Seismic regime of a single fault model

A special experimental technique enabled us to study in detail seismic events on a fault model in a uniaxial stress field. The recording system used made it possible to investigate the radiation pattern for all the events observed including the precise determination of the dislocation origin.The aim of the present paper is (1) to find the relation between shear and tensile displacements, (2) to check a possible influence of the process of tensile crack generation on the seismic energy release and (3) to compare the seismic regime of a single fault before and after the tensile crack generation, respectively.Results prove the dominating importance of shear mechanism for the seismic energy release. The tensile displacement can be seismoactive only under special contact conditions on the fault plane.The existence of tensile cracks at the fault tips changed the pattern of seismic energy radiation. This feature is probably caused by subsequent changes in contact conditions on the fault plane and in the stress field around the fault.A comparison of some results of the present model experiments with the already published results of geological and seismological measurements and investigations shows the analogous character in laboratory and in nature of the process of tectonic earthquake preparation, the displacement course on the fault during the earthquake and the manner of seismic energy release on faults.     

Gravity ideal-body analysis

Summary This short note contributes to the methods of computing the bounds on some properties of the source of measured data.     

The mechanism of small mining tremors from amplitude inversion

A method of inverting seismic wave amplitudes from mining tremors is proposed to reveal their mechanism. A simple shear-implosive model of a mechanism is proposed. The shapes of theoretical and observed radiation patterns are compared in the least squares norm and the parameters describing the shear-slip together with the ratio of implosive and shear dislocations are optimized. The efficiency of the method, even in the case of a small number of stations, is demonstrated by applying it to weak mining tremors from two mine regions in Czechoslovakia.The weak mining tremors are found to be of a predominantly shear mechanism with a clear coincidence of nodal planes to local tectonics, which could imply their tectonic nature.     

Topographic effects on tidal strains and tilts

Summary Topographic effects on tidal strains and tilts are studied using a homogeneous elastic spherical model. Expressions for local perturbing strains and tilts are derive das functions of the physical and geometrical parameters of the model. It is demonstrated that tidal tilts are affected more by the topography than tidal strains.

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On some of the relations for vertical velocity in the atmosphere

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Protection of groundwater from oil pollution in the vicinity of airports

Airports are potential, and quite frequently also actual, sources of serious groundwater pollution. This is due to the large amounts of liquid fuel being handled all the time, to the physicochemical properties of oil hydrocarbons, and often to technical errors in the transport and storage of fuels. The environment is further affected by liquid and gaseous emissions escaping during the take-off and landing of aircraft Snow in the vicinity of runways has been found to contain oil hydrocarbons in concentrations of tenths to units of milligrams per liter Moreover, soil tends to accumulate carcinogenous benzopyrenes. In rock formations, oil hydrocarbons spread as a separate layer as well as in solution in porous permeable formations, pollution by a free product affects areas on the order of tens of meters, while hydrocarbons in solution penetrate to distances of hundreds of meters or even kilometers. More complex conditions for the spreading of oil-based substances arise in fissured rocks. Aviation kerosene as a separate phase was found to migrate over 700 meters within 5 months through fissure systems in sandstones Prevention is the most efficient way of protecting groundwater from oil pollution. Preventive surveys are based on the drilling of observation wells at suitable points of the potentially endangered areas. Monitoring of these wells provides timely detection of possible leaks of oil products into the aquifer In the case of an emergency, it is necessary to remove, as soon as possible, the oil substances from the surface or to remove the contaminated soil. When the contaminant has penetrated into the aquifer, the reparatory measures are usually based on hydraulic protection which consists of a system of boreholes. The respective hydrocarbon product is removed from the formation by pumping, the process being speeded up by the change in groundwater flow caused by the creation of depression cones The example of Prague Airport is suitable for describing a successful, although complex and expensive, purification of a Chalk aquiter polluted among other things by a leak amounting to 300 m³ of aviation kerosene. Vapex filters have proven very satisfactory for purifying the contaminated water Preventive protection of groundwater and mineral waters using monitoring devices is being carried out at Karlovy Vary Airport No groundwater pollution has so far been observed in this instance. However, a seasonal variation in the content of hydrocarbons dissolved in groundwater has been established. The highest content occurs in the spring months. Observation wells situated in the tectonic zone can also be utilized for reparative pumping     

Geoscience for environmental planning in Lithuania

While consideration of natural environment factors increased in the late eighties, from the very beginning geoscience was outside the planning process. It was a consequence of the state of applied geology in Lithuania. During this time the development of certain industrial projects was stopped; urgent environment protection measures came into use; it was recognised that nonrational utilization depleted resources.     

