Simple analytical Green's functions for ray perturbations in layered media

The total Green's function for two-point boundary-value problems can be related to the propagator for initial-value problems. A very simple expression for the Green's function is obtained when the unperturbed medium may be described by material with a constant gradient in quadratic slowness. The derivation requires a correct understanding of assumptions made in the propagator solution. Expressions are also obtained for Green's function in multilayered media.     

VLF radiation from lightning

Summary. Electrical and magnetic fields due to arbitrarily oriented lightning over an imperfectly conducting ground have been obtained. The theory has been applied to K -changes, return strokes and horizontal lightning. The results are in good agreement with the experimental observations previously reported by many workers.     

Managed relocation: an assessment of its feasibility as a coastal management option

Managed relocation is explained and examined as an option to add to the usual categories considered in relation to managing coastal erosion. The paper considers the relocation of buildings in one unit, as opposed to demolition and re-construction. The standard coastal erosion management options are briefly noted and how managed relocation can fit into these options is explained. This paper focuses on four case studies. Two examples are from the USA and two from the UK; of these, two (one in each of the UK and USA) took place during the nineteenth century. Managed relocation is proposed as being feasible in particular cases, particularly where there are isolated historic or high value buildings.     

Shallow-marine sequences as the building blocks of stratigraphy: insights from numerical modelling

Two types of depositional sequences can be defined within the sequence stratigraphic framework: the parasequence and the high‐frequency sequence. Both sequences consist of stacked regressive and transgressive deposits. However, a parasequence forms under conditions of overall sea‐level rise, whereas a high‐frequency sequence forms as the sea level oscillates which results in typical forced regressive deposits during sea‐level fall. Both depositional sequences may develop over comparable temporal (10–100 kyr) and spatial (1–20 km wide and 1–40 m thick) scales. Numerical modelling is used to compare the architecture, preservation potential, internal volumes, bounding surfaces, condensed and expanded sections and facies assemblages of parasequences and high‐frequency sequences. Deposits originating from transgression are less pronounced than their regressive counterparts and consist of either preserved backbarrier deposits or shelf deposits. Shoreface deposits are not preserved during transgression. The second half of the paper evaluates in detail the preservation potential of backbarrier deposits and proposes a mechanism that explains the occurrence of both continuous and discontinuous barrier retreat in terms of varying rates of sea‐level rise and sediment supply. The key to this mechanism is the maximum washover capacity, which plays a part in both barrier shoreline retreat and backbarrier‐lagoonal shoreline retreat. If these two shorelines are not balanced, then the retreat of the coastal system as a whole is discontinuous and in time barrier overstep may take place.