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We analyze S-receiver functions to investigate the variations of lithospheric thickness below the entire region of Turkey and surroundings. The teleseismic data used here have been compiled combining all permanent seismic stations which are open to public access. We obtained almost 12 000 S-receiver function traces characterizing the seismic discontinuities between the Moho and the discontinuity at 410 km depth. Common-conversion-points stacks yield well-constrained images of the Moho and of the lithosphere-asthenosphere boundary (LAB). Results from previous studies suggesting shallow LAB depths between 80 and 100 km are confirmed in the entire region outside the subduction zones. We did not observe changes of LAB depths across the North and East Anatolian Faults. To the east of Cyprus, we see indications of the Arabian LAB. The African plate is observed down to about 150km depth subducting to the north and east between the Aegean and Cyprus with a tear at Cyprus. We also observed the discontinuity at 410km depth and a negative discontinuity above the 410, which might indicate a zone of partial melt above this discontinuity. [ABSTRACT FROM AUTHOR]

Abstract: A 700km deep seismic velocity cross-section beneath the Lhasa to Golmud transect across the Tibetan plateau is presented. In contrast to the first version of this cross-section, which comprised an 800km wide swath centred on the Lhasa to Golmud transect, due to the recent proliferation of publications concerning the mantle structure beneath Tibet, this study is based only on seismic profiles which either run along or cross the transect and arrays or studies which at least partly cover the transect. The results from the recent INDEPTH IV project indicate that the crustal thickness change from 70km beneath the Songpan–Ganzi terrane and Kunlun mountains to 54km beneath the Qaidam basin is located about 100km north of the Kunlun Fault and almost 45km north of the North Kunlun Thrust. The Qaidam basin Moho is underlain by crustal velocity material for almost 45km and the apparently overlapping crustal material may represent Songpan–Ganzi lower crust underthrusting or flowing northward beneath the Qaidam basin Moho. Thus the high Tibetan plateau may be thickening northward into south Qaidam as its weak, thickened lower crust is injected beneath the stronger Qaidam crust. Beneath the crust, high-velocity, dense, cold Indian lithospheric mantle extends northwards until about the Banggong–Nujiang suture. Northwards, Asian lithospheric mantle is overlain by a low-velocity, less dense, warm Tibetan plate consisting of an upper lithospheric and a lower asthenospheric part. The apparent northwards deepening of the 410 and 660km discontinuities by about 20km implies that the upper mantle beneath north Tibet is slower, less dense and warmer than under south Tibet, in agreement with the observed uppermost mantle velocities. This, in turn, could provide some of the isostatic support for the high elevations in the north where the crust is somewhat thinner than in the southern plateau. [Copyright &y& Elsevier]

SUMMARY Rapid estimation of earthquake rupture propagation is essential to declare an early warning for tsunami-generating earthquakes. An increasing number of seismological methods have been developed to determine rupture parameters, such as length, velocity and propagation direction, especially since the occurrence of the Sumatra-Andaman earthquake that resulted in a devastating tsunami in the Indian Ocean region. Here, we present a new method to follow the rupture process in near real time by a polarization analysis of local and regional P phases that permits a faster determination of rupture properties than using teleseismic records. The new technique has the capability to provide detailed information in less than 10 min. Originally, the method stems from a single-station earthquake location method and is expanded here to monitor P-phase polarization variations through time. As the earthquake source moves away from the hypocentre, the backazimuth of an incoming P phase is expected to change accordingly. With polarization analysis we may be able to monitor the temporal change in P-wave backazimuth to follow the rupture process in near real time. Three component P phases are scanned to determine the azimuthal variation as a function of time. The backazimuth of a moving rupture front is determined by the first eigenvector of the covariance matrix. The linearity of the particle motion is used as a measure of the quality of the data. Seismic stations at local and regional distances () are used. We tested the new method with a theoretical simulation and observed seismograms of the Sumatra-Andaman earthquake (2004 December 26, Mw= 9.3), and we were able to follow the rupture for the first 200 s. For larger ruptures, stations at more than 30° epicentral distances would be required. The method is also successfully applied to the Wenchuan earthquake (2008 May 12, Mw= 8.0). [ABSTRACT FROM AUTHOR]

The article presents a study regarding the lithosphere-asthenosphere boundary with the U.S.Array project. The study observed two major discontinuities such as the crust-mantle boundary (Moho) and a negative boundary which was correlated with the lithosphere-athenosphere boundary (LAB). The result of the study shows that the strongest negative discontinuity was beneth the entire U.S. near 100 kilometers (km).

Teleseismic data have been collected with temporary seismograph stations on two profiles in southern Norway. Including the permanent arrays NORSAR and Hagfors the profiles are 400 and 500 km long and extend from the Atlantic coast across regions of high topography and the Oslo Rift. A total of 1071 teleseismic waveforms recorded by 24 temporary and 8 permanent stations are analysed. The depth-migrated receiver functions show a well-resolved Moho for both profiles with Moho depths that are generally accurate within ±2 km. For the northern profile across Jotunheimen we obtain Moho depths between 32 and 43 km (below sea level). On the southern profile across Hardangervidda, the Moho depths range from 29 km at the Atlantic coast to 41 km below the highland plateau. Generally the depth of Moho is close to or above 40 km beneath areas of high mean topography (>1 km), whereas in the Oslo Rift the crust locally thins down to 32 km. At the east end of the profiles we observe a deepening Moho beneath low topography. Beneath the highlands the obtained Moho depths are 4–5 km deeper than previous estimates. Our results are supported by the fact that west of the Oslo Rift a deep Moho correlates very well with low Bouguer gravity which also correlates well with high mean topography. The presented results reveal a ca. 10–12 km thick Airy-type crustal root beneath the highlands of southern Norway, which leaves little room for additional buoyancy-effects below Moho. These observations do not seem consistent with the mechanisms of substantial buoyancy presently suggested to explain a significant Cenozoic uplift widely believed to be the cause of the high topography in present-day southern Norway. [ABSTRACT FROM AUTHOR]