Refinement of the geopotential scale factorR 0 on

Altimetric measurements of the GEOSAT satellite were used for the determination of geopotential scale factorR ₀. The geopotential valueW ₀ on the geoid surface was then computed (W ₀ =GM/R ₀).The GEOSAT Geophysical Data Records (GDR's) covering an initial period of the Exact Repeat Mission (ERM) were filtered and processed. The necessary corrections were made in order to allow a precise detection of the sea surface. Gravitational geopotential, rotation and permanent tides were taken into account and the equipotential surface which is the best approximation of the sea surface was found.The determination of the potential valueW ₀ on the mean geoid surface in this way is very promising. An associated value withW ₀ - the geopotential scale factorR ₀ - seems to be a very good Earth dimension defining quantity. Moreover, there are many possible applications ofW ₀ (R ₀) in modern geophysics.The incorporation of one of these parameters - we now recommendR ₀ - into the set of the Primary Geodetic Parameters (PGP) is discussed and suggested.     

The Queens' flare: Its structure and development; precursors,pre-flare brightenings,and aftermaths

We continue previous research on the limb flare of 30 April, 1980, 20:20 UT, observed in X-rays by several instruments aboard the Solar Maximum Mission (SMM). It is shown quantitatively that the flare originated in an emerging magnetically confined kernel (diameter ～ 20″) which existed for about ten to fifteen minutes, and from which energetic electrons streamed, in at least two injections, into a previously existing complicated magnetic loop system thus forming a less bright but extended and long-lived tongue. The tongue had a length of ～ 35 000 km and lasted ～ 90 min in X-rays (～ 10 keV); at lower energies (～ 0.7 keV) it was larger (～ 80 000 km) and lasted longer. The total number of energetic electrons (≈ 10³⁷) initially present in the kernel is of the same order as the number present in the tongue after the kernel's decline. This gives evidence that the energetic electrons in the tongue originated mainly in the kernel. The electron number densities in the kernel and tongue at maximum brightness were ～ 4.5 × 10¹¹ and ～ 1 × 10¹¹ cm^#X2212;3, respectively. During the first eight minutes of its existence the tongue was hotter than the kernel, but it cooled off gradually. Its decline in intensity and temperature was exponential; energy was lost by radiation and by conduction through the footpoints of the loop system. These footpoints have a cross-section of only ～ 3 × 10⁶ km². This small value, as well as photographs in a Civ UV emission line, suggests a highly filamentary structure of the system; this is further supported by the finding that the tongue had a ‘filling factor’ of ～ 10^#X2212;2. Several faint X-ray brightenings (? 0.005 of the flare's maximum intensity) were observed at various locations along the solar limb for several hours before and after the flare. At ～ 30 min before the flare's onset a faint (? 0.02) flare precursor occurred, coinciding in place and shape with the flare. First the kernel precursor was brightest but the tongue precursor increased continuously in brightness and was the brightest part of the precursor some 10–15 min after the first visibility of the kernel precursor, until the start of the main flare. This suggests (weak) continuous electron acceleration in the tongue during a period of at least 30 min. The main flare was caused by strong emergence of magnetic field followed by two consecutive field line reconnections and accelerations in a small loop system, causing footpoint heating. Subsequently plasma streamed (convectively) into a pre-existing system of larger loops, forming the tongue.     

Possible accretion instabilities on magnetized rotating neutron stars

The high energy particles emitted by a pulsar prevent the accretion of the interstellar matter onto the star. However, during the life of a pulsar the energy output decreases and after elapsing of critical timet _cr the pulsar mechanism is obviously inhibited and matter may penetrate through the radius of capturer _a . It is proposed that a possible accumulation of this matter in the regionrr _c , wherer _c is the corotational radius, is followed by a sudden fall onto the stellar surface. Short bursts of high energy photons may be expected as a result. A possible explanation of recently observed gamma-ray bursts by this mechanism is discussed.