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Previously-published tomographic images show low-velocity anomalies (shear velocity up to 5% slow relative to the AK135 Earth model) in the asthenosphere beneath the southeastern margin of North America, including the Northern Appalachian (New England), the Central Appalachian (Virginia), and the Northern Gulf (Texas-Louisiana coast) Anomalies. Travel time anomaly ratios and attenuation indicate that they are thermal anomalies associated with mantle upwelling. We use teleseismic P and S wave differential travel times, as determined by cross-correlation of USArray data, and ratios of compressional-to-shear wave travel time fluctuations to characterize the South Coastal Anomaly (SCA), a fourth, weaker anomaly (about half as strong as these others) that stretches from Georgia to Virginia. P-wave tomography indicates that the SCA is about 800 km long in its north-south dimension and at least 300 km wide in its east-west dimension (its eastern edge is not imaged) and it is strongest (∆VP ≈ − 0.1 km/s) in the 100–250 km depth range. Its western edge strikes north-south, parallel to the edge of the Laurentian Craton (LC). The maximum P and S wave travel time anomalies of the SCA are 1.09 ± 0.05 (95%) s and 4.20 ± 0.10 (95%) s, respectively, relative to the LC. The ratio of P-to-S wave differential travel time anomalies is 3.84 ± 0.10 (95%), a value close to the value of ~3.3 predicted for a thermal anomaly and very different from the value of ~1.8 predicted for a compositional anomaly. The compressional velocity is up to 0.41 km/s slower than the LC, which corresponds to a maximum temperature difference of about 700 °C, using a sensitivity of 1713 K-s/km. In the shallow asthenosphere, the SCA appears distinct from the Central Appalachian Anomaly, being weaker in magnitude and more tabular in shape, but the two anomalies may merge below ~250 km depth. Our findings support the notion of the vigorous edge convection along much of the eastern continental margin.

We investigated the crustal structure at 34 stations using the H-κ stacking method and jointly inverting receiver functions with Rayleigh-wave phase and group velocities. These seismic stations are distributed along a profile extending across the Songpan-Ganzi Terrane, Qinling-Qilian terranes and southwestern Ordos Basin. Our results reveal the variation in crustal thickness across this profile. We found thick crust beneath the Songpan-Ganzi Terrane (47–59 km) that decreases to ~ 45–47 km in the west Qinling and Qilian terranes, and reaches its local minimum beneath the southwestern Ordos Block (43–51 km) at an average crustal thickness of 46.7 ± 2.5 km. A low-velocity zone in the upper crust was found beneath most of the stations in NE Tibet, which may be indicative of partial melt or a weak detachment layer. Our observations of low to moderate Vp/Vs (1.67–1.79) represent a felsic to intermediate crustal composition. The shear velocity models estimated from joint inversions also reveal substantial lateral variations in velocity beneath the profile, which is mainly reflected in the lower crustal velocities. For the Ordos Block, the average shear wave velocities below 20 km are ~ 3.8 km/s, indicating an intermediate-to-felsic lower crust. The thick NE Tibet crust is characterized by slow shear wave velocities (3.3–3.6 km/s) below 20 km and lacks high-velocity material (Vs ≥ 4.0 km/s) in the lower crust, which may be attributed to mafic lower crustal delamination or/and the thickening of the upper and middle crust.

We explore the shear-wave lithospheric velocity structure of the Eastern Caribbean and Northern Venezuela using ambient noise tomography with stations deployed around the study area. We construct cross-correlation functions from continuous seismic records, and measure phase velocities of fundamental-mode Rayleigh waves. These velocities are further projected onto 0.6°x0.6° phase velocity grids for each period between 5 s and 50 s. The pseudo-dispersion curve at each grid point is inverted for 1D shear velocity profiles by using a Markov Chain Monte Carlo scheme. The interpolated 3D velocity model shows that the mean shear velocity of the Eastern Caribbean lithospheric mantle is lower than the global average, which is in agreement with values reported in other large igneous provinces. We interpret that low velocities in the lithospheric keel are associated with an anomalous composition and/or an elevated thermal state; this gives the Caribbean plate a high buoyancy that determines the subduction polarities in the region. The results also indicate that: (a) the mantle beneath Northern Venezuela retains compositional anomalies related to extension processes of different ages; (b) the overriding of the Caribbean plate by the Great Antilles arc seems to be much slower than previously suggested; and (c) the localized volcanism in the center of the Lesser Antilles arc is related to asthenospheric flow through the tear induced on the subducted slab by major strike-slip faults.

The aim of this study was to establish a 3D shear-wave velocity model of the transition zone between the Eastern Alps and the Pannonian basin by means of ambient noise tomography. Datasets from permanent networks as well as past and recently deployed temporary networks of broadband seismic stations have been processed. Empirical Green's functions were estimated via cross-correlation of vertical component ambient seismic noise and further processed to obtain Rayleigh-wave group-velocity dispersion curves. They were directly inverted for shear velocities through a wavelet-based sparsity-constrained tomography method avoiding the intermediate step of constructing 2D group velocity maps. A horizontal resolution of 0.2° in the upper crust and 0.3°–0.5° in the lower crust was achieved. Our upper crustal shear velocity model revealed low velocities in the sedimentary depocenters and high velocities below the surrounding mountains. However, at greater depths (24–29 km), high shear velocities beneath the basins suggest crustal thinning accompanied by mantle updoming. An extremely deep low velocity anomaly was mapped beneath the Vienna basin, which we argue is caused by either sediment transfer to the lower crust; ductile deformation suggested by seismic anisotropy; or the presence of fluids.

