Three-dimensional passive imaging of complex seismic fault systems: evidence of surface traces of the Issyk-Ata fault (Kyrgyzstan)

Nowadays, an increasing number of seismological imaging studies are published taking advantage of the increasing popularity of analysing empirical Green's functions obtained from high-frequency ambient seismic noise. However, especially on a local scale results could potentially be biased in regions where topography is not small compared to the wavelength and the penetration depth of the considered waves. Current 2-D seismic techniques are often inadequate when solving such 3-D geophysical problems, which include the complication of seismic imaging for cases where there are pronounced relief effects. For example, information about the geologic subsurface structure and deformational patterns is necessary for accurate site characterization and seismic hazard assessment. Here we show that an ad hoc passive seismic tomography approach can identify and describe complex 3-D structures, which can help to accurately and efficiently map the shear-wave velocities of the surficial soil layers, even in cases of significant topography relief. We test our technique by using simulations of seismic noise for a simple realistic site and show for a real data set across the Issyk-Ata fault, Kyrgyzstan, which is located at southern border of the capital, Bishkek, this novel approach has identified two different small fault branches and a clear shear-wave velocity contrast across the fault.