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  • 1
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    High-resolution body wave tomography beneath the SVEKALAPKO array: I. A priori three-dimensional crustal model and associated traveltime effects on teleseismic wave fronts (2003)
    In:  Geophysical Journal International, Basel, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. 153, no. 1, pp. 75-87, pp. 1009, (ISSN: 1340-4202)
    Details
    Publication Date: 2003
    Keywords: Teleseismic events ; Travel time ; Three dimensional ; Velocity depth profile ; EUROPROBE (Geol. and Geophys. in eastern Europe) ; GJI ; Alinaghi ; GFZ
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    High-resolution body wave tomography beneath the SVEKALAPKO array - II. Anomalous upper mantle structure beneath the central Baltic Shield (2004)
    In:  Geophys. J. Int., Basel, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. 157, no. 1, pp. 200-214, pp. 1009, (ISSN: 1340-4202)
    Details
    Publication Date: 2004
    Keywords: Tomography ; Teleseismic events ; Seismic arrays ; Velocity depth profile ; Earth model, also for more shallow analyses ! ; Fennoscandian ; Shield ; Lithosphere ; GJI ; Alinaghi ; Svecofennian ; Karelian ; Lapland ; Kola ; Sweden ; Finland ; Russia ; Norway
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Structure of the crust and uppermost mantle beneath southern Finland revealed by analysis of local events registered by the SVEKALAPKO seismic array (2004)
    In:  Tectonophysics, Washington, D.C., AGU, vol. 394, no. 1-2, pp. 41-67, pp. 2090, (ISSN: 1340-4202)
    Details
    Publication Date: 2004
    Keywords: Deep seismic sounding (espec. cont. crust) ; Velocity depth profile ; EUROPROBE (Geol. and Geophys. in eastern Europe) ; Seismic arrays ; Local earthquakes ; Alinaghi ; GFZ
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Lithospheric and sublithospheric anisotropy beneath the Baltic shield from surface-wave array analysis. (2006)
    In:  Earth and Planetary Science Letters
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    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 5
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    Non-linear surface wave phase velocity inversion based on ray theory (2002)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: The development of temporary and permanent broad-band seismic arrays reinforces the need for advanced interpretation techniques in surface-wave analysis. We present a new method based on 2-D paraxial ray theory of inverting teleseismic surface-wave phase information and constructing phase velocity maps on a regional scale. Measurements of local phase velocities and propagation directions of Rayleigh waves taken from full waveform synthetic seismograms are used to validate the ray theory for smooth structures on a regional scale. Curved wavefronts created by heterogeneous structure outside the study area are taken into account through joint inversion for the phase velocity field and the shape of the incoming wavefronts. In the forward ray tracing procedure, the curved wavefronts are introduced through the boundary conditions by equating the slowness vector of the ray at the edge of the study region with the known gradient of the arrival time of the wave. To make the inverse problem non-singular we constrain the parameters in the inversion primarily by applying a smoothness criteria on the velocity field and on the incoming wave-field. Inversions of synthetic data sets computed by direct ray tracing and by full waveform modelling show that for 100 km spacing between stations the minimum size of structure that we can image is approximately 150 km. Heterogeneities with a size approximately equal to the wavelength are reconstructed by the ray-based inversion even though velocity variations are underestimated due to the wave-field smoothing of the structures. A minimum signal-to-noise ratio of 3.5 is necessary in order to correctly retrieve the phase velocity field. Inversion of a subset of the SVEKALAPKO data for 60 s period demonstrates the applicability of the method on real data.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 6
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    Influence of the seismic noise characteristics on noise correlations in the Baltic shield (2007)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: It has recently been shown that correlations of seismic noise can contain significant information about the Green's function along the station profile. Using an array of 38 temporary broad-band stations located in Finland between 1998 September and 1999 March, we study the resulting 703 noise correlations to understand how they are influenced by the directivity of the noise field. The latter information is obtained through f-k analysis of data from two permanent seismic arrays in Germany and Norway and from a subset of stations of the array in Finland. Both types of analysis confirm that the characteristic