Bayesian Rayleigh wave inversion with an unknown number of layers

Surface wave methods have received much attention due to their efficient, flexible and convenient characteristics. However, there are still critical issues regarding a key step in surface wave inversion. In most existing methods, the number of layers is assumed to be known prior to the process of inversion. However, improper assignment of this parameter leads to erroneous inversion results. A Bayesian nonparametric method for Rayleigh wave inversion is proposed herein to address this problem. In this method, each model class represents a particular number of layers with unknown S-wave velocity and thickness of each layer. As a result, determination of the number of layers is equivalent to selection of the most applicable model class. Regarding each model class, the optimization search of S-wave velocity and thickness of each layer is implemented by using a genetic algorithm. Then, each model class is assessed in view of its efficiency under the Bayesian framework and the most efficient class is selected. Simulated and actual examples verify that the proposed Bayesian nonparametric approach is reliable and efficient for Rayleigh wave inversion, especially for its capability to determine the number of layers.

     

Remote data analysis, visualization and problem solving environment (PSE) based on wavelets in the geosciences

We discuss here the issues faced by earth scientists in analyzing and visualizing large datasets over a GRID-like setup from a client-server perspective. We approach this problem by using a remote, web-based visualization and data analysis framework, called WEB-IS, and by employing second-generation wavelets as a means for reducing the amount of data transferred and for extracting coherent features in complex geophysical flows and surface faulting patterns. As an example, we describe how onboard processors on satellites can function as a server for beaming down extracted information to the client computer on the ground, thus exemplifying WEB-IS as a viable middleware on a GRID network for geosciences.Reviewed by: Prof. I.D. Clemens, Prof. L. Hanyk     

Stability of the oceanic lithosphere with variable viscosity: an initial-value approach

We have studied the problem concerning the onset of convective instabilities below the oceanic lithosphere. A system of linear partial differential equations, in which the background temperature field is time-dependent, is integrated in time to monitor the evolution of incipient disturbances. Two types of rheologies have been examined. One depends strongly on temperature. The other involves a viscosity which is both temperature- and pressure-dependent. The results from this initial-value approach, in which the viscosity profiles migrate downward with time, reveal the importance of considering temperature- and pressure-dependent rheology in issues regarding the development of local instabilities in upper mantle convection. For temperature-dependent viscosity, viscosities of 0(10²⁰P) are required to produce instabilities with growth-rates of 0(.1/Ma). In contrast, these same growth rates can be attained for a temperature- and pressure-dependent viscosity profile with a mean value close to 0(10²⁰P) in the upper mantle, owing to the presence of a low viscosity zone, 0(10²⁰P), existing right below the lithosphere. Unlike the results of temperature-dependent viscosity, whose growth-rates increase with time, the amplification of disturbances in a fluid medium with temperature- and pressure-dependent rheology reaches a maximum at an early age, < 50 Ma, and decreases thereafter with time. This suggests the potential importance played by initial disturbances in the evolution of the oceanic lithosphere.     

Era-interim Forced Simulation of the Indian Summer Monsoon

Abstract

In the present study, mean rainfall for the months of June-July-August-September (JJAS) during summer monsoon is simulated over India and its adjoining regions for a period between 1982 and 2006. The study was carried out using Regional Climate Model (RegCM) version 4.6 at a resolution of 25?km. The simulated mean JJAS monsoon rainfall was validated against the observational IMD data. Comparison of JJAS seasonal mean summer rainfall for the first decade 1982–1991, with the later decade 1997–2006 indicate that the intensity of rainfall increases over Indian land-mass during the later decade under the forced conditions of Era-Interim. The observed JJAS mean rainfall indicates two maximum rainfall areas i.e. the Western Ghats and the Himalayan region. A significant bias is observed in the central and Jammu and Kashmir (J&K) region. The JJAS mean seasonal surface air temperature distribution at 0.25?×?0.25-degree grids resolution shows a decreasing trend of temperature over the Indian landmass.     

Crack Initiation, Propagation and Coalescence in Rock-Like Material Containing Two Flaws: a Numerical Study Based on Bonded-Particle Model Approach

Cracking and coalescence behavior in a rectangular rock-like specimen containing two parallel (stepped and coplanar) pre-existing open flaws under uniaxial compression load has been numerically studied by a parallel bonded-particle model, which is a type of bonded-particle model. Crack initiation and propagation from two flaws replicate most of the phenomena observed in prior physical experiments, such as the type (tensile/shear) and the initiation stress of the first crack, as well as the coalescence pattern. Eight crack coalescence categories representing different crack types and trajectories are identified. New coalescence categories namely “New 1” and “New 2”, which are first observed in the present simulation, are incorporated into categories 3 and 4, and category 5 previously proposed by the MIT Rock Mechanics Research Group, respectively. The flaw inclination angle (β), the ligament length (L) (spacing between two flaws) and the bridging angle (α) (inclination of a line linking up the inner flaw tips, between two flaws) have different effects on the coalescence patterns, coalescence stresses (before, at or post the peak stress) as well as peak strength of specimens. Some insights on the coalescence processes, such as the initiation of cracks in the intact part of specimens at a distance away from the flaw tips, and coalescence due to the development and linkage of a number of steeply inclined to vertical macro-tensile cracks are revealed by the present numerical study.     

