When a Magnitude 6.9 Earthquake is an Aftershock....

There wasn't a whole lot of information when I wrote about the 8.8 earthquake in Chile in the earliest hours of the morning. Information is starting to flood in now from many sources, and my first impression is media coverage is a bit better than it was for the Haiti quake and other earlier events. When I say "better", I don't mean more cameras, I mean evidence of an effort by the reporters to educate themselves about the basic science of earthquakes.

My first thought is for the people who have been affected, both in Chile and across the Pacific basin. A quake this big is going to have huge impacts. The aftershocks are going to be an issue: my USGS notifications are set for any quakes bigger than 5.5 and there have been 11 of them so far, with the largest at 6.9. For perspective, 6.9 is the size of the Loma Prieta earthquake here in California from 1989. It killed 4 dozen people and did around $10 billion in damage. The quake in Haiti was a somewhat larger 7.0. Aftershocks are going to continue for a long time, over a region about 600 miles long (the size of the fault zone that shifted in this quake).

The tsunami is a huge threat. The size of a tsunami in any particular place is dependent on many factors, including the size of the earthquake (which was colossal), how the quake transferred energy to the ocean water (unknown to me at this point), and the shape and depth of the coastline where the tsunami strikes. All I can say to my Pacific Basin friends is that when the Civil Defense folks set off the sirens, take it seriously! Hawaii in particular has a tragic history with tsunamis, and there has been a vast amount of coastal development since the last major tsunami (in 1960, also caused by an earthquake in Chile). There will be a big problem of people wandering down to the beach to watch the tsunami, which can only be described as an act of idiocy. Get to higher ground or higher floors. If the warnings are inaccurate, you've only lost a bit of time, but if they are accurate, your life will be saved. Don't go to the coast until the "all clear" is given, because there will be more than one surge of water. You can't swim your way out of a tsunami; they are one of the most dangerous of geologic events, as the Indonesian tsunami of 2004 demonstrated.

Big Quake in Chile - Upgraded magnitude 8.8

A huge earthquake has struck offshore of Maule, Chile. Initially reported at magnitude 8.3, the quake has been upgraded to 8.8, making it the sixth largest quake recorded in the world since 1900 (if the revision stands). A tsunami warning has been issued, but there are no reports out of the region yet whether it has materialized. Power outages have been reported in Santiago, but no other reports of damage yet. Needless to say, such a quake is capable of doing grevious damage (the energy of this quake is hundreds of times more than the 7.0 quake that hit Haiti six weeks ago).

The top ten most powerful quakes since 1900 (courtesy of the US Geological Survey)

1. Chile 1960 9.5
2. Prince William Sound, Alaska 1964 9.2

3. Off the West Coast of Northern Sumatra 2004 9.1
4. Kamchatka 1952 9.0

5. Off the Coast of Ecuador 1906 8.8

6. Rat Islands, Alaska 1965 8.7
7. Northern Sumatra, Indonesia 2005 8.6

8. Assam - Tibet 1950 8.6
9. Andreanof Islands, Alaska 1957 8.6
10. Southern Sumatra, Indonesia 2007 8.5
11. Banda Sea, Indonesia 1938 8.5
12. Kamchatka 1923 8.5
13. Chile-Argentina Border 1922 8.5
14. Kuril Islands 1963 8.5