Geological reconstruction in the area of maximum co-seismic subsidence during the 2009 Mw=6.1 L’Aquila earthquake using geophysical analyses and borehole stratigraphy.

InSAR images showed that the 2009 Mw=6.1 normal faulting L'Aquila earthquake (Abruzzi region, central Italy) produced a maximum co-seismic subsidence of ca. 24 cm in the epicentral area. We report new results about the stratigraphic architecture of this area by means of the integration of geophysical and stratigraphic data from a new 151 m deep borehole. According to the indication of preliminary geophysical (electrical resistivity tomography and seismic noise) surveys, the borehole was drilled where maximum thicknesses of fine-grained sediments were expected. The geophysical results were also useful to estimate the basin substrate depth and to define the geometry of the continental deposits, successively constrained by the core stratigraphy. The core is characterized by two sequences separated by an erosional discontinuity. The upper sequence is composed by silty, sandy and gravelly deposits, mainly characterized by high values of electrical resistivity. The lower sequence is characterized by prevalence of grey clayey silt and sandy sediments, with low values of resistivity. Based on correlations among the stratigraphic core and outcrop data of the Aterno Valley, we interpret the upper sequence as related to fluvial-alluvial depositional environment during Middle Pleistocene-Holocene, whereas the lower sequence is related to deposition in a prevalent marshy floodplain environment during Early Pleistocene

Uncovering deformation processes from surface displacements

Today, satellite remote sensing has reached a key role in Earth Sciences. In particular, Synthetic ApertureRadar (SAR) sensors and SAR Interferometry (InSAR) techniques are widely used for the study of dynamicprocesses occurring inside our living planet. Over the past 3 decades, InSAR has been applied for mappingtopography and deformation at the Earth’s surface. These maps are widely used in tectonics, seismology,geomorphology, and volcanology, in order to investigate the kinematics and dynamics of crustal faulting,the causes of postseismic and interseismic displacements, the dynamics of gravity driven slope failures,and the deformation associated with subsurface movement of water, hydrocarbons or magmatic fluids

Microseismicity recorded before geothermal exploitation at Torre Alfina (Italy), (Poster Session - ESC2016-464)

The geothermal field of Torre Alfina is located in Central Italy at the northern extremity of the Vulsini quaternary volcanic complex. Wells drilled in the 1970s and 1980s down to depths ranging from 563 to 2710 m revealed that Torre Alfina is a medium-enthalpy (T=140 C) geothermal field, hosted in buried fractured Mesozoic limestones. Recently a multinational industrial company received the license for the production of geothermal energy up to a maximum of 5 MW. In 2013, the INGV was commissioned to realize a monitoring system that includes the observation of gas emissions, microseismicity and ground deformation. Following the recommendations, described in the Ministerial Decree that regulates the geothermal production activity, the seismic monitoring system should be capable to record the local microseismicity during the phase of geothermal energy production and the natural seismicity since 12 months before the beginning of the production operations. In 2014, we started to install a short-period seismic network called ReMoTA near the future geothermal production site of Torre Alfina. Stations are equipped with 24 bit digitizers and short-period seismometers. The seismic noise level recorded at the single stations is unfavorably high, due to an intensive colonization and numerous settlements of small and medium industries. Transients as well as persistent monochromatic disturbances are recorded very well especially at the southern stations, probably due to a low wave energy dissipation inside the layer of quaternary volcanic rocks. During the period from June 2014 – November 2015 ReMoTA recorded 289 local earthquakes and 19 quarry blasts, with respect to 46 seismic events reported by ISIDE. The depth distribution of the seismic events recorded during 18 months before the beginning of the geothermal exploitation is concentrated inside the upper crust at a depth range between 4 - 8 km. The spatial distribution of the hypocenters seems to dip slightly towards SW beneath the area of Torre Alfina. This tendency together with the focal solutions of the Dec 2014 seismicity cluster highlights the presence of a normal fault with a weak transverse component striking in NW-SE-direction, within splitting distance to the future geothermal production site. The other two seismicity cluster of Mar-2015 and Nov-2015 seem to delineate antithetic structures with respect to the main fault. Considering that the future production level will be at a depth range between 1500 – 2300 m, and being aware of the hypocentral uncertainties, the discrimination between “natural” earthquakes and seismicity triggered by anthropic activity will be an important challenge

