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The distribution of plate motion between multiple fault strands and how this distribution may evolve remain poorly understood, despite the key implications for seismic hazards. The North Anatolian Fault in northwest Turkey is a prime example of a multistranded continental transform. Here we present the first constraints on late Quaternary slip rates on its northern branch across the Cinarcik Basin in the eastern Marmara Sea. We use both deep penetration and high-resolution multichannel seismic reflection data with a stratigraphic age model to show that a depocenter has persisted near the fault bend responsible for that transform basin. Successively older depocenters have been transported westward by fault motion relative to Eurasia, indicating a uniform right-lateral slip rate of 18.5 mm/yr over the last 500,000 years, compared to overall GPS rates (23-24 mm/yr). Thus, the northern branch has slipped at a nearly constant rate and has accounted for most of the relative plate motion between Eurasia and Anatolia since ~0.5 Ma.

The deployment of a worldwide network for infrasound detection requires numerical methods for modeling these signals over long distances. A ray theoretical approach appears robust and efficient. It furthermore allows a straightforward interpretation of recorded phases. We have developed a three-dimensional Hamiltonian ray tracing for modeling linear acoustic waves in the atmosphere. Propagating over distances superior to 500 km requires the curvature of the Earth to be considered, which is achieved by using spherical coordinates. High atmospheric winds are properly handled through a modified Hamiltonian. These winds as well as sound velocity can change significantly during long-lasting propagations; these variations are also included in our modeling. Finally, the amplitude of infrasonic signals is computed by concomitantly solving for paraxial rays and assessing the evolution of the ray tube thus defined. We present the theory for this atmospheric infrasound modeling and some simple applications that establish its robustness and potential.

[1] Classical active seismic methods fail to sharply image the earth’s deep crust. We present the first crustal-scale application of 2-D full waveform inversion based on dense ocean bottom seismic data to investigate the Eastern Nankai subduction system (Japan). This approach allows to quantify seismic velocities up to an unprecedented degree of resolution. Results reveal compressive tectonic features within both the subducting oceanic crust and the backstop. At depth, velocity anomalies along major faults and structural discontinuities bring evidence for the presence of fluids and weakened material and also for a possible coseismic slip partitioning structure. INDEX TERMS: 0902 Exploration Geophysics: Computational methods, seismic; 3025 Marine Geology and Geophysics: Marine seismics (0935); 8010 Structural Geology: Fractures and faults; 8105 Tectonophysics: Continental margins and sedimentary basins (1212). Citation: Dessa, J.-X., S. Operto, S. Kodaira, A. Nakanishi, G. Pascal, J. Virieux, and Y. Kaneda (2004), Multiscale seismic imaging of the eastern Nankai trough by full waveform inversion, Geophys. Res. Lett., 31, L18606, doi:10.1029/2004GL020453.

[1] On November 14, 2001, a strong earthquake occurred on the high plateau of western China. At a distance of 1800 km from the epicenter, coherent infrasonic waves were detected for more than one hour. Using both an inverse location procedure and a complete simulation of the radiated pressure field, distant source regions are accurately located. The seismo-acoustic coupling along a mountain belt is clearly demonstrated. Such an event offers an opportunity to validate velocity models in the atmosphere as well as to improve the understanding of the amplification of ground displacement caused by the topography.