‘Strike-slip’ move­ment of fault lines caused the dis­as­ter

Weekend Argus (Saturday Edition) - - ISSUES - STEVE CON­NOR

THE CARIBBEAN is rid­dled with a com­plex net­work of tec­tonic fault lines re­sult­ing from the move­ment of the Caribbean plate, which is slip­ping east­wards at a rate of about 2cm a year, rel­a­tive to the North Amer­i­can plate fur­ther to the north.

The bound­ary of th­ese two tec­tonic plates lies off the north coast of Haiti, but there are sev­eral fault­line sys­tems to the south that cut across the coun­try from east to west. It was the sud­den “strike-slip” move­ment of one of th­ese fault­lines that led to the dis­as­ter.

Sci­en­tists cal­cu­late that the epi­cen­tre of the earth­quake, which mea­sured 7 on the Richter scale, was about 15km south-west of Haiti’s cap­i­tal, Port-au-Prince. The point be­neath the Earth’s sur­face where the rup­ture be­gan – its hypocen­tre – was just 11km away, mak­ing it a rel­a­tively shal­low shock.

“Close­ness to the sur­face is a ma­jor fac­tor con­tribut­ing to the sever­ity of ground shak­ing caused by an earth­quake of any given mag­ni­tude,” said David Roth­ery, a plan­e­tary sci­en­tist at the Open Uni­ver­sity. “In this case, the epi­cen­tre was only 15km from the cen­tre of Por­tau-Prince, which there­fore suf­fered very heav­ily.”

Sci­en­tists said this week it was the largest earth­quake to af­fect this area of the Caribbean for more than two cen­turies.

Haiti suf­fered a num­ber of earth­quakes in the 18th cen­tury: in 1701, 1751 and 1770. The 1751 earth­quake, which was prob­a­bly about 10 times big­ger than the cur­rent one, de­stroyed the re­cently founded Por­tau-Prince.

Pro­fes­sor Roger Searle, an earth sci­en­tist at Durham Uni­ver­sity, said the earth­quake re­leased the en­ergy equiv­a­lent of half a mil­lion tons of TNT but its im­pact would have been much greater than in de­vel­oped coun­tries be­cause of poor build­ing stan­dards. – The In­de­pen­dent

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