The Central Andes are the Earth's highest mountain belt formed by ocean-continent collision. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust, dominated by tectonic shortening. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovicić discontinuity--generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro-eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10-20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening.

P-to-S converted teleseismic waves recorded by temporary broadband networks across Tibet show a north-dipping interface that begins 50 kilometers north of the Zangbo suture at the depth of the Moho (80 kilometers) and extends to a depth of 200 kilometers beneath the Bangong suture. Under northern Tibet a segmented south-dipping structure was imaged. These observations suggest a different form of detachment of the Indian and Asian lithospheric mantles caused by differences in their composition and buoyancy.

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[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.

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SUMMARY We use data from recently installed broad‐band seismographs on the islands of Crete, Gavdos, Santorini, Naxos and Samos in the Hellenic subduction zone to construct receiver function images of the crust and upper mantle from south of Crete into the Aegean Sea. The stations are equipped with STS‐2 seismometers and they are operated by GFZ Potsdam, University of Chania and ETH Zürich. Teleseismic earthquakes recorded by these stations at epicentral distances between 35° and 95° have been used to calculate receiver functions. The receiver function method is a routinely used tool to detect crustal and upper‐mantle discontinuities beneath a seismic station by isolating the P–S converted waves from the coda of the P wave. Converted P–S energy from the oceanic Moho of the subducted African Plate is clearly observed beneath Gavdos and Crete at a depth ranging from 44 to 69 km. This boundary continues to the north to nearly 100 km depth beneath Santorini island. Because of a lack of data the correlation of this phase is uncertain north of Santorini beneath the Aegean Sea. Moho depths were calculated from primary converted waves and multiply reflected waves between the Moho and the Earth's surface. Beneath southern and eastern Crete the Moho lies between 31 and 34 km depth. Beneath western and northern Crete the Moho is located at 32 and 39 km depth, respectively, and behaves as a reversed crust–mantle velocity contrast, possibly caused by hydration and serpentinization of the forearc mantle peridotite. The Moho beneath Gavdos island located south of Crete in the Libyan Sea is at 26 km depth, indicating that the crust south of the Crete microcontinent is also thinning towards the Mediterranean ridge. This makes it unlikely that part of the crust in Crete consists of accreted sediments transported there during the present‐day subduction process which began approximately 15 Ma because the backstop, i.e. the boundary between the current accretionary wedge of the Mediterranean ridge and the Crete microcontinent, is located approximately 100 km south of Gavdos. A seismic boundary at 32 km depth beneath Santorini island probably marks the crustal base of the Crete microcontinent. A shallower seismic interface beneath Santorini at 20–25 km depth may mark the depth of the detachment between the Crete microcontinent and the overlying Aegean subplate. The Moho in the central and northern Aegean, at Naxos and Samos, is observed at 25 and 28 km depth, respectively. Assuming a stretching factor of 1.2–1.3, crustal thickness in the Aegean was 30–35 km at the inception of the extensional regime in the Middle Miocene.

Abstract. The M w = 9.3 Sumatra earthquake of 26 December 2004 generated a tsunami that affected the entire Indian Ocean region and caused approximately 230 000 fatalities. In the response to this tragedy the German government funded the German Indonesian Tsunami Early Warning System (GITEWS) Project. The task of the GEOFON group of GFZ Potsdam was to develop and implement the seismological component. In this paper we describe the concept of the GITEWS earthquake monitoring system and report on its present status. The major challenge for earthquake monitoring within a tsunami warning system is to deliver rapid information about location, depth, size and possibly other source parameters. This is particularly true for coast lines adjacent to the potential source areas such as the Sunda trench where these parameters are required within a few minutes after the event in order to be able to warn the population before the potential tsunami hits the neighbouring coastal areas. Therefore, the key for a seismic monitoring system with short warning times adequate for Indonesia is a dense real-time seismic network across Indonesia with densifications close to the Sunda trench. A substantial number of supplementary stations in other Indian Ocean rim countries are added to strengthen the teleseismic monitoring capabilities. The installation of the new GITEWS seismic network -consisting of 31 combined broadband and strong motion stations -out of these 21 stations in Indonesia -is almost completed. The real-time data collection is using a private VSAT communication system with hubs in Jakarta and Vienna. In addition, all available seismic realtime data from the other seismic networks in Indonesia and other Indian Ocean rim countries are acquired also directly by VSAT or by Internet at the Indonesian Tsunami Warning Centre in Jakarta and the resulting "virtual" network of moreCorrespondence to: W. Hanka (hanka@gfz-potsdam.de) than 230 stations can jointly be used for seismic data processing. The seismological processing software as part of the GITEWS tsunami control centre is an enhanced version of the widely used SeisComP software and the well established GEOFON earthquake information system operated at GFZ in Potsdam (http://geofon.gfz-potsdam.de/db/eqinfo.php). This recently developed software package (SeisComP3) is reliable, fast and can provide fully automatic earthquake location and magnitude estimates. It uses innovative visualization tools, offers the possibility for manual correction and re-calculation, flexible configuration, support for distributed processing and data and parameter exchange with external monitoring systems. SeisComP3 is not only used for tsunami warning in Indonesia but also in most other Tsunami Warning Centres in the Indian Ocean and Euro-Med regions and in many seismic services worldwide.