of the seismic noise is strongly frequency-dependent. At low frequencies (0.02-0.04 Hz), we observe diffuse noise and/or randomly distributed sources. In contrast, the noise is strongly direction-dependent and not fully diffuse in the intermediate period ranges (0.04-0.25 Hz) which correspond to the first and second micro seismic peak, created at the Irish and Scottish coast and the western coast of Norway In this frequency interval the noise is sufficiently close to a plane wave to introduce systematic errors in group velocities for station pairs which are not parallel to the direction of the dominant incident noise. Phase velocities calculated by slant stack over many traces are however correct, independently of profile direction. In the high-frequency band (0.25-1.0 Hz), the situation is a mix between the low-frequency and the intermediate frequency cases. Average phase velocities and individual group velocities from well-oriented profiles are in excellent agreement with results from Rayleigh wave studies of the area.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 7
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    Structure of the crust and uppermost mantle beneath southern Finland revealed by analysis of local events registered by the SVEKALAPKO seismic array. (2004)
    In:  Tectonophysics
    Details
    Publication Date: 2020-02-12
    Description: In 1998–1999, a large-scale seismic array was deployed in Finland as a part of the EUROPROBE/SVEKALAPKO subproject, involving 14 European universities and research institutes. The objective of the project was to map the deep lithosphere structure and thickness beneath the Fennoscandian Shield by means of teleseismic events. In addition, about 580 local seismic events were registered during the data acquisition period. Among them, only eight local earthquakes were recorded, the rest being quarry blasts from mining sites in Russia, Finland, Estonia and Sweden. In this study, we present the analysis of the seismic wave field from the strongest local events registered by the majority of the stations of the SVEcofennian–KArelian–LAPland–KOla Transect (SVEKALAPKO) array with the aim of mapping the structure of the upper mantle beneath the array. For this purpose, we selected the events corresponding to a single source type and compared these recordings with those from wide-angle reflection and refraction experiments in the area to identify the regional phases. The record sections of selected events demonstrate strong reflections (PmP) from the Moho boundary. The refracted Pn phases can be seen as first arrivals at distances of about 200–400 km from the source. At offsets of about 400–800 km, phases reflected from inhomogeneities in the uppermost mantle (P1) and double reflections from the Moho boundary (PmPPmP) were recorded. Results from 2D forward ray trace modeling of reflected and refracted P-waves along four profile swathes from SVEKALAPKO stations demonstrate that the mantle reflections originate from two different groups of boundaries beneath the array: one group of phases arrive from subhorizontal and gently dipping reflectors below the Moho boundary at a depth of 70–90 km, while the other group are phases originating from a depth of 100 to 130 km. Based on the irregular character of the first group of reflections, their different spatial orientation and correlation with the Moho offsets, we interpret the boundaries of this group as relicts of ancient subduction and collision processes. The second group of reflections can be explained by a transition from mechanically strong to mechanically weak lithosphere.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 8
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    High-resolution body wave tomography beneath the SVEKALAPKO array: I. A priori three-dimensional crustal model and associated traveltime effects on teleseismic wave fronts (2003)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: Assessment of contributions from shallow lithosphere to teleseismic wave front distortion is a prerequisite for high-resolution regional teleseismic tomography. Several methods have been proposed in the past for the correction of these effects, e.g. application of station correction terms. We propose an approach that is independent of the subsequent inversion and uses the available a priori knowledge of the crustal structure to calculate crustal traveltime effects of teleseismic wave fronts. Our approach involves the construction of a 3-D crustal model based on controlled source seismology data and calculation of the associated traveltime anomalies for incoming teleseismic wave fronts. The model for central Fennoscandia shows a maximum crustal thickness of 64 km and includes a high-velocity lower crust as derived for parts of the study area by previous authors. Traveltimes calculated using finite differences for teleseismic waves travelling through this crustal model are compared with those from the standard reference model IASP91 and the residuals are used to correct observed teleseismic arrival times at the SVEKALAPKO array. To test the performance of this approach, in a second part of the study a synthetic traveltime data set is obtained by tracing wave fronts through a mantle structure with known velocity anomalies and the 3-D crustal model. This data set is inverted with and without correction for crustal effects. The 3-D crustal effects alone with a homogeneous mantle are also inverted and the results showthat the crustal effects propagate down to 450 km. The comparison of the inversion results demonstrates the need to apply appropriate 3-D crustal corrections in high-resolution regional tomography for upper-mantle structure beneath the Baltic Shield.