May 13, 2013
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On April 13 at 05:33 (JST), there was a magnitude (M) 6.3 earthquake at a depth of approximately 15 km near Awajishima. This event had a maximum seismic intensity 6 Lower in Hyogo prefecture and caused damage. Since then, the seismicity has shown a mainshock-aftershock sequence. The aftershock activity has been declining. So far, the largest was a M3.9 aftershock that occurred at 05:41 on April 13, and had a maximum seismic intensity 3.
* The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust. The source fault as inferred from the aftershock distribution and the focal mechanism was a reverse fault striking in an N-S direction and dipping to the west. This event occurred in the area adjacent to the southwestern end of the aftershock area of "the 1995 Hyogoken-Nanbu Earthquake".
* According to the GNSS data, small crustal deformations associated with the main shock were observed at the Sumoto observation point (Hyogo prefecture).
* There is the Senzan fault zone as a part of the Rokko-Awajishima fault zone adjacent to the south of the source area. Although the Earthquake Research Committee has evaluated that as to the Senzan fault the whole segment activity will possibly lead to an earthquake of M6.6 or so, the relation between the recent event and the fault zone is uncertain.
(Underlined parts were added or modified for the Evaluation at the 250th Earthquake Research Committee.)