September 6, 2012

Large quake rolls through Costa Rica

Posted by Austin Elliott


Yesterday morning a hefty M7.6 temblor emanated from the subduction zone beneath Costa Rica, setting buildings swaying, pools sloshing, and people scrambling from Panama to Guatemala.

The death toll stands at two, which is remarkable for a quake of this size that didn’t even hit offshore. This may be due to its moderate depth (40km) and relatively remote epicenter, but there were plenty of people that were rocked hard.

Costa Rica apparently has a rather video-savvy populace because there are already a bunch of videos of the quake hitting, and as usual, I’ve compiled them here for you.

First, we can start with IRIS’s always fascinating animation of seismometer data from the U.S. as the seismic waves from this relatively nearby quake ripple northward across the continent:

 

Seismic waves ripple across the U.S. in this display of actual seismometer data from the Incorporated Research Institutions for Seismology, September 5, 2012

Now let’s get to the video footage. First of all there’s the video that’s been replayed by many news organizations that shows some pretty incomprehensible footage from a flailing camera atop a building. meh.

In a more interesting video that really shows the power of the quake, a garage full of vehicles bounces around in a small town outside of the capitol, ~80 miles from the epicenter. In this video you can really see changes in the direction of motion as differently “polarized” surface waves ripple through. I also find it remarkable to note how much time passes before the really strong shaking begins, perhaps lulling people into a false sense of complacency.

There are other videos of bouncing cars, but none as dramatic as that bus. A couple of security cam videos show heavy shaking of people and goods as the quake hits businesses around the country.

Another video shows lampposts swaying as a (fairly gratuitous?) siren sounds the alarm. Perhaps this is a coastal town and the siren is issuing the initial tsunami warning… otherwise I’m personally a little perplexed by the need for sirens to alert people to an earthquake in progress…

The quake elicits a variety of reactions from clerks and customers at a convenience store, who sprint or saunter out of the store depending upon mood. It looks hot there.

A surprised ex-pat marvels at the power that throws her pool water around, even though she herself felt nothing. This should be familiar to the southern Californians who experienced the 2010 Easter Sunday quake at a substantial distance.

Then there’s the aftermath. In one case a local demonstrates the exact wrong thing to do, showing up at the beach to film a potential tsunami, that he soon learns is not coming. Instead he captures shore-parallel fractures in the sand from gravitational failure during the shaking.

The final video is like a natural advertisement for the quake-preparedness bullet points we advocate in the U.S. The house has suffered minor to moderate structural damage, but it’s intact and habitable. However its contents are a wreck. Broken utility lines, shattered glass everywhere, expensive goods thrown to the floor, doors blocked by fallen furniture, and aftershocks startling you while you survey the damage: it’s exactly the scenario described when we warn people how to prepare for the aftermath of a big quake. Let me leave you with this illustrative lesson: