Ray-mode duality for SH waves in earth models with crust and mantle discontinuities—I. The case of one discontinuity

Summary. The method of phase correlation devised by Brune for the evaluation of overtone eigenfrequencies of the Earth from body-wave data involves the explicit use of a ray-mode duality for strictly continuous earth models. Consequently, investigation of the application of the ray-mode duality approach to models containing discontinuities is desirable.
McNabb, Anderssen & Lapwood have obtained an equation for the behaviour of overtone eigenfrequencies from discontinuous earth models. By means of a novel method for the decomposition of multiply-reflected body waves, it can be shown that, for earth models with a single discontinuity between the surface and the core—mantle boundary, the McNabb et al. formulation can be derived from an adaptation of Brune's formula to multiply-reflected SH body waves at small epicentral distances. This establishes a basis for a ray-mode duality for models with a single discontinuity.     

A revision of the Ordovician stratigraphy for the western Ireland Caledonides and implications for tectonic models

The western Ireland Ordovician stratigraphy has been previously used to constrain the timing of docking of an island arc and its fore‐arc basin with the margin of Laurentia for the British and Irish Caledonides. New field relationships and age data indicate that one of the key formations, the Rosroe Formation (459.2 ± 0.8 and 465.1 ± 2.1 Ma), and its supposed lateral equivalent, the Maumtrasna Formation are younger than previously interpreted. New age data for a tuff band in the Maumtrasna Formation (468.9 ± 1.3 Ma) also support previous studies showing it can be correlated to the adjacent Mweelrea Formation. The new field evidence, age data and geochemistry contradict some previous studies and show that the Maumtrasna, Rosroe and Derrylea formations can no longer be considered lateral equivalents. Based on the new stratigraphy a revised tectonic model is required with sedimentation in this part of the Caledonides taking place in a fore‐arc basin outboard of a continental arc and the oceanic arc was an along‐strike equivalent of this arc situated in an embayment of the Laurentian margin. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural identification and mass spectral interpretation of C3n highly branched alkanes in sediment and aquatic extracts and evidence for their anthropogenic origin

The structures of two distinctive series of C_3n highly branched alkanes (HBAs), previously detected in sedimentary and aquatic extracts, were identified as polypropylene (PP) oligomers with different end groups, using gas chromatography (GC) and mass spectrometry (MS) correlation with diastereoisomeric mixtures of authentic C₁₅ and C₁₈ standards. A C₁₅ member of the earlier eluting series was assigned as 2,4,6,8-tetramethylundecane and a C₁₅ member of the later eluting series as 4,6,8-trimethyldodecane. The C_3n HBA GC–MS profiles of extracts from a typical PP GC sample vial lid were also shown to closely match those previously detected in sediment and water extracts, providing convincing evidence that the purported environmental occurrences are a result of PP contamination. Both C_3n series correspond to the first eluting diastereoisomer of the respective standards, also consistent with an industrial isotactic PP source. Mass spectra of all five standards are presented to help assignment of new polymethyl alkanes.     

Cyclic geomorphic patterns of washover on a barrier Island in southeastern North Carolina

A detailed analysis of historic aerial photographs provided the data for determining the magnitude and importance of oceanic overwash on Masonboro Island, southeastern North Carolina. Overwash, which is both temporally and spatially distributed, produces a suite of physiographic features on the subaerial portion of the island. Four physiographic types are recognized including: A) small coalescing loosely vegetated dunes, B) intact, well-vegetated dunes and terraces, C) individual, isolated washover fans, and D) washover terraces. Vegetation patterns, including shrub thickets and black needle rush marshes are related to old fan sites. Sites dominated by saltmeadow cordgrass and goldenrod are associated with recent overwashes. A process-response model, which synthesizes the physiographic types and vegetation patterns, provides input for a management program for the island. Five sections on Masonboro Island are delineated on the basis of washover history and potential for future washovers. The response of Masonboro Island to overwash is similar to that observed on Core Banks, North Carolina; however there are several differences, probably because of the rapidity with which dune ridges redevelop after washovers.     

DEVISE AND RULE: COLONIAL CONSTRUCTIONS OF THE BORNEO DAYAK c.1860–1920

This paper considers some of the ways in which travellers, administrators and academics in the colonial period sought to categorise the indigenous groups of Borneo. It focuses on Sarawak and North Borneo between about 1850 and 1920, and examines the use of stereotypical images of exoticism, fear and loathing in constructing different categories of peoples in the region. The paper argues that such categorisations were important in structuring the relationships between ruler and ruled, and in the development of particular regional and local identities.     

Seismic activity in the snowy mountains region and its relationship to geological structures

Forty‐four tremors which occurred in the Snowy Mountains of New South Wales during the years 1958–1962 have been accurately located, using a network of seismic stations operating in that area. The largest of these were a tremor of magnitude 5 north of Berridale in May, 1959, and one of magnitude 4 near Rock Flat in September, 1958. Fault plane analysis suggests that the former was caused by a high‐angle thrust movement along the plane of the Crackenback Fault, while the latter may be associated with the Murrumbidgee Fault. These conclusions are supported by macroseismic data.

Twenty‐one minor shocks occurred in the vicinity of the Berridale tremor, and their strain release pattern is that of an after‐shock sequence. It is believed that they were produced as a result of secondary strains imposed by the original motion along an edge of the faulted block. The first motion data for these shocks is consistent with the hypothesis that the associated movements were transcurrent.

With the decrease of activity in the Berridale region, tremors became more or less random in the Snowy Mountains. The strain release curve obtained for these movements suggests a gradual rebuilding of the stress field following the Berridale shock.