Search

The Mohorovicic discontinuity, Moho for short, which marks the boundary between crust and mantle, is the main first-order structure within the lithosphere. Geodynamics and tectonic evolution determine its depth level and properties. Here, we present a map of the Moho in central Europe across the Teisseyre-Tornquist Zone, a region for which a number of previous studies are available. Our results are based on homogeneous and consistent processing of P- and S-receiver functions for the largest passive seismological data set in this region yet, consisting of more than 40 000 receiver functions from almost 500 station. Besides, we also provide new results for the crustal Vp/Vs ratio for the whole area. Our results are in good agreement with previous, more localized receiver function studies, as well as with the interpretation of seismic profiles, while at the same time resolving a higher level of detail than previous maps covering the area, for example regarding the Eifel Plume region, Rhine Graben and northern Alps. The close correspondence with the seismic data regarding crustal structure also increases confidence in use of the data in crustal corrections and the imaging of deeper structure, for which no independent seismic information is available. In addition to the pronounced, stepwise transition from crustal thicknesses of 30km in Phanerozoic Europe to more than 45 beneath the East European Craton, we can distinguish other terrane boundaries based on Moho depth as well as average crustal Vp/Vsratio and Moho phase amplitudes. The terranes with distinct crustal properties span a wide range of ages, from Palaeoproterozoic in Lithuania to Cenozoic in the Alps, reflecting the complex tectonic history of Europe. Crustal thickness and properties in the study area are also markedly influenced by tectonic overprinting, for example the formation of the Central European Basin System, and the European Cenozoic Rift System. In the areas affected by Cenozoic rifting and volcanism, thinning of the crust corresponds to lithospheric updoming reported in recent surface wave and S-receiver function studies, as expected for thermally induced deformation. The same correlation applies for crustal thickening, not only across the Trans-European Suture Zone, but also within the southern part of the Bohemian Massif. A high Poisson’s ratio of 0.27 is obtained for the craton, which is consistent with a thick mafic lower crust. In contrast, we typically find Poisson’s ratios around 0.25 for Phanerozoic Europe outside of deep sedimentary basins. Mapping of the thickness of the shallowest crustal layer, that is low-velocity sediments or weathered rock, indicates values in excess of 6km for the most pronounced basins in the study area, while thicknesses of less than 4km are found within the craton, central Germany and most of the Czech Republic.

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region called Tibetan Plate was found in northern and eastern Tibet between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic velocity (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy. The crustal shortening in the southern Tibet is accommodated by underthrusting of the Indian crust below the Asian crust that may reach further north than the YZS. In northern Tibet, crustal shortening is accommodated by homogeneous crustal thickening. The more rugged and higher topography in west Tibet can be supported by the rigid mantle lithosphere there, whereas to the east the lithosphere is weaker due to the existence of the crush zone. Under pressure by Indian and Asian plates, the subducted Indian lithospheric materials moved eastward and divided into four directions when meeting the Sichuan basin, two horizontal (southeastern ward forming Yun-Gui-Chuan plateau, northeastern ward to Erdos) and two vertical(upward forming Longmen Shan and down ward entering deep mantle).

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 largest velocity contrast (3.6–4.7%) is observed at a boundary located at depths of 260–280 km beneath the Archean domains and the older Proterozoic belt. This boundary most likely represents the lithosphereasthenosphere boundary, which shallows to about 200 km beneath the younger Proterozoic belt. Thus, the Kalahari lithosphere may have survived multiple episodes of intense magmatism and collisional rifting during the billions of years of its history, which left their imprint in its internal layering.

The Himalaya and the Tibetan Plateau are uplifted by the ongoing northward underthrusting of the Indian continental lithosphere below Tibet resulting in lithospheric stacking. The layered structure of the Tibetan upper mantle is imaged by seismic methods, most detailed with the receiver function method. Tibet is considered as a place where the development of a future craton is currently under way. Here we study the upper mantle from Germany to northern Sweden with seismic S receiver functions and compare the structure below Scandinavia with that below Tibet. Below Proterozoic Scandinavia, we found two low-velocity zones on top of each other, separated by a high-velocity zone. The top of the upper low-velocity zone at about 100 km depth extends from Germany to Archaean northern Sweden. It agrees with the lithosphere-asthenosphere boundary (LAB) below Germany and Denmark. Below Sweden it is known as the 8°discontinuity, or as a mid-lithospheric discontinuity (MLD), similar to observations in North America. Seismic tomography places the LAB near 200 km in Scandinavia, which is close to the top of our deeper low-velocity zone. We also observed the bottom of the asthenosphere (the Lehmann discontinuity) deepening from 180 km in Germany to 260 km below Sweden. Remnants of old subduction in the upper about 100 km below Scandinavia and Finland are known from controlled source seismic experiments and local earthquake studies. Recent tomographic studies indicate delamination of the lithosphere below southern Scandinavia and northern Germany. We are suggesting that the large-scale layered structure in the Scandinavian upper mantle may be caused by processes similar to the ongoing lithospheric stacking in Tibet.

