For a better understanding of seismological processes it is necessary to know the different forces that generate earthquakes, the geological environment in which they occur, and the physical properties of the structures that generate them.
The earth's crust is constantly subjected to the action of tectonic forces which tend to deform it and, under certain conditions, it can break, generating an earthquake. This phenomenon is produced by the sliding of rock volumes underground along complex fractures called 'faults', accompanied by the release of stress and energy also in the form of seismic waves. In the studio The impact of faulting complexity and type on earthquake rupture dynamics, recently published on Communications Earth Environment by Nature, edited by researchers from the National Institute of Geophysics and Volcanology (INGV) and the Sapienza University of Rome, it demonstrates how the properties of a seismic event change according to the complexity of the structure of the fault that generated the earthquake and its environment tectonic. To know the forces that produce the movements of the earth's crust and which are the basis of earthquakes, it is necessary to analyze increasingly consistent and reliable data as well as increasingly precise techniques for analyzing seismic signals.
“The development of seismic networks and the refinement of the techniques and technologies used in the characterization of seismicity make it possible to analyze many of its properties. Therefore, it is essential to make further theoretical and modeling efforts to systematically continue the analysis of ever more abundant and reliable data. This will allow the development of an overall view of the mechanisms causing earthquakes and a more advanced understanding of the seismological processes affecting the surface (up to 15-20 km depth) and cold part of the crust. Furthermore, the study suggests that in the presence of low double-pair values (two pairs of forces orthogonal to each other that represent the earthquake mechanism) not justified by physical processes, an underestimation of the earthquake magnitude is possible". says Davide Zaccagnino, PhD student at Sapienza University and co-author of the publication.
“Earthquakes are not all the same: the structure of the rupture is influenced by the fact that the crustal volumes tend to overlap, move away or flow parallel to each other: in the first case, the dislocation occurs along a particularly thin and concentrated fracture; in other cases, however, it tends more to diversify into several floors within the crustal volume. The classical seismological models used for the study of earthquakes assume that each rupture occurs in a single fault under the action of a double pair of forces orthogonal to each other and oriented in such a way as to reproduce the observations of the seismographs", explains Carlo Doglioni, co-author of the research. “However strong, the assumptions of current theories are able to explain the main seismological observables and provide some general information regarding an event, such as the magnitude and type of movement of the fault. However, the same hypotheses are restrictive for a detailed description of seismicity, in particular on the type of energy released by the movement, i.e. whether elastic or gravitational, as well as on the involvement of crustal volumes".
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EARTHQUAKES | Faults, geological complexity and the mechanisms of earthquakes
For a better understanding of seismological processes, it is necessary to know the different forces that generate earthquakes, the geological environment in which they take place, and the physical properties of the structures that generate them.
The Earth's crust is constantly subjected to the action of tectonic forces that tend to deform it and, under certain conditions, it can break, generating an earthquake. This phenomenon is produced by the sliding of volumes of rock into the subsoil along complex fractures called 'faults', accompanied by the release of stress and energy also in the form of seismic waves.
in the study The impact of faulting complexity and type on earthquake rupture dynamics, recently published in Nature's Communications Earth Environment, by researchers from the National Institute of Geophysics and Volcanology (INGV) and the Sapienza University of Rome, it is shown how properties of a seismic event change as a function of the complexity of the structure of the fault that generated the earthquake and its tectonic environment. To know the forces that produce the movements of the Earth's crust and which are the basis of earthquakes, it is necessary to analyze increasingly consistent and reliable data as well as increasingly precise techniques for analyzing seismic signals.
"The development of seismic networks and the refinement of the techniques and technologies used in the characterization of seismicity make it possible to analyze many of its properties. It is therefore essential to make further theoretical and modeling efforts to systematically continue the analysis of increasingly abundant and reliable data.This will allow the development of an overall view of the mechanisms at the origin of earthquakes and a more advanced understanding of the seismological processes affecting the superficial (up to 15-20 km deep) and cold part of the crust. the study suggests that in the presence of low double-pair values (two pairs of orthogonal forces that represent the earthquake mechanism) not justified by physical processes, an underestimation of the magnitude of earthquakes is possible", says Davide Zaccagnino, PhD student of Sapienza and author of the publication.
“Earthquakes are not all the same: the structure of the rupture is influenced by the fact that the crustal volumes tend to overlap, move away or flow parallel to each other: in the first case, the dislocation occurs along a particularly thin and concentrated fracture ; in the other cases, it tends to diversify more into several levels within the crustal volume. The classic seismological models used for the study of earthquakes assume that each break occurs in a single fault under the action of a double pair of forces orthogonal to each other and oriented in such a way as to reproduce the observations of the seismographs", explains Carlo Doglioni, co-author of the research. “The assumptions of current theories are able to explain the main seismological observables and provide some general information regarding an event, such as the magnitude and type of movement of the fault. However, the same hypotheses are restrictive for a detailed description of seismicity, in particular on the type of energy released by the movement, that is, if elastic or gravitational, as well as on the involvement of crustal volumes".
Fig 1 – The thickness of the fault zone becomes on average thinner passing from extensional to strike-slip and compressive environments.
Image 1 – The width of the cataclastic band and the sharpness of faults tend to decrease moving from normal faults (NF), strike-slip (SS), to thrust faults (TF).
Fig.2 - Average double-pair percentage (DC) values for global seismicity as a function of the angle describing the type of sliding of rocks along a fault during an earthquake (data from the GCMT catalogue).
Image 2 - Double-couple components for global seismicity (GCMT catalog) as a function of the rake angle describing the type of focal mechanism of earthquakes, ie, thrust-, strike-slip- or normal-faulting eve.
