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  • Articles  (27)
  • earthquakes  (27)
  • 2000-2004  (3)
  • 1990-1994  (24)
  • Geosciences  (27)
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  • Articles  (27)
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  • 1
    Electronic Resource
    Electronic Resource
    Recent tectonics of the Blanco Ridge, eastern blanco transform fault zone (2000)
    Springer
    Marine geophysical researches 21 (2000), S. 423-450 
    Details
    ISSN: 1573-0581
    Keywords: Blanco transform fault zone ; earthquakes ; ridge formation ; submersible
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Bathymetric, hydro-acoustic, seismic, submersible, and gravity data are used to investigate the active tectonics of the eastern Blanco Transform Fault Zone (BTFZ). The eastern BTFZ is dominated by the ∼150 km long transform-parallel Blanco Ridge (BR) which is a right-lateral strike-slip fault bordered to the east and west by the Gorda and Cascadia Depressions. Acoustic locations, fault-parameter information, and slip vector estimates of 43 earthquakes (M w≥3.8) that occurred along the eastern BTFZ over the last 5 years reveal that the Blanco Ridge is a high-angle right-lateral strike-slip fault, with a small component of dip-slip motion, where the Juan de Fuca plate is the hanging wall relative to the Pacific plate. Furthermore, the Cascadia and Gorda basins are undergoing normal faulting with extension predominantly oblique to the transform trend. Seafloor submersible observations agree with previous hypotheses that the active transform fault trace is the elongate basin that runs the length of the BR summit. Brecciated and undeformed basalt, diabase, and gabbro samples were collected at the four submersible survey sites along the Blanco Ridge. These petrologic samples indicate the Blanco Ridge is composed of an ocean crustal sequence that has been uplifted and highly fractured. The petrologic samples also appear to show an increase in elevation of the crustal section from east to west along the Blanco Ridge, with gabbros exposed at a shallower depth farther west along the southern (Pacific plate side) BR ridge flank. Further supporting evidence for BR uplift exists in the seismic reflection profiles across the BR showing uplift of turbidite sequences along the north and south ridge base, and gravity and magnetics profiles that indicate possible basement uplift and a low-density zone centered on the ridge's Pacific plate side. The BR formation mechanism preferred here is first, uplift achieved partially through strike-slip motion (with a small dip-slip component). Second, seawater penetration along the fault into the lower crust upper mantle, which then enhanced formation and intrusion of a mantle-derived serpentinized-peridotite diapir into the shallow ocean crust, causing further uplift along the fault.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026545910893
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  • 2
    Electronic Resource
    Electronic Resource
    Tsunamigenic zones in the Mediterranean Sea (1990)
    Springer
    Natural hazards 3 (1990), S. 183-202 
    Details
    ISSN: 1573-0840
    Keywords: Tsunamis ; earthquakes ; Mediterranean Sea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A list of 300 tsunamis and similar phenomena known in the Mediterranean is given. Data reliability and wave intensity are estimated; mechanisms of tsunami generation are indicated and data from literature sources on the coordinates and magnitudes of tsunamigenic earthquakes are cited. Eighteen zones of excitation and manifestation of tsunamis are identified which can be integrated into four groups with respect to the recurrence period and maximum intensity of the tsunamis. The strongest tsunamis are excited in the Aegean Sea, and the Hellenic and Calabrian island arcs. The focal depth of the earthquake-generating tsunamis in the Mediterranean is, on average, less than that in the Pacific. Correspondingly, the magnitude of tsunamigenic earthquakes is lower. According to preliminary estimates, the Mediterranean tsunamis attenuate with distance more rapidly than do those in the Pacific Ocean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140432
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  • 3
    Electronic Resource
    Electronic Resource
    Assessment of tsunami hazard in the Italian seas (1991)
    Springer
    Natural hazards 4 (1991), S. 267-283 
    Details
    ISSN: 1573-0840
    Keywords: Tsunamis ; earthquakes ; hazard assessment ; Italian Seas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract A method for the evaluation of tsunami potential in the seas surrounding Italy is presented. A major difficulty for performing reliable estimates of tsunami occurrence is that the existing tsunami catalog for Italy includes a small number of cases. This is due partly to the catalog incompleteness, strangely more pronounced in our century, and partly to the relative infrequency of tsunamis along the Italian seas. Evaluation of tsunami activity is therefore deduced by complementing the tsunami catalog data with data on seismicity that are by far more abundant and reliable. Analysis of seismicity and assessment of earthquake rate in coastal and submarine regions form the basis of the present method to perform tsunami