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  • 1
    Electronic Resource
    Electronic Resource
    Source parameters of earthquakes in the Aleutian Islands subduction zone (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The source parameters of seven moderate-sized earthquakes representing different parts of the Aleutian Islands subduction zone are presented. Fault plane solutions are determined by the relative amplitude method. A simple 2-D kinematic source model is assumed and synthetic broad-band (BB) seismograms of displacement are generated. Comparisons with observed BB records of displacement allow the estimation of source dimensions, focal depth, rupture velocity, mean stress drop and the static seismic moment for each event. Normal faulting associated with extensional stresses generated within the subducting plate is determined for one event. However, the majority of solutions indicate compressive mechanisms consistent with the subduction environment. Focal depth is well resolved as depth phases are apparent on most of the seismograms due to the frequency range (0.05-5.0 Hz) of the broad-band records used. The circular or elliptical faults assumed for the source model vary from 3.5 to 8 km in radius depending on body-wave magnitude. The stress drop values obtained are typical of interplate earthquakes (˜30 bar). However, the higher stress drop found for one event at a depth of approximately 180 km in the subducting lithosphere can be attributed to the intraplate character of this earthquake. Seismic moments obtained are similar to those obtained in centroid moment tensor (CMT) solutions, even though the latter are calculated using lower frequency seismic waves. This implies a fairly flat spectral level below the corner frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb01829.x
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  • 2
    Electronic Resource
    Electronic Resource
    On the resolving power of tomographic images in the Aegean area (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 107 (1991), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: bThe imaging of upper mantle heterogeneity by seismic tomography is strongly limited by the uneven global distribution both of seismic recording stations and earthquake sources. This can result in a loss of resolution and significance in the final image, particularly when a sparse data set contains few ray paths which intersect at sufficiently high angles in the volume of interest. In order to investigate the theoretical resolving power of a previously published tomographic image of the Aegean area, synthetic tests of the inversion procedure using a ray-path matrix obtained in this previous study for local and teleseismic P-waves were carried out. The aim was to examine the extent to which the shape of a synthetic lithospheric slab penetrating to different depths is inherently distorted by the tomographic imaging procedure, and to compare the synthetic tomographic images with the results from the actual inversion. The distortion is found to take the form of an artificial stretching of the lithospheric slab. The maximum ‘stretching factor', as indicated by the downdip displacement of the peak amplitude of the synthetic high-velocity anomaly, is found to be a factor of 2 or so, though the distortion is usually less than this. The peak amplitude of the tomographic image of a lithospheric slab is found from the inversion of traveltime data to be at depths at or below 400 km. This indicates that the high-velocity lithospheric slab in the Aegean penetrates deeper than the Benioff zone seismicity of about 200 km. However, no constraints of the maximum depth of penetration could be established with the data set used in the present work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1991.tb01168.x
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  • 3
    Electronic Resource
    Electronic Resource
    The nucleation and rupture process of the 1981 Gulf of Corinth earthquakes from deconvolved broad-band data (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 120 (1995), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Source parameters of the largest three normal faulting earthquakes (MS6.6, 6.3, 6.4), in the 1981 Gulf of Corinth (Greece) sequence are determined using deconvolved broad-band data (recorded by arrays and single stations) and a 2-D finite source model. Such a model enables the spatial extent, rupture velocity and stress drop of the earthquakes to be determined and geological observations of surface slip can be included as a further constraint on the waveform modelling. All three earthquakes were shallow (〈10km) with low stress drops (〈30bars), and exhibited source complexity. The correspondence between the complexity of the earthquake sources and that of the mapped fault breaks implies that the segmentation of surface faulting in Greece is representative of faulting at depth. Tiny initial pulses which correlate across the arrays are seen in the seismograms from the Gulf of Corinth earthquakes at most stations. These initial subevents (〈1 per cent of the total moment) are interpreted as the breaking of small asperities which initiated the main rupture and are used to constrain the attenuation correction (t*= 0.2 s).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1995.tb01827.x
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  • 4
    Electronic Resource
    Electronic Resource
    3-D structure of the lithosphere in the Aegean region (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 102 (1990), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: 5000 P-wave traveltime residuals from about 300 local and 400 teleseismic earthquakes recorded by the Athens seismological network were used to study the structure of the lithosphere in the Aegean region. Teleseismic data included readings from local stations which do not routinely report to the ISC. the large values of the residuals (up to ± 3 s) and their variation with azimuth and epicentral distance indicate significant velocity heterogeneity in the upper mantle. P-wave traveltime residuals were inverted simultaneously for both local and teleseismic earthquakes. Tomographic results, which are best resolved at lithospheric depths, reveal a heterogeneous lithosphere down to a depth of 100 km or so. A high-velocity anomaly is found dipping at an average of 45° to the NE away from the Hellenic trench, and supports the hypothesis of subduction due to a cooler descending slab of oceanic composition. an area of low velocities is observed at depths less than 80 km in the Aegean back-arc, corresponding well with observed, high heat flow values in the area. In contrast, an area of relatively higher velocity anomalies is resolved in the lithosphere underlying the Sea of Crete.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1990.tb00543.x
