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  • 1
    Electronic Resource
    Electronic Resource
    Relationship between the seismicity and geologic structure of the Blanco Transform Fault Zone (1991)
    Springer
    Marine geophysical researches 13 (1991), S. 203-208 
    Details
    ISSN: 1573-0581
    Keywords: Blanco Transform ; divergent wrench-fault ; earthquake ; b-value ; seismic moment ; fault length
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Morphologic studies of an oceanic transform, the Blanco Transform Fault Zone (BTFZ), have shown it to consist of a series of extensional basins that offset the major strike-slip faults. The largest of the extensional basins, the Cascadia Depression, effectively divides the transform into a northwest segment, composed of several relatively short strike-slip faults, and a southeast segment dominated by fewer, longer faults. The regional seismicity distribution (m b ≥4.0) and frequency-magnitude relationships (b-values) of the BTFZ show that the largest magnitude events are located on the southeast segment. Furthermore, estimates of the cumulative seismic moment release and seismic moment release rate along the southeast segment are significantly greater than that of the northwest segment. These observations suggest that slip along the southeast segment is accommodated by a greater number of large magnitude earthquakes. Comparison of the seismic moment rate, derived from empirical estimates, with the seismic moment rate determined from plate motion constraints suggests a difference in the seismic coupling strength between the segments. This difference in coupling may partially explain the disparity in earthquake size distribution. However, the results appear to confirm the relation between earthquake size and fault length, observed along continental strike-slip faults, for this oceanic transform.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369149
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  • 2
    Electronic Resource
    Electronic Resource
    Seismotectonic studies of the coastal areas of India, Pakistan, Bangladesh, and Burma (1993)
    Springer
    Natural hazards 7 (1993), S. 201-210 
    Details
    ISSN: 1573-0840
    Keywords: Indian subcontinent ; geodynamic unit ; seismotectonics ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract Major geotectonic elements that are seismically active in the near-shore areas of the Indian subcontinent are the Mekran fault off the coast of Pakistan, the western part of the Narmada-Son lineament, the West Coast Fault off the west coast of India - a southward extension of the Cambay Rift, the Palghat Gap, the Godavari and Mahanadi grabens, transecting rather at an angle to the eastern coast of India and the Arakan-Yoma arcuate belt of Burma, which is a part of the global Alpine-Himalayan orogenic belt, continuing southwards into the Andaman-Nicobar island complex and the Java-Sumatra trench on the ocean floor of the advancing Indo-Australian Plate. The coastal belt exhibits varied degrees of seismicity from intensely seismic areas, like the Mekran coast off Pakistan, Kutch (India) and the Arakan-Yoma belt of Burma, with earthquake magnitudes of more than 8.0, while the intervening coastal areas of the Peninsular India are moderately seismic to aseismic. The remaining areas, namely, the major part of the coastal belt of Bay of Bengal in India and Bangladesh are broadly aseismic. However, the active Godavari graben and the eastern part of the coast of Bangladesh are frequented by low to moderate magnitude earthquakes. An extension of the active Arakan-Yoma belt in the Bay of Bengal in the form of the Andaman-Nicobar Island complex is highly seismic with a maximum earthquake magnitude of more than 8.0, while the Lakshadweep-Minicoy island complex, situated on the Chagos-Laccadive ridge is moderately seismic. This broad picture of coastal and marginal seismicity is corroborated by the geodynamics of the northern part of the Indo-Australian Plate. Observations along the coastal areas during historic and recent times, however, confirm the absence of significant ‘tsunamis’, though very mild tsunami surges have occasionally been observed along the coastal areas of the Bay of Bengal. No active volcanoes are known to exist in the coastal areas. Water reservoirs situated near the marginal areas of the Peninsular Shield exhibit moderate to intense seismic activities, viz. Ukai, Bhatsa, Koyna, Parambikulam, Sholayar, Idduki, and Kinnersani.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00662646
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  • 3
    Electronic Resource
    Electronic Resource
    Seismic hazard monitoring in Kamchatka and its applications to the M = 6.6 earthquake of 6 October 1987 (1992)
    Springer
    Natural hazards 6 (1992), S. 51-70 
    Details
    ISSN: 1573-0840
    Keywords: Seismic hazard ; seismic monitoring ; earthquake ; Kamchatka
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences
    Notes: Abstract The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained: u The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km3. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s2. Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO3 and H3BO3 concentrations in the underground waters were observed in the wells a week before the main shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00162099
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  • 4
    Electronic Resource
    Electronic Resource
    Computer estimation of intensities: The 1985 Berhida, Hungary, earthquake (1990)
    Springer
    Pure and applied geophysics 132 (1990), S. 533-543 
    Details
    ISSN: 1420-9136
