Tuna Eken | Helmholtz-Zentrum Potsdam (original) (raw)

Papers by Tuna Eken

Geophysical research …, Jan 1, 2003

... TURKELLI Niyazi (1) ; SANDVOL Eric (2) ; ZOR Ekrem (1) ; GOK Rengin (1) ; BEKLER Tolga (1) ; ... more ... TURKELLI Niyazi (1) ; SANDVOL Eric (2) ; ZOR Ekrem (1) ; GOK Rengin (1) ; BEKLER Tolga (1) ; AL-LAZKI Ali (3) ; KARABULUT Hayrullah (1) ; KULELI Sadi (1) ; EKEN Tuna (1) ; GURBUZ Cemil (1) ; BAYRAKTUTAN Salih (4) ; SEBER Dogan (3) ; BARAZANGI Muawia (3) ; ...

Geophysical …, Jan 1, 2003

A 29-station temporary broadband PASSCAL network was operated from late October 1999 to August 20... more A 29-station temporary broadband PASSCAL network was operated from late October 1999 to August 2001 in eastern Turkey in order to decipher the geodynamics of one of the youngest continent-continent collision zones in the world. This paper focuses on the hypocentral distribution of local earthquakes located during the operation of the network and provides new insights into the active faulting in the Anatolian Plateau. A total of 1165 earthquakes were located and classified into four different categories based on the reliability of the locations based on the data coverage. The accuracy of the locations ranked in the best two categories is estimated to be less than 10 km. The results show that seismic activity in Eastern Turkey is higher than previously documented and there were no subcrustal earthquakes beneath the Arabian-Eurasian collision zone or beneath the Anatolian plateau during our deployment. This result suggests no or very little underthrusting of the Arabian plate beneath Eurasia. Our results also suggest that the North Anatolian Fault zone extends farther toward the southeast, well beyond the Karliova triple junction, and that a number of unmapped active, seismogenic faults exist in the region. We observe a possible difference in the seismogenic thickness of the East Anatolian fault zone (EAFZ) and the North Anatolian fault zone (NAFZ).

Geophysical Journal …, Jan 1, 2007

CITATIONS 21 READS 52 4 authors, including: Some of the authors of this publication are also work... more CITATIONS 21 READS 52 4 authors, including: Some of the authors of this publication are also working on these related projects: Numerical simulation of 3D mantle flow in subduction systems in relation to seismic anisotropy beneath eastern Mediterranean and Anatolia View project Tuna Eken Helmholtz-Zentrum Potsdam -Deutsches GeoF… S U M M A R Y Upper-mantle structure under the Baltic Shield is studied using non-linear high resolution teleseismic P-phase tomography. Observed relative arrival-time residuals from 52 teleseismic earthquakes recorded by the Swedish National Seismological Network (SNSN) are inverted to delineate the structure of the upper mantle. The network consists of 47 (currently working) three-component broad-band stations located in an area about 450 km wide and 1450 km long.

Geophys. Res. …, Jan 1, 2004

A recently developed coda magnitude methodology was applied to selected broadband stations in Tur... more A recently developed coda magnitude methodology was applied to selected broadband stations in Turkey for the purpose of testing the coda method in a large, laterally complex region. As found in other, albeit smaller regions, coda envelope amplitude measurements are significantly less variable than distance-corrected direct wave measurements (i.e., L g and surface waves) by roughly a factor 3-to-4. Despite strong lateral crustal heterogeneity in Turkey, we found that the region could be adequately modeled assuming a simple 1-D, radially symmetric path correction for 10 narrow frequency bands ranging between 0.02 to 2.0 Hz. For higher frequencies however, 2-D path corrections will be necessary and will be the subject of a future study. After calibrating the stations ISP, ISKB, and MALT for local and regional distances, single-station moment-magnitude estimates (M w ) derived from the coda spectra were in excellent agreement with those determined from multi-station waveform modeling inversions of long-period data, exhibiting a data standard deviation of 0.17.

