Segmentation and Holocene Behavior of the Middle Strand of the North
Anatolian Fault (NW Turkey)
Abstract
The North Anatolian fault in the Marmara region is composed of three
parallel strands all separated by ~50 km. The activity
of the middle strand, which borders the southern edge of the Marmara
Sea, is much debated because of its present-day very low seismicity. The
weak seismic activity observed today along the middle strand contrasts
with historical, archaeological and paleoseismological evidence, which
suggest several destructive earthquakes have occurred during the last
2000 years. Our study aims to better constrain seismic hazard on the
middle strand by exploring its Holocene paleoseismicity. For this, we
mapped 148 km of the middle strand, using high-resolution satellite
imagery. A series of landforms offset by the middle strand activity have
been systematically measured to recover the past ruptures. Three Late
Pleistocene-Holocene terraces have been dated with the terrestrial
cosmogenic nuclide method, constraining a horizontal slip rate of
~4.3 mm/yr. The statistical analysis of the offsets
evidences several major ruptures preserved in the landscape, with
coseismic lateral displacements ranging between 3 and 6.5 m. This
corresponds to Mw ~7.3 earthquakes able to propagate
along several fault segments. As the approach used can only resolve
large magnitude events, smaller events (e.g. Mw 6.8-7) likely occurred
as well even if their geomorphological signature could not be detected.
Historical seismicity and paleoseismology data suggest that the last
large earthquakes along the MNAF happened in 1065 CE and between the
14th and 18th centuries CE. Since
then, the MNAF may have accumulated enough stress to generate a
destructive rupture.