Crustal Seismic Velocities and Anisotropy in the Chile Ridge Subduction Region from Seismic Noise Cross-Correlation analysis

Surface waves of incoherent seismic noise recorded in the Chile Triple Junction area were used to obtain the impulse response function of the inter-station wave medium in the upper crust. We used one year of data recorded at 38 broadband seismic stations to cross-correlate daily long-period (5-100 sec) wave forms. We obtained nominally 722 Green's function waveforms, from which we extracted the inter-station travel time in different period bands. Crustal velocity models in two-dimensional cells of 30 x 30 km were determined using a linear least squares inversion of the Rayleigh wave travel times. We used two period bands, 5-10 seconds for shallow crustal velocities down to approximately 10 km depth, and 10-20 seconds for velocities down to around 20 km. Preliminary results show that cell velocities correlate well with known geologic features: high crustal velocities appear where the Patagonian Batholith outcrops or is likely present at depth, and low velocities correlate with the active volcanic arc of the Southern Volcanic Zone. High velocities in the mountainous southeastern study area correlate with Paleozoic and highly crystalline metamorphic rocks. In order to produce a 1D velocity model showing the velocity changes with depth, we used stations located at the network boundaries to perform a dispersion analysis of the group velocity as a function of period, and to find the best fit model for crustal velocity variations as a function of depth. Horizontal components of the wave-forms were also cross-correlated to obtain Love wave Green's functions of station-pairs. We calculated the differences in travel-time between different component pairs (vertical, transverse, radial) to produce an anisotropy map of the upper crust. Results will be shown at the meeting.