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  • 5
    Electronic Resource
    Electronic Resource
    FAULTS IN FOCUS (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Terra nova 7 (1995), S. 0 
    Details
    ISSN: 1365-3121
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3121.1995.tb00663.x
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  • 6
    Electronic Resource
    Electronic Resource
    Non-universal scaling of fracture length and opening displacement (1994)
    [s.l.] : Nature Publishing Group
    Nature 367 (1994), S. 160-162 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Krafla fissure swarm (Fig. 1) is one of five volcanotectonic systems in the active rift zone of northeast Iceland, striking (at 10° E) sub-perpendicular to the spreading direction of the Mid-Atlantic Ridge7'8. The swarm is associated with the Krafla central volcano, and takes the form of an ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/367160a0
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  • 7
    Electronic Resource
    Electronic Resource
    Role of pore fluids in the generation of seismic precursors to shear fracture (1992)
    [s.l.] : Nature Publishing Group
    Nature 359 (1992), S. 228-230 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The fracture mechanics model of Main et a/.2 is summarized in Fig. 1. In nature, because crustal deformation is accompanied and accomplished by microcracking and small earthquakes6, sometimes coupled with aseismic deformation, the crust will respond to remotely applied tectonic loading by deforming ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/359228a0
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  • 8
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    Coupled geomechanics flow modelling at and below a critical stress state used to investigate common statistical properties of field production data (2008)
    In:  Geological Society Special Publication 292: 453-468.
    Details
    Publication Date: 2008-01-02
    Description: An areal model of a fractured/faulted reservoir with 49 wells is developed that incorporates fully-coupled geo-mechanics and fluid flow. It is a generic example of a pattern waterflood although it is inspired by a parallel study of the Gullfaks reservoir in the North Sea, in which stress-related, fault-related and long-range correlations in rate fluctuations are observed. Based on this model, three scenarios are examined in terms of different initial stress states prior to production, each of which involves 36 months of production and injection in the presence of fracture sets and faults. The results support the concept that the long-range, stress-related and fault-related characteristics of correlations in rate fluctuations, observed not only in the Gullfaks data, but also in several other fields worldwide, are symptomatic of a system near a geomechanical critical point. These characteristics are not observed in models that are sub-critical. Short-range rate correlations are likely to exist where there are highly permeable zones between producers and injectors. Long-range rate correlations occur only within critically-stressed regions where there is active shearing or fault reactivation. The modelling results are consistent with field evidence suggesting that incipient shearing is an important mechanism coupled with reservoir flow behaviour.
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  • 9
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    The Statistical Reservoir Model: calibrating faults and fractures, and predicting reservoir response to water flood (2008)
    In:  Geological Society Special Publication 292: 469-482.
    Details
    Publication Date: 2008-01-02
    Description: This paper describes the new concept of a Statistical Reservoir Model' to determine significant well-pair correlations. We solve this conceptual problem using a predictive error filter, combined with Bayesian methods that identify those well pairs that are related to each other with statistical significance, for the Gullfaks reservoir in the North Sea. Significant, long-range, correlations in the whole field are found at an optimal time lag of one month. The correlation function for significantly-correlated well pairs, after normalization for the distribution of available wells, shows a long-range power-law decay that is consistent with a critical-point response at the reservoir scale. A principal component analysis shows a strong correlation with the location and orientation of faults that intersect the main producing horizon. A predictive experiment shows that the model performs very well both in history matching and predictive mode on a time scale of about one month.
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  • 10
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    Statistical Modeling of the 1997-1998 Colfiorito Earthquake Sequence: Locating a Stationary Solution within Parameter Uncertainty (2014)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2014-04-04
    Description: The Umbria–Marche region of Italy is a seismically active region that experienced a strong sequence of earthquakes during 1997–1998, with a cluster of magnitude M ≥5 events, during which the average event rate increased from the long-term level by several orders of magnitude. Using maximum-likelihood (ML) inversion of the epidemic-type aftershock sequences model to characterize the seismicity of this region over 22 years, we find, in agreement with previous studies, the event rate during the sequence is underpredicted, based on simulations with the large M ≥5 events fixed. However, by sampling the parameter space around the ML solution within the inversion uncertainty and comparing the simulated event rate with that of the real data, we are able to find near-maximum-likelihood parameters that provide a reasonable match to both the long-term average event rate and the rate during the sequence. We use the shape of the interevent time histogram to infer that the events in the sequence are probably mostly aftershocks of the large events, rather than an increased occurrence of background events. We suggest that event rate comparisons can be useful as an additional constraint on the selection of parameters from within the 95% confidence interval of the ML fit. Our results demonstrate the extra constraint can greatly improve the match between a stationary model and finite catalog data and that care is needed before adding further parameters to ascribe nonstationarity to time-dependent event rate changes.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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