Using cosmogenic 36Cl to determine periods of enhanced seismicity in western Anatolia, Turkey

Mozafari Amiri, Nasim (2017). Using cosmogenic 36Cl to determine periods of enhanced seismicity in western Anatolia, Turkey (Unpublished). (Dissertation, Institute of Geological Sciences, Science)

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Reconstruction of paleoearthquakes is an essential step in order to widen our
understanding of future seismic behavior on specific faults and in a larger extent in a
regional tectonic framework. Fault scarp dating using cosmogenic 36Cl is a powerful
technique to explore the rupture history of faults that provide valuable information to
be contributed in seismic hazard assessment. Western Anatolia is a roughly N-S
rapidly extensional region since early Miocene. Deformation pattern of this
intensively active region is strongly dominated by normal faults, locally built in
carbonates, within the large-scale horst-graben systems. Carbonate bedrock fault
scarps are the most direct indication of past earthquakes in order to explore seismic
behavior of faults using cosmogenic 36Cl. The oldest recorded earthquake in the
Eastern Mediterranean and Middle East dates back to 2100 B.C, whereas the
instrumental earthquakes were recorded only during the last century. However, to
assess the seismic activity of faults, a more complete seismic database within and
prior to the existing seismic archives is required.
In this study, in order to model a long-term seismic history of western
Anatolia, we applied fault scarp dating on several fault scarps within Büyük
Menderes Graben, Gediz Graben, and Gökova half-graben by analysing 584
samples. We could recover at least 12 large seismic events, mostly occurred as
clustered earthquakes with magnitude of 5.4 to 7.1 during the past 15 ka. The
correlation of timing of paleoearthquakes at ca. 2.0, 3.5, 6.0 and 8.0 ka lead us to
assert that western Anatolia experienced at least four periods of high seismic
activity during Holocene, in addition to the recent time with the high record of major
earthquakes. The regional recurrence interval of approximately 2000 years is
concordant with the return period of earthquakes of several faults in the extensional
tectonic setting of Aegean region. The vertical slip rates of faults are estimated to be
in a range of 0.1 to 1.9 mm/yr, which generally increase through time. This indicates
that the largest amount of strain during the whole Holocene time is transmitting to
western Anatolia in recent time.

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