The indirect triggering of a normal faulting earthquake sequence in the Ibaraki-Fukushima prefectural border, Japan by Mw9.0 Tohoku-Oki megathrust: the elusive role of low-angle normal fault slow-slip

Yohai Magen, Asaf Inbal, Alo Ziv, Gidon Baer, Roland Bürgmann, Axel Periollat, & Takeshi Sagiya

Published September 11, 2022, SCEC Contribution #12215, 2022 SCEC Annual Meeting Poster #073

Deep-seated normal faults are common in subduction environments. Although these faults occasionally break with large megathrust, the strain they induce within the crust are poorly constrained. A month-long shallow normal faulting sequence in Ibaraki-Fukushima prefectural border (IFPB), northeast Japan, which followed the Mw 9.0 Tohoku-Oki (TO) earthquake and culminated with the Mw6.7 Iwaki earthquake, provides a window into subduction-to-normal fault interaction.
The IFPB earthquake sequence cannot be explained in terms of direct triggering by the co- and post-seismic TO slip. In quest for an alternative triggering mechanism, we analyzed post-TO GNSS data from eastern IFPB’s, which revealed localized strain along the coastline. We show that the TO indirectly triggered the Iwaki earthquake via the activation of an aseismic transient across a low-angle seaward dipping blind normal fault underlying the IFPB. Stress budget considerations suggest this fault creeps in-between large ruptures, and may accelerate due to stresses induced by subduction slip.

Key Words
subduction, Tohoku-Oki, Normal faulting, Slow Slip

Citation
Magen, Y., Inbal, A., Ziv, A., Baer, G., Bürgmann, R., Periollat, A., & Sagiya, T. (2022, 09). The indirect triggering of a normal faulting earthquake sequence in the Ibaraki-Fukushima prefectural border, Japan by Mw9.0 Tohoku-Oki megathrust: the elusive role of low-angle normal fault slow-slip. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy