Platform subsidence mechanisms and “eustatic” sea-level changes

The boundaries between major world-wide sequences of sediments on continental platforms are due primarily to either eustatic changes or to systematic uplift of the continental interior. If thermal contraction of the lithosphere controls basin subsidence, basins would continue to subside during times of low eustatic sea level. Calculations indicate that significant gaps in the geological record could be produced by modest eustatic sealevel changes even in rapidly subsiding basins. For example, a 95 m withdrawal could have produced the sub-Devonian unconformity in the Michigan Basin. The vertical amplitude of eustatic variations can be determined directly from the depth of paleotopographic valleys (135m for sub-Pennsylvanian of Illinois Basin) and from the present elevation of sediments deposited during highstands (300 m above present sea level). The Illinois Basin aparently continued to subside during the sub-Pennsylvanian regression.     

Sedimentation pattern in Central Anatolia at the Cretaceous-Tertiary boundary

In the Central Anatolia region of Turkey, a mixture of sedimentary and tectonic melanges cover extensive areas, bordering the north, north-west and west of the Kir?ehir Massif. Broadly the age of this melange is Mesozoic; however it includes olistoliths whose ages range from Carboniferous to Cretaceous. A series of interconnected basins existed within the “melange belt” during Late Cretaceous-Early Tertiary times. They have been infilled, throughout the Lower Tertiary, by slump and mass-flow deposits, produced by active tectonic events. These events seem to be a natural continuation of the earlier stronger tectonics which produced the melanges.     

Framework for integrated assessments of global warming impacts

This paper provides a framework for integrated assessment of the impacts of climate change on natural resources and sets the stage for papers that follow in this volume. Integrated assessments are used to organize large quantities of technical information bearing on complex issues (environmental and others) in ways that facilitate application of the information in decision making and policy setting. Any integrated assessment must be based on the best available information. For that reason this paper includes a ‘primer’ on the current (and presumably best available) understanding of the science underlying climatic change. The remainder of the paper describes the component parts of one possible framework for integrated assessment.     

A critical-density closed universe in BransDicke theory

In a BransDicke (BD) cosmological model, the energy density associated with some scalar field decreases as a ^{2[( o +1/2)/( _o +1)]} with the scalefactor a ( t ) of the universe, giving matter with an equation of state In this model, the universe could be closed but still have a non-relativistic matter density corresponding to its critical value, _o =1. Different cosmological expressions, such as luminosity distance, angular diameter, number count and ratio of the redshift thicknessangular size, are determined in terms of the redshift for this model.     

A vector-valued intensity measure for near-fault ground motions

Near-fault ground motions containing high energy and large amplitude velocity pulses may cause severe damage to structures. The most widely used intensity measure (IM) is the elastic spectral acceleration at the fundamental period of the structure (Sa(T₁)); however, Sa(T₁) is not a sufficient IM with respect to the effects of the pulse-like ground motions on structural response. For near-fault ground motions, including pulse-like and non–pulse-like time histories, we propose a vector-valued IM consisting of a new IM called instantaneous power (IP(T₁)) and the Sa(T₁). The IP(T₁) is defined as the maximum power of the bandpass-filtered velocity time series over a time interval of 0.5T₁. The IP(T₁) is period-dependent because the velocity time series is filtered over a period range (0.2T₁-3T₁). This allows the IP(T₁) to represent the power of the near-fault ground motions relevant to the response of the structure. Using two-dimensional models of the 2- and 9-story steel-frame buildings, we show that the proposed [Sa(T₁), IP(T₁)] vector IM gives more accurate estimates of the maximum inter-story drift and collapse capacity responses from near-fault ground motions than using the vector IM consisting of the Sa(T₁), the presence of the velocity pulse, and the period of the velocity pulse. Moreover, for the structures considered, for a given Sa(T₁), the IP(T₁) is more strongly correlated with structural damage from near-fault ground motions than the combination of the velocity pulse and pulse period.