A Graphical Dispersion Curve Editing Tool for Seismic Site Characterization Using Surface Waves

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Analysis of surface waves within a few tens of meters of Earth’s surface may resolve the seismic velocity structure, which is essential data for predicting earthquake ground shaking. Many surface wave techniques, including both active and passive methods, calculate dispersion curves from raw seismic data. These curves are scatter plots that show the relationship between phase velocity and wavelength (or frequency) and may be inverted to yield shear-wave velocity as a function of depth. However, the inversion resolution is limited by non-uniqueness, the computational cost of forward models, and the complexity of empirical dispersion curves, which frequently include multiple modes and considerable noise. The analyst can often overcome these limitations most efficiently by visually inspecting the dispersion curve, removing higher modes and spurious data, and finally substituting a polynomial fit for the trimmed data. Here, we present a computer program for graphically editing and fitting dispersion curves: trimDispCurve v. 1.2. The program is currently coded in Matlab, and a Python implementation is in progress. The program takes as input an array of phase velocity and wavelength (or frequency) data that defines a dispersion curve. The program then plots the dispersion data and allows the user to iteratively select points in the plot for deletion. The user can either select points individually or define polygons to delete larger groups of points. The user may then experiment with polynomial fits of any order. The program outputs both the trimmed dispersion curve and the polynomial approximation as delimited text files that are suitable for input into inversion programs. We expect that this program will be particularly useful for analysts who wish to combine multiple surface-wave methods in order to achieve optimum resolution over a wide range of depths.

Presenting Author: Alan Yong

Authors