M 8.5 quake S of Japan coming in now

[davenn]

Prelim report

8.5 166km WNW of Chichi-shima, Japan 2015-05-30, 11:23:00 UTC, 696.0 km Deep

http://www.sydneystormcity.com/seismograms.htm

At almost 700km, this extremely deep and will result in a significant lack of surface waves

Dave

 

[Borg]

At almost 700km, this extremely deep and will result in a significant lack of surface waves

That's good. Japan doesn't need another tsunami.

 

[davenn]

That's good. Japan doesn't need another tsunami.

yup., so true.
its now been downgraded to a M 7.8 ... mag is likely to vary a bit till all the data is analysed

 

[Astronuc]

M7.8 - 189km WNW of Chichi-shima, Japan
http://earthquake.usgs.gov/earthquakes/eventpage/us20002ki3#general_summary
2015-05-30 11:23:02 (UTC)
Lat/Long = 27.831°N 140.493°E
depth = 677.6 km (421.0 mi)
Nearby Cities

1. 189km (117mi) WNW of Chichi-shima, Japan
2. 771km (479mi) SSE of Shimoda, Japan
3. 781km (485mi) SSE of Oyama, Japan
4. 783km (487mi) SE of Shingu, Japan
5. 874km (543mi) S of Tokyo, Japan

Tectonic Summary
The May 30, 2015 M7.8 earthquake WNW of Chichi-shima, Japan occurred as the result of oblique-normal faulting at a depth of over 660 km beneath the Pacific Ocean. The earthquake is located within the interior of the Pacific plate that subducts beneath Japan starting at the Izu trench, several hundred kilometers to the east of the event (and at the surface of the Earth). At the location of the earthquake, the Pacific plate moves approximately westwards with respect to the Philippine Sea plate at a rate of 39 mm/yr. This earthquake occurred in response to stresses generated by the slow distortion of the Pacific plate at depth, rather than occurring on the interface between the Pacific plate and the overriding Philippine Sea plate.

Earthquakes that have focal depths greater than 300 km are commonly termed "deep-focus". Deep-focus earthquakes cause less damage on the earth’s surface above their foci than is the case with similar magnitude shallow-focus earthquakes. Large deep-focus earthquakes may be felt at great distance from their epicenters. The largest recorded deep-focus earthquake was a 2013 M 8.3 earthquake that occurred at a depth of 600 km within the subducted Pacific plate beneath the Sea of Okhotsk, offshore northeastern Russia. The M 8.3 Okhotsk earthquake was felt all over Asia, as far away as Moscow, and across the Pacific along the western seaboard of the United States. Over the past century, 66 earthquakes with a magnitude of M7 or more have occurred at depths greater than 500 km; three of these were located in the same region as today's event. The largest nearby event at these depths was a 1968 M 7.3 earthquake, several hundred kilometers to the south of this earthquake.

Very deep means little surface action, or rather the energy is distributed over a larger area of the surface, so a significant tsunami would not be likely.

http://earthquake.usgs.gov/earthquakes/eventpage/us20002ki3#scientific_origin:us_us20002ki3Powerful quake strikes off Japan; no tsunami warning
http://news.yahoo.com/powerful-quake-strikes-off-japan-no-tsunami-warning-115852201.html

But the temblor was powerful enough to rattle large parts of Japan's main island of Honshu. Buildings swayed in Tokyo — about 1,000 kilometers (620 miles) north of the Ogasawara islands — and stopped some train services in the city. There were reports that parts of the capital were without power.

The meteorological agency did not issue a tsunami warning because the quake struck so far beneath the Earth's surface. Deep offshore earthquakes usually do not cause tsunamis, and generally cause less damage than shallow ones.