Azimuthal anisotropy in the upper mantle of many continental regions is documented by Swave splitting measurements with SKS techniques. Here we present observations of splitting of the SKS seismic phase at seismograph stations in the Siberian platform, where few such data were known previously. The parameters of splitting are coherent: the fast direction everywhere is around 150°, and the delay of the slow split wave is close to 1.0 s. These observations provide no constraints on the distribution of anisotropy with depth. However, the Siberian platform is remarkable in that it is covered by a network of long-range profiles, where P waves from nuclear explosions are recorded at epicentral distances of 2000 km and more. Depending on epicentral distance these waves sample the upper mantle from the Moho to the transition zone. Two profiles run approximately parallel to the fast direction of the azimuthal anisotropy, whereas the directions of the two others are intermediate between the fast and slow. We examine the observed P traveltimes for their dependence on the azimuth and epicentral distance. With the available data on elastic anisotropy in mantle xenoliths, the values of P-wave anisotropy for horizontal propagation can be used to evaluate S-wave splitting for vertical propagation. It appears that the upper mantle between the Moho and 150 km depth is responsible for not more than about 30 per cent of the large-scale effect in the SKS phase. The major effect is accumulated in a broad low-velocity zone, the top of which is found at a depth of 150 km. Anisotropy within this zone can be caused by recent mantle flow. A similar distribution with depth might explain discrepancies between the estimates of azimuthal anisotropy from phase velocities of surface waves and SKS splitting in North America and South Africa. [ABSTRACT FROM AUTHOR]

Seismic data from central Tibet have been combined to image the subsurface structure and understand the evolution of the collision of India and Eurasia. The 410- and 660-kilometer mantle discontinuities are sharply defined, implying a lack of a subducting slab beneath the plateau. The discontinuities appear slightly deeper beneath northern Tibet, implying that the average temperature of the mantle above the transition zone is about 300°C hotter in the north than in the south. There is a prominent south-dipping converter in the uppermost mantle beneath northern Tibet that might represent the top of the Eurasian mantle lithosphere underthrusting the northern margin of the plateau. [ABSTRACT FROM AUTHOR]

Abstract: We performed a teleseismic P wave tomography study using seismic events at both teleseismic and regional distances, recorded by a temporary seismic array in the Argentine Puna Plateau and adjacent regions. The tomographic images show the presence of a number of positive and negative anomalies in a depth range of 20–300km beneath the array. The most prominent of these anomalies corresponds to a low-velocity body, located in the crust, most clearly seen in the center of the array (27°S, 67°W) between the Cerro Peinado volcano, the Cerro Blanco caldera and the Farallon Negro in the east. This anomaly (southern Puna Magmatic Body) extends from the northern most part of the array and follows the line with the highest density of stations towards the south where it becomes smaller. It is flanked by high velocities on the west and the east respectively. On the west, the high velocities might be related to the subducted Nazca plate. On the northeast the high velocity block coincides with the position of the Hombre Muerto basin in the crust and could be indicating an area of lithospheric delamination where we detected a high velocity block at 100km depth on the eastern border of the Puna plateau, north of Galan. This block might be related to a delamination event in an area with a thick crust of Paleozoic metamorphic rocks at the border between Puna and Eastern Cordillera. In the center of the array the Southern Puna magmatic body is also flanked by high velocities but the most prominent region is located on the east and is interpreted as part of the Sierras Pampeanas lithosphere with high velocities. The position of the Sierras Pampeanas geological province is key in this area as it appears to limit the extension of the plateau towards the south. [Copyright &y& Elsevier]

Abstract: Data from three temporary seismic networks were merged for tomographic inversion. Although the deployments did not coincide in time, spatial overlap was achieved by re-occupying existing sites. Travel times and t ⁎ operators of about 1600 earthquakes were inverted for 3D models of ν p, ν p/ν s and P-wave attenuation (Q p −1). All three attributes provide a consistent image of the entire subduction zone on a lithospheric scale. The tomographic images reveal low velocities and high attenuation in the crust and mantle underlying the Western Cordillera and most of the Puna plateau, indicative of weak rheology and mostly asthenospheric mantle. In contrast, forearc and eastern foreland are characterized by high Q p values, corresponding to cold temperatures in accordance with thermal models. In the backarc, between 23°S and 24°S, a high velocity, high Q p structure beneath the Eastern Cordillera and eastern Puna is interpreted as detaching continental lithosphere that has been thickened in the orogenic process. South of this structure, the mantle is characterized by low velocities, high ν p/ν s ratios, and low Q p values. Here it is believed that lithosphere originally underlying Andean crust has already been removed. This is supported by new estimates of crustal thickness and volcanic activity. [Copyright &y& Elsevier]

A tomographic image of the upper mantle beneath central Tibet from INDEPTH data has revealed a subvertical high-velocity zone from ~100- to ~400-kilometers depth, located approximately south of the Bangong-Nujiang Suture. We interpret this zone to be downwelling Indian mantle lithosphere. This additional lithosphere would account for the total amount of shortening in the Himalayas and Tibet. A consequence of this downwelling would be a deficit of asthenosphere, which should be balanced by an upwelling counterflow, and thus could explain the presence of warm mantle beneath north-central Tibet. [ABSTRACT FROM AUTHOR]