Skip to main content
Fig. 1 | Earth, Planets and Space

Fig. 1

From: 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

Fig. 1

Earthquakes off the Pacific coast of Tohoku district. a Yellow stars represent the epicenters of the 2021 M6.9 and M6.8 earthquakes; open star shows the epicenter of the 2011 M9.0 Tohoku earthquake. Focal mechanism for these earthquakes, obtained by using the focal mechanism catalog of F-net (Full Range Seismograph Network of Japan) by NIED: National Research Institute for Earth Science and Disaster Resilience (Okada et al. 2004), is displayed as a beach ball symbol. Red and blue regions represent preliminary-determined slip areas of the 2021 M6.9 and M6.8 earthquakes, respectively (Tohoku University 2021a). The coseismic slip distribution of the 2011 Tohoku earthquake (Ozawa et al. 2012) is shown by orange contours with an interval of 16 m, except for the interval of 12 m between 4-m contours and 16-m contours. Black contours with an interval of 1 m indicate the afterslip distribution of the same earthquake (Ozawa et al. 2012). Green and purple regions show coseismic slip areas of the 1978 M7.4 off-Miyagi prefecture earthquake (Yamanaka and Kikuchi 2004) and the 2005 M7.2 earthquake that occurred at off-Miyagi prefecture (Yaginuma et al. 2006), respectively. Black rectangle shows the study region in b. AO (Aomori), IW (Iwate), MI (Miyagi), FU (Fukushima), IB (Ibaraki) are abbreviations of prefecture names. b Seismicity (depth 0–100 km, M ≥ 0.5) in and after 2018. Cross-sectional views along the line segments from P1 to P2, indicated by “A” and “B”, are shown in Fig. 3. Red and blue contours with an interval of 0.4 m indicate the coseismic slip distributions of the M6.9 and M6.8 earthquakes, respectively (Tohoku University, 2021a). We traced each slip contour from the original (Tohoku University 2021a), created numerical data that list the longitude and latitude consisting of the slip contours (Additional files 2 and 3 for the M6.9 and M6.8 earthquakes, respectively), and drew the contours using the numerical data

Back to article page