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  • 1
    Electronic Resource
    Electronic Resource
    The Armenian earthquake of 1988 December 7: faulting and folding, neotectonics and palaeoseismicity (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Spitak earthquake of 1988 December 7 is the first well-documented event directly associated with surface breaks in the Transcaucasian regions of the USSR. The earthquake was located within the ESE-WNW oriented Pambak-Sevan thrust and fold zone corresponding to the southern front of the Lesser Caucasus. The mechanism of the earthquake is consistent with the nearly NS compressive tectonics due to the active continental collision between the Arabian block and the Russian Platform. The rupture is composed by several branches, two of which reach the surface. The first branch, oriented N140°, begins near the village of Alavar, has a length of 11 km and disappears at about 4 km SE of Spitak. It consists of a right lateral en échelon system of strike-slip faults, with a maximum offset of 50 cm. The second branch is the main one and breaks for about 8 km between Spitak and Gekhasar, with a general orientation N120°, showing reverse faulting dipping to the north with a right lateral component. Surface ruptures between Gekhasar and Spitak show either a narrow band of pressure ridges in alluvial deposits and soil, or a fault scarp in the bed rocks when soil is absent. Maximum displacements, observed between Spitak and Gekhasar, attain 160 cm of vertical motion and 90 cm of horizontal dextral offset. The displacement also varies within this branch, showing finer segmentation. Few secondary deformations are observed: some normal faults near Gekhasar correspond to the collapse of the uplifted block. An anticline fold, oriented parallel to the fault scarp and situated along its northwestern prolongation, emphasizes the regional compressive tectonics. Landslides were activated on its flanks. A 200 m long reverse fault break observed along the hinge of a secondary fold suggests the occurrence of a blind thrust at depth and that the hidden branches, which continue the main central segment towards the NW, are associated to surface folding. Therefore, the total length of the fault and fold zone is about 40 km in agreement with the rupture length and seismic moment obtained on the basis of surface wave modelling. Well-developed uplifted terraces in the northern block and subsiding valleys in the southern block indicate past Quaternary activity in the fault region. Palaeoseismological evidence of ancient earthquakes has been recognized in trenches across the Spitak fault. One old event occurred between 17 000 years BP and the beginning of the formation of present-day soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00718.x
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  • 2
    Electronic Resource
    Electronic Resource
    Geometry, segmentation and stress regime of the Spitak (Armenia) earthquake from the analysis of the aftershock sequence (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 108 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The aftershock sequence of the Spitak earthquake, as recorded by a dense portable network deployed around the source region, is analysed in order to obtain a precise description of the mechanics of the rupture. A collection of 708 well-recorded events corresponding to a period of about two weeks is studied, their hypocentres are accurately located, and their focal mechanisms are calculated individually as well as by a joint procedure that permits us to estimate the stress regime.The epicentral distribution of these aftershocks indicates that the fault at depth extends well beyond the surface rupture towards the west and northwest. Neotectonic and seismic observations permit us to identify five segments broken during the earthquake. The southeastern one, oriented N140d̀, corresponds to the surface ruptures along the Alavar right lateral shear fault. The main surface ruptures, between Spitak and Gekhasar, correlate well with aftershocks showing a N120d̀ trending fault surface, dipping 50d̀ to the NE and acting as a thrust with a right lateral component. Two similar segments towards the west, are offset and hidden under active folds. A fifth segment, towards the NW, corresponds to a right lateral blind shear fault buried in depth, in the vicinity of the large Pambak-Sevan fault. 14 vertical sections across the fault, including focal mechanisms, illustrate these features.A relocation of the main shock and aftershocks for the period before the installation of the portable network, confirms the spatial extent of the seismicity. The foreshock, the main shock and the strongest aftershock (4 min 20 s after the main shock) have approximately the same epicentre. Thus the rupture started at the crossing of the Pambak-Sevan and Alavar faults and propagated bilateraly from there, although the seismic moment associated to the Alavar branch is only about one sixth of the total moment.The stress regime is one of triaxial compression with a σ1 axis oriented N344d̀. The same orientation is given by the microtectonic observations made on the central segment of the surface ruptures, a result that agrees with previous estimates for the Georgian Caucasus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00860.x
