Quake Watch 2010, page 12

Mike, with reference to your question to me in the Chile thread, I gather all USGS data fro quakes 1.0+ and have been doing since the beginning of 2009 using my QuakeData program. USGS classify the areas in the list and one such area in the "northern mid-atlantic ridge".

This was the classification I was going on, but I think the confusion arises in the spread of latitude they use to classify this area.

I note your search was a circle thus:

FILE CREATED: Sun Feb 28 09:04:00 2010
Circle Search Earthquakes= 17
Circle Center Point Latitude: 10.896N Longitude: 43.442W
Radius: 300.000 km
Catalog Used: PDE
Date Range: 1990/01/01 to 2010/02/27
Magnitude Range: 5.0 - 10.0

This is the data that I have which is classified by them as NMAR

Date/Time UTC,Latitude,Longitude,Magnitude,No Of Rept Stns,Depth(Km),Location,Revised
27/02/2010 19:54:29,10.8963,-43.4424,5.40,196,10.00,northern Mid-Atlantic Ridge,False
13/02/2010 04:30:45,29.7254,-42.5822,4.90,42,10.00,northern Mid-Atlantic Ridge,False
13/02/2010 01:03:00,30.2645,-42.6820,4.90,25,10.00,northern Mid-Atlantic Ridge,False
13/02/2010 01:00:58,29.8059,-42.7754,4.90,33,10.00,northern Mid-Atlantic Ridge,False
12/02/2010 11:20:39,29.7343,-42.7754,5.10,96,10.00,northern Mid-Atlantic Ridge,False
27/01/2010 01:47:59,49.7167,-28.7623,4.80,50,10.00,northern Mid-Atlantic Ridge,True
08/01/2010 03:31:10,15.2651,-45.7733,4.80,26,10.00,northern Mid-Atlantic Ridge,False
02/01/2010 23:05:53,51.7506,-30.7753,4.80,28,9.60,northern Mid-Atlantic Ridge,False
09/12/2009 12:13:26,49.5614,-28.6080,4.90,132,10.00,northern Mid-Atlantic Ridge,False
13/10/2009 03:52:09,46.3869,-27.3403,4.70,48,10.00,northern Mid-Atlantic Ridge,False
10/10/2009 01:40:41,28.7758,-43.4096,4.90,76,10.00,northern Mid-Atlantic Ridge,False
08/10/2009 23:08:36,46.1352,-27.5121,4.80,25,10.30,northern Mid-Atlantic Ridge,False
06/10/2009 00:16:04,46.5020,-27.2756,5.20,173,10.00,northern Mid-Atlantic Ridge,False
05/10/2009 05:51:21,46.3757,-27.3739,4.80,51,10.00,northern Mid-Atlantic Ridge,False
04/10/2009 03:33:26,46.5132,-27.3925,4.60,56,10.00,northern Mid-Atlantic Ridge,False
04/10/2009 00:09:11,46.2249,-27.4478,4.80,31,9.70,northern Mid-Atlantic Ridge,False
03/10/2009 21:58:07,46.5300,-27.2986,4.90,162,8.90,northern Mid-Atlantic Ridge,False
03/10/2009 21:27:19,46.3441,-27.3988,4.90,60,9.80,northern Mid-Atlantic Ridge,False
04/09/2009 00:42:53,19.0725,-46.1309,4.90,97,10.00,northern Mid-Atlantic Ridge,True
08/08/2009 06:43:21,46.6712,-27.4657,4.80,121,10.00,northern Mid-Atlantic Ridge,False
18/07/2009 02:41:28,34.2120,-37.3504,4.80,104,10.00,northern Mid-Atlantic Ridge,False
06/06/2009 20:33:28,23.8595,-46.0837,6.00,293,10.00,northern Mid-Atlantic Ridge,True
13/05/2009 02:38:11,52.5030,-31.7888,4.40,21,10.00,northern Mid-Atlantic Ridge,False
24/03/2009 12:34:55,14.6551,-45.0783,5.20,73,10.00,northern Mid-Atlantic Ridge,False
11/03/2009 23:50:33,15.5568,-46.7589,4.70,26,10.00,northern Mid-Atlantic Ridge,False

Separating the 5.0+ out this gives

Date/Time UTC,Latitude,Longitude,Magnitude,No Of Rept Stns,Depth(Km),Location,Revised
27/02/2010 19:54:29,10.8963,-43.4424,5.40,196,10.00,northern Mid-Atlantic Ridge,False
12/02/2010 11:20:39,29.7343,-42.7754,5.10,96,10.00,northern Mid-Atlantic Ridge,False
06/10/2009 00:16:04,46.5020,-27.2756,5.20,173,10.00,northern Mid-Atlantic Ridge,False
06/06/2009 20:33:28,23.8595,-46.0837,6.00,293,10.00,northern Mid-Atlantic Ridge,True
24/03/2009 12:34:55,14.6551,-45.0783,5.20,73,10.00,northern Mid-Atlantic Ridge,False

The difference between your circle and what they classify as northern mid-atlantic ridge would seem to be the source of our difference in figures.

I have plotted the 5 I have in Google Earth and it really is quite a massive spread. It would seem that they refer to 'northern' as anything north of the equator.