Elastogravity Waves and Dynamic Ground Motions in the Korean Peninsula Generated by the March 11, 2011 MW9.0 Tohoku‐Oki Megathrust Earthquake

• Published in: Journal of geophysical research. Solid earth Vol. 126; no. 2
• Main Authors: Hong, Tae‐Kyung, Kim, Ilgoo, Park, Seongjun, Kil, Dongwoo
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-02-2021
• Subjects: Azimuth; Broadband; Deformation; Displacement; Distance; dynamic ground motions; Earthquakes; elastogravity waves; Frequency ranges; full frequency range; Geological hazards; Geophysics; Ground motion; Hazard mitigation; Lithosphere; megathrust earthquake; Mitigation; P-waves; Properties; Radiation; Ray paths; Records; Seismic activity; Seismic design; Seismic hazard; Seismic waves; Seismograms; Survival; very‐long‐period waves; Korean Peninsula
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2020JB020628

The mass dislocations caused by large coseismic slips in megathrust earthquakes are large enough to produce elastogravity waves. Despite, successful identification of elastogravity‐wave development during megathrust earthquakes, the nature of ground motions and hazard potentials in regional and teleseismic distances remains unknown. The dynamic ground motions from the March 11, 2011 MW9.0 Tohoku‐Oki megathrust earthquake are retrieved from broadband seismic records throughout the Korean Peninsula. The dynamic ground motions of the megathrust earthquake are dominated by low‐frequency (<0.1 Hz) energy that is a mixture of elastogravity waves and seismic waves. The peak dynamic ground displacements in the Korean Peninsula reached ∼20 cm with horizontal permanent displacements of ∼2 cm or more. Radially‐polarized elastogravity waves developed instantly at the event origin time. Very‐long‐period (<0.004 Hz) energy is a mixture of seismic waves and coseismic permanent displacements, presenting radially polarized retrograde particle motions for ∼600 s. The peak ground displacements (PGDs) and velocities for the Tohoku‐Oki earthquake are larger than those for a local MW5.4 earthquake. The peak ground motions vary azimuthally following the source radiation pattern. The tangential PGD increases with distance along continental ray paths due to the development of crustally guided waves. Large and slow dynamic ground motions cause dynamic stress changes of ∼1.8 MPa in the lithosphere of the Korean Peninsula, while the properties of the mantle are scarcely affected by slow dynamic motions. The large long‐period displacements induced by megathrust earthquakes may cause considerable long‐duration distortion on large buildings at regional and teleseismic distances. The characteristic elastogravity‐wave features may be used for detection of mass‐dislocation events.
Plain Language Summary
The long source durations of great earthquakes produce predominantly long‐period waves that survive with large amplitudes over long distances. The slow dynamic deformation of subsurface media and the seismic hazard potentials pertaining to long‐period waves have received relatively little attention. This study, investigates the properties of the dynamic ground motions at far‐regional distances produced by the March 11, 2011 MW9.0 Tohoku‐Oki megathrust earthquake. We retrieve the dynamic ground motions in the full frequency range from broadband seismic records, presenting the elastogravity waves, strong long‐period seismic waves and coseismic permanent displacements. Elastogravity waves develop promptly at the event origin time due to density disturbances in the source region. Large PGDs and peak ground velocities occurred at far‐regional distances as a result of this megathrust earthquake. The dynamic ground motions are characterized by azimuth‐ and distance‐dependent features, which may be crucial for seismic design and seismic hazard mitigation for regional megathrust earthquakes.
Key Points
Far‐regional displacements for a great earthquake are dominated by permanent displacement, elastogravity waves, and long‐period waves
Density disturbance in the great earthquake source region produces elastogravity waves instantly on earthquake occurrence
A great earthquake produces strong ground displacements with minimal ground accelerations at far‐regional distances