We study shear wave velocity structure of the crust beneath the Andaman Island through joint inversion of the teleseismic receiver function and Rayleigh wave group velocity measurements from 10 broadband seismographs over the Island. The group velocities in the periods from 5 to 21 s are obtained using cross-correlation of six month's ambient seismic noise data recorded by these seismic stations. Joint inversion results show ~ 2 to 6 km thick subsurface low shear velocity ( Vs ~ 1.3–2.5 km/s) layer followed by a 12–14 km thick layer of silicic material (average Vs ~ 3.5 km/s). The lower crust is mapped as an 8–12 km thick mafic layer with Vs ~ 4.0 km/s. Uppermost mantle shear wave velocity is ~ 4.55 km/s. The near-surface low-velocity layer is interpreted as the Andaman flysch sediments. The crustal thickness beneath the Andaman Island varies from ~ 24 km in the north to ~ 32 km in the south. The shear wave velocity-depth results show that the crustal structure beneath the Andaman Island is akin to continental crust , possibly the Burma continental crust. The subducting Indian plate may lie down below this overriding plate.

Fault permeability is an important parameter for understanding the occurrence of natural hazards and evaluation of natural gas and oil reservoirs. In this study, effects of shear velocity on the permeability perpendicular to the shear zone formed after large shear displacements are revealed for silica sand. To this end, ring-shear experiments were performed for four shearing velocities under conditions of high effective normal stress. As observed, post-shear permeability values under effective normal stresses of 1 and 2 MPa demonstrated a reduction of two and one order of magnitude, respectively, along with negative velocity dependence. However, no significant difference in permeability was observed under exceeding 3 MPa. In addition, the shear-zone structure under high shear velocity and higher effective normal stress demonstrated existence of a grain-crushed zone, which closely corresponds to reductions in pore-diameter and grain size. Findings of this study indicate the instability mechanism of landslides related to groundwater movement and facilitate understanding of resource systems controlled by natural faults.

A grain based Distinct Element Method and its embedded Grain Based Method are used to simulate the fracturing processes leading to shear rupture zone creation in a calibrated massive (non-jointed) brittle rock specimen deformed in direct shear under constant normal stiffness boundary conditions. Under these boundary conditions, shear rupture zone creation relative to the shear stress versus applied horizontal displacement (load–displacement) curve occurs pre-peak, before the maximum peak shear strength is reached. This is found to be the result of a normal stress feedback process caused by the imposed shear displacement which couples increases in normal stress, due to rupture zone dilation, with shear stress, producing a complex normal-shear stress-path that reaches and then follows the rock's yield (strength) envelope. While the yield envelope is followed, the shear strength increases further and shear stress oscillations (repeated stress drops followed by re-strengthening periods) in the load–displacement curves occur due to fracture creation as the rupture zone geometry smoothens. Once the maximum peak strength is reached (after a series of shear stress oscillations) the largest stress drops occur as the ultimate or residual shear strength is approached. The simulation results provide insight into the fracturing process during rupture zone creation and improve the understanding of the shear stress versus applied horizontal displacement response, as well as the stick-slip behaviour of shear rupture zones that are being created under constant normal stiffness boundary conditions.

A new evaluation of the elastic thickness (Te) structure of the Indian Shield, derived from isotropic fan wavelet methodology, documents spatial variations of lithospheric deformation in different tectonic provinces correlated with episodic tectono-thermal events. The Te variations corroborated by shear velocity, crustal thickness, and seismogenic thickness reveal the heterogeneous rheology of the Indian lithosphere. The thinned, attenuated lithosphere beneath Peninsular India is considered to be the reason for its mechanically weak strength (

Trade-off between the depth of an interface and the average velocity above the interface is well known in receiver function inversion. To resolve model ambiguity, surface wave dispersion data, which are sensitive to vertical shear velocity average, are commonly combined with P receiver functions in the inversion. In this paper, we design a joint inversion scheme using the neighborhood searching algorithm to solve shear velocity structure of the crust and uppermost mantle with receiver function and surface wave dispersion data. Two sets of stretched splines are implemented in the inversion to obtain smooth velocity profiles, separated by a specifically defined Moho discontinuity. We apply this method to the dense Hi-CLIMB seismic array in the central Tibetan Plateau (TP). The Indian crust is observed to subduct and underplate the Tibetan crust between the Yarlung-Zangbo suture and the Bangong-Nujiang suture, at the latitude of about 31.5°N. The crust thickens from about 50 km below the Indian foreland to over 75 km south of Bangong-Nujiang suture and turns shallower at around 65 km under the Qiangtang block. We identify two zones with complicated Moho structure beneath the northern Lhasa block and southern Qiangtang block, indicating highly deformed Moho morphology, and beneath the Himalaya block associated with the underthrusting of the Indian Plate, respectively. A low velocity zone is present in the mid-crust in most parts of the profile under the TP with up to more than 10% velocity reduction. The low velocity structure is not continuous, forming discontinuous patches rather than channels, calling for a revision of the channel flow model.

The formation of the Gulf of California has been related to the cessation of subduction of the Guadalupe and Magdalena microplates. Various studies have identified features that point to the presence of a slab remnant beneath the Baja California peninsula, but its depth range and lateral extent remained unclear. In this study we used surface wave phase velocity and receiver function data of NARS-Baja stations around the Gulf of California to better constrain the location of the slab. For stations in central and southern Baja California the shear velocity models show an upper mantle high-velocity layer with its top in the depth range from 115 to 135km and a thickness varying between roughly 40 and 60km. These high-velocity anomalies are interpreted as subducted slab remnants. In contrast, the models for the northern peninsula show no slab signature. This change directly correlates with the variation in relative motion between the Baja California peninsula and the Pacific plate as measured by GPS data. It is inferred that the stalled slab fragments beneath the peninsula produce strong coupling between Baja California and the Pacific plate. The shear velocity models for stations on the Mexican mainland show a layer of higher velocities above a low-velocity upper mantle. In the North, the low-velocity mantle, starting at a depth of 40km, is associated with upwelling as suggested by previous studies. Further south, the transition from higher to lower mantle velocities occurs around 80km depth, which is a typical value for the lithosphere-asthenosphere boundary. Furthermore, the models show strong crustal thinning towards the gulf, both from the peninsula as well as from the Mexican mainland.

