Borehole Seismogram Calibration and Deconvolution for Ground Motion and Earthquake Source Studies: Applications to the ICDP-GONAF project in NW Turkey
Geophysics
Final Report Abstract
The main objective of this project was to study downhole waveform recordings from the first borehole of the ICDP-driven Geophysical downhole Observatory at the North Anatolian Fault (GONAF) in the Istanbul/eastern Sea of Marmara, Turkey, region. The main focus was on comparing downhole versus surface seismic waveform recordings from the region and deriving a deconvolution method and code for removing surface and near-surface interference effects from GONAF borehole seismograms. This then should serve as a baseline for instituting a standard data analysis procedure aimed at generating the best look at locations and source characteristics of Princes Island area earthquakes as observed from GONAF borehole geophones. From the beginning of the project it was anticipated that the near-source structure of the NAFZ in the target area was complex; this was confirmed by the actual waveform data. The obtained GONAF signals full-filled the expectations in that they 1. Allowed to substantially (by more than order of magnitude) decrease the magnitude-detection threshold of local seismicity and, 2. Were entirely rich in that they contain signals that are mixed in with near-surface reflections at the borehole observation sites. The work carried out in the frame of this project contained several important steps, which are discussed in more detail in the sections 1 and 2 below. Most importantly, these were optimizing detection algorithms for low-noise seismic waveform recordings and using the well log and drilling data to create zero order models of the near-surface velocity structure for correlation with deconvolution results. Of particular relevance in this respect was the location of fractures, lithological boundaries, and attenuation zones. Further important objectives were to establish a practical convolution approach to the incident angle dependent site response and attenuation, and to prepare a function code that combines site response removal with the standard deconvolution of the seismic sensor itself.
Publications
- (2015). Downhole Geophysical Observatories: Best Installation Practices and a Case History from Turkey. Int. J.Earth Sci. (Geol Rundsch), 104:1537–1547
Prevedel., B., Bulut, F., Bohnhoff, M., Raub, C., Kartal, R.F., Alver, F., Malin, P.E.
(See online at https://doi.org/10.1007/s00531-015-1147-5) - (2016). Seismic wave propagation in shallow layers at the GONAF-Tuzla site, Istanbul, Turkey, Bull. Seismol. Soc. Am., 106(3), 912–927
Raub, C., Bohnhoff, M., Petrovic, B., Parolai, S., Malin, P.E., Yanik, K., Kartal, R.F., Kiliç, T.
(See online at https://doi.org/10.1785/0120150216) - (2017). GONAF–A borehole Geophysical Observatory around the North Anatolian Fault in the Eastern Sea of Marmara, Sci. Dril., 5, 1–10
Bohnhoff, M., Dresen, G., Ceken, U., Kadirioglu, F.T., Kartal, R.F., Kilic, T., Nurlu, M., Yanik, K., Acarel, D., Bulut, F., Ito, H., Johnson, W., Malin, P.E., Mencin, D.
(See online at https://doi.org/10.5194/sd-22-19-2017) - Variations of seismic bvalue at different stages of the seismic cycle along the North Anatolian Fault Zone in northwestern Turkey, Tectonophysics, 712-713, 232-248, 2017
Raub, C., Martinez-Garzon, P., Kwiatek, G., Bohnhoff, M., Dresen, G.,
(See online at https://doi.org/10.1016/j.tecto.2017.05.028)
