Abstract
Abstract Hypocenters of main shocks and aftershocks of the 1933 M=7.1, 1936 M=7.4, 1937 M=7.1 and 1978 M=7.4 Miyagi-oki earthquakes are relocated using S-P times reported in the Seismological Bulletin of the Japan Meteorological Agency (JMA) and those re-read from original smoked-paper seismograms observed at the Mizusawa station of the National Astronomical Observatory of Japan (NAOJ) and the Mukaiyama station of Tohoku University. In order to reduce the error caused by inaccuracies of the arrival times and the small number of seismic observation stations, we determined the hypocenters by using a grid search method that assumed that the events occurred at the boundary between the subducting Pacific plate and the overriding plate. The main shock epicenters of these four earthquakes were determined to be close to each other, while the distributions of their aftershocks seem to disperse on the upper boundary of the Pacific plate. These distributions show that aftershock areas of the 1933, 1936 and 1937 events partly overlap with that of the 1978 event and occupy its easternmost, central and westernmost portions, respectively. This result suggests that the 1933, 1936 and 1937 events possibly ruptured a part of the source area of the 1978 event, i.e., its eastern, central and western portions, respectively.
Highlights
An M=7.2 interplate earthquake occurred in the Miyagioki region, northeastern Japan, at 11:46 (JST) on August 16, 2005
We investigated the distributions of the aftershocks of the 1930s’ earthquakes and compared these with those of the 1978, assuming that the aftershock areas nearly correspond with the source areas of these main shocks
The location of the plate boundary is established from aftershock distribution determined by OBS observations conducted immediately following the occurrence of the 2005 Miyagi-oki earthquake (Hino et al, 2005)
Summary
An M=7.2 interplate earthquake occurred in the Miyagioki region, northeastern Japan, at 11:46 (JST) on August 16, 2005. Kikuchi (2004) estimated the coseismic slip area of this event by inverting the seismic waveform data observed at two nearby stations and found that it was located adjacent to an area southeast of the source area of the 1978 event. 2. Data Arrival times for P- and S-waves for previous earthquakes are reported in the Seismological Bulletin of the Japan Meteorological Agency (JMA). SP times on seismograms of the Mukaiyama station were re-picked in the present study and used in locating hypocenters. The location of the plate boundary is established from aftershock distribution determined by OBS observations conducted immediately following the occurrence of the 2005 Miyagi-oki earthquake (Hino et al, 2005). In order to compare locations of aftershocks of the 1930s’ events with those of the 1978 one, we relocate these later events using this same procedure
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
