Coseismic Stress and Strain Field Changes Investigation Through 3‐D Finite Element Modeling of DInSAR and GPS Measurements and Geological/Seismological Data: The L'Aquila (Italy) 2009 Earthquake Case Study

Abstract

We investigate the L'Aquila 2009 earthquake (AQE, Mw 6.3, Italy) through a 3‐D Finite Element (FE) mechanical model based on the exploitation of ENVISAT DInSAR and GPS measurements and an independently generated fault model. The proposed approach mainly consists of (a) the generation of a 3‐D fault model of the active structures involved in the sequence and those neighboring to them, benefiting of a large geological and seismological data set; (b) the implementation of the generated 3‐D fault model in a FE environment, by exploiting the elastic dislocation theory and considering the curved fault geometry and the crustal heterogeneities information; and (c) the optimization of the seismogenic crustal blocks model parameters in order to reproduce the geodetic measurements. We show that our modeling approach allows us to well reproduce the coseismic surface displacements, including their significant asymmetric pattern, as shown by the very good fit between the modeled ground deformations and the geodetic measurements. Moreover, a comparative analysis between our FE model results and those obtained by considering a classical analytical (Okada) model, for both the surface displacements and the Coulomb stress changes, has been performed. Our model permits to investigate the coseismic stress and strain field changes relevant to the investigated volume and their relationships with the surrounding geological structures; moreover, it highlights the very good correlation with the seismicity spatial distribution. The retrieved stress field changes show different maxima: (a) at few kilometers depth, within the main event surface rupture zone; (b) at depths of 5–9 km in correspondence of main event hypocentral area, along the SW dipping Paganica Fault System (PFS); and (c) at depths of 12–14 km, in correspondence of the largest aftershock hypocentral area, along a steep segment of an underlying east dipping basal detachment. Moreover, the main event hypocenter is localized in a region of high‐gradient strain field changes, while a deeper volumetric dilatation lobe involves the largest aftershock zone. From these findings, we argue that the AQE hanging wall downward movement along the steep portion of PFS might have been modulated by the underlying basal detachment; on the other hand, the coseismic eastward motion of the PFS footwall might have triggered further slip on the OS, thus releasing the largest aftershock on an independent source. The retrieved stress and strain field changes, which support the active role of the OS, have been also validated through a comparative analysis with those obtained from independent geological, seismological, and GPS measurements.

Fractal Study of the 1997–2017 Italian Seismic Sequences: A Joint Analysis of Seismological Data and DInSAR Measurements

“…As also discussed in Castaldo et al [29], the retrieved deformation pattern (Figure 3a,b) shows a non-symmetric distribution of the LOS displacements field. The retrieved deformations in the northwestern region reach the value of 17-18 cm and 23-24 cm (corresponding to subsidence processes), for the results relevant to ascending and descending orbits, respectively; moreover, in the northeastern region a maximum displacement of 4-5 cm (corresponding to an uplift of the examined zone) is visible only in the descending map ( Figure 3b).…”

“…We also emphasize that the coseismic deformation patterns present different characteristics for extensional and compressional seismic sequences (see Figures 2-7). Specifically, in the first case the ground deformation pattern is typically an image of the crustal block involvement during faulting processes [29]; accordingly, the deformation pattern retrieved on the Earth's surface is significantly spatially extended with respect to the main fault location (Figures 2, 3, 5, 6, 7 and 11a,b,d,e,f) [26,[28][29][30]. Conversely, in the second case the observed ground deformation pattern is strictly linked to the fault geometry; therefore, the measured ground deformation pattern is spatially less extended with respect to the main fault location (Figures 4 and 11c) [48].…”

“…[47]. These two maps have also been properly combined to retrieve the vertical and the east-west displacement components [29], which are reported in Figure 3c,d.…”

“…During the last 20 years (since 1997), four seismic sequences with M w ≥ 5.5 mainshocks nucleated within different tectonic settings (i.e., extensional and compressional environments) along the Central and Northern Apennines chain, causing casualties and damage: the 1997 Colfiorito, the 2009 L'Aquila, the 2012 Emilia, and the most recent 2016-2017 Central Italy seismic sequences [25][26][27][28][29][30][31]. In this work, we study these four seismic sequences by exploiting the available seismological data and applying fractals theory to them, and by comparing the retrieved spatial and temporal seismological analyses and the DInSAR deformation measurements relevant to the considered seismic events.…”

Coseismic Ground Deformation Reproduced through Numerical Modeling: A Parameter Sensitivity Analysis

“…Main historical seismic events in the L'Aquila area [8]. L'Aquila region 1315 The aftershocks [9], focal mechanism [10], surface deformation detected from DInSAR [2,5,7], GPS measurement inversion [11], and coseismic surface cracks [12] do not converge on a single subsurface slip patch geometry for the L'Aquila earthquake [11,[13][14][15][16][17]. Some studies suggest that the coseismic slip along the Paganica fault reached the Earth's surface [14,18], while other studies infer that the rupture was blind [16].…”