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

Abstract

AbstractThe 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, 2011MW9.0 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 localMW5.4 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.