Data Services Products: Surface-Wave Radiation Patterns - Directional Dependency of Radiation of Seismic Energy from Surface Waves

Summary

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.

Description

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.

Data

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.

Specifications

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°.

Parameter Value
Units m/Hz
Model iasp91
Distance 10°

Technologies

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.

Event-based Surface-Wave Radiation Pattern plot
Event-based Surface-Wave Radiation Pattern plot based on Source Mechanism
provided by Global CMT.

Interactive Radiation Patterns

The database for the generation of event-based radiation patterns is also used for the generation of interactive plots. For the chosen depth, the spectral amplitudes contained in the database are convolved with the moment tensor components and displayed for the chosen frequency using JavaScript and D3. Changing the frequency causes no visible delay in the generation of the plot, but changing the depth of the source requires accessing a new database which has to be downloaded from the IRIS DMC. The events for which static plots exist can also be selected as an input for the interactive radiation pattern product and their source mechanism can be modified for comparison with the radiation pattern based on the source mechanism reported by the Global CMT Project. These plots are available through the Interactive Surface-Wave Radiation Patterns Interface and can be downloaded as images and text files.

Interactive Surface-Wave Radiation Pattern plot
Interactive Surface-Wave Radiation Pattern plot based on User Input.

Citations and DOIs

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:

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.

References

Credits

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)

Timeline

2018-12-03
Released

Contributors

Boris Roesler (boris@earth.northwestern.edu)

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