1:30 PM - 1:45 PM
[J09-1-01] Normal-faulting earthquakes in the northern area of Ibaraki Prefecture, Japan in 2011 and 2016 - Duplicate events detected by InSAR observations -
Following the 2011 Tohoku earthquake, many inland crustal earthquakes have occurred with a source mechanism of normal fault motion in the Fukushima hamadori and northern Ibaraki areas, Japan. Under such a seismological background, an inland earthquake with a moment magnitude (Mw) of 5.9 occurred in the northern area of Ibaraki Prefecture at 21:38 on Dec. 28, 2016. The startling finding derived InSAR observations is that location, spatial distribution, and magnitude of the InSAR-derived crustal deformation is almost same as those observed for the inland earthquake that occurred with Mw6.1 on March 19, 2011.
The InSAR result shows that the deformation has ear-shaped distribution, elongated along the north-south orientation. Another remarkable feature is that a displacement discontinuity with a length of about 2 km is clearly recognized in the northeast of the source region, probably suggesting that a rather shallow slip occurred. The same features were identified in the 2011 event, and in particular, it is surprising that both the position and the length of the discontinuities are the same between the two events.
The fault model for the 2016 event that consists of two fault segments shows (1) west-dipping fault planes with dip angles of 50–60 deg, (2) NNW-SSE (NW-SE) strike direction, (3) nearly pure normal fault motions, and (4) a shallow local slip. The 2011 event also has almost the same features on the fault model (Kobayashi et al, 2011). It strongly suggests that almost the same fault slips have occurred on almost the same fault plane for both the events, which is probably the world's first observation in that we can identify the similarity "visibly".
Acknowledgements: ALOS-2 data were provided from the Earthquake Working Group under a cooperative research contract with JAXA (Japan Aerospace Exploration Agency). The ownership of ALOS-2 data belongs to JAXA.
The InSAR result shows that the deformation has ear-shaped distribution, elongated along the north-south orientation. Another remarkable feature is that a displacement discontinuity with a length of about 2 km is clearly recognized in the northeast of the source region, probably suggesting that a rather shallow slip occurred. The same features were identified in the 2011 event, and in particular, it is surprising that both the position and the length of the discontinuities are the same between the two events.
The fault model for the 2016 event that consists of two fault segments shows (1) west-dipping fault planes with dip angles of 50–60 deg, (2) NNW-SSE (NW-SE) strike direction, (3) nearly pure normal fault motions, and (4) a shallow local slip. The 2011 event also has almost the same features on the fault model (Kobayashi et al, 2011). It strongly suggests that almost the same fault slips have occurred on almost the same fault plane for both the events, which is probably the world's first observation in that we can identify the similarity "visibly".
Acknowledgements: ALOS-2 data were provided from the Earthquake Working Group under a cooperative research contract with JAXA (Japan Aerospace Exploration Agency). The ownership of ALOS-2 data belongs to JAXA.