June 18, 2018
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Earthquake in the Northern Osaka Prefecture on June 18, 2018

* On June 18 at 07:58 (JST), there was a magnitude (M) 6.1 (provisional) earthquake at a depth of approximately 15 km in the northern Osaka prefecture. The maximum seismic intensity 6 Lower was observed in Osaka prefecture and damage was caused by this event.

* The seismic activity after the M6.1 event is confined in the area of about 5 km length in EW and about 5 km length in NS. The largest until June 18 at 17 o'clock were M3.5 (provisional) earthquakes at about 08:08 (JST) and at about 16:31(JST).

* The focal mechanism of the M6.1 earthquake had a compression axis in an E-W direction. This event occurred within the crust. The seismic activity is a mixture of strike-slip fault type and reverse fault type. In the northern part of the aftershock area, earthquakes of the reverse fault type occur, and in the southern part, of the strike-slip fault type.

* According to the GNSS observation, no effective crustal deformation accompanying this event is reported.

* In the area around the event there are Arima-Takatsuki fault zone, extending in an E-W direction, and Ikoma fault zone and Uemachi fault zone, both extending in an NS direction. The recent event may be associated with these fault zones: the details wait the future research and observation results and further study.

* In the area where strong shaking was felt, it is necessary to be prepared for an earthquake with maximum seismic intensity 6 Lower, for a week or so from the occurrence of the earthquake. Especially in a few days or so, an earthquake of a large magnitude often occurs.