Tectonophysics, Jan 1, 2010

CITATIONS 3 READS 50 7 authors, including: Some of the authors of this publication are also worki... more CITATIONS 3 READS 50 7 authors, including: Some of the authors of this publication are also working on these related projects: Numerical simulation of 3D mantle flow in subduction systems in relation to seismic anisotropy beneath eastern Mediterranean and Anatolia View project Multi-disciplinary Seismic Tomography View project Tuna Eken Helmholtz-Zentrum Potsdam -Deutsches Ge… a b s t r a c t Mantle lithosphere Seismic anisotropy Domains and their boundaries in the mantle Body-wave analysisshear-wave splitting and P travel time residualsdetect anisotropic structure of the upper mantle beneath the Swedish part of Fennoscandia. Geographic variations of both the splitting measurements and the P-residual spheres map regions of different fabrics of the mantle lithosphere. The fabric of individual mantle domains is internally consistent, usually with sudden changes at their boundaries.

Proceedings of the …, Jan 1, 2003

The following is an overview of results from ROA01-32 that focuses on an empirical method of cali... more The following is an overview of results from ROA01-32 that focuses on an empirical method of calibrating stable seismic source moment-rate spectra derived from regional coda envelopes using broadband stations. The main goal was to develop a regional magnitude methodology that had the following properties: 1) it is tied to an absolute scale and is thus unbiased and transportable; 2) it can be tied seamlessly to the well-established teleseismic and regional catalogs; 3) it is applicable to small events using a sparse network of regional stations; 4) it is flexible enough to utilize S n -coda, L g -coda, or P-coda, whichever phase has the best signal-to-noise ratio. The results of this calibration yield source spectra and derived magnitudes that were more stable than any other direct-phase measure to date. Our empirical procedure accounted for all propagation, site, and S-to-coda transfer function effects. The resultant codaderived moment-rate spectra were used to provide traditional band-limited magnitude (e.g., M L , m b etc.) as well as an unbiased, unsaturated magnitude (moment magnitude, M w ) that is tied to a physical measure of earthquake size (i.e., seismic moment). We validated our results by comparing our coda-derived moment estimates with those obtained from long-period waveform modeling. We first tested and validated the method using events distributed along the Dead Sea Rift (e.g., ). Next, we tested the transportability of the method to earthquakes distributed across the entire country of Turkey and validated our results using seismic moments of over 50 events that had been previously waveform modeled using the method of Dreger and Helmberger, (1993). In both regions we demonstrated that the interstation magnitude scatter was significantly reduced when using the codabased magnitudes (i.e., M w (coda) and m b (coda)). Once calibrated, the coda-derived source spectra provided stable, unbiased magnitude estimates for events that were too small either to be reliably waveform modeled or to be seen at far-regional and teleseismic distances. In general coda-derived magnitudes are roughly a factor of 3 to 5 more stable than traditional regional magnitudes that use the direct-phases such as P g and L g . This appears to be a universal observation for all regions where the coda methodology has been applied.

Tectonophysics, Jan 1, 2008

Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear... more Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear tomographic inversion of relative arrival-time residuals. 52 selected teleseismic earthquakes recorded by 45 broadband stations of the Swedish National Seismological Network (SNSN) provide 1532 good quality Swave relative arrival times. SV and SH arrival-time residuals were initially analyzed independently, providing two separate models. These reveal several consistent major features, many of which are also consistent with P-wave results. Lateral velocity variations of ±3-4% are observed to depths of at least 470 km. The correlation between the SH and SV models is investigated and shows a pattern of minor but significant differences down to around 150-200 km depth, below which the models are essentially similar. Direct cell by cell comparison of the model velocities reveals a similar pattern, with velocity differences between the models of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially attributed to noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. One of the significant and sharp discrepancies between the S models coincides with a presumed boundary between Archean and Proterozic domains, suggesting different anisotropic characteristics in the two regions.

Eken, T. 2009. Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle. Results ... more Eken, T. 2009. Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle. Results from Analyses of Teleseismic Body Waves. Acta Universitatis Upsaliensis. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 653. 110 pp. Uppsala. ISBN 978-91-554-7548-2.

... Affiliation: AA(Geophysical Institute, Czech Acad. Sci., 141 31 Prague, Czech Republic (tuna.... more ... Affiliation: AA(Geophysical Institute, Czech Acad. Sci., 141 31 Prague, Czech Republic (tuna.eken@gmail.com)), AB(Geophysical Institute, Czech Acad. Sci., 141 31 Prague, Czech Republic (tuna.eken@gmail.com)), AC(Geophysical Institute, Czech Acad. ...