Haiti earthquake FAQ.

Answers to your questions about the news.
Jan. 13 2010 6:24 PM

Haiti Earthquake FAQ

Do buildings in Haiti have earthquake codes? Why do some quakes cause tsunamis and others don't? And what's a "hospital ship," anyway?

Read more about the Haiti earthquake in Slate.

Destroyed buildings in Port-au-Prince, Haiti. Click image to expand.
Destroyed buildings in Port-au-Prince, Haiti

Tens of thousands of people are thought to have died in the 7.0-magnitude earthquake that hit Haiti Tuesday, destroying much of the capital city of Port-au-Prince. The disaster raises a number of questions.

Are Haitian buildings designed to resist earthquakes?
No, for the most part. Haiti has no national building codes. Some construction companies (especially those working with relatively generous budgets) do voluntarily follow codes like the French or Canadian standards or the International Building Code.

Even when developing countries have codes in place to make sure buildings can withstand strong winds or earthquakes, they're rarely enforced, and construction companies end up cutting corners to save money. (The added cost of earthquake-proofing a building is usually around 4 percent.) After a quake hit Mexico City in 1985, for example, investigators discovered that some of the buildings that were destroyed had too much sand mixed in with the concrete, making them weaker. *

What's safer, big buildings in the city or ramshackle houses outside?
That depends entirely on the construction. Big-city buildings with steel-reinforced columns and strong joints are sturdier than slapdash country houses made of stacked concrete blocks. (Adobe huts, more common in earthquake-prone areas of Southeast Asia, are especially dangerous, since they not only crush the inhabitants but suffocate them as well.) But a rural house made of a wood frame with sheet metal nailed to the outside is going to be a lot safer than a giant office building without proper reinforcement. In other words, the height and location of a building matter less than how well it's built.

The Dominican Republic seems to have emerged relatively unscathed. How come?
Because its population centers are so far east. Santo Domingo, the Dominican Republic's capital and its largest city, is about 150 miles east of Port-au-Prince, while the earthquake was centered about 10 miles west of the Haitian capital. Naturally, the effects of a quake get weaker the further one gets from the center.

Advertisement

This map shows how strong the vibrations were in different areas of the island during the initial quake. Shaking intensity is measured both by the speed of the Earth's movement, or "peak ground velocity," and by a subjective measurement called the Modified Mercalli Intensity Scale, based on how the tremor "feels." In Port-au-Prince, the quake rated an "X," meaning the shaking was "violent" or "extreme." In Santo Domingo, by contrast, the quake rated a "III," meaning the vibrations felt "similar to the passing of a truck."

Why do some island earthquakes create tsunamis while others do not?
Because of where and how they happen. If an earthquake occurs underneath the ocean floor, such that the earth's plates shift vertically, the movement from one plate sliding up and another sliding down causes a rush of water that can turn into a tidal wave. The earthquake in Haiti, by contrast, was both underneath the land—about 10 miles west of Port-au-Prince—and horizontally shifting. So there was a lot of shaking ground but no tsunami.

Geologists have issued warnings about the likelihood of deadly aftershocks. How do they gauge the risk of follow-up tremors?
There's a formula. As Jacob Leibenluft explained in 2008:

There are two principles that describe the typical behavior of aftershocks. The first, called Omori's Law, predicts that most shocks will occur immediately following the earthquake and become less and less frequent over time. The other, known as Båth's Law, states that the largest aftershock is, on average, about 1.2 magnitudes smaller than the main quake. (The Richter scale is logarithmic, meaning that an earthquake measuring magnitude 6.0 is 10 times larger than one measuring 5.0.)

While a stronger earthquake produces more aftershocks than a weaker one, big aftershocks are rarer than small ones—again, by a factor of 10 per order of magnitude. For example, a 4.0 magnitude aftershock in Haiti on any given day is 10 times less likely than an aftershock of 3.0 magnitude. *

Experts predict that the aftershocks from the Haiti quake could last another week or so. You can monitor the aftershocks and their magnitudes here.

A Navy hospital ship, the USNS Comfort, is standing by in Baltimore for a possible trip to Haiti. What's a hospital ship?
A ship that's converted into a hospital, of course. The Comfort has all the facilities of a top-of-the-line hospital on land: 1,000 beds, 12 operating rooms, radiological services, a medical lab, a pharmacy, an intensive care ward, dental services, and a morgue. It's also got a staff of more than 1,400.

Most hospital ships are maintained by the military for use in war zones. But their secondary mission is to support disaster relief in the United States and worldwide. It's a war crime to fire on a hospital ship, according to the Hague Convention of 1907. The same treaty says that hospital ships must be clearly marked, must avoid interfering with war ships, and must help wounded people no matter what country they're from.

Got a question about today's news? Ask the Explainer.

Explainer thanks John Ebel of Boston College and Brian Tucker of GeoHazards International.

Correction, Jan. 15, 2010: This article originally implied that any amount of sand weakens concrete. Sand is an ingredient of concrete. Too much sand, however, weakens it. (Return to the corrected sentence.)

Correction, Jan. 19, 2010: This article stated incorrectly that larger earthquakes produce fewer aftershocks than smaller ones. ( Return to the corrected paragraph.)

Christopher Beam is a writer living in Beijing.

TODAY IN SLATE

Culturebox

The End of Pregnancy

And the inevitable rise of the artificial womb.

Doctor Tests Positive for Ebola in New York City

How a Company You’ve Never Heard of Took Control of the Entire Porn Industry

The Hot New Strategy for Desperate Democrats

Blame China for everything.

The Questions That Michael Brown’s Autopsies Can’t Answer

Foreigners

Kiev Used to Be an Easygoing Place

Now it’s descending into madness.

Technology

Don’t Just Sit There

How to be more productive during your commute.

There Has Never Been a Comic Book Character Like John Constantine

Which Came First, the Word Chicken or the Word Egg?

  News & Politics
The Slate Quiz
Oct. 24 2014 12:10 AM Play the Slate News Quiz With Jeopardy! superchampion Ken Jennings.
  Business
Moneybox
Oct. 23 2014 5:53 PM Amazon Investors Suddenly Bearish on Losing Money
  Life
Outward
Oct. 23 2014 5:08 PM Why Is an Obscure 1968 Documentary in the Opening Credits of Transparent?
  Double X
The XX Factor
Oct. 24 2014 8:19 AM Online Misogyny Levels Up as Gamergate Targets Gawker
  Slate Plus
Working
Oct. 23 2014 11:28 AM Slate’s Working Podcast: Episode 2 Transcript Read what David Plotz asked Dr. Meri Kolbrener about her workday.
  Arts
Brow Beat
Oct. 23 2014 6:55 PM A Goodfellas Actor Sued The Simpsons for Stealing His Likeness. Does He Have a Case?
  Technology
Technology
Oct. 23 2014 11:47 PM Don’t Just Sit There How to be more productive during your commute.
  Health & Science
Bad Astronomy
Oct. 24 2014 7:00 AM Gallery: The Partial Solar Eclipse of October 2014
  Sports
Sports Nut
Oct. 20 2014 5:09 PM Keepaway, on Three. Ready—Break! On his record-breaking touchdown pass, Peyton Manning couldn’t even leave the celebration to chance.