La Jornada: They study slow earthquakes on the coast of Oaxaca

With the purpose of understanding how earthquakes and tsunamis work in the Pacific Ocean, as well as having information to face possible disasters, eight ocean floor seismometers and three pressure sensors were installed on the coast of Huatulco, Oaxaca, to analyze slow earthquakes.

The project is carried out by the Secretary of the Navy, the UNAM Institute of Geophysics and students from the University of Kyoto, Japan, through the Oaxaca Oceanographic Campaign.

This was reported in a press conference broadcast on the UNAM Global YouTube channel, in which Captain Jesús Salvador de Olaguibel, director of Oceanography of the Ministry of the Navy, was present; engineer Enrique Guevara Ortiz, director of the National Center for Disaster Prevention (Cenapred); Masaru Kozono, director of the Japanese international cooperation agency; Yoshihiro Ito, director of the Disaster Prevention Research Institute at Kyoto University, and doctor in seismology Víctor Manuel Cruz Atienza, from the UNAM Institute of Geophysics.

Jesús Salvador de Olaguibel highlighted that “this project is something fundamental. Between April 28 and May 1 off Huatulco, Oaxaca, the placement of instruments was carried out, for which we lent the oceanographic research vessel Mazuntein addition to three hydrostatic pressure sensors.”

Guevara Ortiz explained: “this initiative will provide us with data to have better scenarios, models and inputs for decision-making in the event of a disaster and, of course, it can function as educational material, as well as to improve prevention capabilities against earthquakes and tsunamis in Mexico.”

Tripartite collaboration

Masaru Kozono assured that this collaboration is part of a support project between three countries: “we previously used these sensors in the ports of Manzanillo and Acajutla, in El Salvador. Now that they are in Oaxaca we can better analyze the risks of the Mexican Pacific. We hope to form a strong alliance with Mexico and other countries to better understand the earthquakes in those areas.”

Yoshihiro Ito stated: “As a specialist in slow earthquakes, tsunamis and marine earthquakes, I hope that this campaign is not only successful, but that it transcends into a closer collaboration between Mexico, El Salvador, Japan and other colleagues in Latin America. The Guerrero seismic gap gave us very important lessons, such as the 2002 movement, which had a magnitude of 6.7, which was unusually long, with characteristics very similar to those of a tsunami. Thanks to new tools we found “Earthquakes of smaller magnitude than before were imperceptible and that allows us to predict with greater precision what happens.”

The participants prepared at the Cenapred facilities, where researchers, technical staff and students from UNAM and Kyoto University worked together. “We reviewed equipment, shared experience and built trust; it is a very human job. The sea is a very demanding boss, he does not accept ‘now merit’ or ‘in a little while’, you have to be very precise,” said Ito.

Cruz Atienza stated: “We have seen that slow earthquakes have increased in the last 30 years. Since then, there has been a lot of debate about what role these events play in the generation of large earthquakes.”

According to the doctor in seismology, the last five earthquakes with a magnitude greater than 7 were all preceded by a slow earthquake, “we want to find the causal link between both phenomena.” The researcher showed through slides that the area where these phenomena have been generated is the coast of Guerrero.

“We have seen that there are slow earthquakes that change location. In particular, there is one that we studied, which is the one that was generated in the ocean trench near Acapulco. The movement migrated towards the coasts of that port; this caused a magnitude 7 earthquake to trigger on September 8, 2021. We want to build models and theories that tell us how these large earthquakes work and we decided to put the sensors in Oaxaca because we discovered that there are a series of slow earthquakes. that are happening at the bottom of the sea.

“The coasts of Oaxaca are located in front of the collision zone of two tectonic plates, there the subduction of the Cocos plate with that of North America is taking place. It is an earthquake that is already ‘overdue’, it is a region that is going to break, we do not know when but it will happen, perhaps in the not distant future. In that same area the strongest earthquake that we have recorded in Mexican territory occurred, it was in the 18th century, in 1787, estimated magnitude of 8.6, which “It occurred in Pochutla, and generated a tsunami that reached 6 kilometers inland,” he concluded.