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- PublicationOpen AccessShear wave attenuation in the lithosphere beneath Italy and surrounding regions: Tectonic implications(1997)
; ; ; ; ;Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Seber, D.; Cornell University ;Barazangi, M.; Cornell University; ; ; More than 700 waveforms produced by 51 shallow earthquakes and recorded at regional distances (250-1400 km) by the Italian seismic network have been analyzed to characterize the amplitude and frequency contents of the crustal and uppermost mantle shear waves Lg and Sn, respectively. The crustal phase Lg efficiently propagates through the relatively stable Adriatic continental crust, while it is not observed along propagation paths crossing major physiographic features, like the Apennine chain and the basinal domain of the Tyrrhenian and Ionian Seas. Similar to Lg, efficient Sn propagation is observed in the uppermost mantle beneath the Po plain and the Adriatic Sea. Efficient Sn transmission is also observed across the northern Ionian Sea and Sicily and in the area between Sardinia and the northern coasts of Africa. Sn are efficiently transmitted across the Sicily Channel, and rather efficient Sn propagate beneath the Ligurian Sea. On the contrary, inefficient Sn transmission characterizes the uppermost mantle beneath the Apennines, the western margin of the Italian peninsula, and the southern Tyrrhenian Sea. Shear wave attenuation suggests the presence of asthenospheric material in the uppermost mantle, probably related to the present-day extension along the Apennine chain and in the Tyrrhenian basin. This interpretation is consistent with the presence of extensive Neogene and Quaternary volcanic activity in these areas and related high heat flow. Proposed lithospheric delamination processes beneath the Apennines and subduction beneath the Tyrrhenian Sea can reasonably explain the observed high-attenuation zones in the uppermost mantle. In contrast, a high-strength mantle lid is inferred to underlay the Po plain, the Adriatic Sea, and the northern Ionian Sea. The available waveforms also indicate that a continuous mantle lid is present beneath Sicily and the extensional domain of the Sicily Channel, as well as in the marine area south of Sardinia.156 460 - PublicationRestrictedCompressional velocity structure and anisotropy in the uppermost mantle beneath Italy and surrounding regions(1998)
; ; ; ; ; ;Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Seber, D.; Cornell University ;Hearn, T. M.; University of Las Cruces, NM ;Barazangi, M.; Cornell University; ; ; ; Travel times of about 39,000 Pn arrivals recorded from regional earthquakes by the Italian Telemetered Seismic Network and by stations of nearby countries are inverted to image lateral variations of seismic velocity and anisotropy at subcrustal depth in Italy and surrounding regions. This method allows simultaneous imaging of variations of Pn velocity and anisotropy, as well as crustal thickness variations. The Po plain, the Adriatic Sea, and the Ionian Sea have normal to high Pn velocities. In contrast, lower velocities (7.9-8.0 km/s) are imaged in Italy beneath the western Alps, the northern Apennines, and eastern Sicily and nearby Calabria, as well as in northern Albania and beneath the Pannonian basin. Low Pn velocities beneath the northern Apennines correlate with present-day extension and may have resulted from thermal anomalies in the uppermost mantle due to delamination processes. Low velocities are consistent with the high-attenuation zone inferred in the uppermost mantle beneath the internal Apennine units and the Tyrrhenian margin of the peninsula by Mele et al. [1996, 1997]. On the contrary, low velocities beneath the western Alps may be an apparent effect due to the abrupt thickening of the crustal roots. Pn velocity is anisotropic in the study area with a maximum amplitude of ± 0.2 km/s. The largest anisotropic velocity anomalies are observed along the major arc structures of Italy, i.e., the northern Apennines and the Calabrian Arc, indicating that these features are controlled by uppermost mantle processes. The anisotropy anomaly along the Calabrian Arc extends as far as Albania but ends abruptly north of this area, suggesting that a lithospheric discontinuity is present along the northern Albanian border.215 23 - PublicationOpen AccessThe intraplate Euphrates fault system-Palmyrides mountain belt junction and relationship to Arabian plate boundary tectonics(1995-09)
; ; ; ; ; ; ;Alsdorf, D.; Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, NY 14853, U.S.A. ;Barazaugi, M.; Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, NY 14853, U.S.A. ;Litak, R.; Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, NY 14853, U.S.A. ;Seber, D.; Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, NY 14853, U.S.A. ;Sawaf, T.; Syrian Petroleum Company, Ministry of Petroleum and Minerai Resources, Damascus, Syria ;AI-Saad, D.; Syrian Petroleum Company, Ministry of Petroleum and Minerai Resources, Damascus, Syria; ; ; ; ; We interpret seismic data and well logs to indicate that the Euphrates graben, intersecting orthogonally with the Palmyride mountains, is an intraplate transtensional feature that probably developed in response to plate boundary stress created by a latest Cretaceous convergence event along the present-day northern boundary of the Arabian plate. The principal stress direction is proposed to lie generally parallel to the graben; hence, it may have formed as a tear in the Arabian crust while, as previously documented, the Palmyride region under- went shortening and uplift. Arabian plate boundary tectonism as well as shorteningin the Palmyrides were pe- riodically active during the entire Cenozoic, especially in Neogene and Quaternary time. However, the normal fault motions that formed the Euphrates graben were not active within the study area after the end of the Cre- taceous, and were most active during the Campanian-Maastl.ichtian. A broad, Cenozoic depression overlying the Euphrates graben and most of Eastern Syria is possibly related to the Mesopotamian foredeep that devel- oped in response to the nearby Zagros continental collision zone during Neogene and Quaternary time. Cenozoic strike-slip faults lie between the Euphrates graben and the Palmyrides belt and may kinematically separate the Palmyrides from the Euphrates system.222 1178 - PublicationOpen AccessLateral variations of Pn propagation in Italy: Evidence for a high attenuation zone beneath the Apennines(1996)
; ; ; ; ;Mele, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Seber, D.; Cornell University ;Barazangi, M.; Cornell University; ; ; Pn phases recorded by 40 stations of the Italian seismic network are analyzed using the spectral ratio technique to estimate the Q structure of the uppermost mantle beneath the Italian peninsula and nearby Adriatic Sea. A total of 344 digital waveforms are analyzed from 22 earthquakes that occurred within distances of 300 to 1600 km. The calculated apparent Q values are grouped into two categories: Q > 800 characterizes the Adriatic side of the Italian peninsula, indicating that the Adriatic lithosphere is very efficient in propagating Pn phases through the uppermost mantle; Q < 600 characterizes the uppermost mantle beneath the Apennines and western Italy, indicating less efficient wave propagation. The presence of asthenospheric mantle material at shallow depths beneath the Apennines can explain the observed Q.172 182