Borehole Seismogram Calibration and Deconvolution for Ground Motion and Earthquake Source Studies: Applications to the ICDP-GONAF project in NW Turkey

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During the initial 1.5-year period of the project we focused on analyzing seismic recordings from the first vertical seismometer array implemented in the frame of the ICDP-GONAF project, located on the Tuzla peninsula in SE Istanbul. Due to the low-noise conditions and resulting high signal-to-noise ratios at the downhole stations compared to surface stations it was possible to detect numerous microseismic (M<1) events which went undetected by surface arrays. In the frame of the here proposed extension we intend to further enlarge the event data base for the eastern Sea of Marmara by integrating additional recently completed GONAF borehole arrays on the Armutlu peninsula (completed in summer 2014) as well as up to four more arrays which are currently drilled and that shall be in operation by spring 2015 (e.g. on the Princes Islands). For the investigation of the near-surface properties at the Tuzla site such as the velocity structure and attenuation we applied several different techniques. The same methods will be applied to the new GONAF stations to evaluate whether our observations at the Tuzla site are site-specific or transferable also to other geological formations. The comparative analysis of different sites will be of great value for developing a data analysis scheme that also corrects for site effects, a procedure needed to improve for example earthquake source parameter estimations. Furthermore we plan to apply processing techniques from vertical seismic profiling for fault-zone imaging of the NAFZ fault branches below the eastern Sea of Marmara. To do so we will select local seismicity within 20 km epicentral distance (depth range 5-20km) to the GONAF stations and use the different depth levels of the borehole sensors. The waveform recordings of 3-component 1Hz MARK seismometers deployed at 300 m depth for the first time will be studied and are expected to provide new insights in shear-wave characteristics of the study area.