We investigate the time evolution of 3D numerical models of convection in the upper mantle which incorporate both plate motions and thick continental lithosphere. The resultant flow in the upper mantle is driven by a combination of bottom heated convection and applied shear velocity boundary conditions that represents plate motion. Both the plate velocity and continental lithosphere topography are varied in a way to assess the general influence of 3D geometry as well as a more specific tectonic analogue of the Australian plate. Transient thermal events offshore of the trailing passive margin are observed and include plume migration, boundary layer instability growth at the passive margin and variations in surface heat flux. The geometry and plate velocity both play a significant role in controlling the magnitude and duration of these transient features. In particular, there are large differences between the different models in the oceanic region downstream of the trailing edge of the continent. At near-stationary plate speeds, cold linear downwelling sheets propagate away from the 3D edge of the continent, with regions offshore of the continents central axis localising hot cylindrical upwelling plumes. At very fast plate speeds, the shear flow is dominated by the plate motions. This causes regions neighbouring the trailing edge of the continent to produce broad, hot upwellings and the cold linear sheets to migrate around the continent. At moderate (2 cm/yr) plate speeds, oceanic lithosphere neighbouring the passive margin along the trailing edge of the continent is buffered by cold, downwelling instabilities sinking along the edges of the continental lithosphere. Such neighbouring regions are subjected to larger heat flux than for regions distant to the passive margin, yet also record smaller and less variable vertical surface velocities. These dynamics have implications for volcanism and surface topography, for which 3D aspects play a significant role.

This paper investigates the shear velocity structure under the northern East Pacific Rise at the latitude range of 9–18°N, using intermediate-period Rayleigh and Love waves. The selected ocean-bottom seismic records provide source–receiver paths that ideally constrain the lithospheric mantle structure beneath the southern Rivera plate and the Mathematician paleoplate. The Rayleigh wave data infer a relatively thin (∼ 30 km) lithosphere under the eastern side of the present-day East Pacific Rise. The associated shear velocities are consistent with existing models of oceanic mantle beneath this region, and the estimated plate age of 2–3 million years agrees with results from magnetic dating. The west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank, and such structural differences suggest the presence of a relatively old Mathematician paleoplate. The discontinuous change in mantle structure across the East Pacific Rise spreading center are observed in both isotropic and anisotropic velocities. The young oceanic lithosphere east of the rise axis shows strong polarization anisotropy, where the dominant orientation of crystallographic axes roughly parallels the spreading direction. However, the western flank of the rise axis is approximately isotropic, and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation, propagation and dual-spreading on and around the Mathematician paleoplate.

We have measured P- and S-wave velocities on two amphibolite and two gneiss samples from the Kola superdeep borehole as a function of pressure (up to 600 MPa) and temperature (up to 600 degrees C). The velocity measurements include compressional (Vp) and shear wave velocities (Vs1, Vs2) propagating in three orthogonal directions which were in general not parallel to inherent rock symmetry axes or planes. The measurements are accompanied by 3D-velocities calculations based on lattice preferred orientation (LPO) obtained by TOF (Time Of Flight) neutron diffraction analysis which allows the investigation of bulk volumes up to several cubic centimetres due to the high penetration depth of neutrons. The LPO-based numerical velocity calculations give important information on the different contribution of the various rock-forming minerals to bulk elastic anisotropy and on the relations of seismic anisotropy, shear wave splitting, and shear wave polarization to the structural reference frame (foliation and lineation). Comparison with measured velocities obtained for the three propagation directions that were not in accordance with the structural frame of the rocks (foliation and lineation) demonstrate that for shear waves propagating through anisotropic rocks the vibration directions are as important as the propagation directions. The study demonstrates that proper measurement of shear wave splitting by means of two orthogonal polarized sending and receiving shear wave transducers is only possible when their propagation and polarization directions are parallel and normal to foliation and lineation, respectively. (c) 2005 Elsevier B.V. All rights reserved.

The shear wave velocity structure beneath three southern African stations, Lusaka (LSZ), Lobatse (LBTB) and Boshof (BOSA) were estimated using the time domain inversion of stacked teleseismic receiver functions. Broadband teleseismic 3-component waveform data were used in a source equalisation procedure to estimate radial and transverse receiver functions for each station. The radial receiver functions were stacked according to the following criteria, an azimuthal interval of ±15°, similar ray parameter and shape. For the shield-based stations BOSA and LBTB simpler receiver functions than for LSZ, which is located in the Irumide belt, were obtained. The lateral variation in receiver functions with azimuth as observed at each station stems from lateral heterogeneities beneath each station. The velocity models were presented as P wave velocity models. From these models, the crust mantle transition zones beneath LSZ and BOSA were determined at depths of about 37–44 km and 34–38 km respectively. For LBTB, the northeast quadrant velocity model displayed a clear mantle-continent transition zone in the depth range 40–45 km, whilst the Moho depth in the southern quadrants is not as clear. Beneath all the stations, we observed a low velocity zone, which appears to correlate with the cratonic velocity structure. This feature is consistent with crustal structure results obtained in other cratonic or shield-based crustal studies. The results in this study contribute crustal structure information, which has been lacking at BOSA, LBTB and LSZ.

