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Press Release from USGS: 4/14/2010 2:55:24 PM (edited)

Scientists say 2010 is not showing signs of unusually high earthquake activity. Since 1900, an average of 16 magnitude 7 or greater earthquakes — the size that seismologists define as major — have occurred worldwide each year. Some years have had as few as 6, as in 1986 and 1989, while 1943 had 32, with considerable variability from year to year.

With six major earthquakes striking in the first four months of this year, 2010 is well within the normal range. Furthermore, from April 15, 2009, to April 14, 2010, there have been 18 major earthquakes, a number also well within the expected variation.

Large earthquakes will continue to occur just as they have in the past.

This blog goes back and takes a look at the data behind those statements.

Sources

The Data used to create the later Maps is primarily from USGS/NEIC [usgs], [neic] and NOAA which back until 2004 is cross referenced with Geofon [geofon], Russian Academy of SCiences [ras] and EMSC [emsc] Networks.
1940-2004 the main cross referencing used is ANSS and local networks such as Geonet of New Zealand [geonet].
Recent discoveries of other databases such as Instidudo de Geofisica del Peru [cndg], and Dept. de Geofisica, U of Chile [dgfudc]and iiee, the latter containing a vast amount of work done by Dr. Tokuji Utsu, Professor Emeritus of Tokyo University, lists containing more than 10,000 destructive earthquakes in the world from 3000 B.C. are all helping with the cross-referencing and also adding more events to the totals.

As well as the above main sources, the 1900-2002 maps and lists show some events containing magnitude and location details referenced from the following catalogues used to compile the Centennial Earthquake Catalog 1900-1999 by Engdahl, E.R., and A. Villaseñor (2002) [ehb];
[abe] Catalogue of large earthquakes 1897-1980 (1981,1984) and Abe and Noguchi (1983).
[b&d]Catalogue of large earthquakes 1897-1977, Bath and Duda (1979)
[brk] Magnitudes reported by the Seisomographic Station, University of Califonia, Berkley, USA.
[bji] Catalogue of hypocenters and magnitudes, State Seismological Bureau, Beijing, China.
[g&r] Catalogue of hypocenters and magnitudes 1904-1952, Gutenberg and Richter (1954)
[isc] Hypocenters and magnitudes from bulletins by International Seismological Centre, Newbury, UK (1964-1998)
[iss] International Seismological Summary (1918-1963). Also British Asssociation for the advancement of Science bulletins (1913-1917)
[jma] Catalogue of hypocenters and magnitudes1926-present Japan Meteorological Agency, Tokyo, Japan.
[mos] Catalog of earthquakes in the former USSR 1950-1961
[p&s] Catalog of worldwide earthquakes with Ms 7.0> 1900-1989 Pacheco and Sykes (1992)
[pas] Magnitudes reported by California University of Technology, Pasadena, USA.
[rothe] Catalog of worldwide earthquakes with Mag5.5> 1953-1965, Rothe (1969)
[utsu] Catalogue of earthquakes in the Japan region 1885-1925 Utsu (1979,1982)

Magnitudes

The lists show Mw (Moment Magnitude) as the main magnitude type where this is available, where this is not available another type may be used such as Ms, mb or mB. Where the type of magnitude is Unkown the nearest known magnitude is shown on the list, these may go down to 6.5, usually mb. All types are marked on the popup tags if they are available, the colour coding of the icons is set to match the magnitude used on the list. I have not included any earthquakes that have the highest (primary) magnitude in the 6 range i.e. there must be a Mag 7+ reading in the data, even if the magnitude type is unknown.

Pop up Tags

Inside the pop up tags off the maps you will find details of the earthquake, for example

Date/Time: 1919/4/30 7:17:5
Lat: -19 Long: -172.5
Region: E of Tonga
Mw: n/a Ms: n/a
Mb: n/a ML: n/a
Me: n/a Unk: 8.3
Depth: 25 km
Deaths: n/a , Injuries: n/a
Tsunami: yes
Source: noaa

Some events have brief background information about the earthquake, damage, intensity etc, on the popup balloon.
The info is sourced mainly from Historic World Earthquakes and Earthquakes with 1,000 or More Deaths since 1900 both USGS sites and other Historic NZ Earthquakes, and Historic Tsunami and Volcanic eruption records. More recent events may have MM Intensity reports in the tags.

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