Zambrano, Miller

The Irpinia Fault, also known as the Monte Marzano Fault System, located in the Southern Apennines (Italy), is one of the most seismically active structures in the Mediterranean. It is the source of the 1980, Ms 6.9, multi-segment rupture earthquake that caused significant damage and nearly 3,000 casualties. Paleoseismological surveys indicate that this structure has generated at least four Mw ~ 7 surface-rupturing earthquakes in the past 2 ka. This paper presents a comprehensive, high-resolution geophysical investigation focused on the southernmost fault segment of the Monte Marzano Fault System, i.e., the Pantano-Ripa Rossa Fault, outcropping within the Pantano di San Gregorio Magno intramontane basin. The project, named TEst Site IRpinia fAult (TESIRA), was supported by the University of Napoli Federico II to study the near-surface structure of this intra-basin fault splay that repeatedly ruptured co-seismically in the past thousands of years. Our imaging approach included 2D and 3D electrical and seismic surveys, gravimetry, 3D FullWaver electrical tomography, drone-borne GPR and magnetic surveys, and CO2 soil flux assessment across the surface rupture. This multidisciplinary investigation improved our understanding of the basin shallow structure, providing an image of a rather complex subsurface fault and basin geometry. Seismic data suggest that fault activity at the Pantano segment of MMFS is characterized by a near-surface cumulative displacement greater than previous estimations, calling into question earlier assumptions about the timing of its activation. Despite some challenges with our drone-mounted survey equipment, the integrated dataset provides a comprehensive and reliable image of the subsurface structure. This work demonstrates the utility of developing an integrated approach at high-resolution geophysical imaging and interpretation of fault zones with weak morphological expressions.

The determination of ground motion is crucial to plan the appropriate emergency activities, especially in areas characterised by an intense seismic history like the Italian peninsula. Ground motion assessment is generally based on the seismological parameters reported in the instrumental and parametric seismic catalogues. Therefore, the computation of shaking scenarios of historical earthquakes is very challenging, due to the poorly constrained variables (i.e., magnitudes, epicentral location, seismogenic sources), derived from the macroseismic intensity. In this study, we propose a novel approach to investigate the location and parametrization of the seismogenic sources of historical earthquakes and derive shaking scenarios. To this aim, the ground motion of two historical events, the Fabriano (1741, Mw = 6.1, Imax IX MCS) and Camerino (1799, Mw = 6.1, Imax IX–X MCS) earthquakes is simulated. In order to include the site response, a Vs,30 map of the Umbria and Marche regions is created from near-surface data. Different causative faults solutions are tested, finally discussing the ideal seismogenic source based on the residual analysis between observed and simulated macroseismic intensities. The resultant shaking scenarios of the two events are obtained by integrating observed intensities and simulations.

Faults are characterized by a complex internal architecture. In carbonates, the geometry, attitude, and distribution of fault-related fractures and subsidiary faults can largely affect the petrophysical properties and hydraulic behavior of the fault zone. This work investigates the footwall damage zone of a seismic-scale normal fault (throw ∼ 300 m) from a structural, petrophysical and seismic point of view. The studied Venere Fault (VF) bounds the intra-mountain Fucino Basin (central Italy) and crosscuts Lower Cretaceous platform carbonates. A significant portion of the footwall VF damage zone (VF-DZ) is well exposed in the 400 × 200 m Santilli Quarry. There, we assess the amount of outcrop-scale fracture porosity and permeability by in-situ fracture analyses and permeability measurements. The results show a composite power-law decay of fracture intensity away from the main slip surfaces, strongly influenced by subsidiary faults. An outcrop-based, digital 2D model of the VF-DZ is constructed and populated with acoustic properties (Vp, Vs and density) derived from both the matrix and fracture porosities. This model is enlarged five times and used for seismic modelling to investigate the seismic signature of the VF-DZ under different but realistic geological and geophysical conditions. Seismic modelling suggests that within the modelled damage zone and for wave frequencies of 20–40 Hz, seismic impedance contrasts associated with subsidiary faults may be imaged, depending on the degree of fracture porosity, fracture aperture, and the illumination angle (a measure of the maximum dip that can be imaged), the last two parameters being controlled by overburden depth. These results have implications for the seismic interpretation and characterization of fault zones in carbonates, and hence for the evaluation of fluid migration through these structures.

We present a 1:25,000 scale map of the coseismic surface ruptures following the 30 October 2016 M-w 6.5 Norcia normal-faulting earthquake, central Italy. Detailed rupture mapping is based on almost 11,000 oblique photographs taken from helicopter flights, that has been verified and integrated with field data (>7000 measurements). Thanks to the common efforts of the Open EMERGEO Working Group (130 people, 25 research institutions and universities from Europe), we were able to document a complex surface faulting pattern with a dominant strike of N135 degrees-160 degrees (SW-dipping) and a subordinate strike of N320 degrees-345 degrees (NE-dipping) along about 28km of the active Mt. Vettore-Mt. Bove fault system. Geometric and kinematic characteristics of the rupture were observed and recorded along closely spaced, parallel or subparallel, overlapping or step-like synthetic and antithetic fault splays of the activated fault systems, comprising a total surface rupture length of approximately 46km when all ruptures were considered.

We provide a database of the coseismic geological surface effects following the Mw 6.5 Norcia earthquake that hit central Italy on 30 October 2016. This was one of the strongest seismic events to occur in Europe in the past thirty years, causing complex surface ruptures over an area of >400 km2. The database originated from the collaboration of several European teams (Open EMERGEO Working Group; about 130 researchers) coordinated by the Istituto Nazionale di Geofisica e Vulcanologia. The observations were collected by performing detailed field surveys in the epicentral region in order to describe the geometry and kinematics of surface faulting, and subsequently of landslides and other secondary coseismic effects. The resulting database consists of homogeneous georeferenced records identifying 7323 observation points, each of which contains 18 numeric and string fields of relevant information. This database will impact future earthquake studies focused on modelling of the seismic processes in active extensional settings, updating probabilistic estimates of slip distribution, and assessing the hazard of surface faulting.