Site classification map of Italy based on surface geology

In this article a method developed for the creation of a site classification map at a territorial scale, starting from the geological mapping available at 1:100 000 scale, is described. This map has been used to embed amplification factors as provided by the Italian seismic code in seismic hazard studies, in order to consider the contribution of the surface geology on the expected ground motion values. The Italian territory has been divided into polygons classified on the basis of lithologies that the seismic code considers homogeneous in their average seismic response. The data processing has been conducted in a GIS environment, starting from the digital format of the lithological map of Italy at 1:100 000 scale. Our results can be used in seismic risk analyses that take into account the local seismic amplification due to the geological characteristics of an area, and in studies on ground motion prediction equations (GMPE)

Active faulting and continental slope instability in the Gulf of Patti (Tyrrhenian side of NE Sicily, Italy): a field, marine and seismological joint analysis

The Gulf of Patti and its onshore sector represent one of the most seismically active regions of the Italian Peninsula. Over the period 1984–2014, about 1800 earthquakes with small-to-moderate magnitude and a maximum hypocentral depth of 40 km occurred in this area. Historical catalogues reveal that the same area was affected by several strong earthquakes such as the Mw = 6.1 event in April 1978 and the Mw = 6.2 one in March 1786 which have caused severe damages in the surrounding localities. The main seismotectonic feature affecting this area is represented by a NNW–SSE trending right-lateral strike-slip fault system called “Aeolian–Tindari–Letojanni” (ATLFS) which has been interpreted as a lithospheric transfer zone extending from the Aeolian Islands to the Ionian coast of Sicily. Although the large-scale role of the ATLFS is widely accepted, several issues about its structural architecture (i.e. distribution, attitude and slip of fault segments) and the active deformation pattern are poorly constrained, particularly in the offshore. An integrated analysis of field structural geology with marine geophysical and seismological data has allowed to better understand the structural fabric of the ATLFS which, in the study area, is expressed by two major NW–SE trending, en-echelon arranged fault segments. Minor NNE–SSW oriented extensional structures mainly occur in the overlap region between major faults, forming a dilatational stepover. Most faults display evidence of active deformation and appear to control the main morphobathymetric features. This aspect, together with diffused continental slope instability, must be considered for the revaluation of the seismic and geomorphological hazard of this sector of southern Tyrrhenian Sea

Building vulnerability and seismic risk analysis in the urban area of Mt. Etna volcano (Italy)

The tectonic system of the eastern flank of Mt. Etna volcano (Sicily, Italy) is the source of most of the strongest earthquakes occurring in the area over the last 205 years. A total of 12 events with epicentre intensities CVIII EMS have occurred at Mt. Etna, 10 of which were located on the eastern flank. This indicates a mean recurrence time of about 20 years. This area is highly urbanised, with many villages around the volcano at altitudes up to 700 m a.s.l. The southern and eastern flanks are particularly highly populated areas, with numerous villages very close to each other. The probabilistic seismic hazard due to local faults for Mt. Etna was calculated by adopting a site approach to seismic hazard assessment. Only the site histories of local volcano-tectonic earthquakes were considered, leaving out the effects due to strong regional earthquakes that occurred in north-eastern and south-eastern Sicily. The inventory used in this application refers to residential buildings. These data were extracted from the 1991 census of the Italian National Institute of Statistics, and are grouped according to the census sections. The seismic vulnerability of the elements at risk belonging to a given building typology is described by a vulnerability index, in accordance with a damage model based on macroseismic intensities. For the estimation of economic losses due to physical damage to buildings, an integrated impact indicator was used, which is equivalent to the lost building volume. The expected annualised economic earthquake losses were evaluated both in absolute and in relative terms, and were compared with the geographical distribution of seismic hazard and with similar evaluations of losses for other regions

The role of the urban system dysfunction in the assessment of seismic risk in the Mt. Etna area (Italy)