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  • 3
    Electronic Resource
    Electronic Resource
    Tectonic deformation of the Andes and the configuration of the subducted slab in central Peru; results from a microseismic experiment (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 103 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A microearthquake survey was conducted in the central Andes of Peru, east of the city of Lima, to study the seismicity and style of tectonic deformation of the Peruvian Andes. Although most of the stations forming the temporary seismographic network were located on the high Andes, the vast majority of the microearthquakes recorded occurred to the east of the mountain belt: on the Huaytapallana fault in the Eastern Cordillera and beneath the western margin of the sub-Andes. Thus the sub-Andes appear to be the physiographic province subject to the most intense seismic deformation. Focal depths of the crustal events in this region range generally from 15 to 35 km and some events beneath the sub-Andes appear to be as deep as 40-50 km. The fault-plane solutions of events in the sub-Andean margin show thrust faulting on steep planes oriented roughly north-south, similar to that observed in teleseismic earthquakes studied using body wave modelling. The Huaytapallana fault in the Cordillera Oriental also shows relatively high seismicity along a NE-SW trend that agrees with the fault scarp and the east-dipping nodal plane of two large earthquakes that occurred on this fault on 1969 July 24 and October 1. Microearthquakes of intermediate depth recorded during the experiment show a flat seismic zone about 25 km thick at a depth of about 100 km. This agrees with recent observations showing that beneath Peru the slab first dips at an angle of about 30° to a depth of 100 km and then flattens following a quasi-horizontal trajectory. Fault-plane solutions of intermediate-depth microearthquakes have horizontal T axes oriented east-west suggesting slab pull is the dominant force in the downgoing slab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb01747.x
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of seismogenic interplate contact zone and crustal seismicity around Antofagasta, northern Chile using local data (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: During September and October 1988 a microseismic field experiment was carried out around the city of Antofagasta, northern Chile, with 29 portable analogue and digital stations. A total of 197 reliable microearthquake locations and 19 focal mechanisms were determined. It is proposed that it is possible to estimate the maximum depth of the coupled-uncoupled transition of the subducting lithosphere using local data, defined by the depth of the expected change of the stress field from compressional to tensional along the slab. This change is observed at about 70 km depth in the Antofagasta field work. Two estimations of the width of the seismogenic interplate contact are discussed: (1) the maximum depth of the coupled zone defined by the observed maximum depth of the shallow-dipping thrust events recorded during the experiment of 47 km, corresponding to a width of the seismogenic contact zone of about 90 km; and (2) the maximum depth of the coupled zone defined by the depth of the observed change from a compressional to tensional stress field, which is 70 km and corresponds to a width of the seismogenic contact zone of about 130 km. With both values, the maximum magnitude Ms estimated for the region varies between 8.6 and 8.7. No shallow event associated with the Atacama fault system was observed during the experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb03279.x
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  • 5
    Electronic Resource
    Electronic Resource
    The rupture process of the Armenian earthquake from broad-band teleseismic body wave records (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 109 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The destructive earthquake of December 1988 in Armenia (Ms= 6.9) was recorded on broad-band and very long-period channels at teleseismic distances by Geoscope and GDSN networks. These records are well distributed in azimuth, and allow a detailed study of the rupture process of this earthquake. The average focal mechanism obtained by P- and SH-wave modelling (φ= 300°±10 °, δ= 63°±5°, λ= 100°±20°) is compatible with the mechanism obtained from very long-period surface waves and intermediate-period single-station determinations, as well as field observations. The mean depth of the rupture is also fixed by waveform modelling between 5 and 7 km which means that the rupture surface extends from the surface to a