| 8 August 2001 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity in July 2001
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
*On July 20th, there was an M4.8 earthquake at a depth of about 55 km in southwestern Ibaraki Prefecture. The focal mechanism was a reverse fault type with a northwest-southeast pressure axis, and it is believed that this earthquake occurred in conjunction with the subduction of the Philippine Sea Plate.
*On July 26th, there was an M4.2 earthquake at a depth of about 85 km in southern Saitama Prefecture. The focal mechanism was a reverse fault type with an east-west pressure axis, and it is believed that this earthquake occurred in conjunction with the subduction of the Pacific Plate.
*The seismic activity that began on June 29th in the sea 30 to 60 km south of Aogashima experienced an increase in activity from July 4th to July 5th including earthquakes of greater than M5.0, but activity declined following that and had nearly ceased by mid-month.
*Seismic activity in the area from Miyakejima to Niijima-Kozushima is declining, but continues. The results of GPS observation of the area also show that the recent crustal movements have not yet entirely stopped.
*Crustal seismic activity in Suruga Bay and the surrounding area had been at a slightly low level, but has showed recent signs of a return to normal activity. The results of GPS observation of the Tokai Region show that there has been continuing microearthquake activity over the past three months in the area from western Shizuoka Prefecture to southern Gifu Prefecture. to supplementary reports
There was no marked activity. to supplementary reports
There was no marked activity. to supplementary reports
| August 8, 2001 |
| Earthquake Research Committee |
There were 47 M4.0 or greater earthquakes in Japan and the surrounding area (as compared to 64 in June and a monthly average incidence of 46 in the thirty-year period up to the end of 2000). Of that number, 6 events were M5.0 or greater (as compared to 9 in June).
The average number of M6.0 or greater earthquakes in the period from 1998 to 2000 was 16 per year (the 30-year average up to 2000 was also approximately 16 per year). Although none occurred in July, there have been six such events in the period from January 2001 to the present.
The following are evaluations of major seismic activity in the period from July 2000 to June 2001.
| -from the area near Miyakejima to the area near Niijima-Kozushima | ||
| In the period from the end of June to September, there was continued seismic activity in association with magma activity in the area, and on July 1st there was an M6.4 event (at a depth of about 10 km), and another M6.5 event (at a depth of about 10 km) on July 30th. | ||
| -The sea off Ibaraki Prefecture | July 21st 2000, M6.4 (at a depth of 50 km) | |
| -Western Tottori Prefecture(The 2000 Western Tottori Earthquake in western Tottori Prefecture) | ||
| On October 6th, there was an M7.3event (at a depth of about 10 km) | ||
| -Near Iriomotejima | On November 14th 2000, there was an M4.4 earthquake (at a depth of about 10 km) | |
| -Chuetsu region of Niigata Prefecture | 2 January 2001 M4.4 (at a depth of about 10 km) | |
| -Chuetsu region of Niigata Prefecture(about 40 km SSE of the 1/2/2001 event) | ||
| 4 January M5.1 (at a depth of about 10 km) | ||
| -Northern Hyogo Prefecture | 12 January 2001 M5.4 (at a depth of about 10 km) | |
| -Near Niijima-Kodushima | On February 13th 2001, an M3.9 earthquake (at a depth of about 10 km) | |
| -Akinada "2001 Geiyo earthquake" | ||
| March 24 2001, M6.7 (at a depth of about 50 km) | ||
| -Central Shizuoka Prefecture | ||
| April 3rd 2001 M5.1 (at a depth of about 35 km) | ||
There was the following seismic activity in the Hokkaido Region:
- Microearthquake activity has continued near Mt. Yoichidake since April. There was an M3.0 earthquake on July 23rd.
There are no supplements in the Tohoku Region.
"Crustal seismic activity in Suruga Bay and the surrounding area had been at a slightly low level, but has showed recent signs of a return to normal activity. The results of GPS observation of the Tokai Region show that there has been continuing microearthquake activity over the past three months in the area from western Shizuoka Prefecture to southern Gifu Prefecture.":
A long term review of activity shows a somewhat reduced incidence of activity since around 1996 with an even greater reduction beginning around October 2000. But in the past three months, there seems to have been a measurable increase in seismic activity within the crust.
The results of GPS observations over the past three months in the area from western Shizuoka to southern Gifu Prefecture, show a trend toward moderate change beginning in April 2001 and involving movement at a fixed rate to the northwest in conjunction with the subduction of the Philippine Sea Plate to the northwest, on the Pacific side of the Tokai-Chubu region.
(This evaluation coincides with the views (see reference below) expressed at the July 30th procedural meeting of the Regional Assessment Committee for Strengthening Countermeasures against Earthquake Disasters.)
(reference) "Recent seismic and crustal activity in the Tokai Region" (Meteorological Agency, Department of Seismology and Volcanology, July 30 2001)
"There has been a moderate increase in activity within the slab in the Tokai Region and surrounding areas recently, including the M5.1 earthquake that occurred in central Shizuoka Prefecture on April 3rd and related events.
Seismic activity in Suruga Bay and the western coast had been at a moderately low level, but we recognize signs of a resumption of activity. Since July 25th, there has been continued small-scale seismic activity including a maximal M3.1 event in the vicinity of the lower Oikawa River.
Regarding crustal movement in the Tokai and surrounding regions, the results of observations by the National Geological Institute indicate some change over the long term, but nothing that can immediately be linked to earthquakes in the Tokai Region.
There was the following additional activity in the Kanto-Chubu region:
- On July 21st, there was an M4.0 earthquake in northeastern Chiba Prefecture. In this vicinity, there was an M6.1 earthquake on June 3rd 2000.
- In the latter half of July, there was microearthquake activity (maximum M3.1) in central Shizuoka Prefecture (the area of the lower Oikawa River).
- There has been microearthquake activity (maximum M2.9) in the area of Hakone since the latter half of June, which has continued into July. There have also been some minor changes in GPS observations and volumetric strain measurements of the area.
There was the following seismic activity in the Kinki-Chugoku-Shikoku region:
- Since the latter half of May, there had been continued microearthquake activity (maximum M3.6) at a depth of between 10 and 15 km near the border between Wakayama and Nara Prefectures, but beginning in late June, new activity began in an area 2 to 3 km to the north, and in July activity has mainly continued in the north.
There has been the following seismic activity in the Kyushu-Okinawa region:
- In the first half of July, there was seismic activity including a maximal M5.2 event (on July 10th) in the sea near Amami Oshima. There was an M6.6 earthquake in this area on October 18 1995.
| Reference Material 1 Standards to select earthquakes which are to be described in "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) Events of M6.0 or greater. Or, M4.0 or greater (M5.0 or greater at sea) and having a maximum intensity of 3 or greater. Reference Material 2 Standards to describe additional explanation in "Supplementary repot of the evaluation." 1 Reference items relating to seismic activity described in "Evaluation of Seismic Activity". 2 Activity related to seismic activity (of the past 12 months or so) described in "Major Seismic Activity in Evaluation of Seismic Activity." 3 Activity that have been evaluated but not described in "Evaluation of Seismic Activity" because of being within the bounds of normal activity or because the activity is not prominent. |