The IRIS DMC’s Surface-Wave Radiation Pattern product 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. The event-based radiation patterns are accompanied by an interactive plot based on source mechanisms chosen by the user.
The Surface-Wave Radiation Pattern 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.
The database for this product contains the complex special amplitudes for Green’s functions generated with Mineos which computes synthetic seismograms in a spherically symmetric non-rotating Earth by summing normal modes. The spectral amplitudes have been calculated for the model iasp91, an isotropic model that has been constructed to be a summary of the travel time characteristics of the main seismic phases. Surface-wave radiation patterns generated for other models show little differences in the absolute amplitudes and are indistinguishable form each other in the relative amplitudes. It is therefore sufficient to provide a database for one isotropic Earth model.
Mineos has been benchmark tested against other synthetic seismogram generators for frequencies higher than all surface-wave frequencies (Masters, Woodhouse, and Freeman, 2011) and hence, the spectral amplitudes in the database of this product are considered reliable. The spectral amplitudes have been calculated for virtual stations at an epicentral distance of 10° and are in units of m/Hz (table below). The frequencies displayed in the event-based plots are approximations for the frequencies in the database. The azimuthal spacing is 1°.
Event-based Radiation Patterns
Static 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 and made available through DMC’s Event-based Surface-Wave Radiation Patterns repository.
Interactive Radiation Patterns
To cite the source of Surface-Wave Radiation Pattern product:
- Roesler et al., Using Seismic Source Parameters to Predict Frequency-Dependent Surface Wave Radiation Patterns, Seismological Research Letters (in preparation)
To cite the Wave Radiation Patterns Data Product or reference use of its data:
- IRIS DMC (2018), Data Services Products: The Surface-Wave Radiation Patterns, https://doi.org/10.17611/DP/SWRP.1.
To cite the IRIS DMC Data Products effort:
- Hutko, A. R., M. Bahavar, C. Trabant, R. T. Weekly, M. Van Fossen, T. Ahern (2017), Data Products at the IRIS‐DMC: Growth and Usage, Seismological Research Letters, 88, no. 3, https://doi.org/10.1785/0220160190.
This product was sponsored by Integrated Data-Driven Discovery in Earth and Astrophysical Sciences (IDEAS) program, a National Science Foundation Research Traineeship (NRT) program at Northwestern University.
- Boris Roesler, Northwestern University (Programming)
- Frank Elavsky, Northwestern University (Programming)
- Suzan van der Lee, Northwestern University (Concept and Programming)
- Emily Wolin, Northwestern University (Idea)
Boris Roesler (firstname.lastname@example.org)