Investigation of the thickness of continental roots, which migrate coherently with plates belongs to the most systematic keys in order to understand the continental evolution. South Africa’s lithosphere preserves a nearly uninterrupted geological history of more than 3.5 billion years. It was formed during the break-up of the supercontinent Gondwana over a period of 80 million years and therefore is the longest, best-preserved geological record of the planet Earth. To estimate the LAB and other major lithospheric discontinuities beneath South Africa, we used the novel technique of S receiver function, which employs S-to-P conversions and appears promising for detecting the LAB. This technique has already proven its power for mapping the LAB in the tectonically different regions. Although the South African craton has been extensively studied in recent years, especially by SRFs, the depth extent of the lithosphere and its nature varies somewhat between studies. It seems that several differences in methodology and data selection criteria leading to variations in the SRFs obtained. Some authors observed Sto-P conversions at 25-30 s (_250-300 km) and interpreted them as being from the LAB. In contrast, some other authors found these conversions at shallower depths (_150 km). We calculated SRFs for the data of more than 120 stations within South Africa. Such a huge amount of data has not been yet applied for SRF studies in South Africa. Our results clearly shows 3 different LVZs at about 100 (_10s), 150-220 (15-22 s) km and 300-330 km (30-33 s), which were not seen in any of the previous studies. Based on our preliminary results, the deep and sharp LAB phase at 300-330 km is significantly imaged beneath the cratons (Kaapvaal and Zimbabwe cratons; > 2.7 Ga) and the oldest belt (Limpopo belt _ 2.7 Ga). This phase may not be visible northward and southward beneath the much younger mobile belts (Mozambique and Namaqua-Natal belt; _ 1.1 Ga). Instead, a shallower and less sharper boundary at 150-220 km depth can be identified across the whole region. This boundary may show an intralithospheric discontinuity beneath cratons and may reveal the LAB beneath the younger belts. In addition, a 100 km LVZ can be also observed, which may confirm the so-called “8 degree discontinuity” seen in dense, long-range seismic profiles.

The great Sumatra-Andaman earthquake of 26 December 2004 caused seismic waves propagating through the solid Earth, tsunami waves propagating through the ocean and infrasound or acoustic-gravity waves propagating through the atmosphere. Since the infrasound wave travels faster than its associated tsunami, it is for warning purposes very intriguing to study the possibility of infrasound generation directly at the earthquake source. Garces et al. (2005) and Le Pichon et al. (2005) emphasized that infrasound was generated by mountainous islands near the epicenter and by tsunami propagation along the continental shelf to the Bay of Bengal. Mikumo et al. (2008) concluded from the analysis of travel times and amplitudes of first arriving acoustic-gravity waves with periods of about 400–700 s that these waves are caused by coseismic motion of the sea surface mainly to the west of the Nicobar islands in the open seas. We reanalyzed the acoustic-gravity waves and corrected the first arrival times of Mikumo et al. (2008) by up to 20 min. We found the source of the first arriving acoustic-gravity wave about 300 km to the north of the US Geological Survey earthquake epicenter. This confirms the result of Mikumo et al. (2008) that sea level changes at the earthquake source cause long period acoustic-gravity waves, which indicate that a tsunami was generated. Therefore, a denser local network of infrasound stations may be helpful for tsunami warnings, not only for very large earthquakes.

This study images upper-mantle structure beneath different tectonic and geomorphological provinces in southern Scandinavia by P-wave traveltime tomography based on teleseismic events. We present results using integrated data from several individual projects (CALAS, MAGNUS, SCANLIPS, CENMOVE and Tor) with a total of 202 temporary seismological stations deployed in southern Norway, southern Sweden, Denmark and the northernmost part of Germany. These stations, together with 18 permanent stations, yield a high density data coverage and enable presentation of the first high resolution 3D seismic velocity model for the upper mantle for this region, which includes the entire northern part of the prominent Tornquist Zone and the Southern Scandes Mountains. P-wave arrival time residuals of up to ±1 s are observed indicating large seismic velocity contrasts at depths. Relative regional as well as absolute global tomographic inversion is carried out and consistently show upper-mantle velocity variations relative to the ak135 global reference model of up to ±2–3 per cent corresponding to P-wave velocity differences of 0.4–0.5 km s–1 from depths of about 100 km to more than 300 km. High upper-mantle velocities are observed to great depth to the east in Baltic Shield areas of southwestern Sweden suggesting the existence of a deep lithosphere keel. Lower velocities are found to the west and southwest beneath the Danish and North German sedimentary basins and in most of southern Norway. A well defined, generally narrow and deep boundary is observed between areas of contrasting upper-mantle se ismic velocity. In the southern part of the study area, this boundary is localized along and east of the Sorgenfrei–Tornquist Zone. It seems to follow the eastern boundary of a zone of significant Late Carboniferous–Permian volcanic activity from southwestern Sweden to the Oslo Graben area. To the north, it crosses shield units, Caledonides as well as areas of high topography. Supported by independent results of surface wave studies, we interpret this velocity boundary as a first order lithosphere boundary representing the southwestern edge of thick shield lithosphere. In basin areas to the southwest, low upper-mantle velocities are associated with asthenosphere beneath thinned lithosphere and velocity contrasts are likely to arise mainly from temperature differences. To the north structural and geodynamic relations are more complex and both temperature and compositional differences may play a part. Reduced upper-mantle velocity beneath southern Norway also seems, despite relatively low heat flow, to be associated with areas of thinned lithosphere, pointing towards increased temperatures and reduced density in the upper mantle. This feature extends over large areas and seems not directly correlated to the shorter wavelength high topography of the Scandes Mountains, but may contribute with some isostatic buoyancy on a regional scale. For this northern area, there is no obvious geodynamic explanation to reduced upper-mantle velocity. A number of candidates are available including deep transient thermal influence from basin areas to the southwest.

