquake monitoring in Mexico mainly consisted of geodetic observations on land, but in a joint project with partners including the Universidad Nacional Autónoma de Mexico, they introduced the Global Navigation Satellite System (GNSS) on land and on the seafloor to the Guerrero seismic gap in the state of Guerrero on Mexico's Pacific coast, and created an earthquake monitoring network.

Placing seafloor monitoring equipment on the sea bed

They analyzed the data obtained from the earthquake monitoring network on land and on the seafloor, and investigated the association between the three major earthquakes that occurred in Mexico between 2017 and 2019 and slow slip. Slow slip is a phenomenon in which the distortion is released at a much lower fault slip rate than that of regular earthquakes. In this seismic gap, the coupling between the plates is much weaker than it is in surrounding areas, which means that because the adhesion at the boundary between the plates is weak, one plate is sinking smoothly under the other without distortion building up, and slower earthquakes are occurring.
This project was also the first to detect the occurrence of a slow earthquake in the Guerrero seismic gap. This showed that the absence of a major earthquake in the Guerrero seismic gap for almost the last 100 years was due to the release of the distortion by slow earthquakes, and does not mean that a century's-worth of distortion has built up.

Based on the most recent monitoring data for the Guerrero seismic gap, they created an earthquake/tsunami scenario. They also set up a disaster-mitigation education program building on the foundation of the region's social, economic, and cultural background, and made people throughout the region aware of everyday preparations in collaboration with the local disaster prevention bureau.

Children taking part in a tsunami evacuation drill

The outcomes of this project were well received in Mexico, and their use is expected to continue in future. Efforts are now getting underway to extend the tsunami disaster-mitigation education program to other areas of Mexico and to other countries in Central and South America and the Caribbean. The project ended in 2022, but joint research will still continue in future.

Preparing the monitoring equipment on board ship