Tectonics of the Haitian earthquake

A post by Chris RowanA magnitude 7.0 earthquake struck Haiti this evening, causing extensive damage to the capital, Port-au-Prince, and probably causing many casualties. The map below shows where the main shock occurred (red), as well as the epicentres of the numerous aftershocks (orange) that occurred in the following 5 or 6 hours (and continue even as I write).

Haiti.jpg

The main shock appears to have initiated less than 25 km southwest of Port-au-Prince; this close proximity meant that the city would have endured the maximum possible shaking intensity from an earthquake of this size, leading to extensive damage. Here’s the focal mechanism, courtesy of the USGS:

Haitifm.png

With the help of my recent post on focal mechanisms, it is hopefully obvious that the rupture occurred on a primarily strike-slip fault, with the crust on each side of the fault moving horizontally relative to the other side. To understand why there is strike-slip faulting in this area, we need to step back, and look at a simplied map of the entire Caribbean:

Caribbean_plate2.png

The Caribbean is contained on its own separate little plate; a rather diminutive part of the tectonic jigsaw that is the Earth’s crust. It is surrounded on three sides by the much larger North and South American plates, both of which are moving approximately westwards with respect to the Caribbean plate at around 2-3 centimetres a year. On the eastern edge of the plate, the boundary runs perpendicular to the direction of relative plate motion, so there is compression and subduction (and subduction volcanism, exemplified by the likes of Montserrat). However, as the boundary curves around to form the northern boundary of the Caribbean plate, where the Haitian earthquake occurred, it starts to run parallel to the direction of relative plate motion, making strike-slip faulting along E-W trending faults the most likely expression of deformation in this region. This is exactly what the Haitian quake appears to record.

Note also that deformation across the northern plate boundary appears to be distributed – some motion is accommodated on faults that are located a little bit away from the actual plate boundary, further inside the plate interior. The Haitian quake appears to have occurred on one of these faults: based on the position of its epicentre the rupture is extremely close to the Enriquillo Fault, which appears to be a major strike slip fault running across the southern end of Haiti. This is the fault most likely to have ruptured.

Nj10.png
Tectonic map of the Northern Caribbean (Source)

There is nothing particularly unusual about this earthquake given the tectonic context. Unfortunately, however, Haiti is a very poor country – one of the poorest and least developed in the world – so unfortunately, its government was not in a position to really do much to prepare for the inevitable large earthquake, leaving tens of thousands to suffer the consequences.

Update from Anne: Chris has been featured in a Nature News Briefing: “The Haiti Earthquake in Depth” along with more information about the faults in question and the known seismic risk of the area.

Further updates:
Haiti’s seismic future
What next for the Enriquillo Fault?

Categories: earthquakes, geohazards, geology, tectonics

Comments (85)

  1. Ron Schott says:

    Excellent overview, Chris. I’ll be using it in class in a few hours.

  2. Bob O'H says:

    Radio 4 couldn’t contact you this morning, so they grabbed someone else from Edinburgh. He said that in the long term there might be aftershocks to the west, e.g. in Jamaica. is this just because most of the fault is to the west, or is there a deeper reason?

  3. Arikia says:

    Excellent post, Chris. Thanks for writing this.

  4. Pyers Symon says:

    Excellent, clear post.

  5. Deb says:

    Thank you Chris this is a very very clear blog site. I can understand a lot more now. Please take care. My thoughts are of the people of Haiti.

  6. Fantastic post, Chris. I think my hydrogeology students will be getting a little dose of tectonics today thanks to your clear explanation.

  7. Very nice post!! Enriquillo fault was the first thing I though of as soon as I saw the location of the epicenter. I think that of all the Caribbean islands, Hispaniola is one of the more messed up, tectonically, part of the north is even moving in the opposite direction as the rest of the island.

  8. Quick, clear work! Thanks, Chris!

  9. Excellent post. I had also written something and have just added a link to this clear explanation. Thanks.

  10. DrKeithCurrie says:

    Thanks Chris; You have posted a comprehensive overview of the massive earthquake attacked last evening to Haiti. But think we should help them any possible way at least pray for them.

  11. Kim says:

    Thanks, Chris – and great explanation.

  12. Dixie McCormick says:

    Thank-you! Quick, clear, and simple.

  13. Chris Rowan says:

    He said that in the long term there might be aftershocks to the west, e.g. in Jamaica. is this just because most of the fault is to the west, or is there a deeper reason?
    I don’t know for sure, but it may be historical ruptures on this fault were further to the east, so the west is where the most stored elastic strain is waiting to be released.

