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. Orlando says:

    Some comments on construction, which have been referenced above. Haiti’s primary location puts it in the path of hurricanes which makes earthquake codes very hard to enforce due to the danger of death from wind damage and flooding. The usual construction is concrete and from the photographic evidence it looks like the shaking was severe enough to shatter concrete strucutres with steel reinforcement. As Kobe, Jp proved in a similar sized quake in January 1994, this kind of construction leads to high loss of life.
    Question for the geologists out there. This quake is on the same plate boundary as the Honduran quake (7.5) which occured in Q-1 2009 I believe?
    Second question, I haven’t heard (23 feet?)the amount of stored plate (since last major quake on Enriquillo fault in 1770) movement. Has there been an actual movement calculation posted yet?

  2. awesome artcle on the haiti earth quakes

  3. chris says:

    I am going to montego bay jamaica in february is this a good idea? Im worried about earthquakes, tsunamis, etc.

  4. I think you will be ok down there…there will not be any more earthquakes for a little while. go to Jamaica and have a great time. I wouldnt let the small possibility of a earthquake ruin your vacation. Have fun and drink some rum and listen to bob marley.

  5. Lena says:

    Do you know that your post is being used in conspiracy theory propaganda? (Unfairly, of course)
    http://onlinejournal.com/artman/publish/article_5495.shtml
    …Despite the fact that Rowan sees this as a ‚Äústrike-slip in the Caribbean Plate with the crust on each side of the fault moving horizontally relative to the other side,‚Äù and so on, I still feel that the pinpointing of Haiti is not just another predictable earthquake. But read Chris‚Äôs full explanation. A bolt of HAARP energy could have caused that ‚Äústrike-slip.‚Äù…

  6. Chris Rowan says:

    Wow. I’m “official”. Who knew? Perhaps the government beamed the notion to research and write a post directly into my head.
    I do love the idea of a weapon that can cause hurricanes and earthquakes. Them being so similar and all.
    Thanks for all the other comments/questions. I might write a follow-up post to address the latter.

  7. EJ says:

    As a native Barbadian, and middle school science teacher living in South Carolina, US, I found this site the most helpful in understanding the tectonics underlying the Haitian earthquake. I did not realize that there was a microplate (Gonave) in the northern Caribbean.
    The western edge of the Gonave Plate, a divergent boundary, suggests eastern movement. However, the directional arrow as indicated on the eastern portion of the plate along the Enriquillo Fault, which ruptured, (Tectonic Map of the Northern Caribbean) shows a westerly movement of the microplate.
    Question#1: Is the Gonave microplate a fractured portion of the Caribbean Plate? If so, how was it created?
    Question #2: Which type of movement/interaction occurred to cause the Haiti earthquake. Was it the two plates moving in opposite directions along the lateral fault? Or were they moving in the same direction, but at different rates?
    Thanks for any help in addressing these questions. My students are eager to know!

  8. HAARP says:

    Based on my limited geology experience, the aftershocks should spread around the main shock. To me Haiti situation looks like another HAARP intiative – 200,000 blacks gone. You geologists are really strange – those people working in HAARP will be laughing their butt off. You always have plate tectonics for every disaster where people die in mass…
    Go to youtube and search for Jesse Venturas video on HAARP. You can also get videos on HAARP relation to Haiti. By the way if u dont know Jesse Ventura is the only independent elected by americans – not the bull shit democrats and republicans (both sides of the same coin).
    Chris – i think u are a nerd, like many scientisits. Your simple explanation and animations on google earth appeals for people with some scientific knowledge. But do u realize that there are earthquakes that occur without any “nature” intervention.
    Did u ever heard that about a year ago, a new oil field was discovered in Haiti !!!!!!!!!!!!!!!

  9. Chris Rowan says:

    OK, this is notice that any more comments referencing this HAARP rubbish will be summarily deleted. Put your energy into doing something useful for the Haitians instead. But I can’t let this one slide:
    Based on my limited geology experience, the aftershocks should spread around the main shock
    Oh really? ‘Limited’, indeed.

