DSpace Collection:

Integrating geologic fault data into tsunami hazard studies

Thu, 18 Apr 2013 22:00:00 GMT

Title: Integrating geologic fault data into tsunami hazard studies Authors: Basili, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Tiberti, M. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Kastelic, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Romano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piatanesi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Selva, J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Lorito, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: We present the realization of a fault-source data set designed to become the starting point in regional-scale tsunami hazard studies. Our approach focuses on the parametric fault characterization in terms of geometry, kinematics, and assessment of activity rates, and includes a systematic classification in six justification levels of epistemic uncertainty related with the existence and behaviour of fault sources. We set up a case study in the central Mediterranean Sea, an area at the intersection of the European, African, and Aegean plates, characterized by a complex and debated tectonic structure and where several tsunamis occurred in the past. Using tsunami scenarios of maximum wave height due to crustal earthquakes (Mw=7) and subduction earthquakes (Mw=7 and Mw=8), we illustrate first-order consequences of critical choices in addressing the seismogenic and tsunamigenic potentials of fault sources. Although tsunamis generated by Mw=8 earthquakes predictably affect the entire basin, the impact of tsunamis generated by Mw=7 earthquakes on either crustal or subduction fault sources can still be strong at many locales. Such scenarios show how the relative location/orientation of faults with respect to target coastlines coupled with bathymetric features suggest avoiding the preselection of fault sources without addressing their possible impact onto hazard analysis results.

Clues from joint inversion of tsunami and geodetic data of the 2011 Tohoku-oki earthquake

Thu, 26 Apr 2012 22:00:00 GMT

Title: Clues from joint inversion of tsunami and geodetic data of the 2011 Tohoku-oki earthquake Authors: Romano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Piatanesi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Lorito, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; D'Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Hirata, K.; Meteorological Research Institute, Japan Meteorological Agency, 1-1 Nagamine, Tsukuba, Ibaraki 305-0052, Japan; Atzori, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Yamazaki, Y.; Department of Ocean and Resource Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, USA; Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: The 2011 Tohoku-oki (Mw 9.1) earthquake is so far the best-observed megathrust rupture, which allowed the collection of unprecedented offshore data. The joint inversion of tsunami waveforms (DART buoys, bottom pressure sensors, coastal wave gauges, and GPS-buoys) and static geodetic data (onshore GPS, seafloor displacements obtained by a GPS/acoustic combination technique), allows us to retrieve the slip distribution on a non-planar fault. We show that the inclusion of near-source data is necessary to image the details of slip pattern (maximum slip ,48 m, up to ,35 m close to the Japan trench), which generated the large and shallow seafloor coseismic deformations and the devastating inundation of the Japanese coast. We investigate the relation between the spatial distribution of previously inferred interseismic coupling and coseismic slip and we highlight the importance of seafloor geodetic measurements to constrain the interseismic coupling, which is one of the key-elements for long-term earthquake and tsunami hazard assessment.

SKS splittings in the southern Apennines-Calabrian arc region (southern Italy)

Fri, 16 Jun 2006 22:00:00 GMT

Title: SKS splittings in the southern Apennines-Calabrian arc region (southern Italy) Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Steckler, M.S.; LDEO, Columbia University, NY, USA; Lerner-Lam, A.; LDEO, Columbia University, NY,USA; Armbruster, J.; LLDEO, Columbia University, NY,USA; Abruzzese, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: During the years 2003-2006 CAT/SCAN (Calbarian-Apennine-TyrrhenianlSubductionCollision- Accretion Network) temporary broadband stations operate in Southern Apennine and Calabria (Italy). In the same period CESIS-INGV project improved the number of permanent seismic stations in the same area. We analyze the data recorded to study seismic anisotropy and to investigate the mantle flow in the boun(fary-zoile{ between Southern Apennine and Calabriaibeneath and above the subducting slab. In the current work we present new shear wave splittings obtained analyzing SKS phases of 15 teleseisms with epicentral distance ranging from 88.40 to 98.20 and magnitude greater than 6.0. We used the method of Silver & Chan (1991) to obtained anisotropic parameters: delay time and fast polarization direction. The splitting parameters reveal strong seismic anisotropy in the mantle beneath Southern Tyrrhenian Sea- Calabrian Arc System that seems to be controlled by the slab presence. The clear variability in the fast directions allow us to hypothesize the existence of different anisotropic domains: fast polarization directions vary from NNW -SSE in the tyrrhenian side ofthe Southern Apennine to N-S and NE-SW toward the Adriatic Sea. Moving toward the Calabria fast directions are prevalently trench parallel showing a NE-SW orientation following the strike on the mountain chain.

