[1] Combined P and S receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the Aegean region are used to map the geometry of the subducted African and the overriding Aegean plates. We image the Moho of the subducting African plate at depths ranging from 40 km beneath southern Crete and the western Peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern Greece. However, the dip of the Moho of the subducting African plate is shallower beneath the Peloponnesus than beneath Crete and Rhodes and flattens out beneath the northern Aegean. Observed P-to-S conversions at stations located in the forearc indicate a reversed velocity contrast at the Moho boundary of the Aegean plate, whereas this boundary is observed as a normal velocity contrast by the S-to-P conversions. Our modeling suggests that the presence of a large amount of serpentinite (more than 30%) in the forearc mantle wedge, which generally occurs in the subduction zones, may be the reason for the reverse sign of the P-to-S conversion coefficient. Moho depths for the Aegean plate show that the southern part of the Aegean (crustal thickness of 20-22 km) has been strongly influenced by extension, while the northern Aegean Sea, which at present undergoes the highest crustal deformation, shows a relatively thicker crust (25-28 km). This may imply a recent initiation of the present kinematics in the Aegean. Western Greece (crustal thickness of 32-40 km) is unaffected by the recent extension but underwent crustal thickening during the Hellenides Mountains building event. The depths of the Aegean Moho beneath the margin of the Peloponnesus and Crete (25-28 and 25-33 km, respectively) show that these areas are also likely to be affected by the Aegean extension, even though the Cyclades (crustal thickness of 26-30 km) were not significantly involved in this episode. The Aegean lithosphere-asthenosphere boundary (LAB) mapped with S receiver functions is about 150 km deep beneath mainland Greece, whereas the LAB of the subducted African plate dips from 100 km beneath Crete and the southern Aegean Sea to about 225 km under the volcanic arc. This implies a thickness of 60-65 km for the subducted African lithosphere, suggesting that the Aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the Cyclades.

[1] We make use of S receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the South American continent and adjacent areas. The Moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the Andean region. The depth of the lithosphereasthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km. The identification of this phase becomes more difficult when the stations are located near subduction zones. We also observed the base of the subducted oceanic lithosphere down to depths of 220 km.

SUMMARY S receiver functions obtained from seismograms of teleseismic events recorded at 78 European permanent broad‐band stations are used to estimate the thickness of the European lithosphere. Our results provide new, independent information about the lithospheric thickness beneath the Precambrian platform of Eastern Europe and the Phanerozoic platform of central Europe. Detailed high‐resolution images of the lithosphere–asthenosphere boundary (LAB) reveal indications for a typical continental lithosphere of about 100 km thickness beneath a majority of stations within Central Europe, whereas in the vicinity of the Trans‐European Suture Zone (TESZ), the lithosphere thickens to about 130 km. A relatively thin lithosphere of 80 km was found beneath the Upper Rhine Graben region suggesting that the Cenozoic extension affects the whole lithosphere. No clear signal from the LAB was detected beneath the Alps and Carpathians. The LAB Sp phase might be disturbed by complicated structure due to ongoing collision/subduction in these regions, or the data are not yet sufficiently dense. A relatively thicker lithosphere of about 120 km was found beneath the SW part of the Bohemian Massif that was formed during the Variscan orogeny. We found an LAB depth of about 190 km near a single station located in the Vrancea area/Eastern Carpathians, which is characterized by the occurrence of intermediate deep earthquakes. Beneath the stations located in the Precambrian platform of Eastern Europe, the LAB deepens to approximately >200 km, even though the converted phase from the LAB is not as sharp as found beneath other stations located in Central Europe or even is missing.

[1] Based on joint consideration of S receiver functions and surface-wave anisotropy we present evidence for the existence of a thick and layered lithosphere beneath the Kalahari Craton. Our results show that frozen-in anisotropy and compositional changes can generate sharp Mid-Lithospheric Discontinuities (MLD) at depths of 85 and 150-200 km, respectively. We found that a 50 km thick anisotropic layer, containing 3% S wave anisotropy and with a fast-velocity axis different from that in the layer beneath, can account for the first MLD at about 85 km depth. Significant correlation between the depths of an apparent boundary separating the depleted and metasomatised lithosphere, as inferred from chemical tomography, and those of our second MLD led us to characterize it as a compositional boundary, most likely due to the modification of the cratonic mantle lithosphere by magma infiltration. The deepening of this boundary from 150 to 200 km is spatially correlated with the surficial expression of the Thabazimbi-Murchison Lineament (TML), implying that the TML isolates the lithosphere of the Limpopo terrane from that of the ancient Kaapvaal terrane. The

[1] The transition between the lithosphere and the asthenosphere is subject to numerous contemporary studies as its nature is still poorly understood. The thickest lithosphere is associated with old cratons and platforms and it has been shown that seismic investigations may fail to image the lithosphere-asthenosphere boundary in these areas. Instead, several recent studies have proposed a mid-lithospheric discontinuity of unknown origin existing under several cratons. In this study we investigate the Tanzania craton in East Africa which is enclosed by the eastern and western branches of the East African Rift System. We present evidence from S receiver functions for two consecutive discontinuities at depths of 50-100 km and 140-200 km, which correspond to significant S wave velocity reductions under the Tanzania craton and the Albert and Edward rift segments. By comparison with synthetic waveforms we show that the lower discontinuity coincides with the LAB exhibiting velocity reductions of 6-9%. The shallower interface reveals a velocity drop that varies from 12% beneath the craton to 24% below the Albert-Edward rift. It is interpreted as an infiltration front marking the upper boundary of altered lithosphere due to ascending asthenospheric melts. This is corroborated by computing S velocity variations based on xenolith samples which exhibit a dense system of crystallized veins acting as pathways of the infiltrating melt. Mineral assemblages in these veins are rich in phlogopite and pyroxenite which can explain the reduced shear wave velocities. Melt infiltration represents a suitable mechanism to form a mid-lithospheric discontinuity within cratonic lithosphere that is underlain by anomalously hot mantle.

SUMMARY The Alborz Mountains build the northern part of the Alpine–Himalayan orogen in western Asia. They are located south of the Caspian Sea and form an east–west range across the north of Iran. This region is one of the most active tectonic areas, as it undergoes extensive crustal deformation and shortening. In the present work, we used data from 11 permanent stations of the Tehran Telemetry Seismic Network to estimate the thickness of the crust and mantle lithosphere beneath the Central Alborz region by P‐ and S‐receiver function methods. Results of both P and S receiver functions revealed a relatively large crustal thickness beneath this region (∼51–54 km), which can be associated with the shortening process related to the orogenic belt. No remarkable crustal thickening has been detected below the high topography of Central Alborz. A thick crust (∼67.5 km) is observed locally in the region beneath the Damavand volcano, which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region. The S receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of ∼90 km, which we interpreted as the base of the lithosphere. The missing crustal root and the relatively thin lithosphere beneath the Alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the Alborz.

Abstract. We analyze S-receiver functions to investigate variations of lithospheric thickness below the entire region of Turkey and surrounding areas. 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-point stacks yield wellconstrained images of the Moho and of the lithosphereasthenosphere 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 in 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 150 km depth subducting to the north and east between the Aegean and Cyprus with a tear at Cyprus. We also observed the discontinuity at 410 km depth and a negative discontinuity above the 410, which might indicate a zone of partial melt above this discontinuity.

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