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  • 1995-1999  (509)
  • 1950-1954  (355)
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  • 1
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 144 (1995), S. 373-379 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 144 (1995), S. 455-470 
    ISSN: 1420-9136
    Keywords: Tsunami ; numerical computation ; finite-difference method ; Nicaragua earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Numerical computations of tsunamis are made for the 1992 Nicaragua earthquake using different governing equations, bottom frictional values and bathymetry data. The results are compared with each other as well as with the observations, both tide gauge records and runup heights. Comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a small grid size is more effective than to include nonlinear terms in tsunami computation. Linear computation overestimates the amplitude for the later phase than the first arrival, particularly when the amplitude becomes large. The computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights; the average ratio, or the amplification factor, is estimated to be 3 in the present case when the grid size of 1 minute is used. The factor however may depend on the grid size for the computation.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1420-9136
    Keywords: Tsunami ; tsunami earthquakes ; seismic moment ; mantle magnitude
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We study eight tsunamigenic earthquakes of 1992–1994 with data from single near-field 3-component long-period stations. The analysis is made from the standpoint of tsunami warning by an automatic process which estimates the epicentral location and the seismic moment through the variable-period mantle magnitudeM m . Simulations of early warning based on the real-time computation of the seismic moment are also tested with this system, which would give a justified warning in each region of tsunami potentiality. By exploiting the dependence of moment rate release with frequency, the system has the capability of recognizing both “tsunami earthquakes” such as the 1992 Nicaragua and 1994 Java events, as well as instances of the opposite case of low-frequency deficiency, interpreted as indicating a deeper than normal source (1993 Guam event). We report both the results of delayed-time processing of the near-field stations, and the actual real-time warnings at PPT, which confirm the former.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1420-9136
    Keywords: Tsunami ; geopotential ; geomagnetism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The movement of the seawater across the earth's magnetic field produces a large-scale motional electric field. Using the Point Arena, California, to Hanauma Bay, Hawaii, unpowered HAW-1 cable, we have studied the geopotential across this distance to look for possible tsunami-induced fields that might have been produced following the April 1992 Cape Mendocino earthquake. We have used a ten-day interval prior to and including the earthquake as a reference for geopotential signals and for geomagnetic activity. We have also used geomagnetic data from Point Arena, Honolulu and Boulder as reference data. The results of the analyses show that there are tsunami-related effects in the cable geopotential data. These are (a) larger voltage prediction errors (residuals) for the interval following the main shock; (b) enhanced (compared to the 10d reference interval) geopotential spectral power following the main shock: two enhancements are larger than geomagnetically-induced spectral power enhancements in the same time interval; and (c) strong evidence for an ∼30 min “echo” in the cable geopotential signal following the main shock.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1420-9136
    Keywords: Tsunamic ; edge waves ; Cape Mendocino ; Cascadia Subduction Zone ; hazard mitigation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 25 April 1992 Cape Mendocino earthquake generated a tsunami characterized by both coastal trapped edge wave and non-trapped tsunami modes that propagated north and south along the U.S. West Coast. Both observed and synthetic time series at Crescent City and North Spit are consistent with the zero-order edge wave mode solution for a semi-infinite sloping beach depth profile. Wave amplitudes at Crescent City were about twice that observed at North Spit, in spite of the fact that the source region was three times farther from Crescent City than North Spit. The largest observed amplitude was due to an edge wave which arrived almost three hours after the initial onset of the tsunami; since such waves are highly localized nearshore, this suggests that the enhanced responsiveness at Crescent City is at least partly due to local dynamic processes. Furthermore, the substantially delayed arrival of this wave, which was generated at the southern end of the Cascadia Subduction Zone, has significant implications for hazard mitigation efforts along the entire U.S. West Coast. Specifically, this study demonstrates that slow-moving but very energetic edge wave modes could be generated by future large tsunamigenic earthquakes in the CSZ, and that these might arrive unexpectedly at coastal communities several hours after the initial tsunami waves have subsided.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1420-9136
    Keywords: Tsunami earthquake ; Nicaragua earthquake ; body wave inversion ; source process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We analyzed the broadband body waves of the 1992 Nicaragua earthquake to determine the nature of rupture. The rupture propagation was represented by the distribution of point sources with moment-rate functions at 9 grid points with uniform spacing of 20 km along the fault strike. The moment-rate functions were then parameterized, and the parameters were determined with the least squares method with some constraints. The centroid times of the individual moment-rate functions indicate slow and smooth rupture propagation at a velocity of 1.5 km/s toward NW and 1.0 km/s toward SE. Including a small initial break which precedes the main rupture by about 10 s, we obtained a total source duration of 110 s. The total seismic moment isM o =3.4×1020 Nm, which is consistent with the value determined from long-period surface waves,M o =3.7×1020 Nm. The average rise time of dislocation is determined to be τ≈10 s. The major moment release occurred along a fault length of 160 km. With the assumption of a fault widthW=50 km, we obtained the dislocationD=1.3 m. From τ andD the dislocation velocity isD=D/τ≈0.1 m/s, significantly smaller than the typical value for ordinary earthquakes. The stress drop Δσ=1.1 MPa is also less than the typical value for subduction zone earthquakes by a factor of 2–3. On the other hand, the apparent stress defined by 2μE s /M o , where μ andE s are respectively the rigidity and the seismic wave energy, is 0.037 MPa, more than an order of magnitude smaller than Δσ. The Nicaragua tsunami earthquake is characterized by the following three properties: 1) slow rupture propagation; 2) smooth rupture; 3) slow dislocation motion.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1420-9136
    Keywords: Microseismic ; reservoir-induced seismicity ; nonparametric correlation analysis ; b values
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Ridracoli Dam has been operating since 1981. Around the reservoir ISMES installed and operated for 10 years a seismic network, now reduced to a 3-D station. Earthquakes were recorded with completeness from magnitude 0.8 onwards. In the same period, all the parameters relevant to the dam and the environment were measured. This provided a complete data base for RIS studies, unique in its kind in Italy. The main findings of the analyses performed are the following: 1) The filling of the reservoir has not influenced the seismicity of the area for most significant events (M L〉3.5). 2) Lesser seismicity around the reservoir seems to be correlated with water level in the reservoir, but also shows to be dependent on regional seismicity. 3) b value shows a slight increase with time. This may indicate an increase in rock fracturing, which is known to precede the disappearing of Type II RIS.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1420-9136
    Keywords: Porous media ; coupling theory ; Xinfengjiang reservoir ; induced earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Theory of the coupling of stress-pore pressure in the saturated, elastic porous media is used in the study of the formation mechanism of the Xinfengjiang reservoir-induced earthquakes. Based on the results, it is believed that compared with the mechanism of additional stress in the vicinity of the reservoir, the mechanism of the coupling of additional stress and pore pressure may be more well-founded for the occurrence of reservoir-induced earthquakes.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1420-9136
    Keywords: Potential strength of earthquakes ; fuzzy set theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The potential strength of an induced earthquake depends on a series of factors at different levels. It can be effectively assessed and predicted by using the method of fuzzy multifactorial evaluation from a fuzzy set theory. As an illustration of the above-mentioned method, this paper has applied the method to assessing the potential strength of induced earthquakes due to water reservoir.
    Type of Medium: Electronic Resource
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