Changes in the b value in and around the focal areas of the M6.9 and M6.8 earthquakes off the coast of Miyagi prefecture, Japan, in 2021 K. Z. Nanjo1,2,3,*, A. Yoshida2 1. Global Center for Asian and Regional Research, University of Shizuoka, 3-6-1, Takajo, Aoi-ku, Shizuoka, 420-0839, Japan 2. Center for Integrated Research and Education of Natural Hazards, Shizuoka University, 836, Ohya, Suruga-ku, Shizuoka, 422-8529, Japan 3. Institute of Statistical Mathematics, 10-3 Midori-cho, Tachikawa, Tokyo, 190-8562, Japan *Corresponding author: K. Z. Nanjo Email:
[email protected]; Tel: +81-54-5600; Fax: +81-54-5603 ORCID ID: https://orcid.org/0000-0003-2867-9185 1 Abstract We investigated changes in the b value of the Gutenberg-Richter’s law in and around the focal areas of earthquakes on March 20 and on May 1, 2021, with magnitude (M) 6.9 and 6.8, respectively, which occurred off the Pacific coast of Miyagi prefecture, northeastern Japan. We showed that the b value in these focal areas had been noticeably small, especially within a few years before the occurrence of the M6.9 earthquake in its vicinity, indicating that differential stress had been high in the focal areas. The coseismic slip of the 2011 Tohoku earthquake seems to have stopped just short of the east side of the focus of the M6.9 earthquake. Furthermore, the afterslip of the 2011 Tohoku earthquake was relatively small in the focal areas of the M6.9 and M6.8 earthquakes, compared to the surrounding regions.