Aging and strain softening model for episodic faulting

Episodic slip on shallow crustal faults can be qualitatively explained by postulating a fault constitutive law that is the superposition of two limiting material responses: (1) strain softening after peak stress during large strain rates, and (2) strength (peak stress) recovery during aging at small strain rates. A single law permits a variety of seismic and aseismic phenomena to occur over a range of space and time scales. Specific cases are determined by the spatial variation of material constants, recent deformation history, crustal rigidity, and remote forcing.     

Saturn A ring surface mass densities from spiral density wave dispersion behavior

We have undertaken an analysis of the Voyager photopolarimeter (PPS) stellar occultation data of Saturn's A ring. The Voyager PPS observed the bright star δ Scorpii as it was occulted by Saturn's main rings during the spacecraft flyby of the Saturn system in 1981. The occultation measurement produced a ring profile with radial resolution of approximately 100 m, and radial structure is evident in the profile down to the resolution limit. We have applied an autoregressive technique to the data for estimating the power spectrum as a function of radius, which has allowed us to identify 40 spiral density waves in Saturn's A ring, associated with the strongest torques due to forcing from the moons. The majority of the detected waves are observed to disperse linearly in regions beginning a few kilometers from the resonance location. We have used the dispersion behavior for those waves to calculate local surface mass densities in the vicinity of each wave. We find that the inner three-quarters of the A ring (up to the beginning of the Encke gap) has an average surface mass density of , while the outer region has an average surface mass density of . The two regions have different mean surface mass densities with a significance of approximately 0.999993, as estimated with a T-statistic, which corresponds to about 4.5σ. While the mean optical depth of the A ring increases slightly with increasing distance from Saturn, we find that it is not significantly correlated with the surface mass density; the two quantities having a linear Pearson's correlation coefficient of r_corr≈−0.03. The variation of mass density, independent of PPS optical depth, is consistent with previous conjectures that the particle size distribution and composition are not constant across the entire A ring, particularly in the very outer portion. We estimate the mass of Saturn's A ring from our surface mass density estimates as 4.9×10²¹ gm, or 8.61×10⁻⁹ of the mass of Saturn, roughly equivalent to the mass of a 110-km diameter icy satellite. This mass is almost 25% smaller than estimates from previous studies, but is well within the expected errors of the derived mass densities. We also identified three previously unstudied features which exhibit linear dispersion. The strongest of these features is tentatively identified as the Janus 13:11 density wave. The other two features do not fall near any known satellite resonances and may represent density waves created by previously undetected satellites.     

Simplified seismic fatigue evaluation for rigid steel connections

A simplified fatigue-life model is proposed for assessing the seismic inelastic rotational capacity of steel connections. First relations are developed for rigid steel connections under lateral loading. Next this is extended to account for the effects of the welded steel moment frame (WSMF) connections of the so-called pre-Northridge type. The seismic fatigue theory is validated against experimental results. The experiments were conducted under increasing ductility amplitudcs until the onset of fracture. Miner‘ rule was used to convert the test results to given an equivalent constant amplitude cyclic fatigue life. Satisfactory agreement is obtained when comparing the experimental observations with the theoretical predictions.     

Data use and information creation: challenges for marine scientists and for managers

In the coastal waters of European countries and in the offshore waters of the north-east Atlantic, there is an increasing need for scientists to meet challenging objectives, such as to identify meaningful measures of 'quality', and to recommend 'indicators' to underpin implementation of directives, conventions, statutes and other more informal national and international initiatives. Those indicators may relate to particular species or habitats, to changes in physical and chemical characteristics, and even to the use to which the system is put. The problems to be overcome are difficult, but new and developing approaches will make a significant contribution. The approaches include: criteria to identify 'sensitivity' and 'importance', structures to organise information and electronic information resources to access data.The real challenge is to make the results of the various scientific initiatives relevant to and understandable by a wide range of customers with similar overlapping requirements, and thus make a genuine contribution to protecting the marine environment. Above and beyond that is the need for scientists to drive the agenda to enable real and lasting progress to be made towards ecosystem-based management of our seas and a proper consideration of what 'sustainability' may mean in the marine environment and how we utilise its resources.     

Working rivers: the geomorphological legacy of English freshwater mills

Freshwater mills historically were found throughout England serving a wide variety of uses. The decline in the need for water power over the last 100 years saw a reduction in the number of operational mills. Despite this decline, the associated river structures were rarely removed and many of these have exceeded their design life and have failed or are now starting to fail, with important geomorphological implications for the river. This paper investigates the geomorphological impacts of mills and their structures on English rivers, and considers their legacy for the contemporary management of these systems.     

Xxth International Congress of Photogrammetry and Remote Sensing

The XXth International Congress of Photogrammetry and Remote Sensing was held at the Istanbul Convention and Exhibition Centre (ICEC), Turkey, from 12th to 23rd July 2004. Reports are given on the Congress as a whole, including the General Assembly, some Technical Commission activities and the Congress Exhibition. Papers from the Congress are published in Volume XXXV of the International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences.     

Distribution and significance of chlorophyll derivatives and oxidation products during the spring phytoplankton bloom in the Celtic Sea April 2002

The abundances and distributions of chlorophyll a and its common transformation products have been profiled by high performance liquid chromatography during the disruption, re-establishment, growth and senescence of a phytoplankton bloom in the Celtic Sea during April 2002. Transformation products of chlorophyll a indicative of herbivory of the phytoplankton bloom have been identified using atmospheric pressure chemical ionisation liquid chromatography-multistage mass spectrometry and chlorophyll oxidation products, formed by autoxidation, are present in increasing abundance in samples collected during the later stages of bloom development. The formation of oxidation products during the earliest stages in the chlorophyll transformation pathway identifies water column processes as sources of these early intermediates in the formation of geologic aetioporphyrins and/or cycloalkanoporphyrins.     

Stratigraphic expression of the lateral propagation and growth of isolated fault-related uplifts

The lateral propagation of faults and folds is known to be an important process during the development of mountain belts, but little is known about the manner in which along‐strike fault–fold growth is expressed in pre‐ and syntectonic (growth) strata. We use a coupled tectonic and stratigraphic model to investigate the along‐strike stratigraphic expression of fault‐related folds/uplifts that grow in both the transport and strike directions. We consider faults that propagate following a quadratic (nonself‐similar evolution) or linear (self‐similar evolution) scaling law, using different slip distributions per episode of fault propagation, under general background sedimentation. We find that the long‐strike geometry of pre‐ and syntectonic strata and the geometry of growth axial surfaces reflect the mode of fault propagation. The geometry of strata observed in the model is similar to that observed in natural contractional structures when: (1) the evolution of the fault is nonself‐similar, or (2) the fault grows as a result of thrust faulting events with similar displacements along strike that are terminated abruptly at the fault tips.