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| Titel |
Focal mechanisms in the southern Aegean from temporary seismic networks – implications for the regional stress field and ongoing deformation processes |
| VerfasserIn |
W. Friederich, A. Brüstle, L. Küperkoch, T. Meier, S. Lamara, EGELADOS Working Group |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1869-9510
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| Digitales Dokument |
URL |
| Erschienen |
In: Solid Earth ; 5, no. 1 ; Nr. 5, no. 1 (2014-05-09), S.275-297 |
| Datensatznummer |
250115268
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| Publikation (Nr.) |
 copernicus.org/se-5-275-2014.pdf |
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| Zusammenfassung |
| 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 well-constrained 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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