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Karantonis, G.
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Karantonis, G.
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- PublicationOpen AccessTomographic image of the crust and uppermost mantle of the Ionian and Aegean regions(1997-01)
; ; ; ; ; ; ; ;Alessandrini, B.; Istituto Nazionale di Geofisica, Roma, Italy ;Beranzoli, L.; Istituto Nazionale di Geofisica, Roma, Italy ;Drakatos, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Falcone, C.; Istituto Nazionale di Geofisica, Roma, Italy ;Karantonis, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Mele, F. M.; Istituto Nazionale di Geofisica, Roma, Italy ;Stavrakakis, G. N.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece; ; ; ; ; ; We present a tomographic view of the crust and uppermost mantle beneath the Central Mediterranean area obtained from P-wave arrival times of regional earthquakes selected from the ISC bulletin. The P-wave velocity anomalies are obtained using Thurber's algorithm that jointly relocates earthquakes and computes velocity adjustments with respect to a starting model. A specific algorithm has been applied to achieve a distribution of epicentres as even as possible. A data set of 1009 events and 49072 Pg and Pn phases was selected. We find a low velocity belt in the crust, evident in the map view at 25 km of depth, beneath the Hellenic arc. A low velocity anomaly extends at 40 km of depth under the Aegean back arc basin. High velocities are present at Moho depth beneath the Ionian sea close to the Calabrian and Aegean arcs. The tomographic images suggest a close relationship between P-wave velocity pattern and the subduction systems of the studied area.240 164 - PublicationOpen AccessP-wave crustal tomography of Greece with use of an accurate two-point ray tracer(1997-01)
; ; ; ;Drakatos, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Karantonis, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Stavrakakis, G. N.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece; ; The three-dimensional velocity structure of the crust in the Aegean sea and the surrounding regions (34.0º-42.OºN, 19.0ºE-29.0ºE) is investigated by inversion of about 10000 residuals of arrival times of P-wave from local events. The resulting velocity structure shows strong horizontal variations due to the complicated crustal structure and the variations of crustal thickness. The northern part of the region generally shows high velocities. In the inner part of the volcanic arc (Southern Aegean area), relatively low velocities are observed, suggesting a large-scale absorption of seismic energy as confirmed by the low seismicity of the region. A low velocity zone was observed along the subduction zone of the region, up to a depth of 4 km. The existence of such a zone could be due to granitic or other intrusions in the crust during the uplift of the region during Alpidic orogenesis.169 292 - PublicationOpen AccessA tomography image of the Aegean region (Greece) derived from inversion of macroseismic intensity data(1997-01)
; ; ; ; ;Stavrakakis, G. N.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Drakatos, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Karantonis, G.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece ;Papanastassiou, D.; National Observatory of Athens, Institute of Geodynamics, Athens, Greece; ; ; The three-dimensional attenuation structure beneath the Aegean sea and the surrounding regions was determined by inversion of seismic intensity data. A large number of seismic intensity data have been accumulated in a uniform scale in the Aegean region, where the seismic activity is much higher than that of the other Mediterranean regions. Nearly 11000 seismic intensity data from 47 earthquakes that have occurred in these regions were used to determine the seismic attenuation structure. The resulting structure reveals a remarkable contrast of attenuation. In the top layer (depth 0-20 km), low Q is dominant in the central Aegean sea, while high Q is dominant in the surrounding land areas, except for Southwestern Turkey. The low-Q regions correspond to areas of Neogene-Quaternary grabens where the high seismicity of shallow earthquakes appears. In the lower layer (20-40 km) low-Q areas are located in the southeastern part of the Hellenic arc. Some low-Q spots corresponding to the distribution of volcanoes exist along the volcanic arc. The low-Q spots might correspond to diapirs causing subduction volcanism.138 140