SUMMARY The structure of the mantle beneath East Asia down to 800 km depth is investigated using full waveforms of seismic shear and surface waves. Epicentral distances are limited to less than 40°. In contrast with previous waveform inversions, we avoid ray‐theoretical or path‐integral approaches. Instead, we use (1) exact 3‐D waveform sensitivity kernels that correctly reflect off‐path sensitivity and the existence of Fresnel zones. We apply (2) an accurate 3‐D forward modelling technique based on a coupled‐mode, multiple‐forward‐scattering approach, allowing us (3) to iterate the inversion procedure through several 3‐D models and (4) to evaluate the true misfit between the data and the synthetics for the 3‐D model. Average lateral resolution of the model in regions with good path coverage is 400 km throughout the upper mantle. In the depth range from 100 to 250 km the lateral resolution even approaches 200 km. Since wave front healing is taken into account, the amplitudes of velocity perturbations are larger than in other tomographic models. Moreover, the waveform sensitivity kernels provide an intrinsic physical smoothing of the model, stabilizing the inversion. Finally, owing to the use of exact sensitivities, better resolution can be achieved with a given set of seismograms. Major features of the model are high‐velocity subducting slabs along the West Pacific subduction zones stagnating at the 660 km discontinuity, a strong low‐velocity zone between 80 and 250 km depth in the West Pacific backarc regions, a plume‐like low‐velocity feature beneath the southern tip of the Baikal rift zone extending into the transition zone, a low‐velocity region under the Tien Shan with connection into the transition zone and thick crust under Tibet reaching its maximum thickness of approximately 80 km close to the 35th parallel. The lithospheric mantle underneath southern Tibet is very fast indicating underthrusting of the Indian lithosphere. In contrast, the upper mantle beneath northern Tibet exhibits average‐to‐slow values from the Moho down to the 660 km discontinuity. Very high S velocities are again observed beneath the Tarim Basin. The high‐velocity mantle lithospheres under southern Tibet and the Tarim join beneath the Karakorum range at the western tip of the Tibet Plateau.

The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations Electronic supplementary material The online version of this article (https ://doi.org/10.1007/s1071 2-018-9472-4) contains supplementary material, which is available to authorized users. operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth.

S U M M A R YWe present a new method to calculate complete synthetic seismograms for a spherically symmetric earth model which uses neither eigenfrequencies and eigenfunctions nor an earth-flattening transformation. The response of the earth to a moment tensor point source is evaluated in the frequency domain for both spheroidal and toroidal motion by numerical integration of the appropriate system of ordinary differential equations with source term and summation over vector spherical harmonics. Attenuation is included by using complex elastic moduli. Owing to the discrete sampling of the response in the frequency domain, the numerical effort is proportional to the length of the desired time series for a fixed maximum frequency. This makes the method much more efficient than normal-mode calculations for higher frequency applications, where often seismogram lengths of 20 to 40 min are sufficient. Since the angular degree of the spherical harmonics provide a natural discretization in the wavenumber domain, spatial aliasing is unimportant. Time aliasing is suppressed by evaluating the response at complex frequencies with constant imaginary part.We have compared synthetic seismograms obtained by the new method with normal-mode seismograms up to a frequency of 20 mHz and achieve excellent agreement for all three components. The accuracy of the method is further corroborated by comparisons with real data up to a frequency of 200mHz. We tested the numerical scheme up to frequencies of 1 Hz and harmonic degrees of 12 000 and did not find any numerical instabilities. Incidentally, the approach sheds some light on how normal modes make up body waves.

[1] Regional seismic tomography provides valuable information on the structure of shields, thereby gaining insight to the formation and stabilization of old continents. Fennoscandia (known as the Baltic Shield for its exposed part) is a composite shield for which the last recorded tectonic event is the intrusion of the Rapakivi granitoids around 1.6 Ga. A seismic experiment carried out as part of the European project Svecofennian-Karelia-Lapland-Kola (SVEKALAPKO) was designed to study the upper mantle of the Finnish part of the Baltic Shield, especially the boundary between Archean and Proterozoic domains. We invert the fundamental mode Rayleigh waves to obtain a three-dimensional shear wave velocity model using a ray-based method accounting for the curvature of wave fronts. The experiment geometry allows an evaluation of lateral variations in velocities down to 150 km depth. The obtained model exhibits variations of up to ±3% in S wave velocities. As the thermal variations beneath Finland are very small, these lateral variations must be caused by different rock compositions. The lithospheres beneath the Archean and Proterozoic domains are not noticeably different in the S wave velocity maps. A classification of the velocity profiles with depth yields four main families and five intermediate regions that can be correlated with surface features. The comparison of these profiles with composition-based shear wave velocities implies both lateral and vertical variations of the mineralogy.

SUMMARY We present a new, S‐velocity model of the European upper mantle, constrained by inversions of seismic waveforms from broad‐band stations in Europe and surrounding regions. We collected seismograms for the years 1990–2007 from all permanent stations in Europe for which data were available. In addition, we incorporated data from temporary experiments. Automated multimode inversion of surface and S‐wave forms was applied to extract structural information from the seismograms, in the form of linear equations with uncorrelated uncertainties. The equations were then solved for seismic velocity perturbations in the crust and mantle with respect to a 3‐D reference model with a realistic crust. We present two versions of the model: one for the entire European upper mantle and another, with the highest resolution, focused on the upper 200 km of the mantle beneath western and central Europe and the circum Mediterranean. The mantle lithosphere and asthenosphere are well resolved by both models. Major features of the lithosphere–asthenosphere system in Europe and the Mediterranean are indentified. The highest velocities in the mantle lithosphere of the East European Craton (EEC) are found at about 150 km depth. There are no indications for a deep cratonic root below about 330 km depth. Lateral variations within the cratonic mantle lithosphere are resolved as well. The locations of kimberlites correlate with reduced S‐wave velocities in the shallow cratonic mantle lithosphere. This anomaly is present in regions of both Proterozoic and Archean crust, pointing to an alteration of the mantle lithosphere after the formation of the craton. Strong lateral changes in S‐wave velocity are found at the northwestern margin of the EEC and may indicate erosion of cratonic mantle lithosphere beneath the Scandes by hot asthenosphere. The mantle lithosphere beneath western Europe and between the Tornquist–Teisseyre Zone and the Elbe Line shows moderately high velocities and is of an intermediate character, between cratonic lithosphere and the thin lithosphere of central Europe. In central Europe, Caledonian and Variscian sutures are not associated with strong lateral changes in the lithosphere–asthenosphere system. Cenozoic anorogenic intraplate volcanism in central Europe and the circum Mediterranean is found in regions of shallow asthenosphere and close to changes in the depth of the lithosphere–asthenosphere boundary. Very low velocities at shallow upper‐mantle depths are present from eastern Turkey towards the Dead Sea transform fault system and Sinai, beneath locations of recent volcanism. Low‐velocity anomalies extending vertically from shallow upper mantle down to the transition zone are found beneath the Massif Central, Sinai and the Dead Sea, the Canary Islands and Iceland.