As Alfred Wegener already recognized 100 years ago, the giant southern continent, Gondwanaland, broke about 200 million years ago into several pieces which drifted apart. One part, India, drifted northward until it collided 50 million years ago with Eurasia. This collision created the Himalayan mountain chain and the Tibetan plateau, which are not only very significant geological structures, but are also important parts of the Earth System. The influence of Tibet on the atmospheric circulation and world climate and the ongoing threat of giant collisional earthquakes to the megacities in the Ganges plain must be emphasized. In international cooperation, the GFZ conducted a number of seismic experiments in Tibet, known as INDEPTH experiments, to study details of the deformation of the tectonic plates as a consequence of the collision. As a result the presence of the Indian lithosphere was for the first time seismologically demonstrated to exist several hundred kilometers northwards below Tibet. During the collision the Indian crust was peeled off and contributes to the thickening of the Tibetan crust. The latest phase of the INDEPTH experiments was focused on the northern margin. Using active and passive seismic techniques (wide-angle profiling, receiver functions, surface wave tomography), we have imaged the deep structure below Tibet, showing the configuration of the Tibetan lithosphere between the Indian and Eurasian plates. We also found evidence for unusual properties of the lower crust, which are likely to be responsible for the prevalence of crustal flow in northern Tibet.

The dense deployment of seismic stations so far in the western half of the United States within the USArray project provides the opportunity to study in greater detail the structure of the lithosphere-asthenosphere system. We use the S receiver function technique for this purpose which has higher resolution than surface wave tomography, is sensitive to seismic discontinuities and has no problems with multiples like P receiver functions. Only two major discontinuities are observed in the entire area down to about 300km depth. These are the crust-mantle boundary (Moho) and a negative boundary which we correlate with the lithosphere-asthenosphere boundary (LAB) since a low velocity zone is the classical definition of the seismic observation of the asthenosphere by Gutenberg (1926). Our S receiver function LAB is at a depth of 70-80km in large parts of westernmost North America. East of the Rocky Mountains its depth is generally between 90 and 110km. Regions with LAB depths down to about 140km occur in a stretch from northern Texas over the Colorado Plateau to the Columbia Basalts. These observations agree well with tomography results in the westernmost USA and at the east coast. However, in the central cratonic part of the USA the tomography LAB is near 200km depth. At this depth no discontinuity is seen in the S receiver functions. The negative signal near 100km depth in the central part of the USA is interpreted by Yuan and Romanowicz (2010) or Lekic and Romanowicz (2011) as a recently discovered mid lithospheric discontinuity (MLD). A solution for the discrepancy between receiver function imaging and surface wave tomography is not yet obvious and requires more high resolution studies at other cratons before a general solution may be found. Our results agree well with petrophysical models of increased water content in the asthenosphere, which predict a sharp and shallow LAB also in continents (Mierdel et al. 2007). We are comparing our results from North America with other regions (South Africa, South America, Europe).

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 Pwave 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 (>∼ 30◦) 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).

