Olivine phenocrysts of Hawaiian olivine tholeiite and oceanite

Olivine phenocrysts of Hawaiian tholeiites display a variety of textures and a variation in composition which is due to supercooled crystallization. The highest forsterite content measured is 91%, and the highest magnesia content estimated for a tholeiitic liquid is 17%, using the olivine geothermometer. The liquid of this composition may be either a primary magma or a primitive magma. It is not yet possible to specify any particular composition range for the primary Hawaiian tholeiites.     

Numerical Modeling of the Ston-Slano (Croatia) Aftershock Sequence

The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (M _L 4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock.     

Analysis of sustained long-period activity at Etna Volcano, Italy

Following the installation of a broadband network on Mt. Etna, sustained Long-Period (LP) activity was recorded accompanying a period of total quiescence and the subsequent onset of the 2004–2005 effusive episode. From about 56000 events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th, 2003–September 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the 0.5–10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters, and extending to a maximum depth of ≈ 800 m beneath the surface. No causal relationships are observed between LP, VLP and tremor activities and the onset of the 2004–2005 lava effusions, thus indicating that magmatic overpressure played a limited role in triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods, and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system.     

跨采软岩巷道锚注支护试验研究

通过对鲍店煤矿北翼跨采软岩巷道的调查与分析，说明了巷道的破坏机理，并根据跨采软岩巷道的特点提出了各类巷道的支护技术方案。通过巷道数值模拟、相似材料模拟及井下试验应用，取得了较好的技术经济效果。     

山西沁水煤层气田采收率预测

采用地质类比、等温吸附曲线及储层数值模拟 3种方法对山西沁水煤层气田主力气层———二叠系山西组 3# 煤层、石炭系太原组 15 # 煤层的煤层气采收率进行了预测 ,结果 3# 煤层的煤层气采收率为 6 2 % ,15 # 煤层的采收率为 5 5 % ,总平均采收率为 5 9%。分析对比了这 3种方法的运用条件及优缺点 ,指出煤层气采收率的预测必须采用多种方法 ,并结合具体的煤层气地质特点进行综合分析 ,才能得出合理的结论。     

Application of the photoacoustic method for characterization of natural galena (PbS)

Electron transport properties of single crystal and polycrystalline natural mineral galena (PbS) samples from the Trep?a mine, Yugoslavia, were determined using the photoacoustic frequency transmission technique. Their thermal diffusivity (D _T≈0.16 × 10^?5 m² s^?1), the coefficient of diffusion (D between 0.15×10^?2 0.16×10^?2 m² s^?1) and lifetime of the excess carrier (τ≈35 μs and the front and rear recombination velocity (s _g≈65.5 m s^?1 and s _b≈66.4 m s^?1, respectively), were calculated by comparing the experimental results and the theoretical photoacoustic amplitude and phase signals. The lattice parameter obtained by X-ray work was a?=5.936?Å. The free carrier concentration of these single-crystal samples was measured using the Hall method (N?=?3×10¹⁸ cm^?3). Measurements of the optical reflectivity of the same samples, as a function of wavelength, in the infrared and far infrared ranges, were performed. In the far infrared range a free electron plasma frequency was observed and numerically analyzed, using the least-squares fitting procedure. The values of optical parameters were calculated and the value of the free carrier concentration obtained by the Hall method was confirmed.     

Polyhedral approximations in physical geodesy

Summary A procedure is derived for the upward continuation of unevenly spaced gravity data. The topographic relief is approximated by a polyhedron with triangular faces and vertices placed at small distances around the surface of a sphere. The usual Fredholm integral equation of the second kind is modified considering the discontinuity of the normal vector. It is solved by successive approximations assuming the unknown function is linear inside each face at every step of the iteration process. An approximate formula to obtain the anomalous potential from the Bouguer anomaly is discussed. The potential of a homogeneous polyhedron is derived and used to compute relief corrections to the geoid undulations. Numerical applications are presented with respect to the Romanian territory.Partially presented at theJoint Symposium of IGC and IGC, Graz, Austria, 11–17 September 1994     

Ice-sheet growth and high-latitudes sea-surface temperature

The response of the LLN 2-D climate model to the insolation and CO₂ forcings during the Eemian interglacial is compared to reconstructions obtained from deep-sea cores drilled in the Norwegian Sea and in the North Atlantic. Both reconstructions and modeling results show a decrease of sea-surface temperature (SST) in the higher latitudes (70–75 °N zonal belt for the model and the Norwegian Sea for the proxy records), associated with a more moderate cooling at lower latitudes (50–55 °N and North Atlantic), at the middle of isotopic substage 5e, several millenia before the beginning of continental ice-sheet growth. Such a comparison between the simulated SST and ice volume of the Northern Hemisphere has been extended to the whole last glacial-interglacial cycle. The influence of the insolation forcing on SST and the shortcomings of the model due to its zonal character are discussed. Received: 6 July 1995/Accepted: 19 December 1995