4 (1 to 31 Dec, 1998)
| 13 January 1999 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity in Japan December 1998
* There was no unusual activity.
* A magnitude (M) 4.6 earthquake occurred on 10 December in southern Tokachi Administrative District at a depth of 55km. Previous earthquakes occurring on 20 April 1998 and 12 May 1998, both M4.2, had nearly the same hypocenter.
* There was no unusual activity.
* There was no unusual activity.
* Results of GPS observation of the Shizuoka-Aichi-Gifu area showed no notable variation.
* There was no unusual activity.
* An M4.7 earthquake occurred on 7 December in the coastal waters of the island Amami Oshima at a depth of about 60km.
* An M5.5 earthquake occurred on 16 December in the waters off Miyazaki Pref. at a depth of about 30km. The hypocenter of this earthquake was near that of the M6.0 earthquake that occurred on 30 April 1994. The focal mechanism of this most recent earthquake was of the reverse-fault type with a compressional axis extending northwest to southeast.
* An M5.6 earthquake occurred on 9 January in the vicinity of Iturup Island at a depth of about 120km.
* An M5.0 earthquake occurred on 2 January offshore of Ibaraki Pref. At a depth of about 50km.
* An M4.3 earthquake occurred on 11 January in the Reihoku district of Fukui Pref. At a depth of about 10km.