  14. BrianR says:

    I’m gonna get on the bandwagon here … great post, exactly the information I wanted to know about this event.

  15. Erin says:

    For some reason I was trying to google “tectonic plates Haiti earthquake” before I went “duh! I bet Chris has it” – and lo and behold I was right! You answered everything I wanted to know – great job!

  16. Laurel says:

    Great post, it’s nice to learn the science behind the earthquake. As you pointed out, Haiti is a very poor country with few resources to help recover from this event. If people would like to help there are a variety of organizations they can donate to. I like Mercy Corps https://donate.mercycorps.org/

  17. chezjake says:

    Has there been an upthrust of land?
    Just noted on the BBC live update page that at 1733:

    melindayiti tweets: talking to Joe in Jacmel…says the city is destroyed, the Alcibiade is missing a part, the Hotel Lamandou… many places damaged… the hospital also seriously damaged and turning people away…the ocean receded a half mile from the coast

    My italics.
    http://news.bbc.co.uk/2/hi/americas/8456322.stm

  18. Maitri says:

    Structural geology enthusiasts: Looks like a perfect example of plate interaction in transpression.

  19. Roland says:

    It’s too bad Haiti has been denuded of trees, unlike the DR. Result: few wooden buildings, too many brick/masonry buildings. I would bet that’s the main cause of casualties.

  20. rm says:

    Good post but a comment on “maximum shaking”.
    If the aftershock and mainshock locations are correct, then the earthquake ruptured from east to west and away from Port-au-Prince. This would mean the maximum possible shaking did NOT occur in the city but likely at the west end of the fault due to directivity effects (which can be significant).
    When a large earthquake occurs, the rupture begins at one point and then progresses along the fault, usually at about shear wave velocity (perhaps 2 – 3 km/s). Seismic waves radiated in the direction of the rupture propagation tend to have higher amplitudes than the waves moving in the opposite direction. In the case of the Haiti earthquake, the location of the mainshock denotes the likely nucleation point and the aftershocks will be (typically) clustered along the total rupture. Therefore, *if* the locations on the map are correct, the earthquake started in the east and the fault ruptured along a line to the west.
    That said, ground motion also depends on site conditions – if much of the city was built on soft soil rather than bedrock, this would likely increase shaking.
    In general, maximum shaking does not always occur near the fault.
    http://earthquake.usgs.gov/regional/nca/rupture/directivity/

  21. Alan B says:

    Thank you. Excellent explanation.

  22. steve says:

    Anyone know how long the quake lasted?

  23. Kitty says:

    I wanted to get your opinion on whether the Earthquake which happened in Northern California (N. American plate) triggered the movement of the Carribean/N. American plates to result in the Haitian quake.

  24. bo says:

    We haven’t heard any reports from Jamaica or Cuba of quake effects. Is this because it is a relatively small quake, or is it simply that slip occurred along a very small portion of the fault?

  25. Dave Crane says:

    @chezjake: The motion along that plate boundry has been mostly left-lateral strike-slip since the Cretaceous. That is also what is seen along the Montagua fault in Guatemala. However, Cretaceous limestone is also exposed there with a little additional uplift on the north exposing low-grade metamorphics.
    http://sp.lyellcollection.org/cgi/content/abstract/328/1/219

  26. zeke says:

    We haven’t heard any reports from Jamaica or Cuba of
    quake effects. Is this because it is a relatively small
    quake, or is it simply that slip occurred along a very
    small portion of the fault?
    The earthquake originated at shallow depth. That reduces areal coverage, but then ground motions are more violent where it is felt.

  27. Dave Crane says:

    @kitty: Fault movement in California doesn’t affect the faults in the Caribbean. Too far away and too many faults in between that would have been subjected to far greater stress – or absorbed it. This earthquake was predicted, based on local tectonics, in 2008 at a Caribbean Geological Congress by Paul Mann, (et al,) of the University of Texas. “Since the last major event in south-central Dominican Republic was in 1751, that yields ~2 meters of accumulated strain deficit, or a Mw=7.2 earthquake if all is released in a single event today. The two largest cities within 30 km of the fault zone are Port-au-Prince, Haiti, and Kingston, Jamaica, with a combined population of 3.65 million inhabitants.”
    See http://www.ig.utexas.edu/jsg/18_cgg/Mann3.htm

  28. Dave Crane says:

    @zeke: It was felt in Jamaica, but the fault does not seem to have released that far from Haiti. Jamaica is next on the watch list; the quakes are occurring from west to east after several hundred years of stress accumulation. http://sflcn.com/story.php?id=7734

  29. bo says:

    Thanks Zeke, my geology is rusty. Just a note: Haiti is the same size as the county I live in; we have fewer than 40,000 inhabitants. I can’t imagine stuffing nearly 10 million people into the same space. That seems like a disaster in itself. I feel badly for Haitians and all other human beings living in those conditions.