The western Bohemian Massif is known for geodynamic phenomena such as earthquake swarms, CO2 dominated free gas emanations of upper-mantle origin, and Tertiary/ Quaternary volcanism. Among other explanations, a small-scale mantle plume has been suggested. We used data from the international passive seismic experiment BOHEMA (2001-2004) and of a previous seismic experiment to investigate the structure of the upper-mantle discontinuities at 410 km and 660 km depth (the ‘410’ and the ‘660’) beneath the Bohemian Massif with the P receiver function method. More than 4500 high-quality receiver function traces could be utilized. Two stacking techniques were used: stacking by station (common station method, CSM) and stacking by piercing points in the mantle transition zone (common conversion point method, CCM). Since the station spacing is very close, rays from different stations have similar piercing points in the mantle transition zone. Therefore CCM is sensitive in the transition zone and CSM is sensitive to the uppermost structure of the mantle. The CSM shows delayed conversion times from the 410 km discontinuity beneath the western Bohemia earthquake region, which indicate a slow uppermost mantle. When stacking our data by CCM, we observe thickening of the transition zone towards the Alpine foreland, which agrees with tomographic results by Piromallo and Morelli. The thickness of the mantle transition zone beneath the western Bohemian Massif is normal, with a faint hint to thinning in the northern part. Our conclusion is that a plume-like structure may exist in the upper mantle below the western Bohemia earthquake region, but with no or only weak imprint on the 410 km discontinuity.

Seismological imaging has identified the Indian lithosphere penetrating underneath Tibet up to 500km to the north and to a depth of at least 200km along a front that is more than 1000km long. This is a classical case of continental subduction. In contrast, the collision of Tibet with the stable Tarim Basin in the north-west caused thickening of the Tibetan lithosphere to about 200km, whereas collision with the Sichuan Basin in the east caused thinning of the Tibetan lithosphere to about 70km. No sufficient seismic data on the mantle lithosphere have been available up to now at the boundary of Tibet to the Qaidam Basin, where subduction of the Asian lithosphere beneath Tibet was suggested. We report on results from a recent seismic passive source experiment in this region, which continued the series of INDEPTH experiments to the Qaidam Basin in the north-east. We used the S receiver function technique for data analysis, which is especially sensitive for observations of the lithosphere-asthenosphere boundary (LAB). As a surprising result, we found evidence that a newly identified relatively thin Tibetan lithosphere is overriding the flat subducting Asian lithosphere.

We use two different techniques to investigate the region between Antofagasta and Arica in northern Chile for crustal velocity changes. Data are taken from the 19 broadband stations of the IPOC project (Integrated Plate Boundary Observatory Chile) operating partly since 2006 by GFZ and Institut de Physique du Globe de Paris (IPGP). In the neighborhood of the seismic stations an M7.0 earthquake occurred near Tocopilla on 14 November 2007. Other studies have shown that in the course of such earthquakes seismic velocities may be changing (e.g. Brenguier et al. 2008). The first method is testing for phase shifts in receiver functions. To avoid varying travel paths of different events we compare events located in small source regions. Although temporal variations have been found in receiver functions for the Parkfield M6.0 and San Simeon M6.5 earthquakes (Audet 2006) we cannot find any variations exceeding the noise level of our dataset at the time of the M7.0 earthquake near Tocopilla. Therefore the data is analyzed with the help of cross-correlation technique of ambient seismic noise (Bensen et al. 2007). Compared to the first method it has the advantage of regularly available correlation functions (e.g. 1 per day). We report on first results.

We present here the results obtained using the data form our passive seismic array in the southern Puna plateau between 25°S to 28°S latitude in Argentina and Chile. In first instance we have been able to calculate P and S receiver functions in order to investigate the Moho thickness and other seismic discontinuities in the study area. The RF data shows that the northern Puna plateau has a thicker crust and that the Moho topography is more irregular along strike. The seismic structure and thickness of the continental crust and the lithospheric mantle beneath the southern Puna plateau reveals that the LAB is deeper to the north of the array suggesting lithospheric removal towards the south. Later we performed a joint inversion of teleseismic and regional tomographic data in order to study the distribution of velocity anomalies that could help us to better understand the evolution of the Andean elevated plateau and the role of lithosphere-asthenosphere interactions in this region. Low velocities are observed in correlation with young volcanic centers (e.g. Ojos del Salado, Cerro Blanco, Galan) and agree very well with the position of crustal lineaments in the region. This is suggesting a close relationship between magmatism and lithospheric structures at crustal scale coniciding with the presence of hot asthenospheric material at the base of the crust probably induced by lithospheric foundering.

