Essential Maintenance: All Authorea-powered sites will be offline 9am-10am EDT Tuesday 28 May
and 11pm-1am EDT Tuesday 28-Wednesday 29 May. We apologise for any inconvenience.

loading page

Systematic differences in energy radiation processes between regular and inland low-frequency earthquakes in and around the focal area of the 2008 Mw 6.9 Iwate-Miyagi, Japan, earthquake
  • +3
  • Masaki Orimo,
  • Keisuke Yoshida,
  • Toru Matsuzawa,
  • Taka'aki Taira,
  • Kentaro Emoto,
  • Akira Hasegawa
Masaki Orimo
Tohoku University

Corresponding Author:[email protected]

Author Profile
Keisuke Yoshida
Tohoku University
Author Profile
Toru Matsuzawa
Tohoku University
Author Profile
Taka'aki Taira
University of California, Berkeley
Author Profile
Kentaro Emoto
Kyushu University
Author Profile
Akira Hasegawa
Tohoku University
Author Profile

Abstract

Many unknowns exist regarding the energy radiation processes of the inland low-frequency earthquakes (LFEs) often observed beneath volcanoes. To evaluate their energy radiation characteristics, we estimated the scaled energy for LFEs and regular earthquakes in and around the focal area of the 2008 Mw 6.9 Iwate-Miyagi earthquake. We computed the source spectra for regular earthquakes, deep LFEs, and shallow LFEs by correcting for the site and path effects from direct S-waves. We computed the radiated energy and seismic moments, and obtained the scaled energy (eR) for 1464 regular earthquakes, 169 deep LFEs, and 52 shallow LFEs. The eR for regular earthquakes is in the order of 10-5 to 10-4, typical for crustal earthquakes, and tends to become smaller near volcanoes and shallow LFEs. In contrast, eR is in the order of 10-7 and 10-6 for deep and shallow LFEs, respectively, one to three orders of magnitude smaller than that for regular earthquakes. This result suggests that LFEs are associated with a much lower stress drop and/or slower rupture and deformation rates than regular earthquakes. Although the energy magnitudes derived from radiated energy generally show good agreement with the local magnitudes for the three types of earthquakes, the moment and local magnitudes show a large discrepancy for the LFEs. This suggests that the local magnitude based only on the maximum amplitude of the observed seismic records may not provide good information on the static sizes of LFEs whose eR values are substantially different from those of regular earthquakes.
29 Jul 2023Submitted to ESS Open Archive
04 Aug 2023Published in ESS Open Archive