Deep shear wave velocity profiles of the Santiago Basin for evaluation of seismic response

Abstract

Evaluation of the seismic response of the Santiago Basin requires a shear wave velocity model with vertical and lateral variations that may explain the site effects reported during the 2010 Maule Earthquake. In order to investigate the velocity structure of the Basin, we used a temporal broadband station network that continuously recorded months of ambient seismic noise and crosscorrelated the vertical components of the records. Identification of zero-crossings in the real part of the cross spectrum between stations were associated with the zeros of the zero-order Bessel function to obtain phase-velocity dispersion curves. These curves were combined using a least-squares inversion to obtain phase velocity maps for periods ranging between 0.8s and 5s. The spatial distribution of the temporal broadband network was complemented with a permanent accelerometer network that allows imaging longer periods associated to the deeper Basin structure and a smaller portable geophones network that allows defining shorter periods dominated by the shallower soil deposits. The phase velocity maps were used to generate a 1D shear wave velocity profiles using the Neighborhood algorithm. The profiles resolve changes in velocity up to 3 km depth and predict velocities that rapidly reach 1 km/s at relatively shallow depths.