  30. I totally agree Bo, we are over populated…and some long term plan needs to be formulated…

  31. Rabbit Cages says:

    I dont know if we are over populated at this time….but we are getting very close. China, india, philipines, and haiti are all very dense population centers…before long we will not be able to feed them.

  32. bo says:

    Population control: two words that send many people into an irrational preference for high casualties in natural disasters, including famine. Nature will continue with mathmatical risk management: quantity versus quality.

  33. Nicolas Gomez says:

    tank’s, it’s an example of plate interaction in transpression.

  34. percyF says:

    Tectonics, Schmectonics. Pat Robertson, that font of gentle wisdom KNOWS it was some pact with the devil.
    So much for your SCIENCE …

  35. kuswantoro says:

    Thanks Chris, I really appreciate ur posting. Kus-Indonesia

  36. Thank you for a great post. I just found your blog but will continue to follow.

  37. kip says:

    what type of earthquake was it that happend and why?

  38. Molly Roberts says:

    Very good, precise analysis of the situation. One thing that I wanted to ask was if this may be a “Montserrat” in the making? Could there be more than just quaking going on? Could there be a volcanic eruption coming soon for that island? Perhaps the governments involved in the recue of people should be considering evacuations instead? Thank you and continued success in your field.

  39. FC says:

    Thanks; good explanation. The Haitian part of Hispaniola seems to be multiply accretionary and sitting right on top of several jammed subduction zones (the active transform fault on which the earthquake occurred intersecting one of them.) What, if anything, does this suggest about current and future tectonic activity in the region?

  40. Toni says:

    Do you think the North American plate will push back on the Caribbean plate and cause activity on the other side of the plate?

  41. It seems Mann et al. (2008) had predicted that an event of such magnitude might occur.
    Here
    is the link to the abstract of the presentation given at the 18th Caribbean Geological Conference.

  42. Here’s an interactive map of the Caribbean plate

  43. Mike (UK) says:

    Clearest of any of the articles I have seen. Thanks

  44. Leanne Flynn says:

    Awesome explanations! I was wondering if this had anything to do with the earthquake that took place in the Gulf of Mexico a couple of years ago. I didn’t think there were any faults there and this earthquake was felt (mostly) in western FL (Tampa Bay area). Could there be something bigger coming for FL? I’ve always thought that FL was immune to earthquakes, could I be mistaken?

  45. Tito says:

    Is it possible to know when the aftershocks will stop in Haiti and is it possible for Haiti to get hit by a similar quake in the upcoming years?

  46. EKoh says:

    @38 Molly, rest assured this quake is no way related to any volcanism

  47. hanny m says:

    could you explain to me what the red dots mean?

  48. Judy says:

    Thank you for this information. I am in the North of Haiti where we felt the earthquake but not nearly as bad. This is helpful in explaining what happened to many terrified people. I have 2 questions… 1. the red dots on the one map that almost cover Jamaica, is that pressure build up that it is showing or what? 2. What are the chances that the northern fault will rupture soon? I am hearing reports that it could rupture tomorrow or in 100 years… do you have any more details?
    Thank you!

  49. WILLIAM CHE says:

    giving the fact that haiti lies in a risk zone,it should have been one of the priorities of the government to see that good housing standards are in place so as to be prepared for such eventualities.moreover the people have added to these due to the fact that this country has been in very unstable governments for a long time and as such proper planning has not been in place.a magnitude earthquake of 7 and a population of 3 million which has been affected cannot cope with the fact that only a single airport with a single runway is used to mobilise efforts.this is a really worrisome situation and needs to proper strategic planning to rebuilt the country

  50. william che says:

    the number of aftershocks shows that the rate of destruction on the plate was so massive and as such the effects radiated outwards and as such this destruction.also am not sure an erruption can occur in haiti since subsidence might have already occured in a large scale due to this massive quake.however,out mathematization can be ignored by nature.

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