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  • 1
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    A model for the Hellenic subduction zone in the area of Crete based on seismological investigations (2007)
    In:  Geological Society Special Publication 291: 183-199.
    Details
    Publication Date: 2007-12-12
    Description: The island of Crete represents a horst structure located in the central forearc of the retreating Hellenic subduction zone. The structure and dynamics of the plate boundary in the area of Crete are investigated by receiver function, surface wave and microseismicity using temporary seismic networks. Here the results are summarized and implications for geodynamic models are discussed. The oceanic Moho of the subducted African plate is situated at a depth of about 5060 km beneath Crete. The continental crust of the overriding Aegean lithosphere is about 35 km thick in eastern and central Crete, and typical crustal velocities are observed down to the upper surface of the downgoing slab beneath western Crete. A negative phase at about 4 s in receiver functions occurring in stripes parallel to the trend of the island points to low-velocity slices within the Aegean lithosphere. Interplate seismicity is spread out about 100 km updip from the southern coastline of Crete. To the south of western Crete, this seismically active zone corresponds to the inferred rupture plane of the magnitude 8 earthquake of AD 365. In contrast, interplate motion appears to be largely aseismic beneath the island. The coastline of Crete mimics the shape of a microseismically quiet realm in the Aegean lithosphere at 2040 km depth, suggesting a relation between active processes at this depth range and uplift. The peculiar properties of the lithosphere and the plate interface beneath Crete are tentatively attributed to extrusion of material from a subduction channel, driving differential uplift of the island by several kilometres since about 4 Ma.
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  • 2
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    Lithospheric structure of the Aegean obtained from P and S receiver functions (2006)
    American Geophysical Union
    Details
    Publication Date: 2006-12-01
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 3
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    A model for the Hellenic subduction zone in the area of Crete based on seismological investigations (2007)
    Geological Society of London
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    Publication Date: 2007-01-01
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society of London
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  • 4
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    Earthquake Cluster: What Can We Learn from Waveform Similarity? (2008)
    Seismological Society of America
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    Publication Date: 2008-12-01
    Description: The seismograms of earthquakes, which have closely spaced hypocenters, tend to be similar due to the similarity of the Green"s functions characterizing the source-receiver paths. Based on the lambda /4 criterion, it is frequently argued that similar earthquakes may represent repeated slip of the same patch of a fault. Because of the phenomenological nature of waveform similarity, such interpretations are strongly dependent on seismic signal characteristics and on the way, the waveform similarity is defined. In this article, we use two-dimensional synthetic wave-field simulations in lateral heterogeneous media to investigate how the waveform similarity of closely spaced hypocenters changes with interevent separation. We analyze the influence of correlation window length, signal frequency bandwidth, and source-receiver geometry on the waveform similarity and discuss under which conditions the lambda /4 criterion can be applied to the synthetic data set. With the correlation window length defined as 2.8 times the travel-time difference between the S- and P-phase onsets, we find a correlation threshold value of 0.95 independent of the signal frequency bandwidth. We use the same threshold value for two field data examples that are similar to the synthetic data in frequency content and waveform complexity, and we discuss the implications of the lambda /4 criterion. For three microearthquakes occurring during a fluid-injection experiment at the German deep drilling site (Kontinentale Tiefbohrung [KTB]), the interevent separation constrained by the lambda /4 criterion is sufficient to identify these events as a sequence of repeating earthquakes in the sense that at least a fraction of the source area experienced repeated slip. For a second data example of four natural (micro-) earthquakes occurring near the island of Crete, the lambda /4 criterion does not sufficiently constrain the hypocenter location to identify these events as repeating earthquakes due to the lack of high-frequency information.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America
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  • 5
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    Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network (2009)
    Springer
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    Publication Date: 2009-05-14