potential estimates for Italy. One essential limitation of the method is that only tsunamis of seismic origin are taken into account, which leads to an underestimation of the tsunami potential. Since tsunamis generated by earthquakes are much more frequent than events produced by slumps or volcanic eruptions, the underestimation is not dramatic and very likely affects only a limited portion of the Italian coasts. In the present application of the method, eight separate regions have been considered that together cover all the coasts of Italy. In each region, seismicity has been independently examined and the earthquake potential has been calculated in small 20′ × 20′ cells. Then, on the basis of suitable assumptions, tsunami potential has been evaluated in each cell. According to this study, the Italian coasts that are the most exposed to the attacks of locally generated tsunamis are to be found in the Messina Straits, in Tyrrhenian coasts of Calabria, in the Ionian Sicilian coasts around Catania, and in the Gargano promontory in the Southern Adriatic Sea. Furthermore, this study confirms that the Northern Adriatic Sea has a low level of tsunami potential, in agreement with recent studies emphasizing that the large historical events concerning this region included in the first versions of the Italian tsunami catalog are largely overestimated and must be decreased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00162792
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  • 4
    Electronic Resource
    Electronic Resource
    Nonseismic phenomena in the generation and augmentation of tsunamis (1990)
    Springer
    Natural hazards 3 (1990), S. 403-412 
    Details
    ISSN: 1573-0840
    Keywords: Tsunamis ; earthquakes ; volcanoes ; landslides ; causes ; subsidence ; pyroclastics ; submarine eruptions ; base surges ; tsunami warning systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract While earthquakes generate about 90% of all tsunamis, volcanic activity, landslides, explosions, and other nonseismic phenomena can also result in tsunamis. There have been 53 000 reported deaths as a result of tsunamis generated by landslides and volcanoes. No death tolls are available for many events, but reports indicate that villages, islands, and even entire civilizations have disappeared. Some of the highest tsunami wave heights ever observed were produced by landslides. In the National Geophysical Data Center world-wide tsunami database, there are nearly 200 tsunami events in which nonseismic phenomena played a major role. In this paper, we briefly discuss a variety of nonseismic phenomena that can result in tsunamis. We discuss the magnitude of the disasters that have resulted from such events, and we discuss the potential for reducing such disasters by education and warning systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00124396
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  • 5
    Electronic Resource
    Electronic Resource
    Multifractal analysis of earthquakes (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 591-610 
    Details
    ISSN: 1420-9136
    Keywords: Multifractal ; generalized dimension ; earthquakes ; epicenter and hypocenter distribution ; energy distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Multifractal properties of the epicenter and hypocenter distribution and also of the energy distribution of earthquakes are studied for California, Japan, and Greece. The calculatedD q-q curves (the generalized dimension) indicate that the earthquake process is multifractal or heterogeneous in the fractal dimension. Japanese earthquakes are the most heterogeneous and Californian earthquakes are the least. Since the earthquake process is multifractal, a single value of the so-called fractal dimension is not sufficient to characterize the earthquake process. Studies of multifractal models of earthquakes are recommended. Temporal changes of theD q-q curve are also obtained for Californian and Japanese earthquakes. TheD q-q curve shows two distinctly different types in each region; the gentle type and the steep type. The steeptype corresponds to a strongly heterogeneous multifractal, which appears during seismically active periods when large earthquakes occur.D q for smallq or negativeq is considerably more sensitive to the change in fractal structure of earthquakes thanD q forq≥2. We recommend use ofD q at smallq to detect the seismicity change in a local area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876340
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  • 6
    Electronic Resource
    Electronic Resource
    Triaxial testing of Lopez Fault gouge at 150 MPa mean effective stress (1994)
    Springer
    Pure and applied geophysics 142 (1994), S. 749-775 
    Details
    ISSN: 1420-9136
