The political subdivision of Southeast Asia and Northwest Africa in the Flinn-Engdahl Regionalization Scheme

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Claude George
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1 Geophys. J. Int. () 3,23-2 RESEARCH NOTE The political subdivision of and in the Flinn-Engdahl alization Scheme J. B. Young' and B. W. Presgrave2 'AWE Blacknest, Brimpton, Reading, Berks RGI RS, UK 'National Earthquake Information Center, US Geological Survey, Stop 1, Box, Denver Federal Center, Denver, CO 022, USA Accepted April. Received April ; in origmal form October 2 The Flinn-Engdahl alization Scheme is the standard list of names and boundary definitions used by seismologists to specify regions of the Earth. The Scheme conforms to the work of Gutenberg & Richter (), who studied over 000 large earthquakes, plotted the epicentres, and drew 1 regions numbered 1-1 on a world map. This regionalization divided the Earth, with the numbered regions of low seismicity being, in general, larger in area than those regions of high seismicity. Flinn & Engdahl(l) took 0 of the regions (merging special region 1 in Romania into the Middle East-Crimea- Balkans region number 30) and subdivided each one (with minor adjustments of boundaries) to form a mosaic of geographical/political regions within seismic regions. These geographical regions were numbered 1-2. Flinn & Engdahl's subdivision, like Gutenberg and Richter's, also tended to create larger geographical regions within the seismic regions of low seismicity and smaller ones within high-seismicity regions. The smaller regions delineate political and geographical areas better than the larger ones. The current Flinn-Engdahl alization Scheme is known as the F-E Code (Flinn, Engdahl & Hill ) and has 0 seismic regions (numbered 1-0) and 2 geographical regions (numbered 1-2: region 2 is no longer in use). In, the Commission on Practice of the International Association of Seismology and Physics of the Earth's Interior (IASPEI) established a Working Group on alization under the chairmanship of Dr E. A. Flinn. The Working Group has the task of defining the new standard for the seismo-geographical regionalization of the Earth. At its meetings in at the IUGG in Vancouver, the Working Group decided that the new standard would be based on polygons defining 'local' regions of seismic, tectonic, geographical and other features. It was also agreed that the new standard would benefit from some correction to the current F-E Code prior to its introduction. Existing boundary definitions remain fixed, with new geographical regions being additional to the existing regions. Young () and Young & Wiens (0) give the reasons for having additional regions and propose new oceanic regions. At its meeting in, the Working Group reviewed the problem of larger geographical regions having disparate areas, in particular land-based regions with low seismicity. It was decided that there were two large geographical regions which, if subdivided, would improve the current F-E Code. These two regions are region 2,, and region 0, Northwest Africa. It was agreed that the easiest subdivision would be political, as region 0 contains 1 countries and region 2 contains four countries and an area of sea. This work was presented in 1 at the IUGG in Vienna and has been approved by the Commission on Practice of IASPEI. The purpose of this paper is to complement the two previous papers by Young () and Young & Wiens (0) in order to complete the task of correcting the current F-E Code initiated by the Working Group under the Chairmanship of Dr Ted Flinn, who died in. Any comments should be addressed to the first author, who is the current Chairman of the Working Group. The new geographical regions are described below, defined in Tables 1 and 2, and illustrated by maps (Figs la-b). REGION 2: SOUTHEAST ASIA This existing region is subdivided into four political regions and one seismo-geographical region, which are numbered is reduced to the 'not in use' category within the F-E Code to maintain compatibility with previous codes. The seismic region number remains 2. The new geographical region numbers and names allocated are: Downloaded from by guest on December 1 0 RAS 23

