It has been a while since I have drifted from my usual theological and polity discussions into my area of professional work.  Yesterday’s Mw=7.0 earthquake in Haiti has prompted me to now digress to the natural world for this discussion.

I am sure that most of you are aware of the major earthquake on the west end of the island of Hispaniola in the Caribbean.  The epicenter of the earthquake was about 10 miles west of Port-au-Prince, the capital of Haiti which is on the western part of the island.

I should begin by saying that while the occurrence of the earthquake was not a surprise I was a bit surprised by the size.  While magnitude 5 and 6 earthquakes occur regularly around the Caribbean we don’t see magnitude 7 earthquakes that often – this is one of six in the last 10 years around the Caribbean basin.  In this area there was another magnitude 6.5 to 7 earthquake off the northeast side of the island in 2003.  Of these Caribbean earthquakes this one was a bit unique in that it occurred on land and not in the ocean.  And there was a Mw=8 earthquake centered on the east end of the island in 1946.

One of the big questions when an earthquake gets this large is where the fault broke.  Up to magnitude 5 the length of fault that breaks is relatively small so the epicenter does a good job of describing the location of the earthquake.  For larger earthquakes the epicenter is nothing more than the point it starts at and major fault slip can occur some distance away.  In this case the good news, if you want to call it that, is that all the major aftershocks are to the west of the epicenter giving strong evidence that the fault broke to the west away from Port-au-Prince.  So not only was the strongest shaking not in the capital but the energy was directed away from it.  Yes, little consolation considering the scale of the damage that we are seeing.

The presence of this earthquake, and in fact the presence of the island of Hispaniola itself, can be attributed to this area being on a sliver being pushed up on the boundary between the Caribbean and North American plates.  There is a major fault zone just off the north shore of the island and then this one that cuts across and through the south side.

Having knowledge of the tectonic setting of Haiti and the presence of these faults it is not surprising that there is a moderate seismic hazard for the region.  However, don’t let the colors fool you – the highest hazard areas in this region are still an order of magnitude lower than most of the “low hazard” areas here in Southern California.  (And no, I’m not even going to attempt to explain what the numbers mean other than to say that it is related to the probably of experiencing damaging shaking in 50 years.)

There is one more very interesting (at least to me) behavior we see in earthquakes and that is a ten-to-one ratio of number of earthquakes as the magnitude increases.  This holds for the whole world, regions of the world, and aftershock sequences like this one.  So far the numbers are right on as demonstrated by the fact that as of now there are reported 35 earthquakes greater than, or equal to, magnitude 4.5.  If we increase one magnitude point to earthquakes greater than or equal to 5.5 there are four, including the main shock.  The magnitude-frequency ratio is holding.  (For the real geeks and seismologists I come up with a b-value of 1.05 currently but that presumes completeness of the IRIS catalog down to 4.5.)

If you want more maps and technical details on this earthquake you can check out the USGS information page for it.

Let me return to Presbyterianism to conclude.  I know that mission boards are trying to get information and status reports from workers in the country — my brother-in-law has not been able to reach his contacts there yet.  From the reports there is extensive damage to an already weak infrastructure so news may be slow getting out.  There were mission trips from New Jersey and Wisconsin churches in the country and news just appeared that the both groups are safe.  And disaster aid is being collected by PWS&D (PC Canada), PDA (PC(USA)). (I’ll add others as I see them.)  UPDATES: The PC(USA) now has a press release about mission workers, mission teams, and disaster assistance.  There is now an update from the OPC.  The PCA Mission to North America is evaluating the situation and taking contributions.  And there is an announcement that the Canadian Government will match donations to PWS&D. The Cumberland Presbyterian Church has made a donation, and encourages more, through Church World Service.

Finally, a couple of years ago I wrote about a “theology of earthquakes,” if you will.  If you want more on how I fit my professional work into my theological framework check that out.

And keep praying, not just for the devastation in Haiti but in areas all around the world that need help recovering from whatever disasters have struck them.