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| Titel |
Resolving the Western Black Sea Fault Using Microtremor Measurements? -Preliminary Results- |
| VerfasserIn |
Savas Karabulut, Faruk Caglak, Muammer Tun, Mualla Cengiz Cinku, Timur USTAOMER, Oguz Ozel, Stefano Parolai, Okan Tezel, Ferhat Özçep  |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096706
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| Publikation (Nr.) |
 EGU/EGU2014-12218.pdf |
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| Zusammenfassung |
| Two terrain-bounding major fault zones occur in the Marmara Sea and the northern onshore
areas. The first of these is the dextral, E-W trending, North Anatolian Fault Zone which cuts
through the deep basins within the Marmara Sea and is known to be one of the most
seismically active fault zones on the Earth. The second is the inferred West Black Sea Fault
Zone (WBFZ), a NNW-SSE trending, dextral boundary fault which separates the Istranca
Massif to the west and the Istanbul Terrane to the east. The WBFZ is thought to
have accommodated the opening of the east Black Sea basin (Okay et al., 1994).
This fault zone and the two adjacent continental blocks are covered by Middle to
Upper Eocene sediments and therefore the WBFZ is considered to be an inactive
fault. Nevertheless, it forms a major crustal zone of weakness in the vicinity of
Istanbul.
Scientists and researchers are confident that there will be in the comparatively near future
a major earthquake in the Marmara Sea in the vicinity of Istanbul. Therefore, a major concern
is to estimate possible damages to the heavily populated living areas due to such an event.
Many studies have been conducted, accordingly, focusing on the offshore (Marmara Sea) and
onshore areas (i.e., the City of Istanbul). We have initiated a new project with the aim of
constraining the West Black Sea Fault and its local site effects by using geophysical methods.
This fault is especially important for the determination of the possible damage
area, whereas evidence of some basins which cut through this fault is considered to
be potential risk of a site effect problem during a possible earthquake. Within the
framework of our project, a series of geophysical methods, such as microtremor single
station measurements, the Spatial Autocorrelation Method (SPAC), gravity, Vertical
Electrical Sounding (VES), Multi-channel analysis of Surface Wave Data (MASW), and
Magnetotellurics (MT) are planned in the area between the Büyükçekmece and
Küçükçekmece Lakes.
The first phase of the project collected 3- component single station microtremor
measurements at 278 points in the study area between 18 and 24 December 2013. The grid
space chosen was 600x600 meters. The duration of measurements at each point were between
20 minutes to 60 minutes using a Guralp CMG 6TD short period seismometer, with a
sampling rate of 100 Hz. As a result of the evaluation of these observations, we obtained
soil fundamental frequencies and amplifications, as well as bedrock depth from
the peak frequency of the microtremors records. According to the resulting soil
thickness maps, possible lineament structures were identified. Our results indicate two
different frequency distribution in the studied area. The soil fundamental frequency is
obtained below 1 Hz along the western and eastern section, while a gradual decrease is
shown towards the west and then once again a increase. In the north however, soil
transfer peaks of 1 Hz and above are remarkable. Three different types of basins are
derived by mapping the thickness of the sediments. The evolution of these basins
are still under discussion whether they arise from a tectonic origin or formed as
a result of the alteration of the Eocene limestones which distributed in an wide
area.
In the next phase of the project, we will continue to collect other geophysical data such
as gravity and electrical tomography etc. The results of this project will play an
important role in the determination of the impact of the Western Black Sea Fault on an
earthquake occurring in the Sea of Marmara and therefore serve as input to urban |
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