Possible error in the ANSS database July 2012?

I was looking at earthquakes greater than Magnitude 6.0 in the ANSS database today as I check the progress of earthquake magnitude revisions for up to one year from the event date.

Generally speaking in the ANSS database earthquakes are reported either in mb scale or Mw and sometimes Ms.

DateTime,Latitude,Longitude,Depth,Magnitude,MagType,NbStations,Gap,Distance,RMS,Source,EventID
2012/06/26 12:32:37.34,-21.8070,-176.6660,187.60,6.30,ML,261,,,0.84,NEI,2012062610
2012/06/29 13:15:23.44,-23.8410,179.8150,553.00,6.10,ML,175,,,0.65,NEI,2012062910

sourced from the ANSS Worldwide Earthquake Catalog provided by the Northern California Earthquake Data Center (NCEDC) and the Advanced National Seismic System (ANSS).

These kind of stand out as since 2000 there are only 8 events in ML scale. There are more earlier but since 2000 Mw has definitely been in use.

There is actually a third one in July

DateTime,Latitude,Longitude,Depth,Magnitude,MagType,NbStations,Gap,Distance,RMS,Source,EventID
2012/06/14 11:04:03.54,-22.2390,179.7060,561.90,6.60,ML,187,,,0.60,NEI,2012061410

sourced from the ANSS Worldwide Earthquake Catalog provided by the Northern California Earthquake Data Center (NCEDC) and the Advanced National Seismic System (ANSS).

The first no longer has an available web page but here are the details as posted by USGS in their listings.

Date/Time UTC,Latitude,Longitude,Magnitude,Depth(Km),Location
2012-06-14T11:04:03.000Z,-22.239,179.706,5.4mb,561.9,south of the Fiji Islands

5.4 mb very approximately translates to 5.7 Mw so this is not a Mag 6, yet the ANSS data is saying 6.6 ML. That definitely does not seem right.

The other two are similar

The phase data for that is shown below:

At 4.8 mb, translating to around 5.27 Mw or about 5.05 ML this 6.1 ML value seems to be way out.

The second one


Also 4.8 mb and therefore similar to the other the reported ML is 6.3 which again seems way our – even further out that the first one.

Whilst two of these are ~550km depth the other is ~187km

My point really is that if people do not investigate, and take the ANSS figure as correct, are they actually being given erroneous information?

I don’t know the answer to that but it does seem might odd. I can’t check back any earlier than 2009 but I can say that the next prior event was 27 Feb 2010 Mag 6.0 ML

Date/Time UTC,Latitude,Longitude,Magnitude,Depth(Km),Location
2010-02-27T10:30:32.000Z,-33.96890,-72.87910,6.0000,35.0000,offshore Valparaiso. Chile

No particular problems with that one, and the one before that was 15 July 2009

Date/Time UTC,Latitude,Longitude,Magnitude,Depth(Km),Location
2009-07-15T09:41:53.000Z,-46.03570,165.93750,5.8000,12.0000,off the west coast of the South Island of New Zealand

No particular problem with that one either.

Data from the above sourced as follows:

This makes it seem even more possible that these three are errors.

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About PuterMan

A retired programmer.
This entry was posted in ANSS, Earthquakes 2012 and tagged , . Bookmark the permalink.

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