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  • 1995-1999  (118)
  • 1996  (118)
  • 1
    ISSN: 1420-9136
    Keywords: Fault ; parameter ; lithosphere ; extension ; stress ; rift ; experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Quantitative relationships between major fault parameters from geological observations and laboratory experiments are compared. Relationships are established between fault length, number, depth of fault penetration, amplitude of displacement and other characteristics. The width of destruction zones is estimated. Spacing between parallel faults of compatible length is evaluated. It is shown that there is a stable correlation between fault length and number, which is independent from the mode of loading the material under destruction. Destruction of the lithosphere is believed to occur according to the laws of deformation of Maxwell elasto-viscous body.
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  • 2
    ISSN: 1420-9136
    Keywords: Earthquake ; polar motion ; earth rotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The mass redistribution in the earth as a result of an earthquake faulting changes the earth's inertia tensor, and hence its rotation. Using the complete formulae developed byChao andGross (1987) based on the normal mode theory, we calculated the earthquake-induced polar motion excitation for the largest 11,015 earthquakes that occurred during 1977.0–1993.6. The seismic excitations in this period are found to be two orders of magnitude below the detection threshold even with today's high precision earth rotation measurements. However, it was calculated that an earthquake of only one tenth the size of the great 1960 Chile event, if happened today, could be comfortably detected in polar motion observations. Furthermore, collectively these seismic excitations have a strong statistical tendency to nudge the pole towards ∼140°E, away from the actually observed polar drift direction. This non-random behavior, similarly found in other earthquake-induced changes in earth rotation and low-degree gravitational field byChao andGross (1987), manifests some geodynamic behavior yet to be explored.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 146 (1996), S. 3-4 
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
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  • 4
    ISSN: 1420-9136
    Keywords: P nl waves ; historical earthquake ; Canadian earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Timiskaming earthquake, which occurred near the Quebec-Ontario border at the northwest end of the Western Quebec seismic zone in 1935, is one of the five largest instrumentally recorded southeastern Canadian earthquakes. Previous studies of this earthquake concentrated on modeling teismograms recorded at regional distances, a better constrained focal mechanism is obtained. The waveforms indicate thrust faulting on a moderately dipping northwest striking plane at a depth of 10 km. TheM w of 6.1 determined in this study is in good agreement with previous magnitude estimates (m b 6.1,M s 6.0, andm bLg 6.2–6.3). The focal mechanism is similar to those of many recent small to moderate earthquakes in the region, and the inferred (from theP axis) acting stress of northeast compression is consistent with the overall eastern North American stress field. The “Lake Timiskaming Rift Valley” in which the earthquake occurred, comprises several northwest striking faults consistent with the strike of the 1935 event. Thus, the 1935 earthquake appears to be a result of faulting on the reactivated Timiskaming graben.
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  • 5
    ISSN: 1420-9136
    Keywords: Historic earthquakes ; southeastern Caribbean earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We have conducted body waveform modeling studies of 13 historic earthquakes to provide a better understanding of the long-term spatial and temporal pattern of seismicity and deformation within a region extending from Barbuda, Lesser Antilles, to Cumana, Venezuela. Our results suggest that shallow earthquakes (〈50 km deep) along the South American-Caribbean plate margin reflect right-lateral and extensional deformation. Intermediate depth events (≥100 km) show left-lateral strike-slip motion beneath the Paria peninsula of Venezuela. In the Lesser Antilles the 1960 Barbuda and 1946 Martinique earthquakes appear to be interplate thrust events, however the greatest moment release in the region has occurred at intermediate depths as a mixture of normal and strike-slip faulting, generally along trends oblique to the arc. The deformation rate estimated from the seismic moment release between 1926 and 1960 is only 1 to 10% of the estimated plate convergence rate for the region.
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  • 6
    ISSN: 1420-9136
    Keywords: Intraplate seismicity ; historical earthquakes ; deconvolution ; source-time function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Historically, large and potentially hazardous earthquakes have occurred within the interior of Alaska. However, most have not been adequately studied using modern methods of waveform modeling. The 22 July 1937, 16 October 1947, and 7 April 1958 earthquakes are three of the largest events known to have occurred within central Alaska (M s =7.3,M s =7.2 andM s =7.3, respectively). We analyzed teleseismic body waves to gain information about the focal parameters of these events. In order to deconvolve the source time functions from teleseismic records, we first attempted to improve upon the published focal mechanisms for each event. Synthetic seismograms were computed for different source parameters, using the reflectivity method. A search was completed which compared the hand-digitized data with a suite of synthetic traces covering the complete parameter space of strike, dip, and slip direction. In this way, the focal mechanism showing the maximum correlation between the observed and calculated traces was found. Source time functions, i.e., the moment release as a function of time, were then deconvolved from teleseismic records for the three historical earthquakes, using the focal mechanisms which best fit the data. From these deconvolutions, we also recovered the depth of the events and their seismic moments. The earthquakes were all found to have a shallow foci, with depths of less than 10 km. The 1937 earthquake occurred within a northeast-southwest band of seismicity termed the Salcha seismic zone (SSZ). We confirm the previously published focal mechanism, indicating strike-slip faulting, with one focal plane parallel to the SSZ which was interpreted as the fault plane. Assuming a unilateral fault model and a reasonable rupture velocity of between 2 and 3 km/s, the 21 second rupture duration for this event indicates that all of the 65 km long SSZ may have ruptured during this event. The 1947 event, located to the south of the northwest-southeast trending Fairbanks seismic zone, was found to have a duration of about 11 seconds, thus indicating a rupture length of up to 30 km. The rupture duration of the 1958 earthquake, which occurred near the town of Huslia, approximately 400 km ENE of Fairbanks, was found to be about 9 seconds. This gives a rupture length consistent with the observed damage, an area of 16 km by 64 km.
