Seismic-Wave Propagation in Shallow Layers at the GONAF-Tuzla Site, Istanbul, Turkey

摘要: Using the first dataset available from downhole Geophysical Observatory of North Anatolian Fault, we investigated near‐surface seismic‐wave propagation on Tuzla Peninsula, Istanbul, Turkey. We selected a 26 seismograms recorded at sensor depths 0, 71, 144, 215, and 288 m. To determine velocities attenuation structures, waveforms all sensors were pairwise deconvolved stacked. This produced low‐noise empirical Green’s functions for each borehole depth interval. From functions, identified reflections free surface low‐velocity layer between ∼90 ∼140  m depth. The presence zone was also confirmed by sonic log run in borehole. structure, plus high P ‐ S ‐wave ∼3600–4100 ∼1800  m/s, lead to complex interference effects upgoing downgoing waves. As result, determination quality factors ( Q ) with standard spectral ratio techniques not possible. Instead, forward modeled time domain effective values refine our velocity estimates. intervals 0–71, 0–144, 0–215, 0–288 m found be 19, 35, 39, 42, respectively. For waves, obtained an 20 interval 0–288 m. Considering assumptions made modeling approach, it is evident that these are biased impedance contrasts observation points. Our results show that, even after correcting free‐surface factor 2, motion 1.7 times greater than 71 m efforts illustrate some difficulties dealing site strongly heterogeneous subsurface. Online Material: Plots resistivity caliper logs spectra events.