Abstract
During the last 20 years (1997 to 2017), four seismic sequences with Mw ≥ 5.5 mainshocks nucleated along the Central and Northern Apennines chain (Italy), causing casualties and damage: the 1997 Colfiorito, the 2009 L’Aquila, the 2012 Emilia, and the most recent 2016–2017 Central Italy seismic sequences. In this work, we perform a novel joint analysis of seismological and remote-sensing data to achieve new insights into the faulting process evolution during the considered seismic sequences. To this aim, we study these seismic sequences by exploiting the available seismological data and by applying fractals theory to them. In particular, we characterize the different behavior of compressional and extensional seismic sequences by examining the temporal evolution of the fractal dimension values. In addition, we compare the Differential Synthetic Aperture Radar Interferometry (DInSAR) displacement maps relevant to the considered seismic events (already published in our past papers) and the performed spatial and temporal seismological analyses, in order to emphasize some significant aspects of the different faulting processes active during these Italian seismic sequences. The analysis of the fractal dimension values shows that over time extensional seismic sequences are spatially distributed within a volume, whereas compressional ones are aligned along a preferential surface. These spatio-temporal patterns are confirmed by: (1) the spatial distribution of hypocenters for the events that occurred between the mainshock and the post-seismic synthetic aperture radar (SAR) acquisition; (2) the spatial extension of coseismic DInSAR ground-deformation patterns. The proposed seismic and ground-deformation analyses can thus typify different geodynamic contexts in Italy, providing a distinct image of articulated faulting processes.
Highlights
Every day moderate- to large-magnitude earthquakes occur, generating instantaneously coseismic ground deformations of the Earth’s crust, and Italy can be considered as one of the most tectonically active regions of the world [1,2,3]
As the fractal dimension is indicative of the geometrical features of a faulting process [23,49], it means that over time extensional seismic sequences are spatially distributed within a volume, whereas compressional ones are aligned along a preferential rupture surface
Starting from the results retrieved from the fractal dimension computation, we show that over time extensional seismic sequences are spatially distributed within a volume, whereas compressional ones are aligned along a preferential rupture surface
Summary
Every day moderate- to large-magnitude earthquakes occur, generating instantaneously coseismic ground deformations of the Earth’s crust, and Italy can be considered as one of the most tectonically active regions of the world [1,2,3]. Since at least Pliocene time, the central Apennines fold-and-thrust belt underwent extensional tectonics associated with the Tyrrhenian back-arc basin opening in the west; this extensional tectonics followed and replaced the previous compressional one which formed the accretionary prism, presently shifted to the east (western Adriatic Sea) [8]. This extensional process generated a system of NW–SE-oriented normal faults, which dissected the fold-and-thrust belt [9] and represent the seismogenic structures that generate, over the centuries, medium-high intensity earthquakes in the axial and western parts of the mountain belt (Figure 1a) [4,10]. Strike-slip faulting is rare in Italy and spatially restricted to areas located along the southern Apennines foredeep and in eastern Sicily [11,12,13]
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