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  • 1995-1999  (82)
  • 1997  (82)
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  • 1995-1999  (82)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 150 (1997), S. 113-120 
    ISSN: 1420-9136
    Keywords: Key words:ω-values, circum-Pacific belt, mechanical structure.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —A data set of earthquakes which occurred in the circum-Pacific regions has been used to compute the ω values. This parameter is obtained through Gumbel’s third asymptotic distribution of extreme values and is well known as upper bound magnitude. The results show relatively higher ω values in South America, Central America and Mexico, than in the western part of the circum-Pacific belt. The results are interpreted in terms of the different mechanical structure (heterogeneity) of the materials in the eastern and western parts of the examined area.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9136
    Keywords: Key words: Dial-up telemetry, spectral analysis, seismic source parameters, greek earthquakes.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —A regional dial-up PT telemetric network of eight digital short-period seismic stations has been in full operation since the beginning of 1995 in Greece. During the first year of full operation, three destructive earthquake sequences struck different regions of central and northern Greece. The dial-up network managed to successfully record more than 85% of these seismic events including foreshocks, main shocks and aftershocks, and 45 of these events were selected in order to determine their seismic source parameters by spectral analysis. The results show that seismic moment correlates very well with earthquake magnitude, fault radius and fault displacement. The determined scaling relations are in general agreement with those obtained by other studies for Greek earthquakes that used different methodologies. Since digital seismic instrumentation is now expanding in Greece, these first results from spectral analysis of digital short-period data can be considered useful for future seismic hazard studies.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 150 (1997), S. 19-36 
    ISSN: 1420-9136
    Keywords: Key words: Strike-slip fault, coalescence, link distance, combined fault length, bend.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The maximum fault link distance (lateral separation) between two interacting strike-slip faults is studied in relation to fault length (combined length of the two interacting faults). Data collected for laboratory generated strike-slip faults indicate that fault linkage takes place when the lateral separation between two strike-slip faults is less than one tenth of the combined length of the two faults. Strike-slip faults developed in clay models require a smaller link distance than those developed in gouge materials. About 98% of the data collected for natural strike-slip faults and 93% of earthquake rupture data derived from Knuepfer (1989) follow the rule. These observations support a simple scaling relationship for strike-slip faults, i.e.,W≤ 0.1 L where Wis lateral link distance and L the combined fault length (An and Sammis, 1996a). Two possible explanations are discussed. Assuming a fault continues to be dominantly strike-slip after various fault coalescences, the fault link distance for both compressional coalescence (leading to restraining bend) and extensional coalescence (leading to releasing bend) can be constrained within 0.134 L. Assuming fault coalescence is caused by interaction between breakdown zones at fault tips, then the scaling relationship b = 0.1 l between the size of a breakdown zone, b,and the individual fault length, l (Scholz et al.,1993), leads to the scaling relationship W max = 0.1 L where W max is the maximum link distance.¶The above observed relationship between W max and L may not hold if faults coalesce through preexisting faults, if a fault has a mixed mode other than strike-slip, or if a fault bend is caused by cross faulting rather than fault coalescence. Limited exposure of natural fault traces may also lead to errors in link distance measurements.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1420-9136
    Keywords: Key words: Indian Ocean, moment tensor solution.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Rayleigh and Love waves generated by sixteen earthquakes which occurred in the Indian Ocean and were recorded at 13 WWSSN stations of Asia, Africa and Australia are used to determine the moment tensor solution of these earthquakes. A combination of thrust and strike-slip faulting is obtained for earthquakes occurring in the Bay of Bengal. Thrust, strike slip or normal faulting (or either of the combination) is obtained for earthquakes occurring in the Arabian Sea and the Indian Ocean. The resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor (CMT) solution of earthquakes occurring in different parts of the Indian Ocean. The resultant compressive stress directions are changing from north-south to east-west and the resultant tensional stress directions from east-west to north-south in different parts of the Indian Ocean. The results infer the counterclockwise movement of the region (0°–33°S and 64°E–94°E), stretching from the Rodriguez triple junction to the intense deformation zone of the central Indian Ocean and the formation of a new subduction zone (island arc) beneath the intense deformation zone of the central Indian Ocean and another at the southern part of the central Indian basin. The compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis. The north-south to northeast-south west compression and east-west to northwest-southeast extension in the Indian Ocean suggest the northward underthrusting of the Indian plate beneath the Eurasian plate and the subduction beneath the Sunda arc region in the eastern part. The focal depth of earthquakes is estimated to be shallow, varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the Indian Ocean.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1420-9136