A dispersion analysis of Rg waves generated by local earthquakes surrounding the Alboran Sea (Western Mediterranean) has been undertaken to obtain its shear-wave velocity structure at shallow depths. We have used single-component short-period stations belonging to the Regional Seismic Network of Andalucia and the Spanish National Seismic Network. Our database includes seismograms generated by 18 earthquakes that occurred in the area during the period of 1992–95. The seismic events, with magnitudes between 2.9 and 4.9 and focal depths ranging from 2.7 to 12 km, were recorded at 13 stations at distances between 91 and 245 km from the source. We have analysed a total of 20 source-station Rg-wave paths. These seismic trajectories across the Alboran Sea provide irregular path coverage due to their geographical location. Despite sparse sampling the data collected have been processed with the help of digital filtering and group velocity dispersion curves have been obtained. The path group velocities vary from 1.21 to 1.91 km s −1 within the 1.7–5.8 s period interval. Then using a generalised inversion approach we have obtained 1D shear-wave velocity models for all source-station paths. Inversion for shear velocity structure gives velocity profiles down to a depth of 5 km. The shear-wave velocities range between 0.7 and 3.2 km s −1 within the standard deviation band of 0.05–0.17 km s −1 , and show significant variations from each other in the region of the Alboran Basin. We have applied an imaging technique aimed at volumetric modelling and data visualisation and we hereby present the tomographic results based on ray-path seismic velocities that were obtained for the basin. We have got an overall view of the sedimentary cover of the area regarding its geometry and S-wave velocity structure at very shallow depths (0–5 km). Although the relationship between lateral change in Rg dispersion and geologic structure may not be straightforward, we have observed a good correlation between those changes and surface geology.

The NARS-DEEP project involves the deployment of broadband seismological stations in Russia, Belarus and the Ukraine. Six stations were installed in 1995, two in 1997, and more stations were to be installed from 1998 onwards. The NARS-DEEP project was initiated as a temporary deployment, but funding from the European Community enabled the stations to become permanent. In this paper we present first results of the NARS-DEEP project. A surface waveform inversion for the upper mantle structure along a profile from Egypt to Spitsbergen shows evidence for strong variations in the shear-velocity structure for the different tectonic units. The most striking features of the model comprise strong lithospheric anisotropy beneath the Eastern Mediterranean and a lithospheric thickness of approximately 200 km beneath the shield areas. The crustal structure beneath the seismic station in St. Petersburg was investigated using the receiver function method. The results of a Monte Carlo inversion for the receiver functions of this station show evidence for a sedimentary layer with a thickness of less than 1 km overlying an upper crustal layer extending to a depth of approximately 16 km. The Moho depth cannot be resolved from the receiver functions of this station.

Constitutive relations for an isotropic poro-power-law fluid are proposed in which the effective viscosities in both shear and dilation have the same power-law dependence on the second invariant of the deviatoric stress alone, but the viscosity in dilation is 1/ν times the viscosity in shear. The shear rate is otherwise proportional to the deviatoric stress and the dilation rate to an effective mean stress. The behavior may either involve Darcy flow of a pore fluid whose viscosity is much less than that of the solid matrix, or involve dissolution, diffusive transport, and precipitation of a soluble phase, as in pressure-solution. Linearized relations for small additional rate-of-deformation and stress superposed on a basic-state flow are obtained. These are used to treat the deformation due to a shallow, narrow indentation at the interface between a layer and an adjacent medium when both undergo bulk uniform layer-parallel shortening or extension. If the layer, the medium, or both, are nonlinear fluids with large stress exponent, shear-band like structures, extending from the indentation, and `reflecting' from any weak, slipping interface, occur in both the instantaneous velocity field and in the strain field. Since the materials considered have constant and uniform properties — e.g., they do not exhibit strain-softening — these features leave no imprint in the medium. They persist over mean strains of 10–20%, but are, like the indentation, ephemeral. It is hypothesized that localization due to an interfacial irregularity of this sort would produce bona fide shear bands if the material were strain-softening. The development of shear bands is enhanced if the adjacent medium has a large stress exponent, or if it is a poroviscous fluid with low resistance to dilation. In a poroviscous medium, dilation is concentrated in paired positive and negative lobes at the terminations of shear bands in the adjacent layer. The development of shear bands in a poroplastic layer is mildly suppressed, relative to that in an incompressible layer. Dilation is concentrated in paired loci at shear band terminations, with weaker, paired bands of positive and negative dilation on either side of the shear zone.

Heat flow density (HFD) and thermal gradient calculated on the basis of oil well data in the Rif vary from 50 to 90 mW/m 2 and from 20 to 50°C/km, respectively. Short-term variations in the west can be attributed to water circulation and lateral heat conductivities contrast along the Pre-Rif thrusting front and at the limits between the main structural units (the Gharb basin, the South Rifian ridges and the Pre-Rif nappe). High HFD and thermal gradient values are determined in the southwest of the study area. This zone extends the central Moroccan massif which is well known by its high thermal manifestations. The External Rif shows a tendency of increasing HFD toward northeastern Morocco and the Alboran Sea. In agreement with the geophysical observations (electrical conductive structures, great negative Bouguer anomaly, shear velocity attenuation, high upper mantle P-velocity), the thermal structure of the External Rif would be a consequence of the presence at subcrustal depths of hot and low-density asthenospheric material overlying a high-velocity lithospheric body beneath the Rif-Betic belt.