During the INDEPTH IV controlled-source seismic experiment in June 2007, 949 vertical-component seismographs (IRIS-PASSCAL Texans) at 100-650 m station spacing and 20 broadband and 29 short-period three-component seismographs (34 from GIPP, Germany and 15 from SEIS-UK) at 5-6 km station spacing recorded 5 large shots (1000-2000 kg) and 100 small shots (80 kg) along a 270 km long profile across the Kunlun mountains in northeast Tibet. A detailed tomographic inversion of the well-recorded Sg arrivals observed by these 998 instruments reveals the S-velocity structure of the upper crust down to about 10 km depth beneath the profile. The major lateral variation in upper crustal S-velocities along the profile is from lower velocities beneath the Qaidam basin in the north to higher velocities beneath NE Tibet in the south. Beneath NE Tibet, there are also lateral variations with lower S-velocities beneath the valleys (basins) along which the North Kunlun and South Kunlun Faults run and higher velocities in the mountainous regions between and to the north and south, where older rocks are generally exposed at the surface. From the S-velocity model, there is no evidence within the upper crust for major overthrusting of NE Tibet over the Qaidam basin. Following the controlled-source experiment, 50 broadband seismographs (35 from GIPP, Germany and 15 from SEIS-UK) were deployed for a period of one year along two profiles across the Kunlun mountains and the Jinsha river suture in northeast Tibet. The profile across the Kunlun mountains consisting of 24 stations at 5 km spacing was coincident with the central 120 km of the controlled-source profile. It recorded a number of local earthquakes. Some of these events were in-line and thus the P and S arrivals from these in-line events provided useful additional information regarding the velocity structure below the profile. Together with the S waves generated from the shots a crustal S-velocity model is being derived and will be presented. For this model the boundaries from the now published P-velocity model are incorporated. Initial S velocities for the deeper parts of the model are derived from the P velocities of the published model divided by 1.732. Together, the published P-velocity model and the S-velocity model will provide a Poisson’s ratio model along the INDEPTH IV profile across the Kunlun mountains. From this model, crustal lithologies may be derived which in turn may constrain modes of formation of the Tibetan plateau.

We analyse broad-band SS waveformdata recorded by several networks in Europe with sources mainly in the west Pacific to study the underside reflections of teleseismic SS waves in the lithosphere and the upper mantle beneath eastern Asia and the NW Pacific ocean. SS bounce points sample a corridor from the Aleutian, Kamchatka and Japan subduction zones through the North China Craton and Central Asian Orogenic Belt to the Tibetan plateau. The corridor passes through different tectonic units such as subduction zones, an old continental shield, a fold belt and a high plateau. We investigate the seismic structure of the lithosphere and the mantle transition zone beneath the different geotectonic units along the profile and infer the correlation of geodynamic processes at different depths.We explore the short period frequency content in the SS waveform data and use moveout correction and common midpoint stack to acquire profiles with high lateral and depth resolution from the crust to the mantle transition zone. Clear SS precursors of the 410 and 660 km discontinuities show the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zones. A low-velocity layer has also been detected beneath the 410 km discontinuity and can be traced along the entire profile. Due to the improved resolution acquired by the method presented here we have been able to study the shallower structures such as the Moho and the lithosphere–asthenosphere boundary by SS precursors. The continental Moho can be clearly seen along this corridor. The depth variation agrees well with earlier receiver function results. We also see negative reflectors along the profile at varying depths, which can be interpreted as the lithosphere–asthenosphere boundary.

Structure and dynamics of the upper mantle is important in understanding timing and mechanisms shaping prensent day topography and near surface geology. Debate persists regarding the geological age of the Scandes Mountains. We contribute by imaging upper mantle structure beneath southern Scandinavia using teleseismic P-wave travel time tomography (P-tomography). We include data from mobile stations deployed in projects CALAS, CENMOVE, MAGNUS, SCANLIPS and Tor. Permanent stations included are those available from the University of Uppsala, NORSAR and GEUS. P-wave arrival times generally show differences of up to 1 second across the study area. Upper mantle velocities are relatively high in southern Sweden and southern Norway east of the Oslo Graben. Lower velocities are observed in the Norwegian-Danish Basin southwest of the Sorgenfrei-Tornquist Zone(STZ) and in the southwestern part of Norway. We interpret the southwestern boundary of thick Baltic Shield lithosphere where we observe the highest horizontal P-wave velocity gradient. Thus, we find the boundary of thick lithosphere to more or less coinside with the STZ in the southeastern part of the study area, extending from southern Sweden into the northern part of Jutland. From here it turns north, passing through the Oslo Graben area to about 60_N then turning northwest, approaching the Norwegian west coast around 65_N. Thus, as compared to Baltic Shield, upper mantle velocity is significantly reduced beneath deep sedimentary basins of Denmark and northern Germany.

China is an assembly of ancient continental fragments separated by fold belts accreted from late Proterozoic to Cenozoic. China being sitting on the triple junction of three major plates: Eurasian plate, Indian plate and Philippine sea plate resulted in the tectonic feature of todays like mountain ranges, fold belts, sedimentary basins and high plateaus. This has been the cause of many intraplate earthquakes also. In the Northern part this region is supposed to get some resistance from the Siberian shield. But the major tectonic feature in this region imprinted by two main tectonic events. First, the subduction of the ofWest Pacific plate and Philippine Sea plate to the west in the last 250 Ma. Second, the collision of Indian and Eurasian plate started about 50 Ma. It was this collision responsible for the uplift of Himalayan mountain and Tibetan Plateau. This event left there imprints on the upper mantle structure. It is generally agreed that the lithosphere is thick in west China while much of the lithospheric root was lost beneath some cratons in east China. Still it’s an open debate whether the lithosphere beneath the Tibetan plateau has doubled its thickness as did the crust above or much of the thickened lithosphere was removed by mantle convection and delamination. In our study we try to determine the three dimensional Sv wave speed and azimuthal anisotropy model by analyzing the vertical component multimode Rayleigh wave seismogram. The data which we used are from approx. 40 broadband station from Chinese Seismic network and seismograms recorded by some temporary broadband seismic experiment in China. We construct the three dimensional model in two step procedure. In the first step we use the automated version of the Cara and Leveque [1987] waveform inversion technique in terms of secondary observables for modeling each multimode Rayleigh waveform to determine the path-average mantle Sv wave speed structure. In the second stage we combine the 1-D velocity models in a tomographic inversion to obtain the three dimensional Sv wave speed structure and the azimuthal anisotropy as a function of depth. This gives a much clearer indication of the properties at depth than do group and phase velocity maps which represent a weighted average of the earth structure over a frequency-dependent depth interval. We have taken a source region specific velocity structure from the three dimensional model 3SMAC to improve the source excitation computation. We analyzed the seismograms using a modified (smoothed) version of PREM for the upper mantle velocity structure both for the reference model used in extracting the modal information from the seismogram and for the starting inversion and a priori velocity models employed in determining the path-average mantle structure. However, each path has a path-specific crustal model determined by averaging the crustal part of 3SMAC along the path.

In this study a seismic velocity cross-section of the crust and mantle down to 700 km depth beneath the Tibetan plateau has been constructed. The cross-section is based on the many controlled and passive source seismological experiments and studies which have reported results from within an 800 km swath centred on the main Lhasa-Golmud transect. Beneath the 2.5-7 km thick cover layer, the upper crust down to 15-25 km depth has compressional (P) wave velocities of 5.8-6.1 km/s and low Poisson’s ratios of 0.21-0.23, indicative of felsic rocks rich in quartz in the  state. There are many observations e.g. bright spots in seismic reflection records, low velocity regions in shear (S) wave models derived from receiver function analysis, seismicity drop off and high electrical conductivity which indicate that below 15-25 km depth, temperatures are high enough such that ductile flow and partial melting can occur. One of the main results of this study is the recognition of a boundary at 30-40 km depth. From the velocity values on either side of this boundary it is suggested that it marks the interface between the felsic upper crust and the more mafic lower crust. Within the swath, crustal thickness is greatest (approx. 74 km) beneath the southern part of the plateau south of about 31.5°N, where Indian lower crust forms the basal crustal layer. To the north crustal thickness decreases to about 66 km beneath the southern Qiangtang terrane around 33°N, before again increasing to about 70 km beneath the northern part of the plateau south of the Kunlun mountains. As the Kunlun mountains are crossed the crust thins dramatically to about 54 km beneath the Qaidam basin. Beneath the crust, high-velocity, dense and cold Indian lithospheric mantle extends northwards within the swath until about the Banggong-Nujiang suture, where it downwells to at least 350-400 km depth in a zone about 100-200 km wide centred at about 31.2°N. To the north, low-velocity, less dense and warm Asian lithospheric mantle is present. The lithosphere-asthenosphere boundary occurs at 160-225 km depth under the plateau. The 410 and 660 km discontinuities at the top and base of the mantle transition zone respectively, produce prominent seismic phases beneath the whole plateau in receiver function images, implying that no subducting slab penetrates the mantle transition zone under the plateau. This is, however, at variance with a recent tomographic image which suggests that Indian lithospheric mantle does penetrate into the mantle transition zone. The observation that the 410 and 660 km discontinuities run parallel to each other implies that temperature variations in the mantle transition zone are negligible. On the other hand, the apparent northwards deepening by about 20 km of both discontinuities 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 northern part of the plateau where the crust is somewhat thinner than in the southern portion of the plateau.

We study the underside reflections of precursors to SS waves at the lithosphere and the upper mantle beneath eastern Asia. By analyzing the SS bounce points we have been able to investigate the upper mantle discontinuities along a corridor that extends from the Aleutians to the Tibetan plateau passing through Kamchatka, the Japanese subduction zone and the North China craton. One of our aims was to investigate the interaction between the lithosphere and the mantle transition zone beneath different geotectonic units along this corridor and the interaction of geodynamic processes at different depths. In the analysis, we have used the short period content of SS waveform data and methods like CMP stack and migration techniques to acquire high resolution lithosphere and upper mantle images and to improve the lateral and depth resolution for the upper mantle discontinuities. By using a newly developed method we have been able to detect the presence of the continental Moho at different depths along this corridor. We show that the SS precursors provide high resolution images of upper mantle discontinuities such as the 410 and 660 km and the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zone. Furthermore, we show for the first time, that it is possible to create new possibilities to study shallower structures such as the Moho by using the SS precursors.

