scholarly journals 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

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
K. Z. Nanjo ◽  
A. Yoshida
Keyword(s):  
Source Region ◽  
High Stress ◽  
Tohoku Earthquake ◽  
B Value ◽  
2011 Tohoku Earthquake ◽  
East Side ◽  
Coseismic Slip ◽  
The 2011 Tohoku Earthquake ◽  
Value Analysis ◽  
Miyagi Prefecture

AbstractWe 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. In addition, the focus of the M6.9 earthquake was situated close to the border point where the interplate slip in the period from 2012 through 2021 has been considerably larger on the northern side than on the southern side. The high-stress state inferred by the b-value analysis is concordant with those characteristics of interplate slip events. We found that the M6.8 earthquake on May 1 occurred near an area where the b value remained small, even after the M6.9 quake. The ruptured areas by the two earthquakes now seem to almost coincide with the small-b-value region that had existed before their occurrence. The b value on the east side of the focal areas of the M6.9 and M6.8 earthquakes which corresponds to the eastern part of the source region of the 1978 off-Miyagi prefecture earthquake was consistently large, while the seismicity enhanced by the two earthquakes also shows a large b value, implying that stress in the region has not been very high.

Empirical Fragility Curves of Buildings in Northern Miyagi Prefecture During the 2011 off the Pacific Coast of Tohoku Earthquake

2016 ◽  
Vol 11 (6) ◽  
pp. 1253-1270 ◽  
Author(s):  
Hao Wu ◽  
◽  
Kazuaki Masaki ◽  
Kojiro Irikura ◽  
Susumu Kurahashi ◽  
...  
Keyword(s):  
Pacific Coast ◽  
Fragility Curves ◽  
Ground Motions ◽  
Strong Motion ◽  
Tohoku Earthquake ◽  
2011 Tohoku Earthquake ◽  
The 2011 Tohoku Earthquake ◽  
Kobe Earthquake ◽  
The Pacific ◽  
Miyagi Prefecture

In this study, empirical fragility curves expressed in terms of relationship between damage ratio indices of buildings and ground motion indices were developed in northern Miyagi prefecture located in near-field areas during the 2011 off the Pacific coast of Tohoku Earthquake. The ground motion indices were evaluated from observed ground motions at strong-motion stations and estimated at sites at which no strong-motion accelerometers were deployed during the mainshock. The ground motions at the non-instrumental sites were estimated using the empirical Green’s function method based on bedrock motions inverted from observed records on surfaces from small events that occurred inside the source fault, transfer functions due to underground velocity structures identified from microtremor H/V spectral ratios, and a short-period source model of the mainshock. The findings indicated that the empirical fragility curves as functions of Japan Meteorological Agency (JMA) instrumental seismic intensity during the 2011 Tohoku Earthquake almost corresponded to those during the 1995 Kobe Earthquake and the seven disastrous earthquakes that occurred between 2003 and 2008. However, the empirical fragility curves as functions of peak ground velocity were the lowest. A possible reason for this is that the response spectra of the ground motions in the period ranging from 1.0 s to 1.5 s were small during the 2011 Tohoku Earthquake. Another reason could be the seismic resistant capacities of buildings in the studied districts involved during the 2011 Tohoku Earthquake exceeded those in the cities affected during the 1995 Kobe Earthquake.

scholarly journals FIELD SURVEY AND NUMERICAL ANALYSIS OF 2011 TOHOKU EARTHQUAKE TSUNAMI IN THE NORTHERN PART OF MIYAGI, JAPAN

2012 ◽  
Vol 1 (33) ◽  
pp. 14
Author(s):  
Tomohiro Yasuda ◽  
Taro Kakinuma ◽  
Takashi Tamada ◽  
Gozo Tsujimoto
Keyword(s):  
Field Survey ◽  
Tohoku Earthquake ◽  
2011 Tohoku Earthquake ◽  
The 2011 Tohoku Earthquake ◽  
The North ◽  
Miyagi Prefecture ◽  
Frame Buildings ◽  
Steel Frame Buildings ◽  
Survey Results ◽  
Inundation Height

The field survey results obtained by the team of authors in the north of Miyagi Prefecture are summarized referring to a part of the survey results by other teams of the 2011 Tohoku Earthquake Tsunami Joint Survey Group. The inundation height above sea level was measured using a laser range finder with a reflection prism. The inundation height was generally larger at bay heads, as well as cave tips, except several points, which were sheltered by a peninsula or had a tapering area. The tsunamis reached inland far away from the sea along valleys and rivers. Not only steel frame buildings but also many reinforced concrete buildings were collapsed in Onagawa Town. According to the numerical simulation, the first tsunami from the west coast and the second tsunami from the east coast should come together in Utatsusaki Peninsula, which is consistent with the interviews to survivors.

The Birth Prevalence of Cleft Lip and/or Cleft Palate After the 2011 Tōhoku Earthquake and Tsunami

2019 ◽  
Vol 56 (9) ◽  
pp. 1133-1138
Author(s):  
Yoshimichi Imai ◽  
Takehiko Sanada ◽  
Masahiro Tachi
Keyword(s):  
Cleft Palate ◽  
Outcome Measures ◽  
Cleft Lip ◽  
Control Period ◽  
Tohoku Earthquake ◽  
2011 Tohoku Earthquake ◽  
The 2011 Tohoku Earthquake ◽  
Birth Prevalence ◽  
Miyagi Prefecture ◽  
Government Statistics

Objective: This study examined whether the 2011 Tōhoku earthquake and tsunami affected the birth prevalence of cleft lip and/or cleft palate (CL/P) in Miyagi Prefecture, where the earthquake and tsunami caused severe damage. Design: This was a retrospective cohort study. Setting: The study was conducted at university and children’s hospitals in Miyagi Prefecture. Participants: The annual and monthly numbers of infants born with CL/P were obtained from medical records. The affected period of birth was defined as 1 year from December 1, 2011, to November 30, 2012. The control period was 5 years from January 1, 2006, to December 31, 2010. The annual and monthly numbers of births in Miyagi Prefecture were obtained using e-Stat, which is a portal for Japanese government statistics. Main Outcome Measures: Main outcome measures were birth prevalence of CL/P during the control and affected periods. Results: There were no significant differences between the control and affected periods in the prevalence (per 10 000 live births) of cleft lip with or without palate (13.8 vs 16.7; P = .342), isolated cleft palate (5.2 vs 3.2; P = .267), or overall CL/P (19.0 vs 19.9; P = .799). Conclusions: We did not observe that the 2011 Tōhoku earthquake and tsunami affected the birth prevalence of CL/P in Miyagi Prefecture, even though it severely impacted human health in the area.

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