The shear velocity structure of the Indian lithosphere is mapped by inverting regionalized Rayleigh wave group velocities in time periods of 15-60 s. The regionalized maps are used to subdivide the Indian plate into several geologic units and determine the variation of velocity with depth in each unit. The Hedgehog Monte Carlo technique is used to obtain the shear wave velocity structure for each geologic unit, revealing distinct velocity variations in the lower crust and uppermost mantle. The Indian shield has a high-velocity (4.4-4.6 km/s) upper mantle which, however, is slower than other shields in the world. The central Indian platform comprised of Proterozoic basins and cratons is marked by a distinct low-velocity (4.0-4.2 km/s) upper mantle. Lower crustal velocities in the Indian lithosphere generally range between 3.8 and 4.0 km/s with the oceanic segments and the sedimentary basins marked by marginally higher and lower velocities, respectively. A remarkable contrast is observed in upper mantle velocities between the northern and eastern convergence fronts of the Indian plate. The South Burma region along the eastern subduction front of the Indian oceanic lithosphere shows significant velocity enhancement in the lower crust and upper mantle. High velocities (approximate to 4.8 km/s) are also observed in the upper mantle beneath the Ninetyeast ridge in the northeastern Indian Ocean.

Crustal structure in the Lutzow–Holm Bay region (LHB), East Antarctica, is studied by analyzing seismic waveforms derived from records in the vicinity of Syowa Station (SYO; 69.0°S, 39.6°E). One-dimensional crustal models for shear waves, in particular, are obtained in order to investigate crustal heterogeneity. Radial receiver functions developed from teleseismic P-waveforms of broadband seismographs at SYO in 1990–1993 are used in the time domain inversion. As the starting model in the receiver function inversion, a crustal attenuation model (Qs) for shear waves from local earthquakes of telemetry networks in 1987–1989 is derived by shifting the lapse time of the coda part of S-waves. Lateral heterogeneity is investigated by analyzing several backazimuth groups; namely the 50°–100°, 120°–160°, 210°–250° and 300°–360° sectors are investigated. Velocity changes are recognized as a sharp Moho at 36–38 km depth in the continental areas in the 50°–100° and the 120°–160° sectors; in contrast smooth variation of crustal velocities is revealed together with transitional Moho in the bay backazimuths in the 210°–250° and the 300°–360° sectors. In the continental backazimuths, a difference in crustal velocities is recognized between metamorphic terrain of granulite facies and the granulite–amphibolite transitional zone. Shear velocity models are compared with crustal reflectivity derived from the analysis of refraction data on the Mizuho Plateau. The reflective layers are found at depths of 24–45 km and appear to be related to the Bouguer gravity anomalies. By correlating the seismic models of crustal structure with other geophysical and geological evidence, the crustal evolution in LHB can be explained in relation to the regional metamorphism at 500 Ma and the last break-up of Gondwana at 150 Ma.

Short period (SP) Rayleigh wave dispersion was determined along linear seismic arrays in southern Sweden, using data from the Fennolora and the Eugeno-S seismic refraction projects on the Baltic Shield. The study area consists of crystalline and metamorphic igneous rocks of Precambrian age and has essentially no sedimentary cover. The dispersion curves were classified into dispersion regions and the regional (background) shear velocity structure was determined down to 2–3 km or more. Noise studies were undertaken in order to separate trends caused by the heterogeneous medium from the experimental uncertainties. It was shown that standard errors of the data in the 1–3 Hz band were predominantly significantly smaller than the conventional estimate based on the standard deviation. Thus, the estimates of the shear velocity resolution could be significantly improved, Q-values were determined from the SP Rayleigh waves in each dispersion region. In a broad sense similar Q-values were found in the area, except the northwestern corner that had significantly lower values. Here the lowest shear velocities were also found. However, a clear trend from higher Q in the southeast to lower Q in the northwest could be seen in the 1.7–3.3 Hz averages. The Q-values were inverted to obtain preliminary Qβ-structures. The Qβ-value of the upper km of the crust was 110 in the dominating part of the area and 52 in the northwestern corner. The lowest Q-values could be modelled with the same Qβ-structure below 1 km as in the other parts of the area.

Fundamental-mode surface wave generated by twelve earthquakes, which occurred in northeastern India and nearby regions and were recorded at the Shillong (SHL) and Chiengmai (CHG) seismic stations are used to determine the shear wave velocity structure beneath these regions. The Frequency Time Analysis method is used to determine the group velocities for periods ranging from 4 to 50 s for fundamental-mode Rayleigh and Love waves. A high shear wave velocity (4.2–4.7 km s −1 ) is estimated in the lower 30–34 km of the crust. Crustal thickness is found to vary from 36 to 56 km with an overlying 2–4 km sedimentary thickness of shear wave velocity of 2.55–2.75 km s −1 . The shear wave velocity in the upper 10 km of crust is 3.5–3.7 km s −1 below the sedimentary layer. The inferred high shear velocity for the lower crust beneath these regions suggests an oceanic affinity and they are different from the Indian shield structure. The lower crust must have an oceanic origin as derived from the reminiscent of a certain oceanic lithosphere. The available data do not permit us to estimate the upper mantle structure precisely; however, it shows a higher upper mantle shear velocity of 5.1–5.3 km s −1 . This may be indicative of active tectonism beneath these regions in the uppermost mantle. The Moho boundary is not sharply defined here. The increase in crustal thickness may be due to the collision of the Indian and Eurasian plates in the north and subduction of the Indian plate beneath the Burmese Arc in the east.

