The Alto Tiberina Near Fault Observatory (northern Apennines, Italy)

Abstract

<p>The availability of multidisciplinary and high-resolution data is a fundamental requirement to understand the physics of earthquakes and faulting. We present the Alto Tiberina Near Fault Observatory (TABOO), a research infrastructure devoted to studying preparatory processes, slow and fast deformation along a fault system located in the upper Tiber Valley (northern Apennines), dominated by a 60 km long low-angle normal fault (Alto Tiberina, ATF) active since the Quaternary. TABOO consists of 50 permanent seismic stations covering an area of 120 × 120 km<span><sup>2</sup></span>. The surface seismic stations are equipped with 3-components seismometers, one third of them hosting accelerometers. We instrumented three shallow (250 m) boreholes with seismometers, creating a 3-dimensional antenna for studying micro-earthquakes sources (detection threshold is M<span><sub>L</sub></span> 0.5) and detecting transient signals. 24 of these sites are equipped with continuous geodetic GPS, forming two transects across the fault system. Geochemical and electromagnetic stations have been also deployed in the study area. In 36 months TABOO recorded 19,422 events with M<span><sub>L</sub></span> ≤ 3.8 corresponding to 23.36e-04 events per day per squared kilometres; one of the highest seismicity rate value observed in Italy. Seismicity distribution images the geometry of the ATF and its antithetic/synthetic structures located in the hanging-wall. TABOO can allow us to understand the seismogenic potential of the ATF and therefore contribute to the seismic hazard assessment of the area. The collected information on the geometry and deformation style of the fault will be used to elaborate ground shaking scenarios adopting diverse slip distributions and rupture directivity models.</p>

Moment tensor inversion of early instrumental data: application to the 1917 High Tiber Valley, Monterchi earthquake

“…Nevertheless, the uncertainties in the earthquake locations do not allow to clearly associate a seismotectonic structure with the epicenter in order to fix between the two nodal planes. Moreover, it is possible to associate the high-angle plane dipping toward the east with a synthetic splay of the AtF [Chiaraluce et al 2014] and the low-angle plane dipping toward the west, antithetical to the AtF (e.g., the basal geometry of the Gubbio fault; Mirabella et al [2004]).…”

A catalogue of non-tectonic earthquakes in central-eastern Italy

“…This is the case of areas that had been active in the first period of analysis: a typical example is the "Cantiano" area. On the contrary, areas in which the network growth was very fast, such as the westernmost part, linked to the installation of the TABOO: Alto Tiberina Near Fault Observatory [Chiaraluce et al 2014], the first event detections were already linked with good quality locations, which allowed for a smaller size of the area: typical examples are the "Gubbio" and "Umbertide" areas. In other cases, such as "Cingoli" and "Rossa", the extension of the quarry area (several kilometers) has a larger effect on the selection of the geographical limits.…”

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

“…It is also worth noting that the microseismicity nucleating on the ATF is not able to explain the amount of deformation associated with the short-and long-term slip rate inferred by geological (Collettini and Holdsworth, 2004) and geodetic studies and data (D'Agostino et al, 2009). These observations together with the lack of large-magnitude (M>7) historical earthquakes that ruptured the whole ATF in the past 1000 years (Rovida et al, 2011;Chiaraluce et al, 2014) suggest the occurrence of aseismic deformation or creeping as proposed by Hreinsdottir and Bennett ( 2009) by interpreting regional GPS data. This hypothesis is supported by laboratory experiments performed on fault rock samples of the Zuccale low-angle normal fault, considered the (older) exhumed analogue of the ATF.…”

“…Another way to approach the seismic behaviour of active fault systems is modelling the crustal rheology of the volume containing the active fault segments to explain the deformation observed at surface. Cianetti et al (2008) performed a 2-D plane strain finite element analysis to fit the GPS and geomorphology data to constrain the role and deformation mechanisms of the active faults bordering the Gulf of Corinth in Greece undergoing tectonic extension. Cianetti et al (2008) recognize that only by introducing an elasto-viscoplastic rheology for the crustal volume (defined by a power law constitutive model) can they explain geodetic (GPS) observations.…”

“…Cianetti et al (2008) performed a 2-D plane strain finite element analysis to fit the GPS and geomorphology data to constrain the role and deformation mechanisms of the active faults bordering the Gulf of Corinth in Greece undergoing tectonic extension. Cianetti et al (2008) recognize that only by introducing an elasto-viscoplastic rheology for the crustal volume (defined by a power law constitutive model) can they explain geodetic (GPS) observations. In our modelling, we adopt a simpler approach that relies on an elastic crust.…”