 |
| Titel |
Luminescence dating of offset terraces at the Elmali segment of the North Anatolian Fault (NE Turkey); Implications for long term geologic slip-rate |
| VerfasserIn |
Cengiz Zabcı, Taylan Sançar, H. Serdar Akyuz, Nafiye Güneç Kıyak |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039729
|
|
|
|
|
|
| Zusammenfassung |
| The North Anatolian Fault (NAF) is 1500 km-long dextral strike-slip fault, starts from
Karliova triple junction in the east and terminates at the Aegean Sea in the west with
northward convex arc shaped geometry. In the 20th century, series of earthquakes which
started by 1939 Erzincan (M=7.9) in the east and ended by August 17, 1999 Izmit
(M=7.4) and November 12, 1999 Duzce (M=7.1) events in the west, caused many
causalities and economic loss at settlements all along this zone. Geodetic short
term slip rate is measured to be between 28.0±0.3 mm/yr and 24.2±0.3 mm/yr by
GPS as snapshots of strain accumulation for a relatively short period of time. The
geologic long term slip rates are determined, mostly from west and middle sections
of the NAF, to be between 10 mm to 20.5±5.5 mm/yr, which are slower than the
short term of elastic strain accumulation measured geodetically. This mismatch is
also seen on many fault systems after the dating of many offset geological and
morphotectonic structures at different parts of the Earth. These observations raise several
fundamentally important questions about how strain accumulates and is released
along major plate boundary fault systems. Are geologic slip rates averaged over
thousands to millions of years compatible with short term geodetic rates, or do strain
transients commonly occur? In addition, determination of geologic slip rates at many
locations on the same fault zone helps to understand the uniformity of the slip rate or
an existence of a gradient for the whole system. In this study, we undertook field
and aerial photography research on one of the least known sections of the NAF,
Elmali segment, at the NE Turkey. The NAF is extremely placed on a relatively
narrow zone around Erzincan and 150 to 200 km west of it. However, more to the
east, deformation extends to a wider zone of a width of around 10 km between
the Yedisu basin and Karliova. Here, three different segments form a restraining
double bend and are clearly defined physiographically along the Elmali valley. The
compressional nature of this restraining double bend structure creates an uplift,
which is expressed by formation of fill terraces in alluvial fans as insets on the
geomorphology of the region. We determined two locations, 5 km-apart each other, consist of
dextrally deflected; Dinarbey and Kaynarpinar spots. An alluvial fan is incised by an
active stream, which created two terrace surfaces, at the Dinarbey spot. Terrace
risers, forming boundaries between two terraces and the recent floodplain, have
recorded dextral offset of 67±5 m and 21±5 m with respect to each other. We
used cylindrical metal pipes with 25 cm length and 5 cm diameter to sample the
upper terrace both from the northern and southern blocks of the fault for Optical
Stimulated Luminescence (OSL) dating. These samples yielded ages of 3273±567 yr
BP and 3279±258 yr BP giving a slip-rate of 20.4±2.2 mm/yr for this section of
the fault. Although, we see the same terrace formation at Kaynarpinar spot, it is
not easy to reconstruct the net offset of terrace risers. The lateral erosion of the
stream system modified the geometry of terrace risers not to have any piercing point
for the measurement of the net offset. However, it is morphologically clear that
55±5m net offset of incised stream should have formed after the formation of the
alluvial fan and before the formation of the upper terrace. At this spot, terraces and
lower fan surface are sampled for luminescence dating, which is still in process. |
|
|
|
|
|
|