Active intrusions of magma under the southern Apennines can give rise to earthquakes of significant magnitude and deeper than the typical seismicity of that area. This was revealed by a study signed by INGV and the University of Perugia, published in Science Advances
The earthquakes and aquifers of the southern Apennines reveal the presence of magma in depth in the Sannio-Matese area. To find out, a study conducted by a team of researchers from the National Institute of Geophysics and Volcanology (INGV) and the Department of Physics and Geology of the University of Perugia (DFG-UNIPG). The work 'Seismic signature of active intrusions in mountain chains', published in Science Advances, impacts on the knowledge of the structure, composition and seismicity of mountain chains, on the upwelling mechanisms of magmas and gases and on how to monitor them. (http://advances.sciencemag.org/content/4/1/e1701825).
"Mountain ranges are generally characterized by earthquakes attributable to the activation of faults that move in response to tectonic stresses", explains Francesca Di Luccio, INGV geophysicist and coordinator, with Guido Ventura, of the research group, "however, by studying a seismic event, which occurred in December 2013-2014 in the Sannio-Matese area with a maximum magnitude of 5, we discovered that these earthquakes were triggered by a rise of magma in the crust between 15 and 25 km deep. An anomaly linked not only to the depth of the earthquakes in this sequence (between 10 and 25 km), compared to the more superficial one in the area (< 10-15 km), but also to the waveforms of the most important events, similar to those of earthquakes in volcanic areas”.
The data collected show that the gases released by this magma intrusion consist mainly of carbon dioxide, which reached the surface as free gas or dissolved in the aquifers of this area of the Apennines.
“This result”, adds Guido Ventura, INGV volcanologist, “opens up new paths for the identification of magma rising zones in mountain ranges and highlights how such intrusions can generate earthquakes with significant magnitudes. The study of the composition of the aquifers also makes it possible to highlight the thermal anomaly.
"It cannot be excluded that the magma that has crossed the crust in the Matese area can reach the surface forming a volcano", adds Giovanni Chiodini, INGV geochemist. "However, if the current process of magma accumulation in the crust continues, it cannot be excluded that, on the geological time scale (ie thousands of years), a volcanic structure may form".
During the study, seismic and geochemical data were collected and models of fluid upwelling were developed. The research began with the analysis of the seismicity of the Sannio-Matese sequence, and then concluded with the modeling of the magmatic intrusion conditions. The knowledge of the signals attributable to the ascent of magma in non-volcanic areas must still be extended to other large chains such as the Alpine-Himalayan, Zagros (between Iraq and Iran), the Andes and the North American Cordillera.
"The results achieved so far", concludes Di Luccio, "open new paths not only on the mechanisms of the evolution of the earth's crust, but also on the interpretation and meaning of seismicity in mountain ranges for the purpose of assessing the correlated seismic risk".
Picture 1 - The earthquakes of the Sannio-Matese seismic sequence of 2013-2014 reveal the presence of magma in depth that can be released episodically giving rise to earthquakes.