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Published December 2015 | Supplemental Material
Journal Article Open

Interrogation of the Megathrust Zone in the Tohoku-Oki Seismic Region by Waveform Complexity: Intraslab Earthquake Rupture and Reactivation of Subducted Normal Faults


Results from the 2011 Mw 9.1 Tohoku-Oki megathrust earthquake display a complex rupture pattern, with most of the high-frequency energy radiated from the downdip edge of the seismogenic zone and very little from the large shallow rupture. Current seismic results of smaller earthquakes in this region are confusing due to disagreements among event catalogs on both the event locations (>30 km horizontally) and mechanisms. Here we present an in-depth study of a series of intraslab earthquakes that occurred in a localized region near the downdip edge of the main shock. We explore the validity of 1D velocity model and refine earthquake source parameters for selected key events by performing broadband waveform modeling combining regional networks. These refined source parameters are then used to calibrate paths and further simulate secondary source properties, such as rupture directivity and fault dimension. Calculation of stress changes caused by the main event indicate that the region where these intraslab events occurred are prone to thrust events. This group of intraslab earthquakes suggest the reactivation of a subducted normal fault, and are potentially useful in enhancing our understanding on the downdip shear zone and large outer-rise events.

Additional Information

© 2015 Springer Basel. Received September 3, 2014, revised December 29, 2014, accepted January 16, 2015. Published online: 20 March 2015. This study was supported by NSF Grant EAR-1142020. Broadband and Strong-motion waveforms were obtained from F-net, K-net, and Kik-Net of NIED. The Generic Mapping Tools (GMT) were used for creating some of the in-text figures. We would like to thank Hiroo Kanamori and Zhongwen Zhan for their insightful comments.

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August 20, 2023
October 23, 2023