key | Was the Second Large 7.5 Earthquake an Aftershock?
Nine hours after the first earthquake, a second earthquake occurred to the north, with a magnitude of 7.5. Some definitions of the term “aftershock” exclude earthquakes that are similar in size to the main one, or that occur far from the initial rupture. In this case, it occurred on a different fault and has roughly the same magnitude. This is almost a semantic or academic question, and experts are divided between those who consider it a replica and those who suggest it is a separate seismic event, starting with the initial one.
“The first earthquake of 7.8 was followed a few minutes later by a smaller one of 6.7: they are brothers,” explains seismologist Gina Villalobos from the Autonomous University of Tamaulipas. “7.5 occurs further north and what I interpret is that the whole region was accumulating efforts and it was only a matter of time before the fault. The initial earthquake destabilized the whole region because it was full of energy The area was”, he explains. And he concludes: “It is not a replication, because it does not even occur in the same fault segment.” Itahiza Dominguez from IGN agrees with this diagnosis: “The 7.8 triggered the 7.5, which would have released its energy independently a little later. The initial earthquake affected the tectonics of the region: along a 200-kilometer fault, it It affects everything around it, the stresses which are released in a series with new earthquakes.
However, other experts consider it a replica, such as Luis Cabanas from the National Seismological Network: “It belongs to the same seismic series, although it is on another fault in another direction in the same broad area. It is actually a break.” What has jumped from one side to the other triggers the other: there is no straight line, but the area is full of fractures grouped one on top of the other.