A new technique of eigen mode analysis, Method of Natural Orthogonal Components (MNOC) is used to analyze the ionospheric equivalent current systems obtained on the basis of magnetic data at six meridian magnetometer chains in the northern hemisphere during March 17 - 19, 1978. The results show that the whole current pattern for any given instant consists of a few eigen modes with different intensities. The first eigen mode exhibits a two-cell current construction, characterizing the large-scale magnetospheric convection and directly driven process, while the second eigen mode shows a concentrated westward electrojet at midnight sector, characterizing the substorm current wedge and the loading-unloading process. The first mode consistently exists whenever during quiet periods or at substorms, and its intensity increases from the beginning of the growth phase of substorms, then quickly intensifies in the expansion phase, followed by a gradual decrease in the recovery phase. On the other hand, the intensity of the second mode remains to be near zero during both quiet time and the growth phase of substorrns. Its rapid enhancement occurs in the expansion phase. These characteristics in the current patterns and the intensity variations coincide with the defined physical processes of the directly driven and loading-unloading components. 相似文献
The present paper presents the results of a technique based on Vertical Seismic Profiling (VSP) to quantify the offset of a fault in a context where seismic reflection profiles do not image any reflectors. The case study is located in Greece, in the Aigion area, on the south border of the Corinth Gulf. The Aigion fault, oriented East–West, and dipping at 60°N, has been intersected by the scientific well Aig-10 at 760 m in depth, but some uncertainty remained concerning its exact offset since the depth of the pre-rift sequence is open to debate due to the lack of subsurface data. The pre-rift consists of a Mesozoic low-porosity series (carbonates and radiolarite), while the syn-rift consists of poorly compacted conglomerates and turbidites.
Seismic diffractions on fault edges are expected to be present along the fault surface. We find that a few diffracted events are effectively recorded in P and S wave mode by the 4 components of the VSP survey, and critically refracted arrivals along the Aigion fault plane. These singular events have been used in order to refine the fault geometry and to determine its throw. Additionally, results from a 2D finite difference elastic seismic model of a single fault step geometry have been closely examined in order to illustrate the generation of the singular seismic events observed on the field data, such as P-wave and S-wave refracted and diffracted events, and support their interpretation with higher confidence. As a result, the seismic arrival patterns from full waveform seismic modelling confirm the characterisation of the main fault geometry (mainly its throw: about 200 m) in the well vicinity derived from the actual analysis of the 4 Component Aigion VSP data. 相似文献
Real-time monitoring of pollutant levels from a mobile measuring platform requires fast,flexible dataanalysis methods.This paper reports a method for rapid analysis of passive remotely sensed infrared datawith the aid of a Kalman filter.The background spectra produced by emission from the atmosphere aremodelled at the start of the data collection sequence with a simple principal components model obtainedby eigenanalysis of the initial‘blank’data taken with the spectrometer.The species of interest areincluded in the state space model by a separate measurement of their infrared spectra.It is demonstratedthat for best filter performance in detecting the simulated pollutant species SF_6 in the atmosphere,a filtermodel with two principal components describing the emission background works best.The filter‘maps’of SF_6 closely follow the integrated spectral intensities measured after removal of suitable backgrounds. 相似文献
In order to learn more about the nature of the dynamic processes taking place in the West Bohemia/Vogtland earthquake swarm region, we investigated the temporal and spatial variations of the source mechanisms of the January 1997 swarm beneath Nový Kostel (NKC). Visual analyses of WEBNET seismograms of over 800 events revealed that a specific feature of this swarm was the occurrence of eight classes of multiplet events. The result of single-source, absolute moment tensor inversion of the P and SH peak amplitudes of a subset of 70 events representing all multiplet classes indicated that eight statistically significant types of mechanisms occurred during the swarm. Two of them, typesAandBin our denotation, comprised all ML 1.3 events and predominated in the swarm. TypeAwere pure strike-slip mechanisms or strike-slip mechanisms containing a small normal component, with a nearly pure double-couple source. For classBevents, oblique-thrust faulting and non-double-couple components significant at a fairly high confidence level were typical. TypeAevents predominated in the southern subcluster of the swarm, whereas most of typeBevents occurred in the subcluster northwards from NKC. This indicates that two major seismogenic planes were active during the swarm. The swarm essentially developed in four phases: in the first, typeAevents prevailed and the southern plane was active; during the second, characterised by the occurrence of both typeAandBevents (the former in the southern, the latter predominantly in the northern subcluster), the activity of the swarm culminated; in the third and fourth, the occurrence of typeBevents in the northern plane predominated, and only weak single events occurred southwards from NKC. Mechanisms of typesAB,C,D,E,FandG, which were typical for ML1.2 events, occurred randomly throughout the swarm. TypeABevents were identified in both the southern and northern clusters, typeC,E,FandGmechanisms only southwards from NKC. TypeDevents exhibited a large scatter of hypocentres which fell in neither the southern nor the northern cluster. Focal mechanisms like those reported in this study and with analogous temporal and spatial variations were observed by other authors already fifteen years ago in the 1985/86 earthquake swarm and may, therefore, be typical for the region under study.相似文献