Fabio Villani

Coseismic ruptures of the 24 August 2016, Mw 6.0 Amatrice earthquake (central Italy)

On 24 August 2016, a Mw 6.0 normal faulting earthquake struck central Italy, causing about 300 fatalities and heavy damage. A geological survey collected the coseismic effects observed at the surface in order to evaluate two competing hypotheses about their nature: surface faulting versus gravitational deformation. We find that the most significant geological effect is a 5.2 km-long alignment of ground ruptures along the Mt. Vettore Fault-System. These ruptures are independent from lithology, topography, morphology and change in slope and exhibit an average dip slip displacement of ~13 cm. Geometry, kinematics and dimensional properties of this zone of deformation strongly lead us to favor the primary surface faulting hypothesis that fits well the predicted estimates from experimental scaling-law relationships. Our study provides relevant hints for surface faulting in extensional domains, contributing to implement the worldwide database of the moderate earthquakes.

On the onset of ionospheric precursors 40 min before strong earthquakes

Heki (2011) and Heki and Enomoto (2013) claimed that anomalous, yet similar, increases of ionospheric total electron content (TEC) started ~40 min prior to the 2011 Tohoku-Oki, as well as before other Mw > 8 earthquakes. The authors concluded that the reported TEC anomalies were likely related to the pending earthquakes, suggesting also that TEC monitoring may be useful for future earthquake prediction. Here we carefully examine the findings of Heki (2011) and Heki and Enomoto (2013) by performing new analyses of the same TEC data. Our interpretation is that the 40 min onset of the ionospheric precursors is an artifact induced by the definition of the reference line adopted in analyzing TEC variations. We also discuss this repeatability in the tectonic and geodynamic context of the earthquakes. By performing a Superimposed Epoch Analysis of TEC data, we show that, however, the TEC increase reported by Heki (2011) was not particularly anomalous. We conclude that the TEC precursors reported by Heki (2011) and Heki and Enomoto (2013) are not useful for developing short-term earthquake prediction capabilities.

The Vallo di Diano Fault System: New Evidence for an Active Range-Bounding Fault in Southern Italy Using Shallow, High-Resolution Seismic Profiling

Range-bounding normal faults can presentsignificant challenges for seis- mic exploration. This is the case of the fault system bounding the Vallo di Diano, the largest intermountain basin in the southern Apennines seismic belt. Industry reflection profiles define the large-scale structure of the basin but barely image the shallow fault system due to unfavorable topographic and near-surface conditions along the foothills of the eastern range. We present two high-resolution (HR) wide-aperture profiles recorded attheeastern marginof thebasin acrossunreported scarpsthat affect Middle- Late Pleistocene alluvial fans and slope debris. The survey is aimed at identifying possible recent faulting across these challenging terrains and at understanding the re- lationship between shallow structures and the master range-bounding fault at depth. Common depth point processing of wide-aperture reflection data and first-arrival tra- vel-time tomography provide detailed images of the upper 200-300 m and sounding evidence of recent activity along previously unknown splays of the fault system. These splays dissect the Mesozoic limestone bedrock and alluvial-fan sequences, affecting theirdepositionalpattern.VeryhighresolutionVPandreflectivityimagesalsogivehints ofpossiblecoseismicsurfacefaultinginHolocenecolluvia.Theseresultshaverelevant implicationsfortheevaluationoftheseismogenicpotentialoftherange-boundingfault systemandforseismichazardassessmentofthedenselyurbanizedVallodiDianobasin. Online Material: Table of acquisition and data processing parameters, and figures showing schematic stratigraphy of the Vallo di Diano basin, restoration of fault dis- placement along the HR profile, and resolution of the P-velocity tomographic images for the VHR profile.

The Seismic Microzonation of San Gregorio Through a Multidisciplinary Approach. Seismic Amplification in a Stiff Site

The village of San Gregorio (L’Aquila, Italy) was severely damaged by the April 6, 2009 earthquake. San Gregorio is situated at the base of a carbonate relief bounded by the Aterno river alluvial plain. The geological features of the area are very complex: jointed carbonate bedrock, cemented gravels and alluvial fan crop out in the village. Co-seismic ground fractures were seen along SW dipping active fault segments crossing San Gregorio. We integrated the microzonation studies with new geological, geotechnical and geophysical data for supporting the reconstruction planning of the village. Noise measurements show strong and polarized peaks in the horizontal-to-vertical spectral ratios (H/V) in the 3–7 Hz frequency band. Interestingly, the alluvial fan and the outcropping rock masses show both H/V peaks. To understand the influence of rock mass joint condition on site effect, we performed structural surveys on carbonate bedrock to look for a possible correlation between rock fracturing and ground-motion amplification.

Quaternary geology and paleoseismology in the Fucino and L’Aquila basins

This 2 days-long field trip aims at exploring field evidence of active tectonics, paleoseismology and Quaternary geology in the Fucino and L’Aquila intermountain basins and adjacent areas, within the inner sector of Central Apennines, characterized by extensional tectonics since at least 3 Ma. Each basin is the result of repeated strong earthquakes over a geological time interval, where the 1915 and 2009 earthquakes are only the latest seismic events recorded respectively in the Fucino and L’Aquila areas. Paleoseismic investigations have found clear evidence of several past earthquakes in the Late Quaternary to Holocene period. Active tectonics has strongly imprinted also the long-term landscape evolution, as clearly shown by numerous geomorphic and stratigraphic features. Due to the very rich local historical and seismological database, and to the extensive Quaternary tectonics and earthquake geology research conducted in the last decades by several Italian and international teams, the area visited by this field trip is today one of the best studied paleoseismological field laboratories in the world. The Fucino and L’Aquila basins preserve excellent exposures of earthquake environmental effects (mainly surface faulting), their cumulative effect on the landscape, and their interaction with the urban history and environment. This is therefore a key region for understanding the role played by earthquake environmental effects in the Quaternary evolution of actively deforming regions, also as a major contribution to seismic risk mitigation strategies.

The Seismic Site Characterization of Palazzo Centi in L’Aquila City Centre: The Case Study of a Historical Building Damaged by the April 6th 2009 Earthquake

An extensive geological, geotechnical and geophysical investigation was performed in L’Aquila city centre to restore Palazzo Centi, a historical building, damaged by the April 6, 2009 L’Aquila earthquake. This site investigation consisted of punctual and linear tests that allowed to define a detailed 3D model of the subsoil, irregularly affected by some peculiar conditions and characterized by low and variable values of the shear wave velocity V S in the near surface volume. In particular, the variable thickness of the upper fine-grained residual soils probably determined different ground motion amplifications during the main shock.