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  • earthquake prediction  (4)
  • 1995-1999  (4)
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  • 1
    ISSN: 1420-9136
    Keywords: Load/unload response ratio ; earthquake prediction ; instability of nonlinear systems ; Northridge earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The response to loading is different from that to unloading when the focal media is approaching instability. The ratio of the response rate during loading to that during unloading, called Load/Unload Response RatioY (LURR), could be a measure of the closeness degree to instability and is used in a new approach to earthquake prediction. Retrospective examination of some one hundred earthquake cases (fromM 4 toM 8.6) indicates that for more than 80% of the examined ones, the value ofY is much higher than 1 for a period before the main shock, but theY value always fluctuates slightly about 1 during two decades for seven stable regions, so that the parameterY value always fluctuates slightly degree of an impending earthquake. Several earthquakes occurring on the Chinese mainland in recent years as well as the Northridge California, U.S.A. earthquake (Jan. 17, 1994,M w 6.7) have been predicted beforehand with this method.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9136
    Keywords: En echelon fractures ; subcrack development ; neotectonic activity ; earthquake prediction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Uniaxial compression tests on marble plates containing two prefabricateden echelon fractures were performed in this study. Photographs showing the typical characteristics of subcrack development were taken under direct scanning electron microscope (SEM) observation during the test. From these photographs, the effects of the lengthL of a single fracture, the separation distanced and overlapping proportiona/L between two prefabricateden echelon fractures on the development of subcracks were analyzed. The results show that the interaction betweenen echelon fractures strengthened with decreasingd. Ford≥L, there was little interaction and the development of subcracks near one of theen echelon fractures was unaffected by the existence of the other. Whereas ford〈L, the number of subcracks in the area intermediate betweenen echelon fractures tended to increase with increasinga and decreasingd. In order to ascertain whether the experiment can furnish some implications for research on earthquake prediction and neotectonic activity, the test results were compared with the spatial-temporal development of foreshocks and ground-water anomalies before the 1975 Haicheng earthquake and the structural framework of the Ganzi pull-apart basin. The results of the comparison are encouraging. According to the similarity between the test results in the laboratory and the natural phenomena in the field, the fault on which the Haicheng earthquake would occur, could be inferred immediately from the relative geometry of the two sub-parallel active faults in the area. Thus, it is considered that the test results would advance our understanding of the process of neotectonic activities and give us inspiration for earthquake prediction.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1420-9136
    Keywords: Earthquakes ; hydrogeology ; earthquake prediction ; crustal deformation ; aquifers ; earth tides ; strain ; hydraulic diffusivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two of the four wells monitored near Parkfield, California, during 1985 showed water level rises beginning three days before theM w 6.1 Kettleman Hills earthquake. In one of these wells, the 3.0 cm rise was nearly unique in five years of water level data. However, in the other well, which showed a 3.8 cm rise, many other changes of comparable size have been observed. Both wells that did not display pre-earthquake rises tap partially confined aquifers that cannot sustain pressure changes due to tectonic strain having periods longer than several days. We evaluate the effect of partial aquifer confinement on the ability of these four wells to display water level changes in response to aquifer strain. Although the vertical hydraulic diffusivities cannot be determined uniquely, we can find a value of diffusivity for each site that is consistent with the site's tidal and barometric responses as well as with the rate of partial recovery of the coseismic water level drops. Furthermore, the diffusivity for one well is high enough to explain why the preseismic rise could not have been detected there. For the fourth well, the diffusivity is high enough to have reduced the size of the preseismic signal as much as 50%, although it should still have been detectable. Imperfect confinement cannot explain the persistent water level changes in the two partially confined aquifers, but it does show that they were not due to volume strain. The pre-earthquake water level rises may have been precursors to the Kettleman Hills earthquake. If so, they probably were not caused by accelerating slip over the part of the fault plane that ruptured in that earthquake because they are of opposite sign to the observed coseismic water level drops.
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  • 4
    ISSN: 1420-9136
    Keywords: Seismicity ; earthquake prediction ; seismotectonic ; regionalization ; Italy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The algorithm CN makes use of normalized functions. Therefore the original algorithm, developed for the California-Nevada region, can be directly applied, without adjustment of the parameters, to the determination of the Time of Increased Probability (TIP) of strong earthquakes for Central Italy. The prediction is applied to the events with magnitudeM≥M 0=5.6, which in Central Italy have a return period of about six years. The routinely available digital earthquake bulletins of the Istituto Nazionale di Geofisica (ING), Rome, permits continuous monitoring. Here we extend to November 1994 the first study made by Keilis-Boroket al. (1990b). On the basis of the combined analysis of seismicity and seismotectonic, we formulate a new regionalization, which reduces the total alarm time and the failures to predict, and narrows the spatial uncertainty of the prediction with respect to the results ofKeilis-Borok et al. (1990b). The premonitory pattern is stable when the key parameters of the CN algorithm and the duration of the learning period are changed, and when different earthquake catalogues are used. The anlysis of the period 1904–1940, for whichM 0=6, allows us to identify self-similar properties between the two periods, in spite of the considerably higher seismicity level of the earlier time interval compared with the recent one.
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