Geo-Marine Letters最新文献

The Isla Salamanca coastal barrier on the Colombian Caribbean coast faces significant erosion, driven by climate change-induced, sea level rise and human activities such as highway construction. The Barranquilla-Ciénaga highway, particularly at kilometers 19 and 29, is at risk, with severe consequences for the region’s socio-economic and environmental well-being. Human interventions like the highway construction and seawall installations have disrupted the natural coastal dynamics, leading to increased erosion rates. The study, conducted between 2004 and 2021, reveals that the Isla Salamanca coastal barrier is experiencing substantial transgression, with erosion rates peaking at -16.1 m·yr^− 1. The highway protection measures, with seawall construction, have proven inadequate, exacerbating erosion downstream. The mangrove loss due to hydrological changes and increased salinity is further threatening the fragile ecosystem. The research emphasizes the importance of considering biodiversity loss in the context of rapid erosion rates. The region, declared a Ramsar Site and Biosphere Reserve, hosts vital ecosystems like mangroves and dunes, whose destruction negatively impacts marine biodiversity. The study suggests the relocation of the highway, acknowledging the challenges of preserving wetlands and mangroves in the process. Balancing the need for infrastructure with ecological preservation is essential, and the study proposes comprehensive solutions, including shoreline management, ecosystem-based protection, and community involvement. The goal is to mitigate erosion’s adverse effects on biodiversity, habitat integrity, and the overall health of this ecologically sensitive region.

This study investigates seismic anisotropy in the northeastern region of the Indian plate, including the Eastern Himalayan front, Eastern Himalaya Syntaxis (EHS), Indo-Burmese subduction zone, Shillong Plateau, Assam foredeep, and Bengal basin. Variations in azimuthal anisotropy are interpreted in terms of pre-existing lithospheric structures, mantle flow movement, and dynamic lithospheric stresses. Analysis of shear-wave splitting (SWS) in the waveforms recorded at 64 stations yielded 305 splittings (SKS, SKKS, and PKS phases) and 386 Null measurements. Results reveal an average delay time ((delta )t) of 0.95 ± 0.32 s, indicating significant anisotropy. Modeling the back-azimuthal dependence of the splitting parameters indicates two-layer anisotropy along the Eastern Himalaya, Shillong Plateau, and south of the Dauki fault contiguous with the Indo-Burmese arc. Application of the spatial coherency technique localizes the depth of the anisotropic layers in different tectonic subdivisions. Stresses and lithospheric strain associated with Absolute Plate Motion (APM) of India explain the deformation patterns gleaned from splitting measurements. A vertically coherent crust-mantle deformation is proposed at the Himalayan collision front, where east-west-oriented extensional shear stresses result in north-south compressive strains. APM-related stresses forge anisotropy in the Assam foredeep region that shows a coupled crust-mantle deformation. East-west-oriented fast polarization directions (FPDs) beneath the Shillong Plateau indicate localized mantle flow along the Dauki fault. The fast axes of anisotropy in the Indo-Burmese subduction zone align parallel to the arc. These findings enhance the knowledge of mantle dynamics in the subduction and continent-continent collision zones.

Local earthquake tomography was performed to image the subsurface structure beneath the seismically active Cachar fold and thrust belt in lower Assam, northeast India. A total of 3341 P-phases and 1833 S-phases corresponding to 180 local microearthquakes recorded over 11 months by a temporary, dense network of 76 stations were used to simultaneously locate the hypocenters and estimate the P- and S-wave velocity structure in three dimensions. The entire crust down to a depth of ≈ 40 km is seismically active with about 70% of the microearthquakes ranging in magnitude from 0.5 to 3.5 occurring in the upper crust. The velocity tomograms reveal alternating patterns of high and low velocity anomalies down to a depth of ≈8 km that correlate with the NE-SW trending en-echelon pattern of the anticlines and synclines of the Cachar fold belt (CFB). These structures are distinctly demarcated up to depths of ≈ 4 km revealing the deformation of the low velocity sediments (Vp ≈ 1.8 to 4.3 km/s) beyond which they are correlatable with the relief in the high velocity medium (Vp ≥ 5 km/s). The sediment (Vp < 5 km/s) thickness varies from ≈ 4 km above the anticlinal structural highs to ≈ 8 km in the broad synclines. The shallow (≤ 10 km) microseismicity is aligned in a NE-SW direction correlating predominantly with the major anticlines. The study reveals the geometry and depth extent of the structural features of CFB and their association with seismicity indicating faulting resulting from deformation due to the compressional tectonics in northeast India.

The Bengal Fan, the largest submarine fan in the world, spanning the whole Bay of Bengal resulted from the India-Asia collision event and subsequent Himalayan orogeny. It is a significant depositional feature formed by the major river systems: the Ganges and Brahmaputra. Previous studies revealed the occurrence of an extensive channel-levee system in the Bengal Fan through various marine geoscientific investigations. In the present study, we have successfully mapped a submarine channel-levee segment in the lower Bengal Fan using hull-mounted multibeam bathymetry data collected for the first time. In addition, we conducted a pioneering study of a submarine channel segment using an Autonomous Underwater Vehicle (AUV) within the identified channel. The identified channel, characterized by moderate sinuosity, maintains a smooth morphology throughout its course, with the channel incision increasing towards the lower course. The microbathymetric observations revealed fine-scale features such as mass wasting, sediment waves and scour/depressions indicating the direct interaction between turbidity currents and the channel floor. The newly identified channel is proposed to result from the channel bifurcation of the previously identified channel W6 described by Curray et al. (2003). This study showcases the importance of near-bottom observations in complex submarine channel-levee systems for a better understanding of the formation processes involved in such systems.