Abstract
AbstractSeismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust. Limitations on seismic resolution within the crust and difficulties imaging shallow structures such as the crust‐mantle boundary (Moho) place constraints on the interpretation of seismic images. In this study we retrieve body wave reflections from autocorrelations of ambient seismic noise. The instantaneous phase coherence autocorrelations allow unprecedented ambient noise images of the North Anatolian Fault Zone (NAFZ). Our reflection profiles show a Moho reflected P wave and additional structure within the crust and upper mantle. We image a distinct vertical offset of the Moho associated with the northern branch of the NAFZ indicating that deformation related to the fault remains narrow in the upper mantle.
Highlights
The behavior of fault zones within continental settings is more complex than simple plate tectonics would predict
Seismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust
It has been proposed that ductile flow within the lower crust causes distributed deformation that otherwise occurs within narrow shear zones in the continental upper crust and upper mantle [Bürgmann and Dresen, 2008]
Summary
The behavior of fault zones within continental settings is more complex than simple plate tectonics would predict. While deformation in oceanic environments is typically localized on plate boundaries, deformation within continents occurs across regions that can be thousands of kilometers wide (e.g., the Alpine-Himalayan Belt). It has been proposed that ductile flow within the lower crust causes distributed deformation that otherwise occurs within narrow shear zones in the continental upper crust and upper mantle [Bürgmann and Dresen, 2008]. Understanding how structural changes throughout a fault zone can be used to infer the mechanism of strain localization at lower crustal depths has important implications for our knowledge of lithospheric rheology and our understanding of the earthquake cycle. Seismic imaging of active fault zones has provided two contrasting arguments: some authors, such as Wilson et al [2004], argue that strain is more diffuse in the lower crust and upper mantle, forming a broad shear zone and citing pervasive seismic anisotropy in the lower crust and, in the case of the Marlborough Fault Zone, the lack of visible offsets in the Moho discontinuity beneath the surface signature of the fault
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