    Keywords: Computer ; earthquake ; Hungary ; intensity ; macroseismic ; MSK scale ; questionnaire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this paper a computerized method for the intensity estimation from macroseismic observations is presented. The successive steps of the MSK intensity scale (2° to 10°) receives weights according to the observations marked on the earthquake questionnaires. These weights are summed for the individual scale steps. The distribution of these summed weights and their relation to an experimentally chosen function of the criterion make it possible to estimate the appropriate intensity value and its reliability. By computer evaluation of earthquake reports an objective comparison of estimated intensities given by different seismologists can be made, provided that uniform earthquake questionnaires are used. The application of this method will result in more homogeneous intensity data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876928
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  • 5
    Electronic Resource
    Electronic Resource
    Towards a new view of earthquake phenomena (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 531-548 
    Details
    ISSN: 1420-9136
    Keywords: Fractal ; earthquake ; critical phenomena ; self-organization ; cellular automaton ; multifractal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Recent advances in the theory of fracture and fragmentation are reviewed. Empirical laws in seismology are interpreted from a fractal perspective, and earthquakes are viewed as a self-organized critical phenomenon (SOC). Earthquakes occur as an energy dissipation process in the earth's crust to which the tectonic energy is continuously input. The crust self-organizes into the critical state and the temporal and spatial fractal structure emerges naturally. Power-law relations known in seismology are the expression of the critical state of the crust. An SOC model for earthquakes, which explains the Gutenberg-Richter relation, the Omori's formula of aftershocks and the fractal distribution of hypocenters, is presented. A new view of earthquake phenomena shares a common standpoint with other disciplines to study natural complex phenomena with a unified theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876337
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  • 6
    Electronic Resource
    Electronic Resource
    Energy balance of simple elastodynamic sources (1994)
    Springer
    Pure and applied geophysics 143 (1994), S. 563-586 
    Details
    ISSN: 1420-9136
    Keywords: Double-couple ; earthquake ; elastodynamics ; energy balance ; isotropic source ; near-field waves ; wave energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Complete relations are derived for energy and energy flux of elastic waves generated by an isotropic and double-couple source in a perfectly elastic, homogeneous, isotropic, and unbounded medium. In the energy balance of elastodynamic sources near-field waves play an essential role, transforming static energy into wave energy, andvice versa. For explosive and dislocation sources, the sources surface radiates a positive wave energy that is partially distributed to the medium transforming into static energy. For implosive and antidislocation sources, the source surface generates elastic waves, but it does not necessarily imply that it also radiates a positive wave energy. The energy transported by waves can originate in gradual transformation of the static-to-wave energy during propagation of waves through a stressed medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879498
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  • 7
    Electronic Resource
    Electronic Resource
    Intermediate term earthquake prediction in the area of Greece: Application of the algorithm M8 (1990)
    Springer
    Pure and applied geophysics 134 (1990), S. 261-282 
    Details
    ISSN: 1420-9136
    Keywords: Greece ; earthquake ; intermediate prediction algorithm M8 ; TIP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The 3 strongest earthquakes,M≥7.0, which have occurred since 1973 in the area of Greece were preceded by a specific increase of the earthquake activity in the lower magnitude range. This activation is depicted by algorithm M8. This algorithm of intermediate term earthquake prediction was originally designed for diagnosis by Times of Increased Probability (TIPs) of the strongest earthquake,M≥8.0 worldwide (Keilis-Borok andKossobokov, 1984). At present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions (Keilis-Borok andKossobokov, 1986, 1988). A TIP refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source. Altogether the TIPs diagnosed by the algorithm M8 in the area of Greece occupy less than 20% and the Times of Expectation (TEs) about 10% of the total space-time domain considered. Also there is a current TIP for the southeastern Aegean sea and 1988–1992. It may specify the long-term prediction given inWyss andBaer (1981a,b). The results of this study are further evidence favoring applicability of algorithm M8 in diverse seismotectonic environment and magnitude ranges and support indirectly the hypothesis of self-similarity of the earthquake activity. It also implies the possibility of intermediate term prediction of the strongest earthquakes in the area of Greece.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00877001
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  • 8
    Electronic Resource
    Electronic Resource
    An experimental study of triggered stick-slip (1993)
    Springer
    Pure and applied geophysics 140 (1993), S. 79-94 
    Details
    ISSN: 1420-9136
    Keywords: Stick-slip ; rock friction ; instability ; precursor ; earthquake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Stick-slips have been studied in the laboratory on granite, labrodorite and sandstone samples of two different sizes. Different roughness was achieved on the sawcut surfaces by finishing them with different grinding compounds ranging from grit 40 to grit 1000. Stick-slips occurred as a result of 1) slowly increasing the shear and normal stresses, 2) superimposing a sinusoidal stress modulation (0.1 and 10 Hz) on the slowly increasing stresses, 3) triggering by a stress impulse when the shear stress was well below the levels where stick-slips occurred without the impulse, and 4) foreshocks. Stick-slips triggered by impulses or foreshocks occurred “long” after the beginning of the triggering events, i.e., long in comparison with elastic wave travel times through the sample. All triggered events were very rich in high frequencies (corner