2 2 J. B. Young and B. W. Presgrave Table 1. Changes made to Flinn-Engdahl geographical region 2 boundary cards (similar format to Table 13 of Flinn et al. ). NE Quadrant Number of Lines 1 33 new> NE 12 2 Additional Lines Laon Old< NE Old< NE now> NIP Old< NE Southeant Asia 2 Southeamt Asia REGION 0: NORTHWEST AFRICA This existing region is also subdivided, but into 13 political regions which are numbered 3-. As with region 2, region 0 becomes not in use to maintain compatibility with previous codes. The seismic region number remains 3. The new geographical region numbers and names allocated are: Cote d Ivoire Niger Old< NE new) NE Southeast Aaia Southeat Asia Laon Vie t nam Indicates a Change to the old Line ++ Indicates an Additional Line Note that the region numbers that have been allocated are not consecutive from region 2 to region 0 because the Working Group redefined the region numbers as published in the two previous papers [Young () and Young & Wiens (0)l after its Vienna meetings. The changed geographical region numbers and names are: Northern East Pacific Rise North of Honduras East of South Sandwich Islands Reykjanes Ridge Azores-Cape St. Vincent Ridge Owen Fracture Zone region Indian Ocean Triple Junction Western Indian-Antarctic Ridge Southeast of Easter Island Galapagos Triple Junction region Also note that the region names have been defined according to the conventions specified by Young, Aichele & Presgrave (3). Downloaded from by guest on December 1 0 RAS, GJI 3, 23-2

3 The Flinn-Engdahl alization Scheme 2 2ON 2" 'N -N " 1 O'N.., ,.. - ON.E 1 O'E 1 O.E llo'e w)*r % 0.N 0.N W N 2-N 2PN I I I I -N lo'n SN W N Downloaded from by guest on December 1 1Q.N -N Figure 1. Maps illustrating the new geographical regions. (a) Map centred on "N "E illustrating regions 33 to 3. (b) Map centred on "N 3"W illustrating regions 3 to. 0 RAS, GJI 3, 23-2

4 2 J. B. Young and B. W. Presgrave Table 2. Changes made to Flinn-Engdahl geographical region 0 boundary cards (similar format to Table 13 of Flinn et a/. ) NE Quadrant Number of Line. new> WE Niger new> NE 1 22 Additional Lines Niger new> BE++ + old< RE + + old< WE new) NE new> NEi new> HE++ new > NE old< Nw * + Old< NW + new> NwI + new) NW++ NW Quadrant Burkina Paso Niger Number of Line. Additional Lines new> HE+ + * + + new> NEi + ++ new> NU++ new> Nw++ new> Nw Niger 0 3 Niger 0 Niger 0 Niger 0 Niger 0 0 Niger 0 0 Niger 0 Niger 1 Niger Indicates a Change to the old Line Indicates an Additional Line Burkina Faao 0 RAS, GJl 3,23-21 Downloaded from by guest on December 1

5 The Flinn-Engdahl alization Scheme 2 new> NU REFERENCES Northwent Africa Burkina Paso + Indicates a Change to the old Line ++ Indicates an Additional Line Gutenberg, B. & Richter, C.F.,. Seismicity of the Earth and Associated Phenomena, Princeton University Press, Princeton, NJ. Flinn, E.A. & Engdahl, E.R.,. A Proposed Basis for Geographical and Seismic alization, REV. Geophys., 3, 3-. Flinn, E.A., Engdahl, E.R. & Hill, A.R.,. Seismic and Geographical alization, Bull. seism. SOC. Am.,, No. 3, 1-3. Young, J.B.,. A proposal for additional regions for the Flinn- Engdahl alization Scheme, Geophys. J., 3, 3-. Young, J.B. & Wiens, D.A., 0. A further proposal for additional regions for the Flinn-Engdahl aiization Scheme, Geophys. J. Int., 3, -2. Young, J.B., Aichele, H. & Presgrave, B.W., 3. name conventions in the Flinn-Engdahl alization Scheme, Geophys. J. Int.,, new> NU new> NU ne*> NW I Weatern Sahara Northwest APrica Downloaded from by guest on December 1 0 RAS, GJI 3, 23-2

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