Basin structure estimation by waveform modeling: Forward and inverse methods

We introduce a technique for using broadband seismograms recorded from eart hquakes at local and regional distances to refine basin structure, For the region outside the basin, we assume a one-dimensional (ID) crustal model an d analytical techniques (GRT) to propagate the energy from sources to the b asin edge where the motions are then interfaced with a (2D) finite-differen ce algorithm (Wen and Helmberger, 1996). We parameterize the basin section by isovelocity layers with linear dipping segments between control points. The control point depths are allowed to vary to improve the modeling of wav eform data of stations inside the basin. The comparison between data and sy nthetics is qualified by a fitness function defined by two factors: the tim ing shift required for best alignment and the correlation coefficient. The procedure was applied to a strong-motion waveform profile across the extend ed Los Angeles Basin produced by the 1992 Landers, California earthquake to refine the velocity structure using sensitivity testing and forward modeli ng. Only the correlation coefficient and amplitude were used because absolu te timing was unknown. The procedure was extended to a direct waveform inve rsion by employing a conjugate gradient approach, which uses numerical deri vatives. Numerical tests using the new inversion process with synthetic dat a demonstrate that it is possible to recover a detailed basin structure, if a sufficient amount of high-quality data exists.