frequency of ∼100 kHz). The untriggered stick-slips did not contain much energy at the high frequencies (corner frequency of ∼10 kHz). The dynamic friction coefficients for the triggered stick-slips were smaller than for the untriggered events. The “long” delay between the onset of the trigger and the stick-slip, and the high frequencies may be a consequence of corrosion of asperities. The ultimate triggering and the rate of corrosion are likely related to the interplay of the normal and shear stresses as they load and unload the fault surface. The consistent shape of the high frequency spectra is probably due to sample resonances which are excited rather than being characteristic of the details of the stick-slips. If these laboratory observations are directly applicable to earthquake seismology, the spectra of earthquakes which were triggered by other earthquakes should be anomalously rich in high frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876872
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  • 9
    Electronic Resource
    Electronic Resource
    The 1986 Kermadec earthquake and its relation to plate segmentation (1993)
    Springer
    Pure and applied geophysics 140 (1993), S. 331-364 
    Details
    ISSN: 1420-9136
    Keywords: Tectonics ; subduction ; plate segmentation ; Kermadec ; earthquake ; rupture process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract To evaluate the tectonic significance of the October 20, 1986 Kermadec earthquake (M w =7.7), we performed a comprehensive analysis of source parameters using surface waves, body waves, and relocated aftershocks. Amplitude and phase spectra from up to 93 Rayleigh waves were inverted for centroid time, depth, and moment tensor in a two-step algorithm. In some of the inversions, the time function was parameterized to include information from the body-wave time function. The resulting source parameters were stable with respect to variations in the velocity and attenuation models assumed, the parameterization of the time function, and the set of Rayleigh waves included. The surface wave focal mechanism derived (ϕ=275°, δ=61°, λ=156°) is an oblique-compressional mechanism that is not easy to interpret in terms of subduction tectonics. A seismic moment of 4.5×1020 N-m, a centroid depth of 45±5 km, and a centroid time of 13±3 s were obtained. Directivity was not resolvable from the surface waves. The short source duration is in significant contrast to many large earthquakes. We performed a simultaneous inversion ofP andSH body waves for focal mechanism and time function. The focal mechanism agreed roughly with the surface wave mechanism. Multiple focal mechanisms remain a possibility, but could not be resolved. The body waves indicate a short duration of slip (15 to 20 s), with secondary moment release 60s later. Seismically radiated energy was computed from the body-wave source spectrum. The stress drop computed from the seismic energy is about 30 bars. Sixty aftershocks that occurred within three months of the mainshock were relocated using the method of Joint Hypocentral Determination (JHD). Most of the aftershocks have underthrusting focal mechanisms and appear to represent triggered slip on the main thrust interface. The depth, relatively high stress drop, short duration of slip, and paucity of true aftershocks are consistent with intraplate faulting within the downgoing plate. Although it is not clear on which nodal plane slip occurred, several factors favor the roughly E-W trending plane. The event occurred near a major segmentation in the downgoing plate at depth, near a bend in the trench, and near a right-lateral offset of the volcanic are by 80 km along an E-W direction. Also, all events in the region from 1977 to 1991 with CMT focal mechanisms similar to that of the Mainshock occurred near the mainshock epicenter, rather than forming an elongate zone parallel to the trench as did the aftershock activity. We interpret this event as part of the process of segmentation or tearing of the subducting slab. This segmentation appears to be related to the subduction of the Louisville Ridge, which may act as an obstacle to subduction through its buoyancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879411
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  • 10
    Electronic Resource
    Electronic Resource
    An asperity model to simulate rupture along heterogeneous fault surfaces (1992)
    Springer
    Pure and applied geophysics 138 (1992), S. 549-567 
    Details
    ISSN: 1420-9136
    Keywords: Asperity ; earthquake ; fracture mechanics simulation ; seismicity ; characteristic earthquakes ; b-value
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A model has been developed to simulate the statistical and mechanical nature of rupture on a heterogeneous strike-slip fault. The model is based on the progressive failure of circular asperities of varying sizes and strengths along a fault plane subjected to a constant far-field shear displacement rate. The basis of the model is a deformation and stress intensity factory solution for a single circular asperity under a unidirectional shear stress. The individual asperities are unified through the fault stiffness and the far-field stress and displacement. During fault deformation asperities can fail and reheal, resulting in changes in the local stresses in the asperities, stress drops, and changes in the stiffness of the fault. Depending on how the stress is redistributed following asperity failure and on the strenghts of the neighboring asperities an earthquake event can be the failure of one or more asperities. Following an earthquake event seismic source parameters such as the stress drop, energy change, and moment magnitude are calculated. Results from the model show a very realistic pattern of earthquake rupture, with reasonable source parameters, the proper magnitude-frequency behavior, and the development of characteristic earthquakes. Also the progression ofb-values in the model gives some insight into the phenomenon of ‘self-organized criticality.’
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876338
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