A structural model for the seismicity of the Arudy (1980) epicentral area (Western Pyrenees, France)

The Western Pyrenees presents a diffuse and moderate ( M ≤ 5.7) instrumental seismicity. It nevertheless historically suffered from strong earthquakes (I = IX MSK). The seismic sources of these events are not yet clearly identified. We focus on the Arudy (1980) epicentral area ( M = 5.1) and propose here the reactivation of early Cretaceous normal faults of the Iberian margin as a potential source. The late Cretaceous inversion of this basin, first in a left-lateral strike-slip mode and then in a more frontal convergence, resulted in a pop-up geometry. This flower structure attests of the presence of a deep crustal discontinuity.
The present-day geodynamic arrangement suggests that this accident is reactivated in a right lateral mode. This reactivation leads to a strain partitioning between the deep discontinuity that accommodates the lateral component of the motion and shallow thrusts, rooted on this discontinuity. These thrusts accommodate the shortening component of the strain. The distribution of the instrumental seismicity fits well the structural model of the Arudy basin. Whatever the compressive regional context, the structural behaviour of the system explains too the extensive stress tensor determined for the Arudy crisis if we interpret it in terms of strain ellipsoid. Indeed numerical modelling has shown that this concomitant activity of strike-slip and thrust faulting results in an extensive component that can rise 50 per cent of the finite strain.
We identify too a 25–30 km long potential seismic source for the Arudy area. The size of the structure and its potential reactivation in a strike-slip mode suggest that a maximum earthquake magnitude of ∼6.5 could be expected. The extrapolation of this model at the scale of the Western Pyrenees allows to propose other potential sources for major regional historical earthquakes.     

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     

Optimum expression for computation of the magnetic field of a homogeneous polyhedral body12

An expression which is optimum with respect to the simplicity of the numerical computations is obtained for the magnetic field of a polyhedron with constant magnetization. The high accuracy of the results is illustrated using a realistic numerical model. The existence of the magnetic field at points inside the source and on its boundary is discussed and related to real magnetic data modelling.     

Improved indirect phase reflection height measurement at panská ves — method,equipment, evaluation

Summary Indirect phase reflection height measurements have been performed at the Panská Ves Observatory, Czechoslovakia, for 30 years to monitor solar flare effects (SFA). Only after introducing the new receiver in May 1985, could the indirect phase height analysis (IPHA) method be applied to measurements along the Allouis — Panská Ves 162 kHJ measuring path. The IPHA method allows the electron density and pressure variability in the lower ionosphere to be studied, particularly near the 80 km altitude. This paper describes the theoretical background of the IPHA method, the measuring equipment used at Panská Ves, the method of evaluating records and checking of data, and the program package developed by us both for graphic and numerical processing, as well as our efforts to develop a homogeneous East European IPHA network. The IPHA method has been introduced succesfully at the Panská Ves Observatory.