A total of 431 well-defined and 632 null shear-wave splitting measurements obtained from 115 broadband seismic stations located in the eastern Himalayan syntaxis and adjacent areas is largely inconsistent with predicted fast orientations by absolute plate motion models. Spatial coherency analysis of the splitting parameters suggests that the observed azimuthal anisotropy is mostly located in the upper asthenosphere or the transitional layer between the lithosphere and asthenosphere, and the disagreement between the fast orientations and regional tectonic fabrics suggests an insignificant lithospheric contribution to the observed anisotropy. The observations may be attributed to flow systems that are driven by the westward rollback of the Indian slab beneath the Indo-Burma block and are modulated by a previously revealed gap between the northward and eastward subducting slabs of the Indian plate.

The growing quality and improving spatial coverage of broadband seismic stations on the African (Nubian + Somalian) and Arabian plates motivate us to present a catalog of S-to-P receiver functions (SRFs) from southern Africa to northern Arabia. As in North America where the ability to compare data from cratons to modern rift provinces has led to new insights about lithospheric discontinuities, so, too, in Africa and Arabia can we begin to track and study the Moho, midlithospheric discontinuities, and the lithosphere–asthenosphere boundary (LAB) between tectonothermal provinces and beneath plate boundaries. We utilized 1508 seismic stations recording 9349 teleseismic events to calculate 103,878 SRFs that we stacked in 1° circular bins. We find a robust positive arrival due to a seismic-wavespeed increase downward across the Moho in virtually all our stacked SRF traces at 15–55 km depth, and we verify this is in good agreement with previously published Ps results, thereby validating the quality of our data set. Our stacked SRF traces also show a sub-Moho negative arrival at a delay time equivalent to 50–132 km depth that should correspond to a negative velocity discontinuity at or above the LAB. Our continent-wide, plate-scale database offers the opportunity to explore for spatial and temporal evolution of lithospheric parameters.

No abstract

No abstract

Thorough understanding of seabed fluid flow system is of great significance to geohazard identification and hydrocarbon exploration as it can reshape the seabed and act as an indicator of subsurface hydrocarbon resources. For the first time, an integrated study of side‐scan sonar, single‐ and multi‐channel seismic data and magnetic data reveals a complex fluid flow system composed of various seafloor expressions (i.e. pockmarks and mounds) and shallow fluid migration pathways in the central‐west Bohai Sea off northeast China. Gas chimneys, mud diapirs and a dense network of Quaternary faults are the main fluid migration pathways in the shallow subsurface. The gas chimneys can be classified into three categories (Type A formed by relatively rapid gas escape, Type B formed by episodic fluid expulsion and Type C formed by fluid escape from mud diapirs), based on their distribution and seismic character, implying variability in the formation processes. Sediment remobilization and basement‐involved faults contribute to deep fluid migration into shallow depths. As a seal for up‐moving fluids, the nature and thickness of Holocene marine sediments generally decide the permeability and overburden pressure that may control the distribution of pockmarks and mounds since they are almost distributed above relatively thin Holocene deposits (thickness <20 m) and localized coarse surface sediments. The results of the interpretation gain an improved understanding of the geological processes controlling the genesis and spatial distribution of gas chimney formation and show the significance of gas chimney classification. The distribution pattern of different types of gas chimneys may signify the difference of geological background and fluid flow process, like fluid migration through faults or flow of mobilized sediments, that is crucial for the evaluation of global petroleum systems and Carbon Capture and Storage studies.