Seismic anisotropy and subduction in Southern Italy

Sun, 03 Jun 2007 22:00:00 GMT

Title: Seismic anisotropy and subduction in Southern Italy Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Steckler, M.S.; LDEO, Columbia University, NY, USA Abstract: In the current work we present a large collection of shear wave splitting measurements in the Calabrian Arc-Tyrrhenian basin subduction system. For our analysis we used earthquakes recorded from 2003 to 2005 at the CAT/SCAN temporary network and at the INGV national network. The dataset consists of SKS teleseismic phases (earthquakes with delta 87° - 112° and magnitude greater than 6.0) and of local S phases (events deeper than 150 km). We used the method of Silver and Chan to obtain the splitting parameters: fast direction (φ) and delay time (δt). Shear wave splitting results reveal the presence of a strong seismic anisotropy with a complex pattern of fast directions in the subduction system below the region. The SKS fast polarization directions define three anisotropic domains which correspond to the three different geological and geodynamic regions: the Calabrian Arc domain with fast directions oriented NNE-SSW;the Southern Apennines domain with fast directions oriented NNW-SSE and the Apulian Platform domain with fast directions oriented almost N-S in the northern part and ENE-WSW in the southern. The large number of splitting parameters evaluated for events coming from different back-azimuth allow us to hypothesize the presence of a depth dependence anisotropic structure in each of the identified domains and to constrain at 50 km depth the upper limit of the anisotropic layer. We interpret the trench-parallel φ observed in Calabrian Arc and in Southern Apennines as a mantle flow below the slab, likely due to the pressure induced by the retrograde motion of the slab itself. The pattern of trench perpendicular φ in the Apulian Platform seems to be not a direct result of the roll-back motion of the slab and may be explained as frozen-in lithospheric anisotropy or as asthenospheric flow deflected by the complicated structure of the Adriatic microplate. Results obtained with S phases show an extremely complex pattern of fast directions and delay times. These last measures are mainly located in the south-eastern sector of the Tyrrhenian Sea in correspondence of the high velocity body imaged at 150 km depth by the tomography. We related this strong fast directions variability inside the slab to the complex structure of the slab itself. The variable pattern of SKS and S splitting measurements suggest the presence of a local scale mantle flow strongly controlled by the geometry and motion of the anisotropic slab.

