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  • 1
    Publication Date: 2020-02-12
    Description: Analysis of receiver functions from an eight-station network on the Saudi Arabian shield indicates that the Moho depths vary between 35–38 km. The crust appears to be rather felsic in nature as evidenced by Poisson’s ratios of 0.25–0.27. A prominent negative phase following the Moho conversion is suggestive of a zone of velocity inversion. Indication of mantle stratification is observed beneath the coastal region of Arabia, by way of an additional upper mantle discontinuity at about 240 km. The conversions from the 410 and 660-km discontinuities are significantly delayed, suggesting a slow and hot upper mantle.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 2
    Publication Date: 2020-02-12
    Description: Abstract: We present 1-D models of crustal P and S wave velocity structure in the epicentral region of the devastating 1993 Latur earthquake in southern India. Travel time and relative amplitude modeling of a seismogram section of well located aftershocks out to 80 km offset, by reflectivity synthetic seismograms, reveal alternating low-velocity layers (LVLs) for P and S waves in the upper crust at depths of 6.5-9.0 km and 12.3-14.5 km with about 7% velocity reduction. A lower crustal LVL at 24-26 km depth is also inferred by modeling. The seismic activity in the Latur region is essentially confined to shallow upper crustal depths of less than 6 km, above the LVLs. The upper crustal velocity models further reveal a relatively low Vp/Vs ratio of 1.65, while synthetic seismogram models consistent with the upper crustal P wave reflection phases reveal a Qp/Qs ratio certainly less than 1. A high-conductivity zone at a shallow depth of 6-10 km brought out by broad band MT soundings in this region, is found to be coincident with the upper crustal LVLs. These coincident anomalous properties of the upper crust suggest the presence of fluids (probably in a partially- or slightly under-saturated state) below the hypo-central region of the Latur earthquake and its aftershocks.
    Keywords: 550 - Earth sciences
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  • 3
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 4
    Publication Date: 2020-02-12
    Description: The present geological setting west of Svalbard closely parallels the situation off mid-Norway after the last glaciation, when crustal unloading by melting of ice induced very large earthquakes. The modern Svalbard margin is characterized by an active fluid flow system in continental margin sediments consisting of inter-layered contourite deposits and glacigenic debris flows. Both unloading earthquakes and overpressures have been identified as key factors causing several mega-landslides off Norway during early Holocene deglaciation. The most prominent event was the Storegga Slide 8200 years BP which caused a tsunami up to 23 m high on the Faroe and Shetland islands. Numerical tsunami modeling indicates a smaller (100 m high and 130 km wide) submarine landslide west of Svalbard, which is consistent with the geological information available for the area, would cause a tsunami capable of reaching northwest Europe and threatening coastal areas. Although newly collected seismic data do not show clear precursors to incipient slope failure it may be sensible to install a tsunami warning system based on tilt-meters, which would give a warning time of one to four hours.
    Keywords: 550 - Earth sciences
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  • 5
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 6
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
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  • 7
    Publication Date: 2020-02-12
    Description: Teleseismic earthquake waveform data from 10 broadband stations spread over the Indian shield and in operation since 1997, were analysed to infer the crustal structure, using the receiver function technique. The South Indian shield is characterized by a 33 - 39 km thick, and remarkably simple crust, with an average Poisson's ratio close to 0.25. The Archaean crust is devoid of any prominent intra-crustal discontinuities. The velocity contrast at the well developed Moho is large, resulting in very clear P-to-S conversions as well as first-order multiples. In contrast, the predominantly Proterozoic crust in the northern part of the shield exhibits a complex character, due to the shield exhibits a complex character, due to the presence of additional seismic discontinuities. Moho conversions, which are considerably weaker compared to the Archaean terrains, indicate crustal thicknesses of more than 40 km.
    Keywords: 550 - Earth sciences
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  • 8
    Publication Date: 2020-02-12
    Description: Teleseismic data from six broad-band stations on the south Indian shield have been analysed, primarily to examine the differences in the crustal structure between the eastern and western units of the Archaean Dharwar craton. SV receiver functions for these stations have been computed and modelled down to the Moho level in terms of Poisson's ratio and shear wave velocities. Results show that the crust for the entire Dharwar craton is mainly simple, and has a low (about 0.25) Poisson ratio. It is usually thinner and less complex than the adjacent Proterozoic crust. However, the western Dharwar craton crust (thickness 41 km) with a gradational Moho boundary, is substantially (〉7 km) thicker than its eastern counterpart (thickness 34 km). No substantial differences in average crustal S velocities (3.6-3.8 km s 1) were found. The eastern Dharwar crust below the Proterozoic Cuddapah basin was also found to have remained relatively simple and undisturbed. The continental margin to the west of the Dharwar craton appears to have shifted further west off the coast, where a possible west coast fault has down-thrown a continental crustal block under the seas. The crust constituting the Deccan volcanic province in the western Indian shield is found to be similar to that of the eastern Dharwar craton. The crust underneath the neighbouring Godavari graben is significantly different from the Dharwar crust and resembles that of a typical rift-valley.
    Keywords: 550 - Earth sciences
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  • 9
    Publication Date: 2020-02-12
    Description: Receiver functions derived from teleseismic P waveforms of 297 earthquakes recorded at broadband station Hyderabad (HYB) are analysed to investigate the lithospheric and upper mantle structure in the vicinity of the station, located in the northeastern part of the Archaean Dharwar Craton. The internal structure of the 33±2 km thick crust is simple. It can be approximated by a single layer with S velocity linearly increasing with depth from 3.4 to 4.0 km/s , the average being 3.7±0.2 km/s. The crustal Poisson's ratio is 0.25±0.01. A seismic discontinuity at 90 km depth is inferred from a signal particularly prominent on the SH component and possibly indicative of a layer of depth-localized anisotropy in the lithospheric mantle. The two principal mantle discontinuities are at depths of 406 and 659 km, which are close to the global averages.
    Keywords: 550 - Earth sciences
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