Modifications in aerosol physical,optical and radiative properties during heavy aerosol events over Dushanbe,Central Asia

The location of Central Asia,almost at the center of the global dust belt region,makes it susceptible for dust events.The studies on atmospheric impact of dust over the region are very limited despite the large area occupied by the region and its proximity to the mountain regions(Tianshan,Hindu Kush-Karakoram-Himalayas,and Tibetan Plateau).In this study,we analyse and explain the modification in aerosols'phys-ical,optical and radiative properties during various levels of aerosol loading observed over Central Asia utilizing the data collected during 2010-2018 at the AERONET station in Dushanbe,Tajikistan.Aerosol epi-sodes were classified as strong anthropogenic,strong dust and extreme dust.The mean aerosol optical depth(AOD)during these three types of events was observed a factor of～3,3.5 and 6.6,respectively,higher than the mean AOD for the period 2010-2018.The corresponding mean fine-mode fraction was 0.94,0.20 and 0.16,respectively,clearly indicating the dominance of fine-mode anthropogenic aerosol during the first type of events,whereas coarse-mode dust aerosol dominated during the other two types of events.This was corroborated by the relationships among various aerosol parameters(AOD vs.AE,and EAE vs.AAE,SSA and RRI).The mean aerosol radiative forcing(ARF)at the top of the atmosphere(ARFTOA),the bottom of the atmosphere(ARFBOA),and in the atmosphere(ARFATM)were-35±7,-73±16,and 38±17 Wm-2 during strong anthropogenic events,-48±12,-85±24,and 37±15 Wm-2 during strong dust event,and-68±19,-117±38,and 49±21 Wm-2 during extreme dust events.Increase in aerosol loading enhanced the aerosol-induced atmospheric heating rate to 0.5-1.6 K day-1(strong anthropogenic events),0.4-1.9 K day-1(strong dust events)and 0.8-2.7 K day 1(extreme dust events).The source regions of air masses to Dushanbe during the onset of such events are also identified.Our study con-tributes to the understanding of dust and anthropogenic aerosols,in particular the extreme events and their disproportionally high radiative impacts over Central Asia.     

Quasi-adiabatic shear zones in the lithosphere: numerical and experimental approaches

Continental breakup, or compressive lithosphere scale faulting, requires a physical mechanism for wholesale faulting of the lithosphere. We compared numerical and experimental models for the nucleation of quasi-adiabatic shear bands in polyvinylchloride (PVC) with those in an idealized viscoelastoplastic mantle with olivine rheology. In both materials fault nucleation is caused by elastic stress concentration on pre-existing imperfections, with localized yielding confined to its vicinity. Faulting occurs rapidly after the initial elastic energy in the system is charged sufficiently to cause wholesale yielding. Propagation of the fault, monitored by looking at the dissipation of plastic energy, reveals migration of a sharp, thermal-mechanical “crack”- like instability, which appears in the temperature field as a slightly diffused signal. The initial temperature rise in the crack is subtle but increases suddenly when the plate is severed. This autocatalytic behavior has also been described in ductile polymers, which can be used as mechanical analogues. We suggest that elastoplastic coupling in quasi-adiabatic shear banding is a key for fast (< 1 Ma) nucleation of shear zones. These nonlinear phenomena will be illustrated for both experimental and numerical results by nine movies     

Reuse of Distillery Wastewater with Designed Dose and Pattern for Sugarcane Irrigation

The present investigation aims to optimize dose and pattern of distillery effluent for sugarcane irrigation. The postmethanated distillery effluent (PMDE) was recorded to have significant amount of micro‐ (Na, Zn, Fe) and macro‐ (Ca, Mg, N‐NO₃, P, K, S–SO) nutrients and so was utilized for sugarcane irrigation. Lysimetric studies were conducted to assess the impact of PMDE on sugarcane productivity with different concentrations (50 and 75%) and irrigation patterns (intermittent and pre‐sowing). The intermittent pattern of ferti‐irrigation with 50 and 75% effluent dose for sugarcane crop was found to enhance the growth and quality parameters of crop without impairing the groundwater quality. Results were more pronounced with 75% intermittent irrigation as the percent increase with respect to control for plant length, cane girth, cane weight, number of internodes per cane, dry matter accumulation, juice extraction, sucrose content, and available sugar were 28.0, 42.5, 14.6, 40.2, 54.4, 18.9, 44.9, 57.9, and 50.0%, respectively. It is suggested that PMDE can be used as an alternative of fresh water irrigation and also as a fertilizer for sugarcane, provided that the effluent quality and sugarcane quality is continuously monitored to avoid any contamination.     

The physical Properties of marine sediments as inferred from Wavelet Correlation Analysis

Seismic waves traveling in the water/sediment or sub-bottom sediment interface have been the subject of considerable interest in underwater acoustics in recent years. Some progress has been made in understanding the propagation and attenuation characteristics of interface waves in different geological environments. However, the generating mechanisms are poorly understood. In particular, what is the acoustic-seismic energy conversion process? As seismic waves involve both time and space parameters it should be able to relate directly the propagation characteristics of the ocean bottom interface waves to the shear properties of the sediments over the propagation area. To address these problems we have applied the wavelet correlation method (WCR) to examine the variations of bottom characteristics and their role in coupling waterborne sound into the sea bottom. To confirm the validity of the developed modeling technique, we applied the wavelet correlation analysis for synthetic seismograms and field data. In this discussion paper we present images of the first and second shear modes and the interface wave component as a function of arrival time and frequency. We also discuss the possibility of inverting phase and group velocity information directly from the wavelet cross-correlation function and propose the way of using the WCR method to predict physical dynamic parameters of marine sediments.