Monday, September 03, 2012

Can crocodiles predict earthquakes?

Things have been a little quiet on the Croc Blog of late, so to shake things up here's a curious news item from the Philippines. Apparently seconds before the strong magnitude 7.7 earthquake tremor in East Samar recently, Lolong reacted violently while resting in his enclosure. The news agency suggests that Lolong was able to predict the earthquake, although with seconds to spare I doubt he'll be making that role official. But what's going on? Can crocodiles really predict earthquakes?

Well there is a more reasonable explanation. Lolong was simply responding to low frequency vibrations transmitted through the ground immediately prior to the earthquake. These are termed P waves, or compressional waves, and it's often difficult for humans to detect these. Crocodiles, however, are experts at detecting changes in pressure and vibrations, so it's very likely that Lolong was feeling the P waves produced at the beginning of the tremor. S waves, or shear waves, tend to follow P waves and are the ones that do the damage, and the ones that we are most aware of.

Why did Lolong react to the P waves? We know that crocodiles are highly sensitive to pressure waves, senses that are used not only to detect potential prey but also for social communication. Thunder and vibrations transmitted through the ground frequently trigger a territorial response from large male crocodiles (and a fear, distress response from small, subordinate crocodiles), and an earthquake's P wave would only heighten that response. There wouldn't be many crocodiles capable of giving Lolong a serious territorial challenge, but the P wave of an impending earthquake would very likely feel like one.

Did giant croc 'Lolong' predict 7.6 quake? | ABS-CBN News

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