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  • 7
    ISSN: 1420-9136
    Keywords: Earthquke cycle ; source parameters ; seismic moment ; fault heterogeneity ; P waveforms ; historical earthquakes ; source time function ; seismic gap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Two large shallow earthquakes occurred in 1942 along the South American subduction zone inclose proximity to subducting oceanic ridges: The 14 May event occurred near the subducting Carnegie ridge off the coast of Ecuador, and the 24 August event occurred off the coast of southwestern Peru near the southern flank of the subducting Nazca ridge. Source parameters for these for these two historic events have been determined using long-periodP waveforms,P-wave first motions, intensities and local tsunami data. We have analyzed theP waves for these two earthquakes to constrain the focal mechanism, depth, source complexity and seismic moment. Modeling of theP waveform for both events yields a range of acceptable focal mechanisms and depths, all of which are consistent with underthrusting of the Nazca plate beneath the South American plate. The source time function for the 1942 Ecuador event has one simple pulse of moment release with a duration of 22 suconds, suggesting that most of the moment release occurred near the epicenter. The seismic moment determined from theP waves is 6–8×1020N·m, corresponding ot a moment magnitude of 7.8–7.9. The reported location of the maximum intensities (IX) for this event is south of the main shock epicenter. The relocated aftershcks are in an area that is approximately 200 km by 90 km (elongated parallel to the trench) with the majority of aftershocks north of the epicenter. In contrast, the 1942 Peru event has a much longer duration and higher degree of complexity than the Ecuador earthquake, suggesting a heterogeneous rupture. Seismic moment is released in three distinct pulses over approximately 74 seconds; the largest moment release occurs 32 seconds after rupture initiation. the seismic moment as determined from theP waves for the 1942 Peru event is 10–25×1020N·m, corresponding to a moment magnitude of 7.9–8.2. Aftershock locations reported by the ISS occur over a broad area surrounding the main shock. The reported locations of the maximum intensities (IX) are concentrated south of the epicenter, suggesting that at least part of the rupture was to the south. We have also examined great historic earthquakes along the Colombia-Ecuador and Peru segments of the South American subduction zone. We find that the size and rupture length of the underthrusting earthquakes vary between successive earthquake cycles. This suggests that the segmentation of the plate boundary as defined by earthquakes this century is not constant.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 146 (1996), S. 103-111 
    ISSN: 1420-9136
    Keywords: Prephotographic earthquake depictions ; pictorial macroseismic data ; historical seismicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Prephotographic depictions of earthquakes can contain important information on the types and amount of damage due to a large earthquake in historic times. Care must be used in evaluating such depictions because some are more accurate than others, and many depictions contain little that is of value in making estimates of seismic intensity. Depictions of two earthquakes, in 1692 at Jamaica and in 1843 at Guadeloupe, illustrate the utility of depictions in intensity estimation. A depiction of the scene at Port Royal in Jamaica of the 1692 shock suggests that the major damage was caused by soil slumping and a tsunami, with the ground shaking itself probably only having been about MMI VII. Two depictions of Pointe-à-Pitre at Guadeloupe after the 1843 event contain evidence that the town was damaged by strong ground shaking as well as by major soil failures. The ground shaking here was probably MMI VII–IX. These and other pictures are being assembled for a monograph of prephotographic earthquake depictions in the Americas.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 146 (1996), S. 115-129 
    ISSN: 1420-9136
    Keywords: Fragmentation ; fractal distributions ; self-similarity ; self-organized criticality ; cellular automatons ; computer models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three cellular automaton “toy”-models of fragmentation in two-dimensional lattices are explored. Of the three models, two can be considered in the class of simple bond percolation, and one as correlated bond percolation. Fractal fragment-size distribution in all models is found away from criticality, providing a certain fraction of the bonds is designated with considerably larger strengths than the rest in the system. As the fraction of these bonds is raised from zero, the fragment-size distribution transforms smoothly from exponential forms into a power law. Though each model takes a different path to the fractal distribution, they all show the same fractal exponent of 1.85(5). As might be expected in one dimension, the same models of their variants, failed to produce fractal distributions.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 146 (1996), S. 131-145 
    ISSN: 1420-9136
    Keywords: Multifractal ; general fractal dimension ; epicentral distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The generalized fractal dimension for epicentral distribution of earthquakes in west Taiwan is measured. The entire area is first divided into two zones, i.e., north and south zones, after which the two zones are further separated into three subzones for the former and two for the latter. The logC q (r) versus logr function, whereC q (r) is the generalized correlation integral andr is the distance between two epicenters, shows that a linear relation between logC q and logr exists in the range ofr smaller thanr c . The value ofr c is 25 km for the north zone, 40 km for the south and 12 km for the three north subzones. The valuesr c =25 and 40 km are almost the smallest ones of the width of epicentral distributions of the north and south zones, respectively. The value ofr c =12 km for the three north subzones is approximately the smallest size of the cluster of epicenters. For the plots of two south subzones, the pattern of data points does not bend in the range ofr in consideration, and, thus, there is not such a critical radius. TheD q −q relations forq=0, 1, 2,..., 15 are constructed for the two zones and five subzones. Results show significant multifractality and a spatial variation in multifractality for epicentral distributions of earthquakes in west Taiwan.
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