R. Civico

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.

Characterization of active fault scarps from LiDAR data: a case study from Central Apennines (Italy)

A high-resolution digital elevation model (DEM, 1 ms spacing) derived from an airborne light detection and ranging (LiDAR) campaign was used in an attempt to characterize the structural and erosive elements of the geometry of the Pettino fault, a seismogenic normal fault in Central Apennines (Italy). Four 90- to 280 m-long fault scarp segments were selected and the surface between the base and the top of the scarps was analyzed through the statistical analysis of the following DEM-derived parameters: altitude, height of the fault scarp, and distance along strike, slope, and aspect. The results identify slopes of up to 40° in faults lower reaches interpreted as fresh faces, 34° up the faces. The Pettino fault maximum long-term slip rate (0.6–1.1 mm/yr) was estimated from the scarp heights, which are up to 12–19 m in the selected four segments, and the age (ca. 18 ka) of the last glacial erosional phase in the area. The combined analysis of the DEM-derived parameters allows us to (a) define aspects of three-dimensional scarp geometry, (b) decipher its geomorphological significance, and (c) estimate the long-term slip rate.

Traces of the active Capitignano and San Giovanni faults (Abruzzi Apennines, Italy)

ABSTRACT We present a 1:20,000 scale map of the traces of the active Capitignano and San Giovanni faults in the area of the Montereale basin (central Apennines, Italy) covering an area of about 80 km2. Detailed fault mapping is based on high-resolution topography from airborne LiDAR imagery validated by extensive ground truthing and geophysical prospecting. Our analysis allowed the recognition of several features related to fault activity, even in scarcely accessible areas characterized by dense vegetation cover and rugged terrain. The identified fault traces run at the base of the NW-SE striking Montereale basin-bounding mountain front and along the base of the southwestern slope of the Monte Mozzano ridge, and have a length of about 12 and 8 km, respectively. Improving the knowledge of fault geometry is a critical issue not only for the recognition of seismogenic sources but also for surface fault hazard assessment and for local urban planning. The knowledge of the exact location of the fault traces is also crucial for the seismogenic characterization of the active faults by means of paleoseismological trenching.

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 Contribution of Airborne LiDAR Data to the Assessment of Surface Faulting Hazard for Lifelines Crossing Active Faults: An Example from the Central Apennines, Italy

In case of moderate to strong earthquakes (generally for M > 5.5), coseismic slip along a fault can reach directly the ground surface and produce surface faulting. Although scarcely considered in the Italian legislation, surface faulting hazard can have a relevant societal impact because it exposes to substantial risk urban areas and/or important infrastructures, facilities and critical lifelines that are settled or planned in coincidence of an active and capable fault trace. In this paper we present a case study from the area hit by the Mw 6.1 April 6, 2009 L’Aquila earthquake (Central Italy), where buildings and critical lifelines located across or near the coseismic surface ruptures suffered significant damage. High resolution (1 m) LiDAR topographic data contributed to the assessment of surface faulting hazard through a better imaging of the surface geometrical arrangement of the earthquake causative fault and through the analysis of the spatial relationships between active fault splays and critical lifelines and infrastructures.

Geological and Geophysical Approaches for the Definition of the Areas Prone to Liquefaction and for the Identification and Characterization of Paloeliquefaction Phenomena, the Case of the 2012 Emilia Epicentral Area, Italy

In May–June 2012, a seismic sequence struck a broad area of the Emilia-Romagna region in Northern Italy. The sequence included two mainshocks (on 20th May a ML 5.9 and on 29th May a ML 5.8). The whole aftershocks area extended in an E–W direction for more than 50 km, and included five ML ≥5.0 and more than 1,800 ML >1.5 earthquakes. Instrumental and historical local seismic records show low seismicity rate, the closest and more relevant historical earthquake being the 1570 A.D. earthquake that hit Ferrara. Widespread secondary geological effects were produced by the 2012 Emilia sequence and are mainly related to liquefaction phenomena. A total of more than 1,300 geologic coseismic effects were identified over more than 1,200 km2. We present some preliminary results concerning the study of the liquefactions occurred during the 2012 Emilia seismic sequence with particular emphasis on: (a) the definition of the areas most prone to liquefaction, (b) the identification and characterization of potential paleoliquefaction events. To identify the zones with high, medium or low liquefaction hazard, we show our quantitative approach defined to obtain a GIS based detailed analysis of the geometric relationships between the observed liquefactions and some peculiar geomorphic features of the 2012 epicentral. Differently, for recognition and characterization of paleoliquefaction events we adopted a multidisciplinary approach involving sedimentology, mineralogy and magnetic properties of the 2012 liquefied sands together with geophysical profiling, coring and dating.