New IRIS Data Product: Dynamic Surface Wave Radiation Patterns

Date: 4/25/2019

Time: 02:15 PM

Room: Cascade I

We present the theory and implementation of a new data product at the IRIS DMC. The Surface Wave Radiation Pattern (SWRP) product shows the azimuthal variations of radiated seismic-wave spectral amplitudes for Rayleigh and Love waves computed for frequencies between 0.01 and 0.06 Hz. The amplitudes are obtained from a database of computed excitation coefficients in a layered, spherical Earth, using interpolated normal-mode frequencies to represent the fundamental-mode surface wave branch.

The event-based product generates static plots for every known earthquake with magnitude Mw ≥ 6.0 based on the source mechanisms reported by the Global CMT Project. For hypothetical earthquakes, dynamic radiation pattern plots are based on arbitrary source mechanisms chosen by the user. The database of the interactive product contains the spectral amplitudes of Green's functions computed for a particular hypocenter at virtual stations located around it. These spectral amplitudes are convolved with the components of a moment tensor to display the associated surface-wave radiation pattern. The dynamic plots are displayed in a web browser and updated without delay for every change in frequency of the seismic waves and in source mechanism except its depth.

The radiation pattern product supports researchers in estimating azimuthal variations in earthquake-generated ground motion amplitudes as well as in identifying nodes and anti-nodes of surface wave amplitudes to understand signal-to-noise ratios at seismic stations in the context of moment tensor inversions, wave propagation studies, and seismic tomography.

The ground motion predicted by the surface-wave radiation pattern product is reflected in the ShakeMaps of shallow large earthquakes provided by the USGS. This is not surprising for the modeled areas of the ShakeMaps, but the semblance holds for the areas that are based on observations.

The purpose of the surface-wave radiation pattern is to provide a reference for all researchers studying surface waves from a specific or hypothetical seismic event.

Presenting Author: Boris Roesler

Authors