On the mechanical behaviour of a low-angle normal fault: the Alto Tiberina fault (Northern Apennines, Italy) system case study

Vadacca, Luigi; Casarotti, Emanuele; Chiaraluce, L.; Cocco, M.

doi:10.5194/se-7-1537-2016

Cited by 24 publications

(23 citation statements)

References 51 publications

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“…This low-magnitude seismicity confirms seismic slip occurring along an~20°NNE dipping surface between 4 and 16 km depth ( Figure 2). The depth interval that is involved by the continuous release of microseismicity coincides with the creeping sector of the ATF as proposed by Anderlini et al (2016) and Vadacca et al (2016) on the basis of GPS data.…”

Section: Discussionmentioning

confidence: 99%

“…On the contrary, in the southern portion, the HW seismicity connects with the ATF seismicity below the mapped Gubbio fault (GuF; sections 7 and 8 in Figures 3 and 8). This is the area where the observed seismicity matches well with areas of positive stress build-up modeled by 2-D numerical simulations of interseismic deformation computed by Vadacca et al (2016). Their best fit model suggests creeping along the ATF below 5 km depth and along the flat portion of the GuF, which induces stress accumulation in the ATF-HW, coherently with the generation of the observed multiple M W 3+ seismic sequences in the ATF-HW.…”

Section: Discussionmentioning

confidence: 99%

“…RE are seismic events characterized by near‐identical waveforms that repeatedly rupture the same fault patch and that have been interpreted as the signature of a creeping process (Nadeau et al, ). Then, we investigate the spatiotemporal distribution of RE to map those portions of the ATF characterized by distinctive frictional behavior, i.e., stick slip or stable sliding, as it has been suggested by geodetic data (Anderlini et al, ; Vadacca et al, ).…”

Section: Clusters Of Similar Earthquakes Along the Atfmentioning

confidence: 99%

“…These authors also suggest that the creeping along the ATF plane could favor a stress increase on the high-angle faults located in the ATF hanging wall that are more favorably oriented in the present-day tectonic stress field to frictional slip. A similar deformation pattern, describing an actively slipping ATF with a mostly creeping behavior below 5 km of depth, has been suggested by Vadacca et al (2016) by using 2-D numerical modeling.…”

Section: 1002/2017jb014607mentioning

confidence: 99%

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Mixed‐Mode Slip Behavior of the Altotiberina Low‐Angle Normal Fault System (Northern Apennines, Italy) through High‐Resolution Earthquake Locations and Repeating Events

et al. 2017

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We generated a 4.5‐year‐long (2010–2014) high‐resolution earthquake catalogue, composed of ~37,000 events with ML < 3.9 and MC = 0.5 completeness magnitude, to report on the seismic activity of the Altotiberina (ATF) low‐angle normal fault system and to shed light on the mechanical behavior and seismic potential of this fault, which is capable of generating a M7 event. Seismicity defines the geometry of the fault system composed of the low‐angle (15°–20°) ATF, extending for ~50 km along strike and between 4 and 16 km at depth showing an ~1.5 km thick fault zone made of multiple subparallel slipping planes, and a complex network of synthetic/antithetic higher‐angle segments located in the ATF hanging wall (HW) that can be traced along strike for up to 35 km. Ninety percent of the recorded seismicity occurs along the high‐angle HW faults during a series of minor, sometimes long‐lasting (months) seismic sequences with multiple MW3+ mainshocks. Remaining earthquakes (ML < 2.4) are released instead along the low‐angle ATF at a constant rate of ~2.2 events per day. Within the ATF‐related seismicity, we found 97 clusters of repeating earthquakes (RE), mostly consisting of doublets occurring during short interevent time (hours). RE are located within the geodetically recognized creeping portions of the ATF, around the main locked asperity. The rate of occurrence of RE seems quite synchronous with the ATF‐HW seismic release, suggesting that creeping may guide the strain partitioning in the ATF system. The seismic moment released by the ATF seismicity accounts for 30% of the geodetic one, implying aseismic deformation. The ATF‐seismicity pattern is thus consistent with a mixed‐mode (seismic and aseismic) slip behavior.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Clusters Of Similar Earthquakes Along the Atfmentioning

confidence: 99%

Section: 1002/2017jb014607mentioning

confidence: 99%

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Mixed‐Mode Slip Behavior of the Altotiberina Low‐Angle Normal Fault System (Northern Apennines, Italy) through High‐Resolution Earthquake Locations and Repeating Events

et al. 2017

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“…Several earthquakes with default magnitude estimated from macroseismic effects

M_{w}^{def} > 5.5

are documented from historical catalogs in the Umbria‐Marche region (Figure a), the largest event being a

M_{w}^{def} 6.4

in 1781 [ Rovida et al , ]. The ATF is aseismically creeping deeper than 5 km [ Anderlini et al , ; Vadacca et al , ] where it is well delineated by microseismicity (Figure b). The larger earthquakes are thought to result from seismic slip on the shallower portion of the ATF, which is highly coupled, or along the splay faults located in its hanging wall.…”

Section: Tectonic Settingmentioning

confidence: 99%

Aseismic deformation associated with an earthquake swarm in the northern Apennines (Italy)

Gualandi

Nichele

Serpelloni

et al. 2017

Geophysical Research Letters

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Analyzing the displacement time series from continuous GPS (cGPS) with an Independent Component Analysis, we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity (maximum Mw=3.69 ± 0.09) occurred in the hanging wall of the Altotiberina normal fault (Northern Apennines, Italy) in 2013–2014. The geodetic transient lasted ∼6 months and produced a NW‐SE trending extension of ∼5.3 mm, consistent with the regional tectonic regime. The seismicity and the geodetic signal are consistent with slip on two splay faults in the Altotiberina fault (ATF) hanging wall. Comparing the seismic moment associated with the geodetic transient and the seismic events, we observe that seismicity accounts for only a fraction of the measured geodetic deformation. The combined seismic and aseismic slip decreased the Coulomb stress on the locked shallow portion of the ATF, while the transition region to the creeping section has been loaded.

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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

et al. 2018

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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.

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On the mechanical behaviour of a low-angle normal fault: the Alto Tiberina fault (Northern Apennines, Italy) system case study

Cited by 24 publications

References 51 publications

Mixed‐Mode Slip Behavior of the Altotiberina Low‐Angle Normal Fault System (Northern Apennines, Italy) through High‐Resolution Earthquake Locations and Repeating Events

Mixed‐Mode Slip Behavior of the Altotiberina Low‐Angle Normal Fault System (Northern Apennines, Italy) through High‐Resolution Earthquake Locations and Repeating Events

Aseismic deformation associated with an earthquake swarm in the northern Apennines (Italy)

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

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