The Experts below are selected from a list of 20127 Experts worldwide ranked by ideXlab platform
Noorbakhsh Mirzaei - One of the best experts on this subject based on the ideXlab platform.
-
Lithospheric structure beneath the Zagros Collision Zone resolved by non-linear teleseismic tomography
Geophysical Journal International, 2011Co-Authors: Z. Hossein Shomali, Forough Keshvari, Jamshid Hassanzadeh, Noorbakhsh MirzaeiAbstract:The upper-mantle structure across the Zagros Collision Zone, in southwest Iran, is investigated using a non-linear weighted damped least-squares teleseismic tomography approach. The resolution of the structures/transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks. To investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion, the data were inverted using two different inverse methods (singular value decomposition and a quadratic programming method). New high-quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the Zagros Collision Zone. The image shows a sharp lithospheric boundary at the Main Zagros Thrust between 100 km and 250 km depth with P-wave velocity about 3 per cent faster within the Arabian Shield to the south. A step-like increase in lithospheric thickness across the Zagros Collision Zone is assumed to separate two different mantle structures namely the Arabian (to the south) and the Eurasian (to the north) domains. The most striking feature resolved is a north-dipping slab-like positive velocity anomaly.
Z. Hossein Shomali - One of the best experts on this subject based on the ideXlab platform.
-
Lithospheric structure beneath the Zagros Collision Zone resolved by non-linear teleseismic tomography
Geophysical Journal International, 2011Co-Authors: Z. Hossein Shomali, Forough Keshvari, Jamshid Hassanzadeh, Noorbakhsh MirzaeiAbstract:The upper-mantle structure across the Zagros Collision Zone, in southwest Iran, is investigated using a non-linear weighted damped least-squares teleseismic tomography approach. The resolution of the structures/transitions in the upper mantle is enhanced significantly by correcting the teleseismic relative arrival time residuals for an a priori crustal velocity model and then performing the inversion with fixed crustal blocks. To investigate whether or not the lithospheric blocks and major transitions in the resulting model are required by the data or are artefacts of the inversion, the data were inverted using two different inverse methods (singular value decomposition and a quadratic programming method). New high-quality seismic velocity models show apparent correlation between surface geological features and seismic velocity structures at lithospheric depth across the Zagros Collision Zone. The image shows a sharp lithospheric boundary at the Main Zagros Thrust between 100 km and 250 km depth with P-wave velocity about 3 per cent faster within the Arabian Shield to the south. A step-like increase in lithospheric thickness across the Zagros Collision Zone is assumed to separate two different mantle structures namely the Arabian (to the south) and the Eurasian (to the north) domains. The most striking feature resolved is a north-dipping slab-like positive velocity anomaly.
-
Upper-mantle S-velocity structure across the Zagros Collision Zone resolved by nonlinear teleseismic tomography
Journal of Seismology, 2011Co-Authors: Forough Keshvari, Z. Hossein Shomali, Mohammad Tatar, Ayoub KavianiAbstract:Non-linear teleseismic S-phase tomography across the Zagros Collision Zone in southwestern Iran is used to determine a high-resolution image of the upper-mantle structure. The inversion was done using 41 high-quality earthquakes recorded by 19 broad-band and medium-band stations along a 620 km long profile across the Collision Zone. Smearing from strong crustal velocity anomalies into the upper-mantle is suppressed by travel-time corrections calculated based on a 3-D crustal model for the study area. Our results show that the relatively old and cold Arabian shield has a higher velocity (up to 6% faster, at depths between 70 and 300 km) than the younger lithosphere farther north in Central Iran. These two upper-mantle domains are separated by a sharp near-vertical transition whose surface expression coinciding with the Main Zagros Thrust.
G Weigelt - One of the best experts on this subject based on the ideXlab platform.
-
detection of high velocity material from the wind wind Collision Zone of eta carinae across the 2009 0 periastron passage
Astronomy and Astrophysics, 2010Co-Authors: J H Groh, K E Nielsen, A Damineli, Theodore R Gull, Thomas Madura, D J Hillier, M Teodoro, T Driebe, G WeigeltAbstract:We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He I lambda 10833 extending up to -1900 km s(-1) across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s(-1)) in the ultraviolet resonance lines of Si IV lambda lambda 1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si II lambda lambda 1527, 1533 and CII lambda lambda 1334, 1335, show absorption only up to -1200 km s(-1), indicating that the absorption with velocities -1200 to -2100 km s(-1) originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in He I lambda 10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s(-1) is present in the phase range 0.976 = 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind Collision Zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind Collision Zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega similar to 240 degrees-270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40 degrees-60 degrees. (Less)
-
detection of high velocity material from the wind wind Collision Zone of eta carinae across the 2009 0 periastron passage
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: J H Groh, K E Nielsen, A Damineli, Theodore R Gull, Thomas Madura, D J Hillier, M Teodoro, T Driebe, G Weigelt, Henrik HartmanAbstract:We report near-IR spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using VLT/CRIRES. We detect a strong, broad absorption wing in He I 10833 extending up to -1900 km/s across the 2009.0 spectroscopic event. Archival HST/STIS ultraviolet and optical data shows a similar high-velocity absorption (up to -2100 km/s) in the UV resonance lines of Si IV 1394, 1403 across the 2003.5 event. UV lines from low-ionization species, such as Si II 1527, 1533 and C II 1334, 1335, show absorption up to -1200 km/s, indicating that the absorption with v from -1200 to -2100 km/s originates in a region markedly faster and more ionized than the nominal wind of the primary star. Observations obtained at the OPD/LNA during the last 4 spectroscopic cycles (1989-2009) also display high-velocity absorption in He I 10833 during periastron. Based on the OPD/LNA dataset, we determine that material with v 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We suggest that the high-velocity absorption originates from shocked gas in the wind-wind Collision Zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. Using 3-D hydrodynamical simulations of the wind-wind Collision Zone, we find that the dense high-velocity gas is in the line-of-sight to the primary star only if the binary system is oriented in the sky so that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega ~ 240 to 270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i=40 to 60 degrees.
