Insight into the Crustal Structure of the Eastern Marmara Region, NW Turkey |
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Authors: | Tolga Bekler Cemil Gurbuz |
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Affiliation: | 1. Department of Geophysics, Faculty of Engineering and Architecture, ?anakkale Onsekiz Mart University, ?anakkale, 17020, Turkey 2. Department of Geophysics, Kandilli Observatory and Earthquake Research Institute, Bo?azici University, Istanbul, 34684, Turkey
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Abstract: | In order to investigate crustal structure beneath the eastern Marmara region, a seismic refraction survey was conducted across
the North Anatolian Fault (NAF) zone in north west Turkey. Two reversed profiles across two strands of the NAF zone were recorded
in the Armutlu Highland where a tectonically active region was formed by different continents. We used land explosions in
boreholes and quarry blasts as seismic sources. A reliable crustal velocity and depth model is obtained from the inversion
of first arrival travel times. The velocity-depth model will improve the positioning of the earthquake activities in this
active portion of the NAF. A high velocity anomaly (5.6–5.8 km s−1) in the central highland of Armutlu block and the low velocity (4.90 km s−1) pattern north of Iznik Lake are the two dominant features. The crustal thickness is about 26 ± 2 km in the north and increases
to about 32 ± 2 km beneath the central Armutlu block in the south. P-wave velocities are about 3.95 km s−1 to 4.70 km s−1 for the depth range between about 1 km and 5 km in the upper crust. The eastern Marmara region has different units of upper
crust with velocities varying with depth to almost 8 km. The high upper crust velocities are associated with Armutlu metamorphic
rocks, while the low velocity anomalies are due to unconsolidated sedimentary sequences. The western side of Armutlu block
has complex tectonics and is well known for geothermal sources. If these sources are continuous throughout the portions of
the crust, it may be associated with a granitic intrusion and deformation along the NAF zone. That is, the geothermal sources
associated with the low velocity may be due to the occurrence of widespread shear heating, even shear melting. The presence
of shear melting may indicate the presence of crustal fluid imposed by two blocks of the NAF system. |
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Keywords: | Marmara region North Anatolian Fault (NAF) velocity structure seismic refraction inversion |
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