Seismic anisotropy and attenuation beneath the Southern Italy Subduction zone

Tue, 26 Oct 2010 22:00:00 GMT

Title: Seismic anisotropy and attenuation beneath the Southern Italy Subduction zone Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Steckler, M.S.; LDEO, Columbia University, NY, USA; De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: Subduction zones represent a tectonic region where intense deformations and complex dynamic processes are expected. Although several progress have been made in understanding the structure and the geodynamic evolution of the subduction zones, the active interaction among the subducting slab and the surrounding mantle material remains still debated. The Southern Italy Subduction System is part of the complex tectonic boundary between the Africa-Eurasia macroplates and has been inherited from several phases of fragmentation of the Western Mediterranean subduction zone. It is widely accept that the geodynamic setting of the Southern Italy Subduction System results from the southeast retrograde motion of the northwestward subducting Western Mediterranean slab (i.e. Gueguen et al., 1998; Carminati et al., 1998; Faccenna et al., 2005 and refrences therein). The retrograde motion of the slab was responsible for the creation of the backarc extensional Tyrrhenian Sea and the building of the Southern Apennines and Calabrian arcuate orogenic belts. At present, only the portion of subduction beneath the Calabrian Arc, in the Ionian area, may be active, while a young slab window develops at the Southern Apennines (Lucente et al., 2006). The purpose of this study is to characterize the seismic structure beneath the Southern Italy in order to better define the geometry of the Ionian slab and of the surrounding mantle flows. We therefore analyzed the anisotropic and attenuation properties beneath the study region. Seismic anisotropy is found to be a ubiquitous properties of the Earth due to the mantle deformation and, thus, it is represent a powerful tool to constrain the anisotropic behavior of the upper mantle and of the subducting plate. In particular, the observed anisotropy can help to understand the mantle and the slab deformation and the dynamic processes occurring in the upper-mantle wedge above the sinking oceanic slab and in the mantle below the slab. In this study we present a large collection of shear wave splitting measurements in the Calabrian Arc - Tyrrhenian basin Subduction System. The data analyzed consist of several teleseisms and subduction zone local deep earthquakes (Baccheschi et al., 2007, 2008). We used the method described by Silver and Chan (1991), assuming that shear waves pass through a medium with homogeneous anisotropy and with an horizontal fast axis. We analyzed SKS phases from earthquakes with magnitude greater than 6.0 and epicentral distance Æ° ranging from 87° to 112°. In addition, to obtain the best signal to noise ratio, all teleseisms are band-pass filtered between 0.03-0.3 Hz. The pattern of SKS fast directions, with delay times up to 3.0 s, reveals the existence of a strong seismic anisotropy in the sub-slab mantle region. We observe both trench-parallel and trench-perpendicular fast directions. Fast axes are oriented NE-SW along the Calabrian Arc, parallel to the strike of the subduction. To the N they rotate to NNW-SSE following the curvature of the slab. Fast directions are almost perpendicular to the strike of subduction in front of the slab (Aeolian Islands) and behind the slab (Straits of Messina). In the Apulian domain we observe trench-perpendicular fast directions, oriented N-S and ENEWSW. The pattern of SKS splitting measurements parallel to the strike of the slab suggests that the anisotropy is closely controlled by subduction and by the rollback motion of the slab. These two processes would be responsible for activating mantle flow below and around the slab itself. The pattern of SKS splitting in the Apulian domain seems to be not a direct results of the rollback motion of the slab and may be explained as frozen-in lithospheric anisotropy or as asthenospheric flow deflected by the structure of the Adriatic microplate. In order to obtain a detailed image of the anisotropic structure beneath the Southern Italy Subduction System we also used the direct S waves from earthquake located within the descending Ionian plate. The particular geometry of the Tyrrhenian subduction zone relative to the distribution of the land areas and, consequently, locations of the seismic stations provide an opportunity to collect unique data. In fact, the main massif Calabria is an uplifted fore-arc that lies well trenchward of the volcanic arc. In addition, the slab dips at high angle (about 70°) below Calabria and the lateral extension of the slab is limited and bounded at its edges by the Southern Apennines and Sicily.Seismic stations are distributed in Calabria, in the Southern Apennines and in Sicily and only few are in the Aeolian volcanic arc. This allows most recorded rays to travel through and along the subducted slab. This is not frequently observed worldwide since in most subduction zones, as in Japan, land corresponds to the volcanic arc and trenchward of this the forearc is submerged. This enabled us to sample rays that propagate up the slab and allowed us to separate the different sources of the anisotropy: the subducting lithosphere, the mantle wedge above it and the overriding plate. We analyzed several deep earthquakes, with depth greater tha 150 km, that occurred within the descending slab; S splitting parameters show a complex pattern of anisotropy with variable fast directions across the subduction zone and delay times ranging from 0.1 sec to 2.2 sec. Measurements at single stations are quite variable excluding the overriding plate as main source of anisotropy. The S wave splitting parameters also show frequency-dependent behaviour that we attribute to the presence of small-scale anisotropic heterogeneities. Comparison of the S splitting measurements to the Pwave velocity anomaly at 100-200 km depth shows that where the rays primarily sample the slab the delay times are small. In contrast, where the S rays sample the mantle wedge, the delay times are quite high. This dt pattern depicts the slab as a weakly anisotropic region and suggests that the main source of anisotropy in the subduction zone is the surrounding asthenosphere (Baccheschi et al., submitted to JGR). We also determined the attenuation structure of the slab and of the surrounding regions by the inversion of high quality S-waves t* from slab earthquakes. We obtained high resolution Qs model down to 300 km depth. The results indicate low values of Qs (Qs values down to 200) corresponding to crustal layers (down to 25 km depth), while the slab is characterized by higher but heterogeneous Qs structure (Qs values up to 1100). At 100 km depth the high Qs body is well reconstructed beneath the Calabrian arc and at 200 km depth it is extended offshore the Southern Tyrrhenian Basin beneath the Aeolian Islands. These preliminary attenuation results allowed us to better define the geometry and the boundary of the Ionian slab and distinguish between anisotropy in the slab and in the mantle wedge.

