Enriqillo Fault

The northern Caribbean plate boundary near Haiti consists of two principal surface faults - the Septrional fault in the north and the Enriquillo/Plantain-Gdn fault in the south.

The slip rate on the Enriquillo fault has been estimated by Carol Prentice and others to be about 7 mm/yr. A damaging sequence of earthquakes occurrred on the fault in 1751 and 1770. Hence the slip deficit prior to the earthquake had amounted to about 1.7 m, close to the mean slip that was released by the 12 Jan earthquake. i.e. the earthquake could have, and indeed was foreseen (Calais, Mann, Prentce), although its exact timing was uncertain.

Segments of the fault both to the east and west are likely to slip in the next several decades. The timing of these future ruptures is currently unknown.


 

Haiti Earthquake

A Power point file can be dowloaded here (23Mb)

12 Jan 2010 at 04:53:10 PM local time

location 18.457 deg N, 72.533 deg W, Mw =7.0

The earthquake occurred on an east-west, strike-slip fault. Rupture was roughly 65 km long with mean slip of 1.8 m. According to preliminary models the rupture propagated bilaterally with most of the slip over in the first 15 s, and with maximum slip near the epicenter exceeding 4 m.

The epicenter was roughly 8 km deep and the surface fault will almost certainly have ruptured throughout the pronounced valley that marks its passage through the mountains south of Port au Prince. Aftershocks delineate the east west extent of the rupture.

Population exposure

The urban agglomeration of Port au Prince has expanded rapidly in the past decade and now exeeds 2 million. The death toll is currently estimated at 50,000 (15 January 2010). Max Wyss of WAPMERR issued a forecast up to 60,000 fatalities within 30 minutes of the mainshock based on population density, earthquake magnitude, generalized attenuation, and building fragility.

A recent article discussing the seismic future of cities may be downloaded here. The 12 January earthquake was a relatively modest earthquake, but its large death-toll is caused by its proximity to a poorly constructed city.

A book by Susan Hough and Roger Bilham discusses the increasing problem of urban earthquakes.