Data Services Newsletter

Volume 21 : No 1 : Spring 2019

Surface-Wave Radiation Patterns

The Surface-Wave Radiation Patterns product is a new data product from IRIS DMC that shows the patterns of seismic energy radiation by azimuth around the epicenter for Rayleigh and Love waves. For all events with moment magnitude Mw ≥ 6.0, the product provides plots based on the source mechanism reported by the Global CMT Project (Figure 1). The event-based radiation patterns are accompanied by an interactive plot based on source mechanisms chosen by the user (Figure 2).

 Event-based Surface-Wave Radiation Pattern plot
Figure 1: Event-based Surface-Wave Radiation Pattern plot
based on Source Mechanism provided by Global CMT for
the February 21, 2008, earthquake in Nevada, for six
different Frequencies

Interactive Surface-Wave Radiation Pattern plot
Figure 2: Interactive Surface-Wave Radiation Pattern plot
based on same Focal Mechanism as Figure 1 for 0.05Hz

Generation of Spectral Amplitudes

The new product shows the azimuthal dependency of surface-wave radiation patterns for different frequencies for use in the research on surface waves and their propagation along their path. To compute these patterns, spectral amplitudes for Green’s functions obtained for elementary moment tensors calculated at virtual stations located around the epicenter are convolved with the components of the moment tensor to obtain the spectral amplitudes for Rayleigh and Love waves at each depth.

Usage

Event-based radiation pattern plots are automatically generated for all events with moment magnitude Mw ≥ 6.0 for six frequencies between 0.01 and 0.06 Hz. The interactive product shows the radiation patterns for source mechanisms based on the moment tensor components, depth and frequency chosen by the user. All plots can be downloaded as image files along with text files that contain the displayed spectral amplitude values.

Target Group

The surface-wave radiation pattern product supports researchers in predicting ground motion at different azimuths around the epicenter of an earthquake and in identifying nodes and anti-nodes of surface wave amplitudes to increase the signal-to-noise ratio at seismic stations for moment tensor inversions and tomographic studies. Its purpose is to provide reference for all seismologists studying the surface waves of a specific event.

by Boris Rösler (Northwestern University)

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