    Keywords: Rock mechanics ; earthquakes ; friction ; faulting ; pore pressure ; consolidation ; dilatancy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Triaxial compression experiments were performed on samples of natural granular fault gouge from the Lopez Fault in Southern California. This material consists primarily of quartz and has a self-similar grain size distribution thought to result from natural cataclasis. The experiments were performed at a constant mean effective stress of 150 MPa, to expose the volumetric strains associated with shear failure. The failure strength is parameterized by the coefficient of internal friction μ, based on the Mohr-Coulomb failure criterion. Samples of remoulded Lopez gouge have internal friction μ=0.6±0.02. In experiments where the ends of the sample are constrained to remain axially aligned, suppressing strain localisation, the sample compacts before failure and dilates persistently after failure. In experiments where one end of the sample is free to move laterally, the strain localises to a single oblique fault at around the point of failure; some dilation occurs but does not persist. A comparison of these experiments suggests that dilation is confined to the region of shear localisation in a sample. Overconsolidated samples have slightly larger failure strengths than normally consolidated samples, and smaller axial strains are required to cause failure. A large amount of dilation occurs after failure in heavily overconsolidated samples, suggesting that dilation is occurring throughout the sample. Undisturbed samples of Lopez gouge, cored from the outcrop, have internal friction in the range μ=0.4–0.6; the upper end of this range corresponds to the value established for remoulded Lopez gouge. Some kind of natural heterogeneity within the undisturbed samples is probably responsible for their low, variable strength. In samples of simulated gouge, with a more uniform grain size, active cataclasis during axial loading leads to large amounts of compaction. Larger axial strains are required to cause failure in simulated gouge, but the failure strength is similar to that of natural Lopez gouge. Use of the Mohr-Coulomb failure criterion to interpret the results from this study, and other recent studies on intact rock and granular gouge, leads to values of μ that depend on the loading configuration and the intact or granular state of the sample. Conceptual models are advanced to account for these descrepancies. The consequences for strain-weakening of natural faults are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876063
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  • 7
    Electronic Resource
    Electronic Resource
    Ductile creep and compaction: A mechanism for transiently increasing fluid pressure in mostly sealed fault zones (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 9-40 
    Details
    ISSN: 1420-9136
    Keywords: Compaction ; fault zones ; fluid pressure ; earthquakes ; “weak” faults
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A simple cyclic process is proposed to explain why major strike-slip fault zones, including the San Andreas, are weak. Field and laboratory studies suggest that the fluid within fault zones is often mostly sealed from that in the surrounding country rock. Ductile creep driven by the difference between fluid pressure and lithostatic pressure within a fault zone leads to compaction that increases fluid pressure. The increased fluid pressure allows frictional failure in earthquakes at shear tractions far below those required when fluid pressure is hydrostatic. The frictional slip associated with earthquakes creates porosity in the fault zone. The cycle adjusts so that no net porosity is created (if the fault zone remains constant width). The fluid pressure within the fault zone reaches long-term dynamic equilibrium with the (hydrostatic) pressure in the country rock. One-dimensional models of this process lead to repeatable and predictable earthquake cycles. However, even modest complexity, such as two parallel fault splays with different pressure histories, will lead to complicated earthquake cycles. Two-dimensional calculations allowed computation of stress and fluid pressure as a function of depth but had complicated behavior with the unacceptable feature that numerical nodes failed one at a time rather than in large earthquakes. A possible way to remove this unphysical feature from the models would be to include a failure law in which the coefficient of friction increases at first with frictional slip, stabilizing the fault, and then decreases with further slip, destabilizing it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874322
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  • 8
    Electronic Resource
    Electronic Resource
    The frictional behavior of lizardite and antigorite serpentinites: Experiments, constitutive models, and implications for natural faults (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 317-358 
    Details
    ISSN: 1420-9136
    Keywords: Rock friction ; fault mechanics ; earthquakes ; serpentine ; constitutive behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults. We have conducted friction experiments on antigorite and lizardite serpentinites, rocks common to both continental and oceanic crustal faults. We conducted both velocity-step tests and timed-hold tests on bare surfaces and gouge layers of serpentinite at room temperature. We find that the coefficient of friction of lizardite serpentinite is quite low (0.15–0.35) and could explain the apparent low stresses observed on crustal transform faults, while that of antigorite serpentinite is comparable to other crustal rocks (0.50–0.85). The frictional behavior of both types of serpentinite is well described by a two-mechanism model combining state-variable-dominated behavior at high slip velocities and flow-dominated behavior at low velocities. The two-mechanism model is supported by data from velocity-step tests and timed-hold tests. The low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874334
