排序方式： 共有12条查询结果，搜索用时 15 毫秒
1.
2.
3.
Sandra Barbouteau Patrick Rasolofosaon Noalwenn Dubos‐Sallée Virginie Vassil Valérie Poitrineau Jean‐François Nauroy 《Geophysical Prospecting》2016,64(5):1368-1385
This article introduces an alternative experimental procedure for measuring the elastic properties of a solid material at laboratory scale, using both the principles of passive seismic interferometry and resonance ultrasound spectroscopy. We generate noise into the studied sample with a pneumatic air blow gun, and we cross‐correlate the signals recorded with two passive piezoelectric sensors put in soft contact with the sample surface. Resonance phenomena are induced in the sample, but in contrast with conventional resonance ultrasound spectroscopy experiments, we have no control over the injected frequencies that are sent all together within the noise spectrum. The spectrum of the correlogram is a good approximation of the resonance spectrum of the vibrating sample and can be inverted in terms of the elastic moduli of the constituent material of the sample. The experimental procedure is validated on samples made of standard materials (here, aluminium and Plexiglas) by consistently comparing the inverted elastic velocities with the velocities independently measured with the conventional technique of ultrasonic pulse transmission. Moreover, we got similar positive results on dry rock samples, such as Vilhonneur limestone. These encouraging preliminary results open up promising prospects for monitoring fluid substitution in rock samples using the technique described in this paper. 相似文献
4.
The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed. 相似文献
5.
6.
Neli Jordanova Diana Jordanova Vassil Karloukovski 《Studia Geophysica et Geodaetica》1996,40(1):36-49
Summary The anistropy of low field magnetic susceptibility has been studied for seven outcrops of loess sediments in North-Eastern
Bulgaria. Different sampling methods were applied in order to choose the best technique for obtaining the primary magnetic
fabric of such unconsolidated sediments. AMS results show significant changes in the petrofabric of samples collected by the
first technique which disturbs the original sedimentary fabric. The second applied technique does not cause such a strong
deformation but some disturbance of the magnetic fabric is probable. Typical sedimentary fabric is obtained from hand samples
and it is therefore concluded that this represents the best method for obtaining reliable AMS results from soft sediments. 相似文献
7.
8.
9.
Geologic evolution of Bulgaria in light of plate tectonics 总被引：1，自引：0，他引：1
The Balkanide is a mobile belt within a micro-continent, which included both the Moesian Platform and Rhodope Massif. This micro-continent was rotated counter-clockwise during the Jurassic mainly in response to the sea-floor spreading of the Vardar ophiolite trough. The rotation led to the consumption of Triassic Tethys along the Dobrogea—Crimea—Caucasus Trend, producing the Cimmerian orogenic belt. Cretaceous rotation of the Italo-Dinaridian micro-continent led to the consumption of the Vardar ophiolites. An island arc (Macedonia—Rhodope—North Anatolia) was present at the consuming plate margin. Middle and Late Cretaceous marginal basins behind this arc included the Srednogorie and the Black Sea. Submarine volcanics, radiolarian cherts, and hemipelagic marls were deposited in the Srednogorie “eugeosyncline”. This sequence was folded during the early Tertiary Alpine orogeny, when the front of the Rhodope Massif was overthrust onto the Balkanides. The Black Sea meanwhile remained undeformed and can thus be considered a fossilized Cretaceous marginal basin. 相似文献
10.
Iordanka Dountcheva David Sanz Eduardo Cassiraga Vassil Galabov Juan José Gómez-Alday 《水文研究》2020,34(25):5134-5145
The objective of this study was to analyse periodicities and the long-term variability of monthly Júcar River–Mancha Oriental Aquifer interactions (RAI) and regionally measured precipitation (PP) with special focus on the correlations between these local hydrological variables and the large climatic patterns governing the Iberian Peninsula, represented by their teleconnection indices – the North Atlantic Oscillation index (NAOi) and the Western Mediterranean Oscillation index (WeMOi). To that end, wavelet analysis has been applied since it not only provides insight into the time-series dynamics but also permits statistical interpretation and correlation analysis. As a result, several periodicities have been detected: intermittent semi-annual periodicity in PP and the NAOi and annual periodicity in the RAI, NAOi and WeMOi time series. Long cycles (approximately 14 years) are also observed in the PP and WeMOi time series. The cross-wavelet spectra show a correlation between the RAI and the rest of the variables on the semi-annual and the annual scales, while wavelet coherence detects common behaviour with longer cycles – 5–6 years between the NAOi and the RAI and cycles of both 1–5 years and 7–10 years between PP and the RAI. Furthermore, results show that the periodicities in the teleconnection indices and precipitation propagate into the RAI with certain lead times: 3 months between the RAI and PP and 6 months between the RAI and the NAOi. The results indicate that the detected periodicities and the coherence between the studied variables could have applications in strategic planning on a river basin scale, taking into account the propagation times and the frequency scale. This methodological approach can be applied into strategic water resource planning independently of the geographical location of the hydrogeological system, the basin size and the climate region. 相似文献