ELF/VLF recordings during the 11 March 2011 Japanese Tohoku earthquake

Abstract

Broadband ELF/VLF radio recordings (0.2-40kHz) were made at a site in Onagawa, Japan located ∼102 km from the epicenter of the M9.0 11 March 2011 earthquake, the fifth most powerful earthquake in recorded history. The receiver operated for about two minutes after the start of the earthquake, after which the receiver lost power. Examination of the VLF data shows no radio emissions preceding or coincident with the onset of the earthquake. However, once the secondary seismic waves reached the receiver, a number of impulses and diffuse noise bands arose which may result from the entire power grid shaking or from radio emissions from compressing rocks. Examination of the ELF data (0.2-1kHz) show no precursor effect in the hours preceding the earthquake. Examination of VLF data from narrowband transmitters shows no anomalous activity in the days or weeks preceding the earthquake. Our instrument low-frequency cut-off is ∼200 Hz, and thus we cannot comment on emissions in the ULF range (<10Hz). © 2012. American Geophysical Union. All Rights Reserved.