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| Titel |
3D Tomographic Imaging of the Crustal Velocity Structure beneath the Marmara Sea using Air-gun and Earthquake Data |
| VerfasserIn |
Adil Tarancioglu, Argun H. Kocaoglu, Serdar Özalaybey |
| 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 |
250093898
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| Publikation (Nr.) |
 EGU/EGU2014-9077.pdf |
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| Zusammenfassung |
| The objective of this study is to investigate the local seismicity and obtain a detailed
three-dimensional crustal velocity structure beneath the Marmara Sea in an area
surrounding the North Anatolian Fault Zone (NAFZ) by tomographic inversion using both
controlled-source (air-gun) and earthquake data. The tomographic inversion is carried out by
using the local earthquake tomography code SIMUL2000. Two sets of seismological data,
collected in 2006 (EOSMARMARA experiment) and 2001 (SEISMARMARA
experiment), are re-processed and used in this study. A total of 441 high quality
earthquakes and 452 air-gun shots recorded by a total of 53 Ocean Bottom Seismometers
(OBS) are selected for the simultaneous inversion for velocity and hypocentral
parameters. The OBS location and time-drift errors are identified from air-gun shot
records by a grid search method and required corrections are made on the travel time
data.
The initial (reference) velocity model and earthquake locations required for the three
dimensional tomographic inversion are derived from the one-dimensional velocity model
obtained by using the VELEST algorithm in which a subset of earthquakes are selected such
that phase readings were made by at least five stations and maximum azimuthal gap
was 180o. The inversion results are checked for initial model dependence and the
effect of damping factor. The reliability of the results is also evaluated in terms of
derivative-weighted-sum, resolution-diagonal-elements values and checkerboard
tests.
The hypocenter locations of the local earthquakes have been remarkably improved by the
three-dimensional velocity model obtained from the tomographic inversion. The
three-dimensional velocity model shows that the Tekirdag, Central and Cinarcik Basins are
characterized generally by lower Vp (3.0 - 3.5 km/s) values and most of the earthquakes
across these regions are located at the depths of 10 to 17 km, about 5 km deeper than those
obtained from the one-dimensional reference velocity model. Also, the epicenters of these
earthquakes are observed to coincide with the mapped surface trace of the NAFZ for this
area. A few earthquakes with a hypocenter depth of about 15 km are identified in the
west of Kumburgaz Basin where Vp values are higher (5.5 km/s). In contrast, the
eastern part of Kumburgaz Basin is characterized by lower Vp (5.0 km/s) values and
shows almost no apparent seismicity. Generally, low Vp values are obtained in
the western part of Cinarcik Basin where the seismicity is predominantly located
between the depths of 10 to 15 km. The highest Vp values (up to 6.5 km/s) are
found to be near the northern coastline of the Armutlu Peninsula at a depth of 10
km.
Finally, the comparison of our tomographic cross-sections with the interpreted seismic
reflection sections from previous studies shows a high correlation down to a depth of 12 km.
Future work will involve further investigation of deep structures with the wave propagation
modeling using the finite-difference method. |
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