Joint migration inversion (JMI) technology has great potential in exploiting multiples in seismic data for both velocity model building and seismic migration, but it faces the previously published amplitude-versus-offset (AVO) challenge: the angle-independent wavefield modeling used in the current JMI cannot simulate the correct AVO effect in data, but this modeling engine is still required in order to avoid over-parameterizing a solution space. By using a velocity model and a density model to parameterize the solution space, the AVO challenge can be adequately addressed by one-way operators for 1.5-dimensional (1.5D) media. In this paper, we propose a new concept, which is named 'inverse propagation' of receiver wavefields, for JMI in 1.5D media, and we derive the complete theory behind this new concept. We will demonstrate that our inverse propagation is a physically inverse process to reconstruct wavefields in the subsurface with the effects from transmission, reflection and multiples correctly accounted for, while the old backward propagation scheme for receiver wavefields in the previous JMI technology is a not satisfying approximation. This work paves a solid way to further develop the 1.5D JMI theory.

The traditional joint migration inversion (JMI) technology faces the amplitude-versus-offset (AVO) challenge, which has been demonstrated before. We now apply JMI to 1.5-dimensional (1.5D) media, and use a velocity model and a density model to parameterize its solution space. As physically correct one-way propagation, reflection and transmission operators can be analytically formulated in 1.5D JMI, the AVO challenge is thus resolved. In this paper, we derive the complete theory behind the gradient calculation in 1.5D JMI, and further use a 1.5D synthetic example to demonstrate its correctness. This work is an important component of the 1.5D JMI theory, which will have applications in (locally) horizontally layered media containing strong multiple generators.

After a previous review of the grain-size characteristics of in situ (primary) fine-grained aeolian deposits, reworked (secondary) aeolian deposits, as modified in lacustrine environments and by alluvial and pedogenic processes, are discussed in this paper. As a reference, the grain-size characteristics of primary loess deposits are shortly described. Commonly, pedogenesis and weathering of primary loess may lead to clay neoformation and thus to an enrichment in grain diameters of 4–8 μm, a size which is comparable to the fine background loess. Remarkably, the modal grain-size values of primary loess are preserved after re-deposition in lakes and floodplains. But, secondary lacustrine settings show a very characteristic admixture with a clayey population of 1–2,5 μm diameter due to the process of settling in standing water. Similarly, alluvial settings show often an addition with coarse-grained sediment supplied by previously eroded sediment. However, floodplain settings show also often the presence of pools and other depressions which behave similarly to lacustrine environments. As a result, alluvial secondary loess sediments are characterized by the poorest grain-size sorting when compared with the other secondary loess and primary loess. Despite the characteristic texture of each of these deposits, grain-size characteristics of the described individual sediment categories are not always fully diagnostic and thus grain-size analysis should be complemented by other information, as sedimentary structures and fauna or flora, to reliably reconstruct the sedimentary processes and environments.

Delamination is one of the most important damage in composite materials. It can propagate under fatigue loading and cause failures of composite structures. With the application of damage tolerance design philosophy in engineering and requirement of light weight structures in advanced aircrafts, how to characterize fatigue delamination growth behavior in composite materials and develop reliable prediction models become critical issues for the application of these materials. A large amount of studies have been conducted on the characterization of fatigue delamination growth under constant amplitude loading in composite materials. However, little attention has ever been put into the block loading sequence effect on delamination growth. Referring to fatigue crack growth in metals, shielding mechanism of plasticity deformation around the crack front plays a dominant role in the loading sequence effect. Fibre bridging, acting as the shielding mechanism, therefore can contribute to the loading sequence effect on fatigue delamination growth in composite materials. Double Cantilever Beam (DCB) specimens were designed and manufactured for the mode I fatigue delamination tests with HI-HI and LO-HI block loading sequences. Paris relation was subsequently used to interpret the experimental results. It demonstrates there is an obvious loading sequence effect on fatigue delamination growth in composite materials. The fatigue crack growth in the HI-HI block loading is slower than it in the LO-HI block loading.

Multidirectional DCB specimens with different thicknesses were manufactured and tested to have in-depth understanding of delamination behavior in composite laminates. The initiation crack growth is demonstrated to be ply orientation and thickness independent. However, interlaminar resistance and damage mechanisms in delamination growth are significantly related to the interface configuration as well as thickness. Fractography analysis demonstrated that resistance difference between unidirectional and multidirectional DCB specimens is related to damage mechanisms. Optical microscope observation revealed that crack path in the multidirectional specimens is zigzag. This phenomenon becomes vague with thickness increase. The appearance of zigzag crack indicates both interlaminar and intralaminar damage can occur in the delamination growth. However, interlaminar damage becomes the dominant failure mode in the thick specimens. SEM (Scanning Electron Microscope) observation demonstrated fibre prints and cusps are two typical morphologies located on the fracture surface. These features are even more significant in the multidirectional interface with thickness decrease. This paper will conclude that interface configuration and specimen thickness have significant effects on the damage mechanisms and interlaminar resistance during delamination growth in composite laminates. It is, therefore, insufficient to apply the unidirectional DCB specimen with a given thickness to determine delamination growth and damage mechanisms of a composite material.