The shear velocity structures of the different tectonic provinces of the Arabian Peninsula has been studied using surface wave data recorded by the RYD (Riyadh) station. The inversion of Rayleigh wave group velocities indicates that the Arabian shield can be modeled by two layers, each of which is 20 km thick with a shear velocity of 3.61 km/s in the upper crust and 3.88 km/s in the lower crust. The underlying upper mantle velocity is 4.61 km/s. Inversion of both Love and Rayleigh waves group velocities shows that the Arabian platform upper and lower crusts are comparable in their thicknesses to those of the shield, but with shear velocities of 3.4 and 4 km/s, respectively. The upper mantle velocity beneath the platform is 4.4 km/s and the average total thickness of the crust is 45 km.

A tentative tomography of Iberia based on broadband surface wave data is performed for the first time. In this paper we have complemented a previous study of the northern half of the Iberian Peninsula with a study of the southern half of the peninsula based on a detailed analysis of Rayleigh wave dispersion. Now we present the first shear velocity contour maps at different subcrustal depths. Quality digital records provided by the NARS array have been used. Standard techniques, as multiple filtering and time-variable filtering, are employed to efficiently remove higher mode interference and improve isolation of the fundamental mode Rayleigh wave from the seismograms, and thus to calculate the interstation Rayleigh wave group velocity. Frequency-domain Wiener deconvolution is used to determine the interstation phase velocity. We perform simultaneous inversion of phase and group velocity dispersion data by means of the stochastic inverse operator. The inversion results previously reported for the northern Iberian region together with the results obtained here are used for 3-D mapping of shear wave velocity over the Iberian Peninsula. Lateral variation in velocity at five depth intervals chosen in agreement with the theoretical earth models determined by joint inversion, is displayed for the lithosphere and asthenosphere of Iberia.

Propagation of 0.2–2.5 s short-period Rayleigh-waves across a part of northwestern Iberia is investigated. Analysis of a seismic profile line with recorded seismograms up to distances of 70 km from the shot-point, provides group-velocities and attenuation coefficients of the fundamental mode. First higher-mode group-velocity has been obtained for only one of the studied cases. The studied region has been divided into two subrogions, the northwestern and the southeastern side from the shot-point. Inversion procedures applied to the velocity and attenuation data yield the shear velocity and the Q−1β models up to a depth of about 1.5 km for the NW, and 2.4 for the SE side. From the shear-wave obtained models corresponding to the NW and to the SE sides, it is possible to infer the existence of some degree of lateral variation of S velocity. The NW side presents velocities varying between 1.8 km · s−1 (at the surface) and 3.3 km · s−1 (at 1.2 km depth). The velocities in the SE model, for the same depths, are 2.2 and 3.4 km · s−1, respectively. Using only the fist six traces of the SE side, it is possible to infer a low-velocity region located between 0.4 km and 0.7 km depth. It seems that the velocities are higher in the complex geological region of the SE side than in the NW one, which is in agreement with P velocity models found by others. From the tentative anelastic attenuation coefficients, Q−1β models have been inferred for both sides of the seismic refraction profile. Although the obtained Q−1β models are somehow different in shape, the maximum Q−1β value is about 0.05 in both cases.

The physical properties of a sequence of Paleozoic sedimentary rocks have been examined in detail, with an emphasis on laboratory measurements of density, shear wave velocity, shear wave splitting, and Vp/Vs ratios. Seismic properties of 147 cores from 49 rock samples collected from the Thorn Hill sedimentary sequence of eastern Tennessee are examined in terms of implications for future seismic studies in the southern Appalachians. The shear wave velocities of these rocks are strongly influenced by the relatively high shear wave velocity of quartz. Shear wave velocity anisotropy is present in most of the lithologic groups; it is highest in the shales while being almost insignificant in the dolostones. The related phenomenon of shear wave splitting occurs to some degree in all of the lithologies studied and at high pressures originates from mineral orientation. Splitting, due to preferred mineral orientation, is most prominent in the shales, but also is significant in some of the carbonates. Compressional to shear velocity (Vp/Vs) ratios of approximately 1.82 (dolostones) and 1.95 (limestones) effectively characterize the carbonates while other lithologies display wider ranges of Vp/Vs, primarily due to the influence of accessory minerals such as quartz. Densities of the sample suite range from 2.34 g/cm3 (shale) to 2.86 g/cm3 (dolostone). Using average data for each lithologic group to calculate normal-incidence reflection coefficients, significant differences in the shear and compressional reflectivity of hypothetical interfaces are found. Normal-incidence shear and compressional wave synthetic seismograms approximating the subsurface reflectivity of the entire Thorn Hill section indicate that three zones of high amplitude reflections would be seen on reflection records obtained over this 3327-m-thick sequence. Overall, the shear and compressional synthetics are similar in appearance. Differences are seen at some interfaces in the Mississippian-Devonian interval, which are more reflective to shear waves, and in the Ordovician Martinsburg Formation, which appears more reflective to compressional waves.

Surface wave dispersion for the Baltic Shield area has been investigated through analysis of phase velocities up to periods of about 250 s for the fundamental Rayleigh mode and about 80 s for the first two higher modes. This has enabled investigation of the lithosphere-asthenosphere system and deeper regions down to about 400 km. The shear wave velocitydepth relationship obtained from the inversion of dispersion data for the paths COP-KEV/COP-KRK can be considered as representative of an average model for the Baltic Shield. Moreover the inversion of dispersion data supplemented by previous results from the Scandinavian area suggest the presence of significant lateral heterogeneity down to depths of about 350 km moving from the older Precambrian shield (COP-KEV/COP-KRK) to the peripheral area (NUR-COP). Models with small, if any, differences in average shear velocity are consistent with the data in the depth range 350–450 km for the regions studied.