Lateral Changes of seismic anisotropy in the upper mantle around the Northern Apennines

Sat, 23 Apr 2005 22:00:00 GMT

Title: Lateral Changes of seismic anisotropy in the upper mantle around the Northern Apennines Authors: Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Piana Agostinetti, N.; Osservatorio Ximeniano, Firenze; Piccinini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Plomerova, J.; Geophysical Institute, Praga, Rep. Ceca; Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Park, J.; Yale University, New Haven, USA; Brandon, M.; Yale University, New Haven, USA; RETREAT Seismology Team; INGV Abstract: We performed three-dimensional analysis of anisotropic parameters of body waves to develop a 3D self-consistent dynamic model of the syn-convergent extension in the Northern Apennines within the multidisciplinary project RETREAT. Simultaneous extension within the convergent margin can be the consequence of the retreat of the subducting Adriatic plate from the orogenic front, caused by sub-lithosphere mantle processes that seismic anisotropy can help to decipher. We use data recorded by the RETREAT temporary array consisting of 35 stations complemented by data of permanent INGV observatories. Currently, 18-months of data are available from some stations, representing half of the passive experiment duration. We detect many examples of core-refracted shear-wave splitting within the upper mantle, and observe both distinct lateral variations of anisotropic parameters and their dependence on the direction of propagation. In particular, the fast shear-wave polarization changes from slab-perpendicular to slab-parallel along the Apennines chain. There is also a distinct change in the anisotropic signals across the presumed boundary of the Tyrrhenian and Adriatic micro-plates. Variations of the splitting time delays and orientation of the fast shear waves, together with considerations on the geodynamics of the area, seem to exclude simple sub-lithosphere mantle corner flow as the only source of the observed anisotropy. Alternate models include (1) a frozen-in fabric of different lithosphere domains, and (2) complex mantle flow associated with the Plio-Pleisocene uplift and extension of Tuscany.

Reference seismic velocity Earth model for Italy from local source tomography and 30 years of controlled source seismology data

Sat, 23 Apr 2005 22:00:00 GMT

Title: Reference seismic velocity Earth model for Italy from local source tomography and 30 years of controlled source seismology data Authors: Di Stefano, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Kissling, E.; Institute of Geophysics, ETH, Zurich, Switzerland; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: We present here a new high resolution regional P-wave velocity model for the lithosphere beneath the Italian region obtained by including information on the Moho topography, and integrating results from local earthquake tomography with 30 years of CSS data, applying the method of Waldhauser (1996). For the 3D moho map, we extended the crustal model, already available for the Alps by Lippitsch et al., 2003, to the Italian peninsula, Corsica, Sardinia, and Sicily. The tomographic model is obtained by inverting 166,000 Pg and Pn arrival times large part of which have been automatically picked and consistently weighted with an advanced automatic picking system (Aldersons, 2004). The resolution of the obtained velocity model is consistently higher and the grid spacing consistently smaller than in previous tomographic works targeting the same region. We are able to image the complex geometry of this part of the subduction-collision system between the Eurasian and African plates adding important details to the overview derived by the teleseismic tomography. Our results clearly show the plate boundary at Moho level from the Alps to the Southern Apennines and the Calabrian Arc in a volume unresolved in previous studies. The use of global 1D velocity models based on the flat Earth assumption is a pre-requisite to refine and interpret images and seismic responses of the earth obtained with geophysical studies (P and S tomography, surface wave tomography etc). Our model is suitable as a good starting point for a 3D velocity reference model of the crust and upper mantle beneath the Mediterranean area to be extended to the Adriatic Sea and to the Ionian Sea, with benefit for earthquakes location,teleseismic tomography, focal mechanisms and CMT

Shear wave splitting in southern tyrrhenian subduction zone (Italy) from CESIS and CAT/SCAN projects