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 9
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    High-resolution body wave tomography beneath the SVEKALAPKO array - II. Anomalous upper mantle structure beneath the central Baltic Shield (2004)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: A number of different geodynamic models have been proposed to explain the early tectonic evolution of the Baltic Shield. To provide additional geophysical constraints on these models, we performed a teleseismic tomography traveltime inversion for the central part of the Baltic Shield. The SVEKALAPKO project is focused on the investigation of the lithosphere-asthenosphere structure down to 400 km depth under central Fennoscandia (Baltic Shield). A total of 143 stations were deployed including 15 permanent stations from the Finnish seismic network. The temporal network was composed of 40 broad-band and 88 short-period instruments distributed in a rectangular array of 1000 km by 900 km from 1998 August to 1999 May. The results are based on a non-linear teleseismic tomography algorithm. They reveal significant P-velocity variations (up to 4 per cent) throughout the SVEKALAPKO array. The most prominent feature is a positive anomaly that can be followed down to 250 km depth beneath the centre of the array. We interpret this anomaly as the signature of the tectosphere (Jordan 1978) beneath the Fennoscandian Shield. It correlates spatially with an anomalous high-velocity lower crust. Other shallow (crustal) anomalies can be correlated with magmatic events surrounding this nucleus of high velocity. Comparison of images before and after correction by crustal structure proves that this methodology yields solid and coherent tomographic results. Further observations of relative P traveltime residuals from six teleseismic events with different azimuths show delay variations of ±2.0 s between stations located in the North German basin and stations on the Svecofennian Shield.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 10
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    High-resolution body wave tomography beneath the SVEKALAPKO array: I. A priori three-dimensional crustal model and associated traveltime effects on teleseismic wave fronts (2003)
    In:  Geophysical Journal International
    Details
    Publication Date: 2020-02-12
    Description: Assessment of contributions from shallow lithosphere to teleseismic wave front distortion is a prerequisite for high-resolution regional teleseismic tomography. Several methods have been proposed in the past for the correction of these effects, e.g. application of station correction terms. We propose an approach that is independent of the subsequent inversion and uses the available a priori knowledge of the crustal structure to calculate crustal traveltime effects of teleseismic wave fronts. Our approach involves the construction of a 3-D crustal model based on controlled source seismology data and calculation of the associated traveltime anomalies for incoming teleseismic wave fronts. The model for central Fennoscandia shows a maximum crustal thickness of 64 km and includes a high-velocity lower crust as derived for parts of the study area by previous authors. Traveltimes calculated using finite differences for teleseismic waves travelling through this crustal model are compared with those from the standard reference model IASP91 and the residuals are used to correct observed teleseismic arrival times at the SVEKALAPKO array. To test the performance of this approach, in a second part of the study a synthetic traveltime data set is obtained by tracing wave fronts through a mantle structure with known velocity anomalies and the 3-D crustal model. This data set is inverted with and without correction for crustal effects. The 3-D crustal effects alone with a homogeneous mantle are also inverted and the results show that the crustal effects propagate down to 450 km. The comparison of the inversion results demonstrates the need to apply appropriate 3-D crustal corrections in high-resolution regional tomography for upper-mantle structure beneath the Baltic Shield.
    Language: English
    Type: info:eu-repo/semantics/article
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