Seismic Activity in Japan October 1998

1 Major Seismic Activity

There was no unusual activity.

• Nationwide M4 (1 to 31 Oct, 1998)

2 Seismic Activity in each Region

(1) Hokkaido Region

* There was no unusual activity.

• Hokkaido

(2) Tohoku Region

* Aftershock activity resulting from a Magnitude (M)6.1 earthquake that occurred inland in Iwate Prefecture (Pref.) on 3 September has largely subsided.

* Aftershock activity resulting from an M5.0 earthquake that occurred in southern Miyagi Pref. on 15 September is diminishing.

• Northern Honshu
• Seismic activity inland in northern Iwate Pref. (1 Sep 0hrs to 7 Nov 0hrs, 1998)Routine processing results
• Seismic activity in southern Miyagi Pref.

(3) Kanto-Chubu Region

* An M6.1 earthquake occurred on 27 October at the trench axis (Izu-Ogasawara Trench) to the east of the island Hachijojima.

* Swarm activity that began on 7 August on the border between Nagano and Gifu prefs.(near Kamikochi) and extended its active region to the border of Nagano and Toyama prefs.(near Mount. Noguchigorodake) starting on 5 September continues to be active, centering on the Kamikochi highlands. The largest earthquake in October was M3.4, and the magnitude of individual earthquakes is decreasing.

* Results of GPS observation of the Shizuoka-Aichi-Gifu area showed no notable variation. Results of a levelling survey of Kakegawa- Omaezaki (Hamaoka) showed no notable variation.

• Central Honshu
• Seismic activity to the east of the island Hachijojima.
• Seismic activity on the border of Nagano and Gifu prefs. And the border of Nagano and Toyama prefs.
• Seismic activity in northern Ibaraki Pref.
• Seismic activity in northwestern Chiba Pref.
• GPS continuous observation base-line chart (Vicinity of Kakegawa and Omaezaki)
• Base-line-length variation graph
• Height-difference variation graph
• Secular variation of bench mark 2595 (village of Hamaoka)

(4) Kinki-Chugoku-Shikoku Region

* There was no unusual activity.

• Southern Honshu and Shikoku
• Seismic activity in western Kochi Pref.

(5) Kyushu-Okinawa Region

* On 3 October an M5.8 earthquake occurred at a depth of 220 kms beneath the East China Sea. The focal mechanism of this earthquake had its tension axis in the direction of plate subduction.

• Kyushu
• Seismic activity in the East China Sea
• Seismic activity offshore of the island Amami Oshima.
• Okinawa

3 Addenda

* On 5 November an M4.2 earthquake occurred at a depth of 60kms in northern Ibaraki Pref.

* On 8 November an M4.6 earthquake occurred at a depth of 80kms in northwestern Chiba Pref.

* On 10 November an M4.2 earthquake occurred at a depth of 40kms in western Kochi Pref.

* On 7 November an M4.5 earthquake occurred at a depth of 20kms in the coastal waters of Amami Oshima.