Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms

Bohnhoff, Marco; Harjes, Hans-Peter; Meier, Thomas

doi:10.1007/s10950-005-8720-5

Cited by 85 publications

(55 citation statements)

References 53 publications

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“…Active quaternary normal faults known from geologic and sea-beam observations Armijo et al, 1992) are reported for these areas as well. The activation of these N-S to NNE-SSW trending normal faults is in agreement with the current stress field in eastern Crete (Bohnhoff et al, 2005) and consistent with fault-plane solutions indicating E-W extension in the region east of Crete (Fig. 1).…”

Section: Microseismicity Beneath Cretesupporting

confidence: 84%

“…However, we cannot exclude that this difference is caused by poor hypocentre precision of the historic events. Most of this shallow activity is likely to be caused by relative movements along transtensional structures caused by the oblique subduction and slab roll-back (Kahle et al, 2000; ten Veen and Kleinspehn, 2003;Bohnhoff et al, 2005). In the western offshore area, seismicity is generally confined to the plate interface with low seismic activity at the Ionian trench.…”

Section: Seismicity Of the Hszmentioning

confidence: 99%

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Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

et al. 2009

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Section: Microseismicity Beneath Cretesupporting

confidence: 84%

Section: Seismicity Of the Hszmentioning

confidence: 99%

Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

et al. 2009

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“…Aegean (Hatzfeld et al, 1993;Friederich and Meier, 2008), on Crete (Bohnhoff et al, 2005;Jost et al, 2002;Meier et al, 2004;Becker et al, 2009), in the Cyclades (Bohnhoff et al, 2004;Dimitriadis et al, 2005Dimitriadis et al, , 2009 and in the western Hellenic subduction zone (Haslinger, 1998;Rigo et al, 1996;Papadimitriou et al, 2010). In view of the severe seismic hazard of the region, a central aim of all research efforts is and was to promote the understanding of the current seismotectonics of the Aegean.…”

Section: W Friederich Et Al: Focal Mechanisms and Stress Field In Tmentioning

confidence: 99%

“…Papazachos et al, 1991;Taymaz et al, 1991;Benetatos et al, 2004;Bohnhoff et al, 2005;Kiratzi et al, 2007), via observation of aftershocks which permit inferences on the size of the fault plane and the amount of slip (Drakatos and Latoussakis, 2001) and finally via stress field determinations from catalogues of focal mechanisms (Papazachos and Delibasis, 1969;Bohnhoff et al, 2005;Rontogianni et al, 2011). Besides seismicity, direct observations of plate motions by geodetic measurements (e.g.…”

Section: W Friederich Et Al: Focal Mechanisms and Stress Field In Tmentioning

confidence: 99%

Focal mechanisms in the southern Aegean from temporary seismic networks – implications for the regional stress field and ongoing deformation processes

Friederich

Brüstle

Küperkoch³

et al. 2014

Solid Earth

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Abstract. The lateral variation of the stress field in the southern Aegean plate and the subducting Hellenic slab is determined from recordings of seismicity obtained with the CYCNET and EGELADOS networks in the years from 2002 to 2007. First motions from 7000 well-located microearthquakes were analysed to produce 540 wellconstrained focal mechanisms. They were complemented by another 140 derived by waveform matching of records from larger events. Most of these earthquakes fall into 16 distinct spatial clusters distributed over the southern Aegean region. For each cluster, a stress inversion could be carried out yielding consistent estimates of the stress field and its spatial variation. At crustal levels, the stress field is generally dominated by a steeply dipping compressional principal stress direction except in places where coupling of the subducting slab and overlying plate come into play. Tensional principal stresses are generally subhorizontal. Just behind the forearc, the crust is under arc-parallel tension whereas in the volcanic areas around Kos, Columbo and Astypalea tensional and intermediate stresses are nearly degenerate. Further west and north, in the Santorini-Amorgos graben and in the area of the islands of Mykonos, Andros and Tinos, tensional stresses are significant and point around the NW-SE direction. Very similar stress fields are observed in western Turkey with the tensional axis rotated to NNE-SSW. Intermediate-depth earthquakes below 100 km in the Nisyros region indicate that the Hellenic slab experiences slab-parallel tension at these depths. The direction of tension is close to east-west and thus deviates from the local NW-oriented slab dip presumably owing to the segmentation of the slab. Beneath the Cretan sea, at shallower levels, the slab is under NW-SE compression. Tensional principal stresses in the crust exhibit very good alignment with extensional strain rate principal axes derived from GPS velocities except in volcanic areas, where both appear to be unrelated, and in the forearc where compressional principal stresses are very well aligned with compressional principal strain rates. This finding indicates that, except for volcanic areas, microseismic activity in the southern Aegean is not controlled by small-scale local stresses but rather reflects the regional stress field. The lateral and depth variations of the stress field reflect the various agents that influence tectonics in the Aegean: subduction of the Hellenic slab, incipient collision with continental African lithosphere, roll back of the slab in the southeast, segmentation of the slab, arc volcanism and extension of the Aegean crust.

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“…It forms the plate boundary between the Anatolian plate in the south and the Eurasian plate in the north and slips at a rate of 20-30 mm=yr (McClusky et al, 2000). This kinematic framework is driven by the northward-pushing Arabian plate in the east and the southward-pulling rollback of the Hellenic subduction zone in the west (Flerit et al, 2004;Bohnhoff et al, 2005) (Fig. 1, right, bottom).…”

Section: Tectonic Setting and The Gonaf Projectmentioning

confidence: 99%

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

Raub

Bohnhoff

Petrović

et al. 2016

Bulletin of the Seismological Society of America

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Using the first dataset available from the downhole Geophysical Observatory of the North Anatolian Fault, we investigated near-surface seismic-wave propagation on the Tuzla Peninsula, Istanbul, Turkey. We selected a dataset of 26 seismograms recorded at Tuzla at sensor depths of 0, 71, 144, 215, and 288 m. To determine near-surface velocities and attenuation structures, the waveforms from all sensors were pairwise deconvolved and stacked. This produced low-noise empirical Green's functions for each borehole depth interval. From the Green's functions, we identified reflections from the free surface and a low-velocity layer between ∼90 and ∼140 m depth. The presence of a low-velocity zone was also confirmed by a sonic log run in the borehole. This structure, plus high near-surface P-and S-wave velocities of ∼3600-4100 and ∼1800 m=s, lead to complex interference effects between upgoing and downgoing waves. As a result, the determination of quality factors (Q) with standard spectral ratio techniques was not possible. Instead, we forward modeled the Green's functions in the time domain to determine effective Q values and to refine our velocity estimates. The effective Q P values for the depth intervals of 0-71, 0-144, 0-215, and 0-288 m were found to be 19, 35, 39, and 42, respectively. For the S waves, we obtained an effective Q S of 20 in the depth interval of 0-288 m. Considering the assumptions made in our modeling approach, it is evident that these effective quality factors are biased by impedance contrasts between our observation points. Our results show that, even after correcting for a free-surface factor of 2, the motion at the surface was found to be 1.7 times greater than that at 71 m depth. Our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface.Online Material: Plots of resistivity and caliper logs and the spectra of all 26 events.

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Deformation and stress regimes in the Hellenic subduction zone from focal Mechanisms

Cited by 85 publications

References 53 publications

Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

Seismicity at the convergent plate boundary offshore Crete, Greece, observed by an amphibian network

Focal mechanisms in the southern Aegean from temporary seismic networks – implications for the regional stress field and ongoing deformation processes

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

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