排序方式： 共有26条查询结果，搜索用时 328 毫秒
21.
22.
23.
Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%,
by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms,
carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty
of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform
match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering
a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values.
However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their
mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears
to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin
of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data,
that the Amfilochia earthquake was an almost pure-shear event. 相似文献
24.
A soil geochemical survey was undertaken in the cultivated region of Agia in Thessaly area, Central Greece. The objectives
of the study were to assess the levels of soil contamination in respect to average concentrations of toxic metals in the region,
to determine the associations between the different toxic elements and their spatial distribution and to identify possible
sources of contamination that can explain the spatial patterns of soil pollution in the area. One hundred seventy three soil
samples were collected and analysed by ICP-AES after digestion with a mixture of HClO4–HNO3–H2O. The study focused on eleven elements (Cu, Pb, Zn, Ni, Co, Mn, As, V, Cr, Fe and Mg) and all of them except Pb have mean
concentrations above the average global soil composition. The elements Ni, Cr, Mn and V show concentrations that according
to G.L.C guidelines the Agia soils are classified as slightly contaminated to contaminated. Factor analysis explained 84.02%
of the total variance of the data through four factors. Combined with spatial interpretation of its output, the method successfully
grouped the elements according to their sources and provided evidence about their natural or anthropogenic origin. 相似文献
25.
26.
The procedure through which the occurrence time of an impending major earthquake can be determined is reviewed in the light of the recent advances. This can be achieved by analyzing in natural time the seismicity in the candidate area. To apply this general procedure, we need two important elements: first, to know when we should start the analysis, i.e., set the natural time equal to zero. This is the time at which the system enters the critical stage. Second a reliable estimation of the candidate epicentral area. If geoelectrical measurements are taken and the VAN method (after the initials of the three researchers Varotsos, Alexopoulos and Nomicos) is applied, both these elements become available upon the recording of a precursory Seismic Electric Signals (SES) activity, because its initiation marks the time when the system enters the critical stage, and in addition the SES data enable the determination of the epicentral area of the impending mainshock. On the other hand, if geoelectrical data are lacking, we make use of the following two recent findings by means of natural time analysis: First, the fluctuations of the order parameter of seismicity in a large area exhibit a minimum a few months before a major earthquake almost simultaneously with the initiation of an SES activity. Second, a spatiotemporal study of this minimum unveils an estimate of the epicentral area of the impending major earthquake. Two examples are given that refer to the strongest earthquakes that occurred in Greece and Japan during the last 3 decades, i.e., the M W6.9 earthquake in southwestern Greece on 14 February 2008 and the M W9.0 Tohoku earthquake in Japan on 11 March 2011. 相似文献