11:00 AM - 1:00 PM
[SSS05-P02] Integrated Seismic Source Model of the 2021 M7.1 Fukushima Earthquake
Keywords:Body waves, Earthquake source observations, Seismicity and tectonics
We constructed an integrated rupture model of the 2021 Mw 7.1 Fukushima earthquake, an intraplate earthquake, by resolving both its spatiotemporal distribution of slip-rate and high-frequency (~1 Hz) radiations. We analyzed near-field seismic observations using a novel finite-fault inversion method that allows automatic parameterization and teleseismic data from multiple arrays using the MUSIC Backprojection (BP) method that enhances imaging resolution. The inverted slip distribution obtained from waveforms filtered in the frequency band of [0.02 0.2] Hz showed that the kinematic rupture propagated along both the strike (~30 km) and dip directions (~78 km), and that the large-slip area was located southwest to the hypocenter with a maximum slip of ~0.93 m. Overall, no obvious frequency-dependent rupture behaviors occurred during the rupture process due to the deep nucleation of the Fukushima earthquake on an immature fault where sizes of asperities do not decrease with depth, which sheds light on understanding the rupture dynamics of intraplate earthquakes in subduction zones. Both the slip inversion and BP revealed the general rupture feature of this earthquake with southwestward and up-dip directivity. A comparison of BPs between multiple arrays indicates that the source-receiver geometry and the directivity effect of an earthquake may cause critical discrepancies in BPs of different arrays. Although the 2011 Tohoku-Oki Mw 9.1 earthquake itself discouraged the occurrence of the Fukushima earthquake, the long-term dominance of viscoelastic relaxation increased the Coulomb failure function (CFF) by 0.3-0.7 MPa, indicating that the occurrence of the Fukushima earthquake has been likely promoted by the postseismic deformation due to the Tohoku-Oki earthquake.