São Vicente Cape, Sagres.
Fissure on the tectonic plate, near the São Vicente cable, has been forming at least five million years ago, in a process called ‘delamination’.
200 kilometers off the Cabo de São Vicente, in Sagres, there is a fissure on the tectonic plate for forming at least five million yearswhich was now discovered and can explain the great earthquakes of Lisbon.
A Horsessea geological formation in the Atlantic Ocean not far from the bench’s underwater mountain, on the border between the European and African tectonic plates, is the geographical origin of the earthquake of intensity close to 8 on the Richter scale that and other regions of the country.
The fact that it is a flat geological formation, without great known seismic failures, fed “a enigma”In the scientific community of how it could have been possible a region with these characteristics provoking earthly magnitude, but a study from the Faculty of Sciences of the University of Lisbon this Wednesday in the journal Nature Geoscience brings a new possible explanation.
In that area had never been found “no obvious failure” that explained an earthquake with the magnitude of the 1969, said João Duarteone of the co -authored researchers of the study, geologist, professor at the Faculty of Sciences of the University of Lisbon and researcher at the Dom Luiz Institute. In addition to this puzzle as a motivation of the investigation is also the fact that it has never been found “a failure with sufficient dimensions to generate an earthquake”, which is believed to have had an intensity close to 9 e Richter design.
Part of the plate is separated
According to João Duarte, what is now revealed and which may be the explanation of the origin of both earthquakes is that “there is a portion of the tectonic plate that is separating” in a process called ‘throat‘.
This demaneration implies that the plate is undergoing a horizontal fracture, as if the rock are separated by a blade, opening a fissure that leads to the lower part to be sinkhaving already reached a depth of 200 kilometers toward the Earth’s cloak, when the normal is in 100 kilometers.
The upper part of the plate remains an horizontal position unchanged, making it impossible to perceive by observing the sea bottom any geological change in that place, the investigator told Lusa.
Behavior “a little abnormal”
This process of horizontal separation of the plate, which has been slowly happening for five to 10 million years, was identified with a kind of “Earth Ultrasound”explained the teacher about the use of seismic tomography and the sound captured, the sound of the earth’s own, to realize what goes on below the bottom of the sea.
“We did a study that placed seismometers on the seabed for eight months to record small earthquakes. We realized that in that area there was a cluster, a set of small seismos at great depth, about 30 to 40 kilometers, which is a little abnormal. And therefore, there is a combination of several observations here that point out that there is a process that is generating seismicity, ”explained the researcher.
The work of observation and data analysis joined the creation of computational models that allowed to simulate the process of delamination. It is the friction created and the energy released in the movement of the tectonic plates that explain the earthquakes. The fact that this geological structure described in the study is not a seismic failure, having the ability to generate earthquakes is explained by the fact that the space created by the laminate cut on the plate is not empty.
“We know that the African plate is also moving very slowly, converging with the eurasian plate. It is as if we imagined we have two books and one starts to enter the other. The plates are converging and, in fact, this area where the plate begins to separate, it behaves a little like a sheet, because it begins to get into the other sign. There is always a contact, but it is a more horizontal contact. That is, it is not a hole, it is not a space. This space is later occupied by another rock, ”explained João Duarte.
New submarine cables and were new opportunity
From this study, João Duarte expects to result in more detailed future investigations on that zone. With what is already known, it is inevitable that this process of delamination will be taken into account “in the characterization of dangerousness and seismic risk” in the country, already considered in a high risk area, by the confluence of the two tectonic plates in this region.
In the installation of a New generation of submarine cablescommunications cables that connect the two sides of the Atlantic, passing through the Azores and Madeira archipelagos and also through the area of the abyssal plain of the horseshoe, the researcher sees a opportunity.
“They will have seismic sensors, so the cables will pass in that area, it will be possible to monitor better and characterize that seismicity. And we can probably also have more data, more records,” he said.
The predictability of the earthquakes remains a chimera, but João Duarte believes that the artificial intelligence can allow a step forwardeven if the learning model based on previous events and data is in this case a difficulty, as the great earthquakes are rare phenomena.
The key may be in a more systematic study of the smaller earthquakes that happen every day, including in Portugal, “with some hope” to know the process of seismicity and “make some inferences and use statistics to understand the most magnitude.
