Delta CFF (Coulomb Failure Function) due to the M6.4 earthquake on July 1and the M6.0 earthquake on July 9 in the sea near Kozushima Island
We computed the Delta CFF for the two M6 earthquakes on July 1 and on July 9 to find that strike slip faulting becomes more susceptible to occur in the area off the Nii-jima island. Seismicity in the west to the Niijima Island has become active since July 1, which suggests that the preceding earthquakes in the sea near the Kozushima Island induced the seismicity in the west to the Niijima Island. Why haven't earthquakes occurred in other areas with increased Delta CFF ? Possible answers to the above natural question are either (1) that there is no active structures in those areas with enough potential to generate earthquakes or (2) that the areas are acturally preparing future earthquakes.

Delta CFF in the right-lateral strike slip fault (277/86/163) similar to the fault of the earthquake on July 15 within the crust
Hypocenter Plot: Earthquakes larger than M2 from July 1 to July 14 Processed on ERI TSEIS (Tsuruoka, 1997) by using JMA hypocenter information.
Fault parameter: Refer to EIC Seismological note ,2000 by Dr. Kikuchi and Yamanaka