  10. Chris Rowan says:

    Oh, yes, there are also some excellent questions from EJ to answer:
    Question#1: Is the Gonave microplate a fractured portion of the Caribbean Plate? If so, how was it created?
    That’s a pretty good way of describing it. Because the motion across the plate boundary is distributed across several fault systems, you get fault bounded-slivers that can be treated as independent ‘microplates’ with their own slightly different motion vectors. It’s just an expression of the plate boundary in this region being wider than a single fault.
    Question #2: Which type of movement/interaction occurred to cause the Haiti earthquake?
    Because of the motion being accommodated on the Enriquillo-Plantain Garden (EPG) fault system, the Gonave sliver is moving east relative to the North American plate slightly more slowly than the rest of the Caribbean plate, so there is a net eastward motion of the crust to the south of the EPG zone relative to the crust in the north. This results in left-lateral, of sinistral, strike slip deformation at the fault itself, consistent with the focal mechanism.
    Hope that makes sense to you and your students.

  11. Ivor St Hill says:

    It would seem that at the other end of the Caribbean chain Trinidad is in a similar situation and is stradling the plate boundary just after it turns east/west to run along the Northern regions of South America. There are also several strike/slip faults, El pilar, Cloche, etc. defining this boundary. It would seem that northern Trinidad is sliding past the south of the island. Can we expect “a big one” in Trinidad some time in the future?

  12. patrick says:

    Execcelent work. The quake was predicted in 2008 at 18th Carinean geological conference. But somehow the conference prediction were just filed. Let use science wisely. What is future hold now for Jaimaca?
    Patrick Kamau-Kenya

  13. Michele Madick says:

    I am thinking of going to Jamaica next month, either Montego Bay or Negril, what are the chances of an earthquake occuring there, given the recent one in Haiti>

  14. Jake says:

    Thanks for the post Chris. This is really helpfull because my homework is on how the earthquake in Haiti happened and this is very good.

  15. Shravanee says:

    Thanks for the post Chris. This has really inspired me a lot to study more about seismology and understanding tectonics but it is always good to learn about earthquake and painful to bear the consequences.I pray for the people who have lost there family and house

  16. Andrew says:

    We just started to donate 1$ from each purchase to Haiti quake survivors.
    Thanks to all good people.

  17. dyani says:

    i hear that chicago next to have a earthquake,.

  18. eric luther says:

    how many aftershocks happened in haiti

  19. diana castro says:

    OMG an earthquake will not happen in chicago you people.yaaaaaaa

  20. Walter says:

    Chris:
    Your post is very impressive! What do you think is a risk of an earthquake in Negril Jamaica ?

  21. shazia says:

    excellent work. great answer

  22. shaqwanda eubanks says:

    I would love 2 see happen when the earthquake hit hitis

  23. matete says:

    what a shame thing that happened to Haiti,but i have heared thet people around the world are helping the Haitian people.It’s a good thing that people around the world have hearts..keep up the good work..

  24. Frumusete says:

    thanks, very useful info

  25. joshua says:

    fanks mate, that was very helpful 4 my geograthy homework!!

  26. khuzi says:

    this was just what i wanted for my geography project thanks dude

  27. Missy says:

    I have been in Bon Repos, Haiti for a month now since the quake as humanitarian relief, although supposedly there have been quite a few aftershocks. Early tuesday morning at 126am I felt 2 pops then I heard something like a freight train the 2nd floor of the structure which I am staying in began to shake violently as I heard 4 pops while trying to egress via the outside staircase. 10 minutes later we felt another tremor. We had already felt 3 in Bon Repos Monday morning. It has been quiet for 3 wks, is the plate slipping again? Should we be prepared for a larger quake/aftershock with this new combined activity originating from practically the same epicenter as the 12 January Quake?

  28. douglas randall says:

    haiti might be unlucky last time this happened 20 years later haiti was hit by a bigger earthquake, at the moment this is what worries scientist the fault line didnt break the surface and they recon that next time it will and with bigger shocks,

  29. Missy says:

    Ok. Since Wednesday night February 24 here in Bon Repos, Haiti we have felt a continuous stream of gentle shakes. Most coming every 15 seconds sometimes they are longer and more prominent but not very strong. This has been going on for 3 days since monday and tuesday’s numerous aftershocks. What do they mean?

  30. Excelent work, it it is really educative and the images are good.

  31. claire says:

    This helped me alot for schoo!!! thatnk you!!!!!!!:)

  32. amz says:

    thanks for the information x
    oh hey claire :)

  33. Keely Taylor says:

    Thanks for the information but why did the haiti earthquake kill so many people??? It for school and the rest of the information has helped me a lot, thanks for everything. x :)

  34. kewl says:

    this was for my homework in sience

  35. Harry :) says:

    This website was siccccck :)
    It helped me greatly with my Geography task.
    Thanks baaabe :) xxxxxxx

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