During the INDEPTH IV controlled-source seismic experiment in June 2007, 949 vertical-component seismographs (IRIS-PASSCAL Texans) at 100-650 m station spacing and 20 broadband and 29 short-period three-component seismographs (34 from GIPP, Germany and 15 from SEIS-UK) at 5-6 km station spacing recorded 5 large shots (1000-2000 kg) and 100 small shots (80 kg) along a 270 km long profile across the Kunlun mountains in northeast Tibet. A detailed tomographic inversion of the well-recorded Sg arrivals observed by these 998 instruments reveals the S-velocity structure of the upper crust down to about 10 km depth beneath the profile. The major lateral variation in upper crustal S-velocities along the profile is from lower velocities beneath the Qaidam basin in the north to higher velocities beneath NE Tibet in the south. Beneath NE Tibet, there are Seismik 229 also lateral variations with lower S-velocities beneath the valleys (basins) along which the North Kunlun and South Kunlun Faults run and higher velocities in the mountainous regions between and to the north and south, where older rocks are generally exposed at the surface. From the S-velocity model, there is no evidence within the upper crust for major overthrusting of NE Tibet over the Qaidam basin. P-wave reflections indicate that the Moho lies at about 50 km depth beneath the southern Qaidam basin and that further south prominent boundaries exist within the deep crust beneath the NE Tibetan plateau. Following the controlled-source experiment, 50 broadband seismographs (35 from GIPP, Germany and 15 from SEIS-UK) were deployed for a period of one year along two profiles across the Kunlun mountains and the Jinsha river suture in northeast Tibet.

We study the underside reflections of precursors to SS waves at the lithosphere and the upper mantle beneath eastern Asia. By analyzing the SS bounce points we have been able to investigate the upper mantle discontinuities along a corridor that extends from the Aleutians to the Tibetan plateau passing through Kamchatka, the Japanese subduction zone and the North China craton. One of our aims was to investigate the interaction between the lithosphere and the mantle transition zone beneath different geotectonic units along this corridor and the interaction of geodynamic processes at different depths. In the analysis, we have used the short period content of SS waveform data and methods like CMP stack and migration techniques to acquire high resolution lithosphere and upper mantle images and to improve the lateral and depth resolution for the upper mantle discontinuities. By using a newly developed method we have been able to detect the presence of the continental Moho at different depths along this corridor. We show that the SS precursors provide high resolution images of upper mantle discontinuities such as the 410 and 660 km and the effects of the interaction between the subducted oceanic lithosphere and the mantle transition zone beneath the NW Pacific subduction zone. Furthermore, we show for the first time, that it is possible to create new possibilities to study shallower structures such as the Moho by using the SS precursors.

GPS displacement vectors show that Tibetan crust is squeezed in easterly direction by the northward motion of the Indian plate. The Sichuan Basin is resisting this stream and redirecting it towards Indochina. Seismic anisotropy shows that surface deformations continue to greater depth and indicate crust-mantle coupling. Here, we present results from a dense seismic receiver function profile from eastern Tibet across the Longmen-Shan Fault (LMS) into the Sichuan Basin. We find that the LMS extends down to at least 150 km and marks a sharp steplike boundary between the Tibetan and the Sichuan lithospheres (including a sharp step at the boundary between crust and mantle). That mode of collision between east Tibet and the Sichuan craton is thickening of the Tibetan lithosphere in contrast to subduction at the India-Tibet boundary. Furthermore we find that the mantle transition zone (MTZ, between 410 and 660 km depth in global average) is beneath the Sichuan Basin 30 km thicker (corresponding to 250-300 K lower temperature) than beneath the Sichuan Basin. The reason for this is unclear, as well as a possible connection between the change in MTZ thickness and the step of the lithosphere directly above. Receiver function data in eastern China make it unlikely that flat Pacific subduction is the cause of MTZ thickening below the Sichuan Basin, as it was indicated by tomography. We propose that thinning of the MTZ below eastern Tibet could be caused by dynamical suppression of the 410 discontinuity due to a vertical component of the eastern Tibetan escape flow.

Spatial length, time duration, and direction of an earthquake rupture are important parameters for an early warning of a potential tsunami. With different seismological methods namely polarization analysis of incoming compressional waves (P-waves), directivity effect, and wavelet transform these parameters are tried to estimate from recordings of broadband three-component-seismometers. One important requirement for a successful tsunami warning is a very fast (real time) investigation of seismograms. For some of the methods a dense station network and especially a wide backazimuthal distribution is necessary. The latter is a premise for the investigation of the directivity effect of an earthquake (in the literature this effect is often compared with a kind of doppler-effect). We show for some earthquakes e.g. Sichuan of May 2008, great Andaman of December 2004, and Pakistan of October 2005, that with a simple integration of regional and teleseismic recordings and subsequently plotting them sorted by the azimuth, stations can easily splitted into stations, from which the rupture went away and stations, which lie in the direction of the rupture. With this investigation, the question of the direction of the rupture can quickly be answered.

Seit Oktober hat Professor Rainer Kind die erste Seniorprofessur am GFZ inne. Die GeoForschungsZeitung befragte ihn zu der Zukunft von GEOFON und seinen Forschungsplänen.

Beginning in September 2006, a temporary network of 30 broadband and 45 short-period seismic stations has been set up on both sides of the Dead Sea Basin (DSB). During one and a half year of successful operation, data were continuously recorded in the field at 100 Hz and 200 Hz sample frequency for the broadband and short-period seismic stations, respectively. The raw data were converted to miniseed format and archived as full seed volume in the GEOFON data center of the GFZ. In the present work, the Receiver Function Method has been applied to the three component passive source data to investigate seismic discontinuities from the crust down to the upper mantle. Unusual negative phases at about 1s delay time have been observed at several stations in the Dead Sea region on the top of the assumed salt diapir. First preliminary receiver function analysis reveals a crustal thickness of about 30 -35 km in the investigated area and possibly low-velocity layer beneath the Moho. It also shows a basin which is possibly filled with salt about 10 km thick beneath the Lisan peninsula (Dead Sea).

We investigate whether high topography in southern Norway is associated with an anomalous upper mantle and we identify the western boundary of thick shield lithosphere. Several studies describe crustal structure in southern Scandinavia, whereas high-resolution information on upper mantle structures is sparse.We present relative P-wave travel time residuals (P-residuals) and preliminary tomography from southern Norway, southern Sweden and northern Denmark.We analyze distant earthquakes registered by seismological stations in projects CENMOVE, CALAS, MAGNUS and SCANLIPS together with selected TOR stations, and permanent stations in southern Sweden, southern Norway and Denmark. Station means of P-residuals corrected for topography and contributions from the crust varies by up to about 1 s across the study area.We associate early arrivals to the east of the Sorgenfrei-Tornquist Zone (STZ) and east of the Oslo Graben with thick shield lithosphere. Late arrivals observed in the Norwegian-Danish Basin southwest of the STZ are consistent with thinned lithosphere related to the basin formation. In southern Norway west of the Oslo Graben area, late arrivals indicate reduced P-wave velocity in the upper mantle and perhaps some regional isostatic buoyancy from the upper mantle. However, arrivals are early in the northern part of southern Norway, still in areas of high topography. Thus, a clear spatial correlation with areas of high topography is not observed. We identify the western boundary of thick shield lithosphere by interpretation of station means of P-residuals, together with the azimuthal dependence of single P-residuals in southern Scandinavia. We find this boundary to follow the STZ from the southeast into the northern part of Jutland. From there it proceed northwards. In southern Norway the western boundary of thick shield lithosphere is found around the Oslo Graben, proceeding to the northwest approaching the Norwegian coast.

While the Andean cordillera grab most of the seismological attention due to it’s active tectonics, the stable platform is of mainly importance in understanding what could be considered the normal, out of anomaly earth and, may help to understand what are the final and long term results from such a dynamic process like subduction and other types of convergent and divergent plate boundaries interaction. During the last 15 year the Brazilian Lithospheric Seismological Project (BLSP) has been operating more than 60 temporary three-component broadband seismological stations, collecting seismological data mainly in the Brazilian part of the platform. The stations are mainly distributed from 35°W to 60°W and from 10°S to 25°S, covering most of the Parana basin, Tocantins fold beld, Ribeira fold belt and the San Francisco craton. Beyond this central region, there are still some stations distributed over the northern Brazilian margin, covering parts of the Amazon craton and the Parnaiba basin. To complement our dataset we use data from the GT/CPUP station (Vila Florinda/PY FDSN/IRIS). The processing steps included event selection, rotation to LQT coordinate system using an automatic algorithm based on diagonalization of the coherence matrix (for P-wave receiver function only) and deconvolution of the Q by L component for P-wave receiver function and L by Q for S-wave receiver function. The profile images were made by stacking the resulted receiver functions by piercing points locations following pre-defined lines crossing the main tectonic units. At each profile we highlighted the desired Ps and Sp conversion phase for each of the discontinuities and its time readings and errors were estimated by bootstrapping the traces during the stacking procedure. For drawing the conclusions we compared the times each other and with theoretical times computed from the IASPEI91 model and models that presented a ± 5% change in the P- and S-wave mantle velocities. The most important results observed are: 1) A clear cratonic signature, consisting of higher wave velocities for the mantle under the cratons and normal (410km and 660km) depths for the discontinuities 2) Strong presence of the Nazca subducted plate near 410 and 660 km discontinuities under the Southern part of the Parana basin 3) Lack of variation in the Transition Zone thickness and in the mantle velocities due to the presence of the possible plume proposed in 1995 by Vandecar at the Northern Parana basin region and 4) A possible transition zone thinning near the Matiqueira complex, at the Ribeira fold beld, near the Atlantic passive margin.