Luigi Improta

An integrated geophysical investigation of the upper crust in the epicentral area of the 1980, Ms=6.9, Irpinia earthquake (Southern Italy)

Abstract In this paper, we investigate the upper crustal structure of the Irpinia region, Southern Apennines thrust belt, Italy, through analysis and joint interpretation of gravity data, seismic reflection lines and subsurface information from many deep wells. The investigated region includes the epicentral area of the 1980 (Ms=6.9) Irpinia earthquake and is one of the Italian regions with the highest seismic hazard. The upper crustal structure is imaged by modeling a series of 15 SW-trending gravity profiles, spaced about 5 km apart, plentifully constrained by seismic reflection lines and wells, thus reducing the inherent ambiguity of the gravity modeling. Despite of the complexity of the modeled Bouguer anomalies, the application of a calibrating procedure to constrain the range of variability of the density values, as well as the use of geometric constraints, results in a good level of stability in the final density cross-sections, which in fact appear coherent both in the density values and in the geometrical features. The inferred model shows important lateral density variations that can be mostly related to NW-trending geologic structures. High-density bodies delineate carbonate platform thrust sheets and broad antiforms involving Mesozoic basinal rocks, while low-density shallow bodies are associated with Pliocene basins. In addition, important density (i.e. lithological) variations are evident along the strike of the range, the most relevant being an abrupt deepening of the Apulia Carbonate Platform in the southeastern part of the investigated region. In the epicentral region of the 1980 event, we find that the geometry of the high-density, high-velocity carbonates of the Apulia Platform appears correlated with the distribution of the aftershocks and with the P-wave velocity anomaly pattern as inferred from a previous local earthquake tomography. The structural highs of the Apulia Platform correspond to high-velocity regions, where aftershocks and coseismic slip of the mainshock are concentrated. This correlation suggests that the Apulia Carbonate Platform geometry played an important role in the rupture propagation and in the aftershock distribution.

High frequency strong ground motion modelling in the Catania area associated with the Ibleo-Maltese fault system

A hybrid statistical-deterministic approach has been applied to estimate strong ground motion parameters (PGA, spectral ordinates) in South-Eastern Sicily for a M = 7 earthquake. A number of 100 different rupture processes have been simulated along a composite fault system representing two segments of the Ibleo-Maltese fault scarp. Map at regional scale of mean PGA in the 0.5–20 Hz frequency band shows highest values (0.4–0.5 g) nearby and North of Catania, due to a dominant directivity effect. The COV parameter, which expresses the variability of PGA values as a function of source complexity, is higher in the region nearby and South of the town of Augusta, where, depending on the rupture history, rather large PGA values can be observed (>0.4 g). PGA attenuation curves suggest that an azimuthal variation could be related to the source extent and directivity. The response and pseudo acceleration spectra are computed for different sites in the town of Catania including an approximate 1D site response. Ground motion amplification effects at high frequency (5–20 Hz) are produced by thin shallow layer of soft clay, loose pyroclastites and fill. We observe small amplification effects, in the frequency ranges 2–3 Hz and 5–10 Hz, in sites where recent alluvia reach a thickness of some tens of meters. Otherwise, sites located on outcrops of massive lavas show moderate attenuation.

Waveguide effects in very high rate GPS record of the 6 April 2009, Mw 6.1 L'Aquila, central Italy earthquake

This work has partially benefited from the activities performed in the NERA project (Network of European Research infrastructures for earthquake risk Assessment and mitigation, 262330), funded by the European Commission FP7 program, and in the FIRB-Abruzzo project, funded by the Italian Ministery of Education, University and Research.

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.

New insights into crustal structure, Cenozoic magmatism, CO2 degassing and seismogenesis in the southern Apennines and Irpinia region from local earthquake tomography

We present high-resolution Vp and Vp/Vs models of the southern Apennines (Italy) computed using local earthquakes recorded from 2006 to 2011 with a graded inversion scheme that progressively resolves the crustal structure, from the large scale of the Apennines belt to the local scale of the normal fault system. High-Vp bodies defined in the upper crust and midcrust under the external Apennines are interpreted as extensive mafic intrusions revealing anorogenic magmatism episodes that broadened on the Adriatic domain during Paleogene. Under the mountain belt, a low-Vp region, annular to the Neapolitan volcanic district, indicates the existence of a thermal/fluid anomaly in the midcrust, coinciding with a shallow Moho and diffuse degassing of deeply derived CO2. In the belt axial zone, low-Vp/Vs gas-pressurized rock volumes under the Apulian carbonates correlate to high heat flow, strong CO2-dominated gas emissions of mantle origin, and shallow carbonate reservoirs with pressurized CO2 gas caps. We hypothesize that the pressurized fluid volumes located at the base of the active fault system influence the rupture process of large normal faulting earthquakes, like the 1980 Mw6.9 Irpinia event, and that major asperities are confined within the high-Vp Apulian carbonates. This study confirms once more that preexisting structures of the Pliocene Apulian belt controlled the rupture propagation during the Irpinia earthquake. The main shock broke a ~30 km long, NE dipping seismogenic structure, whereas delayed ruptures (both the 20 s and the 40 s subevents) developed on antithetic faults, reactivating thrust faults located at the eastern edge of the Apulian belt.

