Theory and Observations – Normal Modes and Surface Wave Measurements

Laske, G.; Widmer‐Schnidrig, Rudolf

doi:10.1016/b978-044452748-6.00003-1

Cited by 12 publications

(9 citation statements)

References 247 publications

(187 reference statements)

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“…S-wave velocities at 65 m depth are about the same, but show higher velocities of up to 5 per cent for the S-wave profile derived from the Love wave inversion below 65 m. Above 12 m, small velocity differences can correspond to large percentage differences due to the slow velocities in the upper few metres. Furthermore, the sensitivity of surface waves to P-wave velocity and density can be large at shallow depths (Laske & Widmer-Schnidrig 2007). More important is the observed velocity difference of up to 15 per cent between the S-wave velocity profile derived from Rayleigh wave and Love wave dispersion curve between 12 and 65 m (Fig.…”

Section: Velocity-depth Profile From Surface Wave Inversionmentioning

confidence: 98%

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

et al. 2016

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S U M M A R YAn L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency-slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ∼150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn-air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.

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Section: Velocity-depth Profile From Surface Wave Inversionmentioning

confidence: 98%

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

et al. 2016

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“…Additional phase velocity maps are shown in Figure S3 in the supporting information. Their depth sensitivity is period dependent: Longer periods penetrate deeper and are sensitive to the mantle lithosphere and the asthenosphere (100 s period, ∼150–200 km), whereas short periods are particularly sensitive to the crust (15 s period, ≤15–30 km) (e.g., Laske & Widmer‐Schnidrig, 2007; Lebedev et al., 2013).…”

Section: Phase Velocity Mapsmentioning

confidence: 99%

The Slab Puzzle of the Alpine‐Mediterranean Region: Insights From a New, High‐Resolution, Shear Wave Velocity Model of the Upper Mantle

El‐Sharkawy

Meier

Lebedev

et al. 2020

Geochem Geophys Geosyst

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Mediterranean tectonics since the Lower Cretaceous has been characterized by a multiphase subduction and collision history with temporally and spatially variable, small‐scale plate configurations. A new shear wave velocity model of the Mediterranean upper mantle (MeRE2020), constrained by a very large set of over 200,000 broadband (8–350 s), interstation, Rayleigh wave, phase velocity curves, illuminates the complex structure and fragmentation of the subducting slabs. Phase velocity maps computed using these measurements were inverted for depth‐dependent, shear wave velocities using a stochastic particle‐swarm‐optimization (PSO) algorithm. The resulting three‐dimensional (3‐D) model makes possible an inventory of slab segments across the Mediterranean. Fourteen slab segments of 200–800 km length along‐strike are identified. We distinguish three categories of subducted slabs: attached slabs reaching down to the bottom of the model; shallow slabs of shorter length in downdip direction, terminating shallower than 300 km depth; and detached slab segments. The location of slab segments are consistent with and validated by the intermediate‐depth seismicity, where it is present. The new high‐resolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the Mediterranean realm.

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“…Additional phase velocity maps are shown in Figure S3 in the supporting information. Their depth sensitivity is period dependent: Longer periods penetrate deeper and are sensitive to the mantle lithosphere and the asthenosphere (100 s period, ∼150-200 km), whereas short periods are particularly sensitive to the crust (15 s period, ≤15-30 km) (e.g., Laske & Widmer-Schnidrig, 2007;Lebedev et al, 2013).…”

Section: Phase Velocity Mapsmentioning

confidence: 99%

The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle

El‐Sharkawy

Meier²,

Lebedev

et al. 2020

Preprint

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The fascinatingly complex tectonic make-up of the Mediterranean region comprises small, strongly-curved retreating subduction zones, associated back-arc basins, and the continental collisions along the northern and eastern margins of the Adriatic microplate. It remains a challenge to resolve the geometry of the subducted slabs in the Mediterranean upper mantle. Here, we present new evidence for the location and lateral and vertical extent of slab segments from a new, high-resolution, Rayleigh-wave tomography. The tomographic model spans the depth range from the crust down to 300 km and is complemented by intermediate-deep seismicity data in the circum-Mediterranean region.An automated procedure to measure inter-station Rayleigh wave phase velocities is applied to a large, heterogeneous dataset from all publically available stations around the Mediterranean in the time period from 1990 to 2015. Furthermore, for the first time, data from the Egyptian National Seismological Network (ENSN) are used regional seismic tomography. The resulting large set of about 200,000 inter-station phase velocity measurements is inverted for a set of phase-velocity maps spanning a very broad period range (8 - 350 s). The maps are then inverted, point by point, for a 3D, S-velocity model using a stochastic, particle-swarm-optimization inversion.We distinguish between attached slab segments reaching down to the bottom of the model and shallow slabs of shorter length or detached slab segments resulting both from horizontal tearing. We discuss evidence for continental subduction east of Cyprus, for continuous NE-dipping subduction in the Antalyan region and NW dipping subduction in the SE Aegean in the area of Rhodes. An attached slab is imaged beneath the Hellenides reaching down to at least 300 km depth whereas beneath the Dinarides a short slab is found down to about 150 km depth above a slab tear. The slab in the southern Carpathians seems to be partly detached. A south-dipping slab is imaged in the central Alps but shallow bivergent subduction is favoured in the eastern Alps. In the western Alps, a shallow slab east-dipping Eurasian slab segment is in close proximity to the nearly vertically dipping attached slab segment beneath the northern Apennines and the southern Po plain. In the central Apennines a slab gap is found whereas the NE-dipping Calabrian Slab seems to partly detached along the northern Sicilian coast. The Kabylides Slab that appears to be attached along the North African coast but detached along the margin of the shelf in the Sicily Channel, is clearly separated from the Calabrian Slab in the NE and the Alboran-Betics Slab in the west. According to our model, the latter slab consists of two segments: a shallow Alboran one and a detached Betics slab segment. We summarize our interpretations in a map of the Mediterranean slab segments and indicate open questions.

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Theory and Observations – Normal Modes and Surface Wave Measurements

Cited by 12 publications

References 247 publications

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica

The Slab Puzzle of the Alpine‐Mediterranean Region: Insights From a New, High‐Resolution, Shear Wave Velocity Model of the Upper Mantle

The Slab Puzzle of the Alpine-Mediterranean Region: Insights from a new, High-Resolution, Shear-Wave Velocity Model of the Upper Mantle

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