depth between 10 and 14 km, in agreement with aftershock depth distribution. The rupture is found to be complex, composed of a weak beginning or a small foreshock and two pulses well separated in time. The time delay between the two events is estimated for each station by waveform modelling and by spectral analysis. The azimuthal variation of this time delay is interpreted in terms of direction and velocity of rupture on the fault plane. A more detailed analysis of the source implies the use of additional information coming from aftershock studies and tectonics. We use forward modelling to investigate several rupture mechanisms. A three-source model gives an acceptable fit to the observed records but the western mechanism is at odds with observed tectonics and, furthermore, rupture propagation is not well simulated. A five-segment model of the source obtained from field seismotectonic data gives a better waveform fit, a time sequence of individual breaks that simulates a rupture propagating away from the hypocentre, and subsource mechanisms that are compatible with surface tectonics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb00085.x
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  • 6
    Electronic Resource
    Electronic Resource
    The Spitak (Armenia) earthquake of 7 December 1988: field observations, seismology and tectonics (1989)
    [s.l.] : Nature Publishing Group
    Nature 339 (1989), S. 675-679 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The epicentre of the destructive earthquake that devastated northern Armenia, the strongest in the region since historical times, is located within the Lesser Caucasus, a mountain country subjected to north–south compression by the push of the Arabian plate. A French-Soviet field expedition ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/339675a0
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  • 7
    Electronic Resource
    Electronic Resource
    Seismotectonics of the El Asnam earthquake (1981)
    [s.l.] : Nature Publishing Group
    Nature 292 (1981), S. 26-31 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The mechanism of the El Asnam earthquake of 10 October 1980 (Ms = 7.2), the strongest recorded in northwestern Africa is compatible with a convergence between the African and European plates. The thrust is also consistent with field observations and with long period data from the global ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/292026a0
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  • 8
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    The Armenian earthquake of 1988 December 7: faulting and folding, neotectonics and palaeoseismicity (1992)
    Oxford University Press
    Details
    Publication Date: 1992-07-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 9
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    Mechanism of the 1992 Erzincan earthquake and its aftershocks, tectonics of the Erzincan Basin and decoupling on the North Anatolian Fault (1997)
    Oxford University Press
    Details
    Publication Date: 1997-04-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 10
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    Reexamination of the magnitudes for the 1906 and 1922 Chilean earthquakes using Japanese tsunami amplitudes: implications for source depth constraints (2016)
    Wiley
    Details
    Publication Date: 2016-12-15
    Description: Far-field tsunami records from the Japanese tide gauge network allow the reexamination of the moment magnitudes (Mw) for the 1906 and 1922 Chilean earthquakes, which to date rely on limited information mainly from seismological observations alone. Tide gauges along the Japanese coast provide extensive records of tsunamis triggered by six great (Mw 〉8) Chilean earthquakes with instrumentally-determined moment magnitudes. These tsunami records are used to explore the dependence of tsunami amplitudes in Japan on the parent earthquake magnitude of Chilean origin. Using the resulting regression parameters together with tide gauge amplitudes measured in Japan we estimate apparent moment magnitudes of Mw 8.0-8.2 and Mw 8.5-8.6 for the 1906 central and 1922 north-central Chile earthquakes. The large discrepancy of the 1906 magnitude estimated from the tsunami observed in Japan as compared with those previously determined from seismic waves (Ms 8.4), suggests a deeper than average source with reduced tsunami excitation. A deep dislocation along the Chilean megathrust would favor uplift of the coast rather than beneath the sea, giving rise to a smaller tsunami, and producing effects consistent with those observed in 1906. The 1922 magnitude inferred from far-field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes (Ms 8.3) that were likely affected by the well-known saturation effects. Thus, a repeat of the large 1922 earthquake poses seismic and tsunami hazard in a region identified as a mature seismic gap
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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