K E Nielsen - One of the best experts on this subject based on the ideXlab platform.
-
detection of high velocity material from the wind wind Collision Zone of eta carinae across the 2009 0 periastron passage
Astronomy and Astrophysics, 2010Co-Authors: J H Groh, K E Nielsen, A Damineli, Theodore R Gull, Thomas Madura, D J Hillier, M Teodoro, T Driebe, G WeigeltAbstract:We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He I lambda 10833 extending up to -1900 km s(-1) across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s(-1)) in the ultraviolet resonance lines of Si IV lambda lambda 1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si II lambda lambda 1527, 1533 and CII lambda lambda 1334, 1335, show absorption only up to -1200 km s(-1), indicating that the absorption with velocities -1200 to -2100 km s(-1) originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in He I lambda 10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s(-1) is present in the phase range 0.976 = 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind Collision Zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind Collision Zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega similar to 240 degrees-270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40 degrees-60 degrees. (Less)
-
detection of high velocity material from the wind wind Collision Zone of eta carinae across the 2009 0 periastron passage
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: J H Groh, K E Nielsen, A Damineli, Theodore R Gull, Thomas Madura, D J Hillier, M Teodoro, T Driebe, G Weigelt, Henrik HartmanAbstract:We report near-IR spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using VLT/CRIRES. We detect a strong, broad absorption wing in He I 10833 extending up to -1900 km/s across the 2009.0 spectroscopic event. Archival HST/STIS ultraviolet and optical data shows a similar high-velocity absorption (up to -2100 km/s) in the UV resonance lines of Si IV 1394, 1403 across the 2003.5 event. UV lines from low-ionization species, such as Si II 1527, 1533 and C II 1334, 1335, show absorption up to -1200 km/s, indicating that the absorption with v from -1200 to -2100 km/s originates in a region markedly faster and more ionized than the nominal wind of the primary star. Observations obtained at the OPD/LNA during the last 4 spectroscopic cycles (1989-2009) also display high-velocity absorption in He I 10833 during periastron. Based on the OPD/LNA dataset, we determine that material with v 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We suggest that the high-velocity absorption originates from shocked gas in the wind-wind Collision Zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. Using 3-D hydrodynamical simulations of the wind-wind Collision Zone, we find that the dense high-velocity gas is in the line-of-sight to the primary star only if the binary system is oriented in the sky so that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega ~ 240 to 270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i=40 to 60 degrees.
C. Thomas - One of the best experts on this subject based on the ideXlab platform.
-
multiple frequency tomography of the upper mantle beneath the african iberian Collision Zone
Geophysical Journal International, 2014Co-Authors: Mickael Bonnin, Antonio Villaseñor, G. Nolet, J. Gallart, C. ThomasAbstract:During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take advantage of the dense broad-band station networks now available in the Alboran Sea region, to develop a high-resolution 3-D tomographic P velocity model of the upper mantle beneath the African/Iberian Collision Zone that will better constraint the past dynamics of this Zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centred between 0.03 and 1.0 Hz, and for the first time interpreted using multiple frequency tomography. Our model shows, beneath the Alboran Sea, a strong (4 per cent) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly, and its extent at depth, are coherent with a lithospheric slab, thus favouring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper mantle, high intensity slow anomalies are widespread in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at the surface with the position of the Rif and Atlas orogens and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot?) upper mantle, but without clear indication for a lateral spreading of the Canary plume to the east.
-
Multiple-frequency tomography of the upper mantle beneath the African/Iberian Collision Zone
Geophysical Journal International, 2014Co-Authors: Mickael Bonnin, Antonio Villaseñor, G. Nolet, J. Gallart, C. ThomasAbstract:During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take advantage of the dense broad-band station networks now available in the Alboran Sea region, to develop a high-resolution 3-D tomographic P velocity model of the upper mantle beneath the African/Iberian Collision Zone that will better constraint the past dynamics of this Zone. The model is based on 13200 teleseismic arrival times recorded between 2008 and 2012 at 279 stations for which cross-correlation delays are measured with a new technique in different frequency bands centred between 0.03 and 1.0 Hz, and for the first time interpreted using multiple frequency tomography. Our model shows, beneath the Alboran Sea, a strong (4 per cent) fast vertically dipping anomaly observed to at least 650 km depth. The arched shape of this anomaly, and its extent at depth, are coherent with a lithospheric slab, thus favouring the hypothesis of a westward consumption of the Ligurian ocean slab by roll-back during Cenozoic. In addition to this fast anomaly in the deep upper mantle, high intensity slow anomalies are widespread in the lithosphere and asthenosphere beneath Morocco and southern Spain. These anomalies are correlated at the surface with the position of the Rif and Atlas orogens and with Cenozoic volcanic fields. We thus confirm the presence, beneath Morocco, of an anomalous (hot?) upper mantle, but without clear indication for a lateral spreading of the Canary plume to the east.