Studies of the mechanical deformation of the earth's mantle are traditionally made under the assumption of Newtonian flow. There is much evidence, however, that the relationship of stress to deformation rate in mantle materials at high temperature and pressure is not linear, but rather a power-law relationship. Thus an antiplane model of a plate sheared from below and terminated by a transform fault was devised to investigate the consequences of an upper mantle with a power-law constitutive relationship. Applying finite-difference numerical techniques to this two-dimensional non-linear problem, several conclusions were drawn: 1. (a) For all situations examined, the non-Newtonian strain-rate fields are more concentrated near the fault boundary than the Newtonian ones. 2. (b) For velocity fields imposed on the bottom of the plate, as the stress exponent n increases, the velocity and strain-rate are less dispersed as they propagate up through the plate. As n → ∞ the fields at the surface become the same as those imposed at the bottom. 3. (c) For the case of shear stress imposed along the bottom, the shear stress parallel to the fault changes little with changing n. 4. (d) For a velocity bottom condition, the shear stress parallel to the fault becomes more uniform throughout the plate with increasing n. 5. (e) For a shear stress bottom condition, the velocity and strain-rate fields become concentrated near the fault as n increases. As n → ∞ all the strain is at the fault boundary. 6. (f) A multilayer model with velocity bottom condition deforms much the same as a single-layer model. 7. (g) The time-dependent case is not geophysically significant. The implications of these results for an earth exhibiting power law creep are: 1. (1) The length scale over which surface fields vary is less indicative of the depth scale of deformation as n increases. 2. (2) The strain field cannot be more concentrated at the surface than at depth for a velocity bottom condition. 3. (3) For shear stress bottom conditions, even broad spatial variations in the stress or strain fields in the mantle can concentrate strain near the fault. This method of analyzing non-linear flow problems can be applied to a wide variety of tectonic situations, such as post-glacial uplift.

The source mechanism of the Saitama earthquake (36.07°N,139.40°E, M s = 5.4) of July 1, 1968, is studied on the basis of P-wave first motion, aftershock, long-period surface-wave data and low-magnification long-period seismograms recorded in the nearfield. A precise location of the aftershocks is made using P and S—P time data obtained by a micro-earthquake observatory network. The synthetic near-field seismograms based on the Haskell model are directly compared with the observed near-field seismograms for wave form and amplitude to determine the dynamic fault parameters. The results obtained are as follows: source geometry, reverse dip slip with considerable right-lateral strike-slip component; dip direction, N6°E; dip angle 30°; fault dimension, 10 × 6 km 2 ; rupture velocity, 3.4 km/sec in the direction S30°E; average dislocation, 92 cm; average dislocation velocity, 92 cm/sec; seismic moment, 1.9 · 10 25 dyn-cm; stress drop, 100 bar. The effective stress is about the same as the stress drop. For major earthquakes in the Japanese Islands, the dislocation velocity, 〈. D 〉, is found to be proportional to the stress drop, σ. This relation can be expressed by 〈. D 〉 ∼- ( β / μ ) σ , where β is the shear velocity and μ is the rigidity. This result has an importance in engineering seismology because the stress drop scales the seismic motion in the vicinity of an earthquake fault.

Rayleigh wave group and phase velocities and attenuation coefficients are investigated in the 15–60-s period range for earthquakes occurring in the European area and registered at European stations. Observed group and phase velocities show clear differences in the period range 20–40 s, whereas attenuation coefficients are differentiated from 45 s to larger periods. From the shape of dispersion and attenuation curves, two broad zones have been isolated and designated as Western Europe and Southeastern Europe. Although some scatter is present, specially for attenuation, the data suggest that in general the shear velocity and Q β values are higher for Southeastern Europe than for Western Europe. For Southeastern Europe there is a channel of low velocity and low Q β , apparently correlated, located at the lower crust: in both regions there is a channel of low velocity and low Q β values located at the uppermost mantle. In each case there also exists a channel of high Q β values located at the lower crust but at slightly different depths.

Several recent measurements of Rayleigh wave dispersion in the Pacific and Atlantic oceans have demonstrated conclusively that phase and group velocities in the period range 20–200 seconds increase systematically with increasing age of the sea floor. The increase in velocity can be explained by the growth and cooling of the oceanic lithosphere as it moves away from the mid-ocean ridges. If the base of the lithosphere is defined as the top of the low-velocity zone, the average lithospheric thickness can be no more than 25 km for a region from the ridge axis to an isochron of 5 million years. Within 10 m.y. after formation, the lithosphere reaches a thickness of about 60 km. As the mantle continues to cool, the thickness gradually increases, reaching a maximum of about 90 km in old ocean basins. In addition to the slow growth after 10 m.y., there is a gradual increase in shear velocity within the lithosphere from about 4.4 km s−1 at 10 m.y. to 4.6 to 4.7 km s−1 beneath old sea floor. The increase has also been found in regional studies of Sn velocity in the Atlantic. Beneath the lithosphere extending to a depth of about 175 km, there is a zone of very low shear velocities apparently associated with partial melting. There is a significant increase in the shear velocity within this low-velocity zone with increasing age. A narrow zone of low Q and increased partial melting has been outlined directly beneath the ridge axis by observations of lateral variation in attenuation of longperiod S-waves and Rayleigh waves. This zone is roughly coincident with the elevated region of low compressional and shear velocities under sea floor which is less than 10 m.y. old. The seismic data are consistent with a model of the oceanic lithosphere as a thermal boundary layer growing at the expense of a laterally homogeneous asthenosphere. Substantial partial melting occurs at shallow depths beneath the ridge axis where the asthenospheric mantle material rises near the surface. The boundary-layer model is consistent with the change in elevation of the sea floor with age and with recently revised estimates of oceanic heat flow.

