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

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 M(W)9.0 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 similar to 20 cm with horizontal permanent displacements of similar to 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 similar to 600 s. The peak ground displacements (PGDs) and velocities for the Tohoku-Oki earthquake are larger than those for a local M(W)5.4 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 similar to 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 M(W)9.0 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.

Automated summary

The study reveals that the dynamic ground motions induced by the 2011 Tohoku-Oki megathrust earthquake in the Korean Peninsula are mainly composed of elastogravity waves and seismic waves. The large and slow dynamic ground motions of this megathrust earthquake have caused significant peak ground displacements and velocities at far-regional distances, with variations depending on source radiation pattern and continental ray paths.