Triggered earthquakes and deep well activities

Earthquakes can be triggered by any significant perturbation of the hydrologic regime. In areas where potentially active faults are already close to failure, the increased pore pressure resulting from fluid injection, or, alternatively, the massive extraction of fluid or gas, can induce sufficient stress and/or strain changes that, with time, can lead to sudden catastrophic failure in a major earthquake. Injection-induced earthquakes typically result from the reduction in frictional strength along preexisting, nearby faults caused by the increased formation fluid pressure. Earthquakes associated with production appear to respond to more complex mechanisms of subsidence, crustal unloading, and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material. As each of these different types of triggered events can occur up to several years after well activities have begun (or even several years after all well activities have stopped), this suggests that the actual triggering process may be a very complex combination of effects, particularly if both fluid extraction and injection have taken place locally. To date, more than thirty cases of earthquakes triggered by well activities can be documented throughout the United States and Canada. Based on these case histories, it is evident that, owing to preexisting stress conditions in the upper crust, certain areas tend to have higher probabilities of exhibiting such induced seismicity.     

On the application of the mode-acceleration method to structural engineering problems

Mode-superposition has been extensively used in computing the dynamic response of complex structures. Two versions of mode-superposition, namely the mode-displacement method and the mode-acceleration method, have been employed. The present paper summarizes the results of a systematic study comparing the accuracy of the mode-displacement and mode-acceleration methods when applied to structures with various levels of damping or various excitation frequencies. The paper also discusses several details concerning the implementation of the mode-acceleration method.     

Mass motions in a heated flare filament

Energy transport in a hot flare plasma is examined with particular reference to the influence of fluid motion. On the basis of dimensional considerations the dynamical timescale of the flare plasma is shown to be comparable to the timescale for energy loss by conduction and radiation. It is argued that mass motion is likely to have a profound influence on the evolution of the flare.The detailed response of a flare filament to a localized injection of energy is then analyzed. Radiative, conductive and all dynamical terms are included in the energy equation. Apart from greatly enhancing the rate of propagation of the thermal disturbance through space, mass motion is found to be significant in transferring energy through the moving fluid.Finally the predicted thermal structure is discussed and it is concluded that the presence of mass motions in the flare may be inferred from the form of the soft X-ray differential emission measure.     

The thermal nature of soft X-ray flares

Soft X-ray flare data in the wavelength range 2.6–10 Å are used to examine the time variation of emission measure and electron temperature. The thermal plasma parameters were derived according to a two-temperature model proposed by Herring and Craig (1973). Estimates of electron density and source volume are made by assuming conductive and radiative cooling mechanisms. It is suggested that the present observations imply a multi-thermal interpretation of the soft X-ray flare.     

Rotating disk electrode oxygen sensor and corrosion rate probe

A rotating disk electrode (RDE) is applied as a dissolved oxygen sensor and corrosion rate probe. As an oxygen sensor, the RDE is capable ofpm0.004-ml/l resolution andpm0.17-ml/l accuracy. As a corrosion rate probe, the RDE behaves more closely to theory than stationary electrodes. These applications make use of the RDE's unique hydrodynamic properties.     

Thermonuclear detonations in collapsing white dwarf stars

Collapsing white dwarf stars (or degenerate cores) may occur in binary systems, in the formation of Type I supernovae or in the formation of pulsars. These collapsing configurations may explode their nuclear fuel (¹²C or¹⁶O) by the detonation wave mechanism. A combination of analytical and numerical models is used to investigate the formation of detonation waves. The tentative conclusion is that a detonation wave will form which will lead to the ignition of esentially all the fuel in such a collapsing star. This potentially explosive configuration will be strongly affected, however, by rapid beta processes which occur in the detonated matter and which should cause a fraction of the stellar mass to collapse toward a neutron star state. The nature and effect of such beta processes, which have not yet been incorporated in the dynamical calculations, are discussed.An appendix gives approximate expressions for the pressureP(,T) and the internal energy densityU(,T) for a degenerate relativistic electron gas and an analysis of the errors expected in making such approximations to the standard parametric form of the equation of state. These expressions are useful in analyzing shock waves in a degenerate electron gas.Supported in part by the National Science Foundation [GP-15911, GP-9114, GP-19887] and the Office of Naval Research [Nonr-220 (47)] at the California Institute of Technology, and National Science Foundation Grant GP-12455 at the University of Colorado.