2 earthquakes, 2 days: same exact location AND depth? (near Fukushima), page

Hi guys,

I haven't really spent all that much time in this forum, but I found this article in relation to Fukushima, and I thought I'd post it here mainly for feedback from a geological perspective.

enenews.com...

I decided to do my own research, as it seemed a little odd to me. Here is the first quake, both on the Japan Meteorological Agency and on the US Geological Service sites:

www.jma.go.jp...

earthquake.usgs.gov...

Here's the second quake on the JMA site, but I can't seem to find this event on the USGS site:

www.jma.go.jp...

Here's the info for those who cbf clicking:

03:46 JST 26 Mar 2012 37.8N 141.8E 50 km 3.9 Fukushima-ken Oki
22:22 JST 25 Mar 2012 37.7N 141.8E 50 km 5.2 Fukushima-ken Oki

Now I don't know all that much about seismic activity, but from what I understand clusters of activity is a common thing with earthquakes, but the exact same position and depth? Does this seem like an anomaly to anyone else?

I don't want to come across too tin-foil hatty (not that there's anything wrong with that) but it seems weird to me that there's no info on this second quake on the USGS site (that I can tell)

earthquake.usgs.gov...

There are more recent quakes than the second 3.9 quake near Fukushima from all over the world posted on the USGS site, some of them at a lesser magnitude than this quake.

Can anyone who has more experience with these sites and knowledge of seismic activity shed more light on this?

The "same depth" parameter is due to computer generated information, oftentimes initial parameters (magnitude, location, depth) are set to a default number then later modified once reviewed by a seismologist.

Not too uncommon at all.

The depth where the earthquake begins to rupture. This depth may be relative to mean sea-level or the average elevation of the seismic stations which provided arrival-time data for the earthquake location. The choice of reference depth is dependent on the method used to locate the earthquake. Sometimes when depth is poorly constrained by available seismic data, the location program will set the depth at a fixed value. For example, 33 km is often used as a default depth for earthquakes determined to be shallow, but whose depth is not satisfactorily determined by the data, whereas default depths of 5 or 10 km are often used in mid-continental areas and on mid-ocean ridges since earthquakes in these areas are usually shallower than 33 km.

USGS

---

ETA

The reason the second quake is not (and not like to be) listed is that the USGS rarely reports anything below 4.5 outside the US.

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