Seismoturbidite record as preserved at core sites at the Cascadia and Sumatra–Andaman subduction zones

Turbidite deposition along slope and trench settings is evaluated for the Cascadia and Sumatra-Andaman subduction zones. Source proximity, basin effects, turbidity current flow path, temporal and spatial earthquake rupture, hydrodynamics, and topography all likely play roles in the deposition of the turbidites as evidenced by the vertical structure of the final deposits. Channel systems tend to promote low-frequency components of the content of the current over longer distances, while more proximal slope basins and base-of-slope apron fan settings result in a turbidite structure that is likely influenced by local physiography and other factors. Cascadia's margin is dominated by glacial cycle constructed pathways which promote turbidity current flows for large distances. Sumatra margin pathways do not inherit these antecedent sedimentary systems, so turbidity currents are more localized.Keywords: Fore arc, Submarine landslides, Deep sea sedimentation, Radiocarbon age calibration, Holocene earthquakes, San Andreas Fault, Magnetic susceptibility, Megathrust earthquakes, Active deformation, Late pleistocen

Submarine landslide megablocks show half of Anak Krakatau island failed on December 22nd, 2018

As demonstrated at Anak Krakatau on December 22nd, 2018, tsunamis generated by volcanic flank collapse are incompletely understood and can be devastating. Here, we present the first high-resolution characterisation of both subaerial and submarine components of the collapse. Combined Synthetic Aperture Radar data and aerial photographs reveal an extensive subaerial failure that bounds pre-event deformation and volcanic products. To the southwest of the volcano, bathymetric and seismic reflection data reveal a blocky landslide deposit (0.214 ± 0.036 km3) emplaced over 1.5 km into the adjacent basin. Our findings are consistent with en-masse lateral collapse with a volume ≥0.175 km3, resolving several ambiguities in previous reconstructions. Post-collapse eruptions produced an additional ~0.3 km3 of tephra, burying the scar and landslide deposit. The event provides a model for lateral collapse scenarios at other arc-volcanic islands showing that rapid island growth can lead to large-scale failure and that even faster rebuilding can obscure pre-existing collapse

Angular Range Analysis (ARA) and K-Means Clustering of Multibeam Echosounder Data for Determining Sediment Type

Backscatter value was a key to determine seabed characteristic. Level of intensity or backscatter informed through seabed type. One approach was use to analyze seabed type based on the value of backscatter was Angular Range Analysis (ARA). ARA utilize influence of angle backscattering intensities. The aim of this research was to determine value of backscatter from the bottom and used to initial prediction of seabed. Extraction processes of raw data obtained by acoustic signal processing techniques. Analysis of backscatter data was conducted by using K-means method to look the proximity of the centroid backscatter value against other values. Backscatter intensity from this sites ranged from -41,93 dB to -27 dB. The range value divided into three major classes based on Wenworth scale classification. Substrate type in the study site consists of sand, silt, and clay. Grain size diameter of each type include: sand 0.122713 mm (phi = 3.02), silt 0.018171 mm (phi = 5.78) and clay 0.002690 mm (phi= 8.53). Based on this result, signal processing multibeam echosounder able to classify seabed backscatter values to determine the seabed type   Keywords: Angular Range Analysis, multibeam echosounder, K-Mean

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Seismoturbidite record as preserved at core sites at the Cascadia and Sumatra–Andaman subduction zones

Turbidite deposition along slope and trench settings is evaluated for the Cascadia and Sumatra–Andaman subduction zones. Source proximity, basin effects, turbidity current flow path, temporal and spatial earthquake rupture, hydrodynamics, and topography all likely play roles in the deposition of the turbidites as evidenced by the vertical structure of the final deposits. Channel systems tend to promote low-frequency components of the content of the current over longer distances, while more proximal slope basins and base-of-slope apron fan settings result in a turbidite structure that is likely influenced by local physiography and other factors. Cascadia's margin is dominated by glacial cycle constructed pathways which promote turbidity current flows for large distances. Sumatra margin pathways do not inherit these antecedent sedimentary systems, so turbidity currents are more localized