    Keywords: Key words: Monsoon, fluxes, friction velocity.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The atmospheric surface layer over land may behave differently in the tropics, particu larly during the monsoon. A preliminary attempt is made to observe the behavior of surface layer characteristics such as fluxes of momentum, sensible heat and latent heat, friction velocity, friction temperature, M-O length scale, Richardson number and Bowen’s ratio over Kharagpur (22°20′N, 87°18′E), a typical moist tropical station. The diurnal and day-to-day variations have been studied. It is observed that during the active phase of the monsoon the sensible heat flux and Bowen’s ratio are low. The diurnal variation is apparent for most parameters. Mostly near neutral conditions are observed.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1420-9136
    Keywords: Key words: Earthquakes, seismotectonics, Greece, Ionian Islands.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Properties of the earthquake sequence of the 23 January, 1992 (5.8 M S  ) earthquake in Cephalonia Island, Western Greece, are investigated. The parameter b in the frequency-magnitude relation is found equal to 1.084 while the decay parameter p of the time distribution of the aftershock sequence is found equal to 0.991. The principal parameters method is applied to the aftershock sequence and the average strikes of N156°E (±20°) and N61°E (±10°) were obtained denoting also very small dips. The major strike which resulted from the aftershock epicentre distribution was NW–SE, similar to Miocene-Neogene basins on Cephalonia Island.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1420-9136
    Keywords: Key words: Spectrum analysis, magma, Vp/Vs ratio.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —The Nikko region, in northern Kanto, central Japan, which is a high seismicity region, is located near the volcanic front. Many seismic observations have been carried out around the Nikko region because the seismograms of the shallow earthquakes occurring in this region show an S-wave reflected phase (SxS) and an S-to-P mode-converted and reflected phase (SxP) from a mid-crustal seismic velocity discontinuity. The depth of the mid-crustal reflector was estimated to be about 9–16 km. From the amplitude analyses of SxS and SxP phases, the material of the mid-crustal layer just beneath the reflector was expected to be a low rigidity layer, which was interpreted as partially molten rocks. No evidence has been shown for the internal properties of the material of the reflector. The Vp/Vs ratio is a good measure to distinguish between the two candidates for seismic reflectors; i.e., partially molten rocks and rocks containing water. We investigate the Vp/Vs ratio of the reflector using the spectrum analyses of the data observed by a seismic array. From spectrum analysis of the data, we indicate that the Vp/Vs ratio of 2.5 is better than that of 1.8 to explain the observed data, which shows that the material beneath the reflector consists of partially molten rocks.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1420-9136
    Keywords: Key words: SP interpretation, polarized structures, least-squares method.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —We have developed a least-squares minimization approach to determine the shape (shape-factor) of a buried polarized body from a residual self-potential anomaly profile. By defining the zero anomaly distance and the anomaly value at the origin on the profile, the problem of the shape-factor determination is transformed into the problem of finding a solution of a nonlinear equation of the form f(q) = 0. Procedures are also formulated to estimate the depth of polarization angle, and the electric dipole moment. The method is applied to synthetic data with and without random noise. The obtained shape-factor agrees very well with the model shape-factor when using synthetic data. After adding ± 2 percent random error in the synthetic data, the shape factor obtained is within ± 4 percent. Finally the validity of the method is tested on a field example from the Ergani copper district, Turkey.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 150 (1997), S. 157-180 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1420-9136
    Keywords: Key words: Seismic tomography, cross-borehole, local inhomogeneities, ray tracing.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —This numerical study is devoted to distortions of local anomalies which are revealed by 2-D and 3-D cross-borehole seismic tomography based on first arrival travel times. The fact that prolonged subvertical anomalies may disappear in the final velocity model is well known. But distortions are also inherent to images of local inhomogeneities. These distortions are accompanied with false anomalies of the opposite sign located just above and below true ones. I offer a semi-empirical explanation of their existence, proving that they are an inherent consequence of observation geometry incompleteness. To improve the quality of the model obtained with cross-borehole tomography, a 3-D acquisition geometry may be used when additional boreholes are positioned around the target object. Results of 3-D tomographic experiments however may be considerably distorted for another reason nonaccounted bending of seismic rays.¶To generate the travel times, a ray-tracing procedure making use of the graph theory was applied. Tomographic inversion was performed by an algorithm based on the assumption of the unknown function smoothness.
    Type of Medium: Electronic Resource
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