Interpreting intraplate tectonics for seismic hazard : a UK historical perspective

It is notoriously difficult to construct seismic source models for probabilistic seismic hazard assessment in intraplate areas on the basis of geological information, and many practitioners have given up the task in favour of purely seismicity-based models. This risks losing potentially valuable information in regions where the earthquake catalogue is short compared to the seismic cycle. It is interesting to survey how attitudes to this issue have evolved over the past 30 years. This paper takes the UK as an example, and traces the evolution of seismic source models through generations of hazard studies. It is found that in the UK, while the earliest studies did not consider regional tectonics in any way, there has been a gradual evolution towards more tectonically based models. Experience in other countries, of course, may differ

A Dual Digital Signal Processor VME Board For Instrumentation And Control Applications

A Dual Digital Signal Processing VME Board was developed for the Continuous Electron Beam Accelerator Facility (CEBAF) Beam Current Monitor (BCM) system at Jefferson Lab. It is a versatile general-purpose digital signal processing board using an open architecture, which allows for adaptation to various applications. The base design uses two independent Texas Instrument (TI) TMS320C6711, which are 900 MFLOPS floating-point digital signal processors (DSP). Applications that require a fixed point DSP can be implemented by replacing the baseline DSP with the pin-for-pin compatible TMS320C6211. The design can be manufactured with a reduced chip set without redesigning the printed circuit board. For example it can be implemented as a single-channel DSP with no analog I/O.Comment: 3 PDF page

DTI Strategic Environmental Assessment Area 4 (SEA4) : sub seabed geology

The SEA 4 region is underlain by continental crust situated on the north-western part of the Eurasian tectonic plate. The oldest continental crust >590Ma (Pre-Cambrian) of interest to oil production, it is divided by a major fault, the Moine Thrust, into ages ranging in age from >2500Ma (Archaean) to the west in which potentially commercial hydrocarbons been discovered and 2500 - 590 Ma (Proterozoic) to the east which is not currently prospective for commerciallyproduced hydrocarbons. The <590Ma sedimentary basins and intervening highs have evolved from pre-, syn- and postdepositional responses to deformation during crustal compression and extension. Many of the modern regional crustal structures retain a NE-SW trend, inherited from events 440-410Ma year ago (Caledonian Orogeny). The results from <65Ma regional NW-SE trending deformation events are also included within the major basin structural configurations. During 60-50 Ma (Late Paleocene to Early Eocene) the region was affected by uplift and in the NW by extrusion of thick volcanic lavas and intrusion of igneous sills. Interactions between historically significant shifts of long-term global climate cooling, an increase in the short-term periodicity and intensity of global climate change and changes to the rates and orientation of crust deformation have been particularly important from 25Ma to the present day (Neogene to Quaternary). These interactions have driven global-to-local changes to basin geological structure, marine circulation, sea level and sediment supply and removal rates and have resulted in the evolutionary changes to submarine basin geometries and lithologies. The modern seabed habitat has thus resulted from the remoulding of inherited basin geometries and lithologies by the processes affecting seabed. The structural history of the region has created a wide variety of potential hydrocarbon trapping mechanisms. The 154-136Ma (Late Jurassic, Kimmeridgian to Ryazanian) Kimmeridge Clay Formation is the principal source rock of the area. The Foinaven and Schiehallion oilfields started production in late 1997 and 1998 respectively both from 60-55Ma (Upper Paleocene) sandstone reservoirs. Geological and technical problems have so far prevented the development of the massive 440-390Ma (Devono-Carboniferous) Clair Field which is the largest undeveloped oilfield on the UK continental shelf. Other hydrocarbon accumulations have been discovered in 245-208Ma (Triassic), 208-146Ma (Jurassic) and 146-65Ma (Cretaceous) intervals in the West Shetland area in the most prospective parts of the SEA 4 region

Homological algebra for osp(1/2n)

We discuss several topics of homological algebra for the Lie superalgebra osp(1|2n). First we focus on Bott-Kostant cohomology, which yields classical results although the cohomology is not given by the kernel of the Kostant quabla operator. Based on this cohomology we can derive strong Bernstein-Gelfand-Gelfand resolutions for finite dimensional osp(1|2n)-modules. Then we state the Bott-Borel-Weil theorem which follows immediately from the Bott-Kostant cohomology by using the Peter-Weyl theorem for osp(1|2n). Finally we calculate the projective dimension of irreducible and Verma modules in the category O

A commutant realization of W^(2)_n at critical level

For n\geq 2, there is a free field realization of the affine vertex superalgebra A associated to psl(n|n) at critical level inside the bc\beta\gamma system W of rank n^2. We show that the commutant C=Com(A,W) is purely bosonic and is freely generated by n+1 fields. We identify the Zhu algebra of C with the ring of invariant differential operators on the space of n\times n matrices under SL_n \times SL_n, and we classify the irreducible, admissible C-modules with finite dimensional graded pieces. For n\leq 4, C is isomorphic to the W_n^{(2)}-algebra at critical level, and we conjecture that this holds for all n.Comment: Some corrections and expository improvements, references added, final version. arXiv admin note: text overlap with arXiv:1201.016

The G0 Experiment: Apparatus for Parity-Violating Electron Scattering Measurements at Forward and Backward Angles

In the G0 experiment, performed at Jefferson Lab, the parity-violating elastic scattering of electrons from protons and quasi-elastic scattering from deuterons is measured in order to determine the neutral weak currents of the nucleon. Asymmetries as small as 1 part per million in the scattering of a polarized electron beam are determined using a dedicated apparatus. It consists of specialized beam-monitoring and control systems, a cryogenic hydrogen (or deuterium) target, and a superconducting, toroidal magnetic spectrometer equipped with plastic scintillation and aerogel Cerenkov detectors, as well as fast readout electronics for the measurement of individual events. The overall design and performance of this experimental system is discussed.Comment: Submitted to Nuclear Instruments and Method