A 7.0 magnitude earthquake struck Port-au-Prince yesterday around 5 p.m. local time (Haiti earthquake feared to have killed many, Fierce Quake Devastates Haitian Capital, Quake hits Haiti; reports of `catastrophe of major proportions' emerging). The quake was foreseen at least as long ago as 2008, but Haiti was too poor to prepare (Possibilty of Earthquake in Port-au-Prince?). There have been more than a dozen aftershocks, some of substantial magnitude (Latest Earthquakes in the World - Past 7 days, Historic World Earthquakes - Magnitude 6.0 and Greater). As a rule of thumb, the energy of a 4.0 magnitude quake is comparable with the energy of 1 kiloton of TNT (Moment magnitude scale). Rough math indicates this quake had energy equivalent to 29,791 kilotons of TNT. That would be a 29 megaton bomb. As I write this, current time in Port-au-Prince is a little after 3:30 am Wednesday (EST). Sunrise is at 6:24 AM EST (Port-Au-Prince, Haiti - Weather Conditions). I expect the images of devastation will be horrific. Sadly, I think that Haiti will be lucky if the death toll is less than 100,000. Donations to the relief effort can be made through UNICEF, the Red Cross and other organizations. My thoughts are with Haiti tonight.

Just look at the before and after pictures of the National Palace. The force of the quake was tremendous to have done that much damage. Various news sources have mentioned collapsed hospitals as well. Hopefully international aid comes soon since it sounds like they're in no shape to provide aid themselves.

After further review of methods for comparing the energy released by an earthquake with the energy released in a nuclear explosion, the 29 megaton figure cited above lacks a seismic efficiency factor. If a factor of 0.5% is used, the result is 158 kilotons for the initial tremor.

Here's a quick table relating magnitude to raw energy and with 0.5% seismic efficiency factored in.

4 | 1 kiloton * sqrt(1000) ^ 0 |     1 kiloton  |   5 ton5 | 1 kiloton * sqrt(1000) ^ 1 |  31.6 kiloton  | 158 ton6 | 1 kiloton * sqrt(1000) ^ 2 |  1000 kiloton  |   5 kiloton7 | 1 kiloton * sqrt(1000) ^ 3 | 31622 kiloton  | 158 kiloton

The USGS link of current earthquakes records 13 after shocks of magnitude 5 or greater. The largest of these were magnitude 5.9, 5.7 and 5.5.

Thoughts and prayers go out to all of those impacted. Terrible stuff.

The forces of nature are too overwhelming.

My girlfriend's parents were actually on vacation in the Virgin Islands this week, so it's scary to think just how close they were to the quake... I mean, what if they had chosen a location slightly further west? [sad]

I realize this may be a vague question but I'll ask anyway: what magnitude earthquake can you generally feel? I noticed on the Latest Earthquakes link that Haiti had a LOT of aftershocks, all of them above 4.0 (many above 5.0). Living in California, I've been through a few earthquakes but I don't remember ever experiencing so many aftershocks. Why the difference?

Edit: Ah. Found something on the wiki. Seems you can start feeling quakes in the 3s and 4s do minor damage. Still curious about my last question though.

Quote: Original post by GameCreator
I realize this may be a vague question but I'll ask anyway: what magnitude earthquake can you generally feel? I noticed on the Latest Earthquakes link that Haiti had a LOT of aftershocks, all of them above 4.0 (many above 5.0). Living in California, I've been through a few earthquakes but I don't remember ever experiencing so many aftershocks. Why the difference?

It depends on lots of factors. Obviously the distance from the epicenter is important. The depth of the quake is important. There are different types of waves (P-waves, L-waves, and S-waves?) that Google can tell you about. Some waves are mostly harmless wiggles, other waves are massively destructive up-and-down waves that pull the foundations out of buildings.

People can feel 2.0 on the Richter scale if they are very close to it. I've felt several 2.x and 3.x quakes in my life, and also seen the window blinds shake and heard the small rattle from them.

To further refine my earlier comments regarding the energy comparisons. The USGS has published a similar table here: Q: How much energy is released in an earthquake?

Magnitude	Es (from Me)	Es (from Ms or Mw)	Tons of TNT 	Nuclear Bomb Equivalence (# of bombs)4	        0.22E+11	0.63E+11	15.	        0.005	        0.71E+12	0.20E+13	475.	        0.026	        0.22E+14	0.63E+14	15023.	        0.797	        0.71E+15	0.20E+16	475063.	        25.08	        0.22E+17 	0.63E+17	15022833.	790.69	        0.71E+18	0.20E+19 	475063712. 	25,003.3

It appears that 0.5% efficiency is too low. The USGS appears to have used 1.5%.

@GameCreator, this might answer your question: Q: At what magnitude does damage begin to occur in an earthquake? A: It isn't that simple. There is not one magnitude above which damage will occur. It also depends on other variables, such as the distance from the earthquake, what type of soil you are on, etc. That being said, damage does not usually occur until the earthquake magnitude reaches somewhere above 4 or 5.

Not to downplay the disaster in any way but I think it's really cool how the international community is coming together on this one. There's nothing to be gained by helping Haiti and yet the US is sending a bunch of military/medical aid, other countries are already donating large amounts of money and people, and even the Dominicans (with plenty of problems of their own) are reaching out a hand.

We are in a unique time in history where the entire world is ready to lend a hand to a country at need and I think it's really awesome. I also hope that this tragedy brings some much needed attention to the area. $20 a month can support a child 100% with clothing, food, medicine, and education.