    Description: We investigate microseismic activity at the convergent plate boundary of the Hellenic subduction zone on- and offshore south-eastern Crete with unprecedented precision using recordings from an amphibian seismic network. The network configuration consisted of up to eight ocean bottom seismometers as well as five temporary short-period and six permanent broadband stations on Crete and surrounding islands. More than 2,500 local and regional events with magnitudes up to ML = 4.5 were recorded during the time period July 2003-June 2004. The magnitude of completeness varies between 1.5 on Crete and adjacent areas and increases to 2.5 in the vicinity of the Strabo trench 100 km south of Crete. Tests with different localization schemes and velocity models showed that the best results were obtained from a probabilistic earthquake localization using a 1-D velocity model and corresponding station corrections obtained by simultaneous inversion. Most of the seismic activity is located offshore of central and eastern Crete and interpreted to be associated with the intracrustal graben system (Ptolemy and Pliny trenches). Furthermore, a significant portion of events represents interplate seismicity along the NNE-ward dipping plate interface. The concentration of seismicity along the Ptolemy and Pliny trenches extends from shallow depths down to the plate interface and indicates active movement. We propose that both trenches form transtensional structures within the Aegean plate. The Aegean continental crust between these two trenches is interpreted as a forearc sliver as it exhibits only low microseismic activity during the observation period and little or no internal deformation. Interplate seismicity between the Aegean and African plates forms a 100-km wide zone along dip from the Strabo trench in the south to the southern shore-line of Crete in the north. The seismicity at the plate contact is randomly distributed and no indications for locked zones were observed. The plate contact below and north of Crete shows no microseismic activity and seems to be decoupled. The crustal seismicity of the Aegean plate in this area is generally confined to the upper 20 km in agreement with the idea of a ductile deformation of the lower crust caused by a rapid return flow of metamorphic rocks that spread out below the forearc. In the region of the Messara half-graben at the south coast of central Crete, a southward dipping seismogenic structure is found that coalesces with the seismicity of the Ptolemy trench at a depth of about 20 km. The accretionary prism south of Crete indicated by the Mediterranean Ridge showed no seismic activity during the observation period and seems to be deforming aseismically. © 2009 Springer Science+Business Media B.V.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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  • 6
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    Modeling the influence of Moho topography on receiver functions: A case study from the central Hellenic subduction zone (2005)
    American Geophysical Union
    Details
    Publication Date: 2005-06-01
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by American Geophysical Union
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  • 7
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    Comparison between LDG-network and GERESS-array with respect to regional detection and location results (2006)
    Details
    Publication Date: 2019-11-04
    Description: The design of a global seismic system to monitor compliance with a ban on underground nuclear testing considerably deviates from previous concepts of international seismic data exchange. The new concept relies on centralized processing of continuous data from a fixed station network (“alpha” stations) which provides the primary detection and location capability. This alpha station network is augmented by additional stations (“beta” stations) which send data on request to refine the hypocentres of events which were detected by the alpha network. To test this concept we have used the GERESS array in Germany as a prototype alpha station and investigated its regional detection and location capability for events in France and surrounding areas. For this region, data from the national French network operated by LDG provide an excellent reference data base. Within a 5 degree distance, GERESS showed an excellent performance in terms of detection and location down to magnitude M(LDG) = 3. Between a 5 degree and 10 degree distance, the detection capability is still high but very often it is not sufficient to locate events below M(LDG) = 4. Generalizing these results, we can conclude that either the maximum distance between alpha stations should be 10 degrees or the contribution of beta stations has to play a significant role in a future monitoring system.
    Description: JCR Journal
    Description: open
    Keywords: locations ; array ; seismic monitoring ; alpha stations ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 2296389 bytes
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  • 8
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    Preliminary calibration of candidate alpha stations in the GSETT-3 network (2006)
    Details
    Publication Date: 2019-11-04
    Description: The technical concept of a future global seismic monitoring system includes 50 to 60 core stations, mostly arrays, which provide the primary detection and location capability. Due to the average station distance, these core (“alpha”) stations form a teleseismic network. Many of the proposed stations are to be newly installed and before the network can be regarded as fully operational, the stations have to be calibrated. As for traditional seismic networks, the station residuals - compared to a standard earth model - have to be determined. The standard earth model is defined in terms of travel-time tables and amplitude-distance curves. After recording a representative set of events, station residuals with respect to travel-time and magnitude can be calculated. In case of arrays, the determination of mislocation vectors (azimuth and slowness residuaIs) are of ulmost importance if array slowness vectors are used as starting solutions in a location procedure. Finally, in a monitoring context it is very important to estimate the station sensitivity for varying background noise conditíons and - in case of arrays - to know the frequency dependent improvement by beamforming. This paper uses the newly installed high-frequency GERESS array in Germany to demonstrate the calibration procedure.
    Description: JCR Journal
    Description: open
    Keywords: global seismic networks ; station calibration ; array location ; magnitude residual ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 3213412 bytes
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