Tectonically-driven mud volcanism since the late Pliocene on the Calabrian accretionary prism,central Mediterranean Sea

Mud volcanoes recently discovered on the offshore Calabrian Arc are investigated at two sites 60 km apart, in water depths of 1650--2300 m, using swath bathymetry, 2D&3D multichannel seismic and cores. The seabed and subsurface data provide information on their formation and functioning in relation to tectonic activity during the rapid Plio-Quaternary advance of the accretionary prism. Fore-arc extension and thrust-belt compression are seen to have involved two main phases of activity, separated by a regional unconformity recording a mid-Pliocene (3.5–3.0 Ma) tectonic reorganization. The two sites of mud volcanism lie in contrasting tectonic settings (inner fore-arc basin vs central fold-and-thrust belt) and record differing forms of seabed extrusive activity (twin mud cones and a caldera vs a broad mud pie). At both sites, subsurface data show that mud volcanism took place throughout the second tectonic phase, since the late Pliocene; differing forms of mud extrusion were accompanied by subsidence to form depressions beneath and within extrusive edifices up to 1.5 km thick. The basal subsidence depressions point to sources within the succession of thrusts underlying the inner to central Arc, consistent with microfossils within cored mud breccias from both sites that are derived from strata as old as Late Cretaceous.     

Spatiotemporal mixed effects modeling for the estimation of PM2.5 from MODIS AOD over the Indian subcontinent

ABSTRACT

The physical processes associated with the constituents of the troposphere, such as aerosols have an immediate impact on human health. This study employs a novel method to calibrate Aerosol Optical Depth (AOD) obtained from the MODerate resolution Imaging Spectrometer (MODIS – Terra satellite) for estimating surface PM_2.5 concentration. The Combined Deep Blue Deep Target daily product from the MODIS AOD data acquired across the Indian Subcontinent was used as input, and the daily averaged PM_2.5pollution level data obtained from 33 monitoring stations spread across the country was used for calibration. Mixed Effect Models (MEM) is a linear model to deal with non-independent data from multiple levels or hierarchy using fixed and random effects of dependent parameters. MEM was applied to the dataset obtained for the period from January to August 2017. The MEM considers a fixed and random component, where the random components model the daily variations of the AOD – PM_2.5 relationships, site-specific adjustment parameters, temporal (meteorological) variables such as temperature, and spatial variables such as the percentage of agricultural area, forest cover, barren land and road density with the resolution of 10 km × 10 km. Estimation accuracy was improved from an R² value of 0.66 from our earlier study (when PM_2.5 was modeled against only AOD and site-specific parameters) toR² value of 0.75 upon the inclusion of spatiotemporal (meteorological) variables with increased % within Expected Error from 18% to 35%, reduced Mean Bias Error from 3.22 to 0.11 and reduced RMSE from 29.11 to 20.09. We also found that spline interpolation performed better than IDW and Kriging inefficiently estimating the PM_2.5 concentrations wherever there were missing AOD data. The estimated minimum PM_2.5 is 93 ± 25μg/m³ which itself is in the upper limit of the hazardous level while the maximum is estimated as 170 ± 70μg/m³. The study has thus made it possible to determine the daily spatial variations of PM_2.5 concentrations across the Indian subcontinent utilizing satellite-based AOD data.     

Numerical studies of gas hydrate systems: sensitivity to porosity-permeability models

The formation of sub-seafloor gas hydrates in marine environments can be described as a coupled transport and thermodynamic process inside a host sediment matrix undergoing structural evolution. The transport processes are driven by the sedimentary load and induced overpressure gradients, controlled by sediment permeability. In order to accurately model the resulting fluid flow profile, the decrease of sediment permeability during hydrate precipitation has to be taken into account, which affects both the transport of solutes and sediment compaction. In this paper, we investigate how total hydrate abundance is affected by regions of low permeability which deflect the flow field in their vicinity. For this purpose, a two-dimensional numerical hydrate system model was set up which permits to quantify this effect in scenarios where changes in water depth cause lateral variations of the thickness of the hydrate stability field, as well as of hydrate saturation and sediment permeability. The microscopic structure of gas hydrate crystals in the host sediment matrix defines the evolution of the permeability reduction during hydrate formation. Grain-coating precipitates have a stronger tendency to clog flow paths through pore throats than do pore-filling precipitates. Our results clearly show that these pore-scale processes affect the large-scale flow field and hydrate abundance. The sensitivity depends on the model geometry and, for a 5° slope of the seafloor, 4.1% relative difference is predicted for the hydrate saturation according to different porosity-permeability relationships.