We present a summary of the available information on Rayleigh-wave dispersion data for the Fennoscandian region. The observations have been combined to produce regional dispersion relations which have then been subjected to the “hedgehog” inversion procedure. The results are presented on a map outlining the thickness of the lid and the shear velocities in both the lid and the asthenosphere channel. Lid thickness up to around 135 km is found in the Bothnia-north-central Finland area with, if any, weak shear velocity contrast to the underlying layer. The surrounding areas are characterized by lid thickness up to around 75 km; a stronger low-velocity zone to lid contrast may be found in the Caledonian and Baltic Sea area (0.25÷0.45 km/s). Taking into account Moho depth data and the aforementioned results, a map of the lithosphere-asthenosphere system was derived.

Surface waves recorded at Dumont D'Urville (DRV) in Terre Adelie have been analyzed to determine the upper mantle structure between Antarctica and the Southeast Indian Ridge. Rayleigh wave group velocities have been determined in the period range 15–60 s by using the single station method applied to earthquakes located on the Southeast Indian Ridge. An 8% decrease of group velocity is observed when passing from paths coming from the north of DRV to those coming from the east. Variations in both the lithospheric thickness and the upper mantle shear velocity are needed to explain this group velocity decrease by means of isotropic models. The corresponding change in the upper mantle structure does not appear to be correlated with the age of the seafloor. It suggests the existence of a low velocity region, several hundred kilometers in extent, in which transform faulting is active. A strong azimuthal anisotropy of Rayleigh wave velocity in the investigated area could also, but only partially, account for the observed velocity variations.

Phase and group velocity dispersions of fundamental mode Rayleigh waves for the path Port Moresby-Rabaul have been computed. The structural interpretation of dispersion curves for the Solomon Sea reveals the channel shear velocity as about 4.35 km/s and the channel starts around 95 km below the earth's surface. In other words, the elastic velocities-depth structure beneath the Solomon Sea is very similar to that beneath the northern part of the Western Mediterranean Basin. Further, group velocity dispersion of fundamental mode Rayleigh waves at the PMG and the RAB seismic stations have been computed. The structural interpretation of a dispersion curve for the orogenic belt of Papua New Guinea reveals a crust of about 62.5 km thick and uppermost mantle shear velocity of about 4.3 km/s.

A model of the crustal structures beneath the Rhinegraben rift system has been derived based on results of seismic refraction and reflection measurements. Observations along two lines parallel to the strike of the graben and along two overlapping profiles traversing the rift normal to its axis provided the necessary data. They were supplemented by results of deep seismic reflection experiments carried out within the graben and in its adjacent regions. Important findings are the existence of two velocity inversions within the crust and of a characteristic “rift cushion” with a compressional velocity of 7.6–7.7 km/sec and of a correspondingly high shear velocity. This body is considered to be the driving mechanism of the rifting process. Immediately below the pronounced low-velocity channel in the upper crust an intermediate layer with lamellar structure and of presumably basic composition has been found. The most conspicuous feature of the crustal cross-section is its asymmetry. It seems as if the rifting process must have started at the eastern margin of the graben. Complete bilateral symmetry of the structure has not yet been achieved.

Up until now, Portugal lacked a countrywide shear velocity model sampling short length-scale crustal structure, which limits interpretations of seismicity and tectonics, and predictions of strong ground motion. In turn, such interpretations and predictions are important to help mitigate risk of destruction from future large on- and offshore earthquakes similar to those that Portugal has experienced in the past (e.g. the Mw 8.5–8.7 tsunamigenic event in 1755). In this study, we measured teleseismic Rayleigh Wave Ellipticity (RWE) from 33 permanent and temporary seismic stations in Portugal with wave periods between 15 s and 60 s, and inverted it for 1-D models of shear wave velocity (Vs) structure beneath each station using a fully non-linear Monte Carlo method. Because RWE is strongly sensitive to the uppermost few kilometres of the crust, both RWE measurements and Vs models are spatially correlated with surface geology in Portugal. For instance, we find that sedimentary basins produced by rifting that had begun in the Mesozoic such as the Lusitanian Basin (LB) and the Lower Tagus-Sado Basin (LTSB) are characterised by higher RWE (lower Vs). Interestingly, we observe similar RWE (and Vs) values in the interior of the Central Iberian Zone (CIZ), which is a metamorphic belt of Paleozoic age. Together with reduced crustal thickness previously estimated for the same parts of the CIZ, this suggests that the CIZ might have experienced an episode of extension possibly simultaneous to Mesozoic rifting. The Galicia-Tras-os-Montes-Zone (GTMZ) that has undergone polyphased deformation since the Paleozoic is characterised by the lowest RWE (highest Vs) in Portugal. Ossa Morena Zone and the South Portuguese Zone exhibit intermediate Vs values when compared to that of basins and the GTMZ. Our crustal Vs model can be used to provide new insights into the tectonics, seismicity and strong ground motion in Portugal.

We have used digitally recorded long period seismic data from the HGLP and SRO networks to obtain estimates of multiple ScS travel times and spectra and have used these to place constraints on the lateral variations in upper-mantle shear velocity and attenuation structure. The travel time results are consistent with our previous findings: to a first approximation, upper-mantle heterogeneity as expressed in vertical travel time differences can be correlated with surface tectonic features. A spectral stacking procedure for retrieving the attenuation operator for SH polarized multiple ScS waves has been applied to seismograms representing a variety of tectonic provinces. The spectral analysis has yielded stable estimates of the phase and amplitude response of the attenuation operator in the frequency interval 6–60 mHz. These estimates indicate that the apparent Q can also be correlated with surface tectonic regimes.