Sat, 01 Apr 2006 22:00:00 GMT

Title: Shear wave splitting in southern tyrrhenian subduction zone (Italy) from CESIS and CAT/SCAN projects Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Abruzzese, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Armbruster, J.; LDEO, Columbia University, NY,USA; Steckler, M.S.; LDEO, Columbia University, NY,USA; Lerner-Lam, A.; LDEO, Columbia University, NY,USA; Amato, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: In the years 2003 -2006 several broad band stations were installed in Southern Italy: 15 permanent ones (CESIS project), improved the INGV Italian national network and 40 temporary ones were installed in the frame of CAT/SCAN NSF project.We present shear wave splitting measurements obtained analyzing SKS phases and local S phases from slab earthquakes. We used the method of Silver & Chan to obtain shear wave splitting parameters: fast direction and delay time. Shear wave splitting measurements reveals strong seismic anisotropy in the mantle beneath Southern Tyrrhenian subduction system. The SKS splitting results show fast polarization directions varying from NNW-SSE in the Southern Apennines to N-S and to E-SW in Calabria, following the strike of the mountain chain. Moving toward the Adriatic sea the fast directions rotate from N-S to NE-SW. Fast directions could indicate the mantle flow below the slab, due to its retrograde motion but also the lithospheric fabric of the subducting plate. In the Tyrrhenian domain, above the slab, from Sardinia to the Italian and Sicilian coasts the dominant fast direction is E-W and could be related to the opening of the Tyrrhenian basin and to the corner flow in the asthenospheric wedge. In Sicily fast directions depict a ring around the slab edge supporting the existence of a slab tear and of a return flow from the back to the front of the slab. Measurements obtained with intermediate and deep earthquakes slab S phases show an extremely complex pattern of fast directions. They are mostly distributed in front of the Tyrrhenian Calabrian coast in correspondence of the fast velocity anomaly imaged at 150 km depth by tomography. We can relate this fast directions variability to the complex structure of the slab itself. The complex pattern of SKS and S splitting measurements suggests the presence of local scale mantle flow controled by the motion of an anisotropic slab.

Seismic structure of the Calabrian subduction zone

Tue, 11 Sep 2007 22:00:00 GMT

Title: Seismic structure of the Calabrian subduction zone Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Di Stefano, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Lucente, F.P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Margheriti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Montuori, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Piromallo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: During the last decades, many studies have been addressing the seismic structure of the crust and upper mantle beneath the Tyrrhenian-Calabrian Arc, crucial to define the deep and shallow geometry of the subducting plate and the circulation of the surrounding mantle. We present the INGV contribution to the understanding of the subduction system from a seismological point of view. We illustrate the most recent results on relocated deep seismicity,on high resolution local earthquake tomography, and on teleseismic tomography with ocean bottom seismometers data. The pattern of mantle flow is imaged by a large collection of shear-wave splitting measurements from national network and temporary deployments. The 3D geometry of the narrow (about 200 km) subducting lithosphere shows a well defined shallow bend from sub-horizontal to 70-75 NW dipping. Lithosphere dives down to 400 km depth and turns again horizontal in the transition zone. Low seismic velocity in the wedge correspond to the Tyrrhenian basin and Aeolian Arc. Focused mantle circulation is induced by the slab motion, with evidences of return flow from behind the subducted lithosphere around the south-western slab edge.

Seismic attenuation tomography beneath the retreating Southern Tyrrhenian Sea subduction system

Sat, 02 Apr 2011 22:00:00 GMT

Title: Seismic attenuation tomography beneath the retreating Southern Tyrrhenian Sea subduction system Authors: Baccheschi, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: We investigate the seismic attenuation structure of the Ionian slab and surrounding mantle beneath the Southern Tyrrhenian subduction system. We present a high-resolution Vp, Vp/Vs, Qp and Qs models obtained by the inversion of high quality P- and S-waves t* from slab earthquakes. In our analysis we first located 304 earthquakes with M>= 2.8 , depth >= 30 km and azimuthal gap <= 200 and we used a 3D a priori Vp and Vp/Vs model. Then, t* values were measured from spectra of P and S waves. For computing t* we have determined the corner frequency (fc) which has been estimated using a grid search over the frequency range 1 - 10 Hz using all the recordings for each event. The obtained t* values are then used in the inversion for the 3-D attenuation structure using, and kept fixed, the 3-D velocity model. Tomographic inversion show high-attenuation regions corresponding to the crustal layers with low values of Qs (values down to 200) but high values of Qp. The subducting slab is identified as a body of low attenuation, but heterogeneous in the Qs and Qp structure (Qs values up to 1100; Qp values up to 1200), surrounded by high-attenuation regions beneath the Aeolian magmatic arc. At 100 km depth the high Qp and Qs body is well reconstructed beneath the Calabrian arc and at 200 km depth it is extended offshore the Southern Tyrrhenian Basin beneath the Aeolian Islands. Between 100 and 200 km depth, the Ionian slab is characterized by intermediate depth seismicity, but Qp and Qs models clearly show the existence of high-attenuation region, with low values of Qs and high Qp/Qs structure. The observed low Qp and Qs anomalies could likely due to the fluids released from dehydrating minerals associated to the slab metamorphism. The observed low Qs anomalies regions between the slab and the Aeolian volcanic arc could be indicative of melting processes in the mantle and also of the large-scale serpentinization.