Enriqillo Fault

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

The slip rate on the Enriquillo fault has been estimated by Manaker and others to be about 8 mm/yr. A damaging sequence of earthquakes occurrred near or on the fault in 1751 and 1770. Hence the slip deficit locally 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 (Manaker, Calais, Mann, Prentice), although its exact timing was uncertain, and it is not clear that the 12 January actually occurred on the Enriquillo fault.

No surface rupture

The 12 January earthquake may have occurred, not on the Enriquillo fault, but on a splay fault adjoining the throughgoing plate boundary. It is also possible that its magnitude exceeded Mw 7.1. Rupture on the fault clearly terminated 2-4 km below the Earth's surface - deeper near the epicenter and shallower in the west near Leogane. Various interpretations have been offered to explain sinestral surface shear and uplift south of Leogane. The uplift that raised several coral platforms above sea level may have occurred on a north dipping strike slip fault with reverse slip (See USGS moment tensor solution).

The earthquake occurred on an east-west, strike-slip fault with a minor amount of convergence. Rupture was roughly 60 km long with mean slip of 1.8 m. The rupture propagated to the west with most of the slip over in the first 15 s, and with maximum slip near the hypocenter exceeding 3 m. Aftershocks delineate the east -west extent of the rupture.

It is possible that the slip may be eventually be manifest at the surface in the form of afterslip, or the earthquake may resemble the 1989 Loma PrietaMw=6.9 earthquake with no surface rupture.

Future damaging earthquakes

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. Calculations showed a less than 2% chance of this occurring within a month of the mainshock (Lin et al 2010). The effects of stress enhancement are delayed by shorter or longer periods through mechanisms that we understand very little.

Haiti Earthquake 9 Mar 2010 Update

Tide Gauge Data from 6 March on line

click on map for pdf. Historical earthquakes from Bill McCann. Size of ellipsii proportional to approximate magnitude, locations approximate.

Lessons from the Haiti Earthquake- Nature 18 Feb

Democracy Now - Amy Goodman Interview

Surficial fractures (updated 21 Feb 2010)

Helicopter traverse 25 January (Plate boundary

Liquefaction Port au Prince Harbour (23 January)

Damage report (22 & 23 January)

Clickable Uplift/Subsidence/Intensity Map

Post seismic PowerPoint File for classroom use (! 21Mb)

Mainshock 12 Jan 2010 at 04:53:10 PM local time at 8 km

Prelim. Epicenter 18.457 deg N, 72.533 deg W, Mw =7.0 USGS centroid solution 18.826 -72.162 HCMT solution 18.62 N, 72.59 E.

Numerous large jpegs can be downloaded for educational use through links at the bottom of this pag .

Fatalities

The urban agglomeration of Port-au-Prince has expanded rapidly in the past decade and before the earthquake exeeded 2 million. The death toll was estimated at 230,000 (12 Feb) but it is likely that the true count will never be known precisely.

With a Richter magnitude of M=7 the Haiti earthquake is classed as a major earthquake, however, no previous M=7 earthquake has resulted in this many fatalities (the Messina earthquake of 1908 killed 82k). At 230k, the deathtoll is close to being the most lethal earthquake since 1900, and the second most lethal earthquake ever. The large death-toll was caused by the almost complete absence of earthquake resistance in most of the structures in Port-au-Prince and the surrounding towns and villages.

I estimate the cost of reconstructing Port au Prince and its surroundings as approximately $20 biliion. The estimate is based on rebuilding of 250,000 dwellings and civic buildings (schools etc) at an average cost of $80k including associated infrastructure - temporary housing, water supply, sewer, power distribution, roads and port facilities. Economists at the Inter-American Development Bank on 17 Feb 2010 suggested the figure may be as low as $8-$14 billion.

A recent article (2009) discussing the seismic future of cities may be downloaded here. It forecasts a rising deathtoll from earthquakes, especially in the developing nations, where earthquake resistance building codes are either absent or not enforced. A two page building code existed in Haiti before the earthquake, which was used by engineers but not by most of the contractors in the country. After the Earth Quakes by Susan Hough and Roger Bilham (2001) discusses the increasing problem of urban earthquakes. In a Feb 2010 Nature article I argue that the UN should implement a global task force to prevent the construction of non-earthquake resistant structures in any city with a history of damaging earthquakes. Unsafe buildings are weapons of mass destruction.

Link to Photos of damage in Port au Prince

Link to helicopter views Leica

Link to helicopter views Sony

Link to views of Port Damage, Cite Soleil and Villagers west.

Paul Mann's website

Eric Calais' website