A procedure for seismic risk assessment is applied to the Mt. Etna area (eastern Sicily, Italy) through assessment of urban system dysfunction following the occurrence of an earthquake.The tool used is based on the Disruption Index as a concept implemented in Simulator QuakeIST, which defines urban disruption following a natural disaster. The first element of the procedure is the definition of the seismic input, which is based on information about historical seismicity and seismogenic faults. The second element is computation of seismic impact on the building stock and infrastructure in the area considered. Information on urban-scale vulnerability was collected and a geographic information system was used to organise the data relating to buildings and network systems (e.g., building stock, schools, strategic structures, lifelines). The central idea underlying the definition of the Disruption Index is identification and evaluation of the impact on a target community through the physical elements that most contribute to severe disruption. The procedure applied in this study (i.e., software and data) constitutes a very useful operational tool to drive the development of strategies to minimise risks from earthquakes

The new release of the Italian contemporary stress map

We provide an updated present-day stress map for the Italian territory. Following the World Stress Map (WSM) Project guidelines, we list the different stress indicators, explaining the criteria used to select data. We discuss the data, which will also be included in the 2016 release of the WSM, highlighting the areas for which we have added stress information. Our map displays the minimum horizontal stress orientations inferred from crustal stress indicators down to 40 km depth using data of A–C quality, updated for earthquakes until December 2015. We have completely reviewed all data, and the data set now contains 855 entries, in contrast to the previous 715. The number of data with A–C quality of 630 corresponds to an increase of 26 per cent relative to the previous data set. In particular, the new data set contains the results of the analysis of borehole breakouts, critically reviewed data from earthquake focal mechanisms, data concerning active faults, formal inversions of focal mechanisms of seismic sequences or of restricted areas and one stress determination from overcoring. The new data set defines the stress field in areas not well covered by the previous data: the region north to the Po Plain and the central Adriatic sea, both characterized by a thrust- and strike-faulting regime, the northern Sicilian belt with a prevailing normal-faulting regime, and the Ionian sea with a strike-slip regime

Observing Volcanoes from the Seafloor in the Central Mediterranean Area

The three volcanoes that are the object of this paper show different types of activity that are representative of the large variety of volcanism present in the Central Mediterranean area. Etna and Stromboli are sub-aerial volcanoes, with significant part of their structure under the sea, while the Marsili Seamount is submerged, and its activity is still open to debate. The study of these volcanoes can benefit from multi-parametric observations from the seafloor. Each volcano was studied with a different kind of observation system. Stromboli seismic recordings are acquired by means of a single Ocean Bottom Seismometer (OBS). From these data, it was possible to identify two different magma chambers at different depths. At Marsili Seamount, gravimetric and seismic signals are recorded by a battery-powered multi-disciplinary observatory (GEOSTAR). Gravimetric variations and seismic Short Duration Events (SDE) confirm the presence of hydrothermal activity. At the Etna observation site, seismic signals, water pressure, magnetic field and acoustic echo intensity are acquired in real-time thanks to a cabled multi-disciplinary observatory (NEMO-SN1 ). This observatory is one of the operative nodes of the European Multidisciplinary Seafloor and water-column Observatory (EMSO; www.emso-eu.org) research infrastructure. Through a multidisciplinary approach, we speculate about deep Etna sources and follow some significant events, such as volcanic ash diffusion in the seawater

The economic assessment of seismic damage: an example for the 2012 event in Northern Italy

The study aims at quantifying the monetary losses caused by a moderate earthquake happened on a densely populated and economically well-developed area. The loss estimation refers to the damage of residential buildings and takes into account the cumulative effects of the sequence of the 2012 Emilia earthquake, characterized by a series of shocks with a magnitude range between 5.5 and 6 that lasted for nearly a month. The earthquake ground shaking was characterized by long-period component amplifications due to the presence of thick banks of sediments; nevertheless, there was a great damage to ordinary residential structures, characterized by short periods. The present study estimated the building damage using an approach based on the definition of the EMS-98 macroseismic scale, which is able to depict a damage scenario by means of observed intensity. Then we used the value of real estate assets (OMI) to quantify the economic losses, instead of the commonly adopted cost of reconstruction, because it is both an official and a yearly updated economic indicator. As the trade negotiations value is easily available throughout all the national territory, the present loss assessment can be effortlessly reproduced in case of future events. The proposed method consists of a multidisciplinary approach taking advantage of seismic, engineering, and economic skills, which is able to depict an attainable ex-post losses scenarios