I'm going to walk you through my chain of thinking while I was researching this question, not because it's brilliant, but because you'll see how I thought about it, and pick up what works and what doesn't.
Start: I began with the obvious query, [ Haiti earthquake duration ] -- I also tried [ how long was the Haiti earthquake ] -- but neither of these gave me great results. I was a bit surprised by this as I'd figured it would be a pretty simple thing.
So I started checking out the USGS.gov site because I knew that they have detailed records of earthquakes. My next query was [ Haiti earthquake site:USGS.GOV ]
And that's when I realized that this wasn't going to be simple. I looked at a bunch of pages at USGS and quickly learned about fitting models to earthquakes, tensors for representing earthquakes and a bunch of very technical abbreviations for things that I had to keep looking up.
For example: the quake occurred on the EPGFZ. (That's the Enriquillo-Plaintain Garden fault zone for us non-seismologists.) I had to learn that acronym in order to figure out what I was reading. I also picked up that the quake was considered a shallow quake--but it was around 13km deep. That's shallow? Clearly, I have a lot to learn about earthquakes (and I've lived through a bunch of big quakes).
I also found great summaries of the quake and the events on the EPGFZ from USGS (see: http://earthquake.usgs.gov/earthquakes/eqarchives/poster/2010/20100112.pdf for a nice summary chart about the geophysics of the earthquake)
But I wasn't getting an answer to the duration!
One strategy to use in questions like this is to try and get the original data for yourself. I know that seismographs record earthquake data, so I thought I might be able to get the raw data from a sesmiograph. Hence, my next query: [ Haiti earthquake seismograph ]
This also didn't work too well. When I looked through the results, I found lots of seismographs, but no charts or real data I could inspect.
Hmmmm... Where were the earthquake charts I'd been expecting?
As I read one description of a seismograph that had recorded the quake, I saw the word "seismogram" and realized what a mistake I'd been making. A "seismograph" is the device that records quakes, a "seismogram" is the RECORDING of the quake.
So my query searching for a seismograph was looking for the instrument, not the data!
New query: [ Haiti earthquake seismogram ] -- and I started finding the charts I was expecting. Boston College (http://bcespquakes.wordpress.com/2010/01/12/351/) has a nice chart, but not a lot of time details.
A few results down is the REV (Rapid Earthquake Viewer) site run by the University of South Carolina Sesmiology Department. Now I was getting somewhere!
It was pretty quick to navigate their site and drill down to the Haiti earthquake of Jan 12, 2001. (Yeah, one of the skills of a good searcher is being able to figure out what deep web information a given site has and use their controls to get to what you really want).
In a couple of clicks I got to a nice compilation of seismograms from the Univ. South Carolina REV site: http://rev.seis.sc.edu/earthquakes/?eq_dbid=3286658
It's easy to see that the farther you get away from Haiti, the earthquake shock gets spread as the pressure waves propagate through the earth. Ideally, to see the duration of actual on-the-ground-shaking you'd like to see the sesimogram from nearby. In this chart you can see they list eleven charts from nearby (the Domincan Republic) and far away (Christmas Island).
If you look at just the seismogram below, you can see that the intense shaking is for around 10 seconds.
On the other hand...if you look at this next chart, you can see that the main shocks are for about 10 seconds, but then the ground keeps shaking at a lower level for quite some time. I added the red dotted lines below to estimate the "normal background" shaking.
So the question now has been transformed: How do you define the end of earthquake shaking?
Uh oh. No WONDER people don't talk about the duration of the earthquake. There are many factors that influence how long you feel the earth shaking. Blog commenter Robin found this great FAQ from USGS that explains all of these different factors in great detail.
Then, to make matters worse, I also found this chart on Wikipedia:
This chart on Wikipedia from Bezur shows the incidence of fairly large aftershocks for quite some time immediately after the first earthquake. This just makes the point even clearer--when do you say "the earth stopped moving"?
Search Lessons: As I said above, there are multiple lessons to learn from this challenge.
(1) Don't get discouraged by all of the arcane and confusing terminology you might find on the way. Embrace it! Revel in it! Realize that as you learn arcane and hyper-specific terms, you're also learning how to find future items in this domain with great precision. For example, I now know about the EPGFZ and the difference between a seismograph and a seismogram. Next time I do an earthquake search, I'm going to be a little faster.
This leads to my first Law of Search: When searching, expect to learn a lot about the domain of interest. You need to become an instant expert on the topic you're searching.
(2) Be certain of your search terminology. I got hung up on the "seismograph" vs. "seismogram" difference and wasted a bunch of time looking for the wrong thing. This happens to everyone. The trick is to not let it stop you. Pay attention to the clues in what you're reading and learn to follow the information scents you pick up along the way. (I would have SWORN that I was looking for a seismograph chart. Wrong.)
(3) Learn to use the site's own features and tools. Many sites (particularly technical ones like these) have lots of tools for drilling down into their data. The search engines can't see into the underlying data, so it's up to you, the searcher, to use the tools they give you to "search within" the site.
(4) Expect your problem to shift as you learn more. I learned that "duration" is a slippery concept for earthquakes, and I changed my search goal to one of understanding what makes such a simple idea (earthquake duration) so difficult to define.
But, for Scott, the answer is "around 10 seconds for the initial earthquake." He's in the 4th grade, so that's a good answer for him.
Next year we'll talk about aftershocks and differential pressure wave conductance velocities....