Inversion of inherited thrusts by wastewater injection induced seismicity at the Val d’Agri oilfield (Italy)

Since 2006 wastewater has been injected below the Val d’Agri Quaternary basin, the largest on-land oilfield in Europe, inducing micro-seismicity in the proximity of a high-rate injection well. In this study, we have the rare opportunity to revise a massive set of 2D/3D seismic and deep borehole data in order to investigate the relationship between the active faults that bound the basin and the induced earthquakes. Below the injection site we identify a Pliocene thrusts and back-thrusts system inherited by the Apennines compression, with no relation with faults bounding the basin. The induced seismicity is mostly confined within the injection reservoir, and aligns coherently with a NE-dipping back-thrust favorably oriented within the current extensional stress field. Earthquakes spread upwards from the back-thrust deep portion activating a 2.5-km wide patch. Focal mechanisms show a predominant extensional kinematic testifying to an on-going inversion of the back-thrust, while a minor strike-slip compound suggests a control exerted by a high angle inherited transverse fault developed within the compressional system, possibly at the intersection between the two fault sets. We stress that where wastewater injection is active, understanding the complex interaction between injection-linked seismicity and pre-existing faults is a strong requisite for safe oilfield exploitation.

From 3D to 4D passive seismic tomography: The sub-surface structure imaging of the Val d’Agri region, southern Italy

Local earthquakes (passive seismic) tomography (LET) is a well established tool for the imaging of the sub-surface structure. Alternative to active seismics, the main advantages of using natural sources are the better sounding in deeper portions of the upper crust, the relatively low cost, and the direct availability of S-waves. The main drawback is the achievable model resolution, which is limited by the density of the seismic network and the distribution of elastic sources, rather than the elastic wave frequency. Recently, 4D variations (in space and time) of velocity anomalies have been recognized in active volcanoes (Patane et al., 2006) and normal faulting systems and ascribed to the medium response to transient geological processes, like dyke intrusions or fluid pressure increase on fault planes. In this paper we show how LET contributes to the imaging of the upper crust in a very attractive region like the Val d’Agri in southern Italy, which hosts both significant oil fields and seismogenic structures. We show that LET allows to improve the definition of the crust structure, at depths larger than those sampled by conventional seismic profiles, and detect the space-time dependency of elastic properties in response to local variations of fluid pressure.

Sessione S 4. Fluid-rock interactions: metamorphism, geothermal resources, faulting processes and induced seismicity

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79

Non-linear 2-D Traveltime Inversion In Complex Media: Application to the Southern Apennines Thrust Belt (Italy).

Summary A new traveltime inversion method based on a non linear approach and multi scale process has been applied to a seismic data set acquired with a non conventional acquisition layout in a thrust-belt region. First arrivals and a main reflected phase have been hand picked. A first inversion is realized with only the first arrival traveltimes in order to obtain a 2D velocity image. The latter has been then used as background model for the interpretation of the reflected phase using another non linear multi scale inversion technique. Finally, the whole data set has been jointly inverted. The final velocity images are compared in order to assess the resolution and smearing effect. Moreover, the availability of a VSP survey allows us to independently assess the reliability of our results. Introduction In May 1997 an active seismic experiment was performed by Enterprise Oil Italiana S.p.A. on a test line in the Southern Apennines overthrust-belt (Italy). A high quality data set was acquired with a global offset acquisition configuration (Dell’Aversana et al., 2000) by deploying 160 receivers and 233 sources along a profile 14600 m long. The investigated area is characterized by a high structural complexity (i.e. strong vertical and lateral velocity variations) and presents a rugged topography. In such a context, seismic imaging of the crust by conventional reflection seismic is a difficult task. Aimed at investigating whether complex shape reflectors and velocity structures can be properly imaged by non-linear traveltimes inversion, we used the global offset data set to test three new methods for the traveltime inversion of first-arrivals and reflected phases. First, the information of the first-arrivals have been used to obtain an accurate 2-D P-velocity model by tomography. Then, we use the retrieved image as background velocity model for the traveltimes inversion of near-vertical/wide angle reflections in order to define the shape and the location of the corresponding interface. Finally, both the first- and the secondary arrival times are jointly inverted. The comparison of the three images obtained with the different techniques allows us to discuss the problem of resolution and smearing effect when the target medium is very complicated. A VSP survey performed in a nearby well allows for the verification of the results.