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  • 9
    Electronic Resource
    Electronic Resource
    Chaotic seismic faulting with a mass-spring model and velocity-weakening friction (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 569-589 
    Details
    ISSN: 1420-9136
    Keywords: Seismicity ; slide-blocks ; chaos ; earthquakes ; fractals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present a systematic analysis of the dynamical behavior introduced by fault zone heterogeneities, using a simple mass-spring model with velocity-weakening friction. The model consists of two sliding blocks coupled to each other and to a constant velocity driver by clastic springs. The state of this system can be characterized by the positions of the two blocks relative to the driver. Symmetry stabilizes the system and generates only cyclic behavior. For an asymmetric system where the frictional forces for the two blocks are not equal, the solutions exhibit chaotic behavior. The transition from stable cyclic behavior to chaos is characterized by the period-doubling route to chaos. Lyapunov exponents are computed to quantify the deterministic chaos and to locate the onset of the chaotic evolution in parameter space. In many examples of deterministic chaos, chaotic behavior of a low-order system implies chaos in similar higher order systems. Thus, our results provide substantial evidence that crustal deformation is an example of deterministic chaos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876339
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  • 10
    Electronic Resource
    Electronic Resource
    Lateral structure of the subducting pacific plate beneath the Hokkaido corner from intermediate and deep earthquakes (1990)
    Springer
    Pure and applied geophysics 134 (1990), S. 385-404 
    Details
    ISSN: 1420-9136
    Keywords: Subduction ; slab-tearing ; Kuril ; Honshu ; seismicity ; stress ; focal mechanism ; earthquakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present a study of the lateral structure and mode of deformation in the transition between the Kuril and Honshu subduction zones. We begin by examining the source characteristics of the January 19, 1969, intermediate depth earthquake north of Hokkaido in the framework of slab-tearing, which for the December 6, 1978 event has been well documented by previous studies. We use a least-squares body wave inversion technique, and find that its focal mechanism is comparable to the 1978 event. To understand the cause of these earthquakes, which in the case of the 1978 event occurred on a vertical tear fault but does not represent “hinge” faulting, we examine the available International Seismological Centre [ISC] hypocenters and Harvard centroid-moment tensor [CMT] solutions to determine the state of stress, and lateral structure and segmentation in the Kuril and northern Honshu slabs. These data are evaluated in the framework of two models. Model (A) requires the subducting slab at the Hokkaido corner to maintain surface area. Model (B) requires slab subduction to be dominated by gravity, with material subducting in the down-dip direction. The distribution of ICS hypocenters shows a gap in deep seismicity down-dip of the Hokkaido corner, supporting model (B). From the CMT data set we find that three types of earthquake focal mechanisms occur. The first (type A) represents dip-slip mechanisms consistent with down-dip tension or compression in the slab in a direction normal to the strike of the trench. These events occur throughout the Honshu and Kuril slabs with focal mechanisms beneath Hokkaido showing NNW plungingP andT axes consistent with the local slab geometry. The second (type B) occurs primarily at depths over 300 km in the southern part of the Kuril slab with a few events in the northern end of the Honshu deep seismicity. These earthquakes have focal mechanisms with P axes oriented roughly E-W, highly oblique to the direction of compression found in the type A events, with which they are spatially interspersed. The third (type C) group of earthquakes are those events which do not fit in either of the first two groups and consist of either strike-slip focal mechanisms, such as the tearing events, or oddly oriented focal mechanisms. Examination of the stress axes orientations for these three types reveals that the compressional axes of the type C events are consistent with those of type B. The slab tearing events are just differential motion reflecting the E-W compressive states of stress which is responsible for the type B family of events. There is no need to invoke down-dip extension which does not fit the slab geometry. We conclude that these two states of stress can be explained as follows: 1) The type A events and the seismicity distribution support model (B). 2) The type B and C events upport model (A). The solution is that the slab subducts according to model (B), but the flow in the mantle maintains a different trajectory, possibly induced by the plate motions, which produces the second state of E-W compressive stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00878739
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