Friday Afternoon: Deep Creep, and Science from the Rest of the World

As AGU winds down, an earthquake swarm and a stroll through the posters

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Radar detects changes in Earth's surface
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Radar imagery identifies changes in the height of the Earth's surface before and after a swarm of earthquakes in September. Many of the differences are from changing surface and ground water levels. (photo by Hugh Powell)

A view of the International Space Station from an inflatable planetarium
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Inside the inflatable planetarium, I look at Hawaii from the International Space Station. (photo by Hugh Powell)

Scientists exit the inflatable planetarium
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Inside the inflatable planetarium, I discovered more than a few eminent geophysicists watching the show.
(photo by Hugh Powell)

The final tally was 11,903 people attending the conference, and most of them were still going strong Friday morning. Next week, they will be back in their labs, grinding up rocks or designing new computer models, and drinking coffee with their usual office mates. But for now there’s still one more afternoon of 15-minute research talks, poster session madness, and rubbing shoulders with thousands of colleagues. I rubbed shoulders with Rowena Lohman, who told me about earthquake swarms.

Strangely enough, the story's setting was a September meeting of earthquake scientists in Palm Springs, California. Lohman's colleague Jeff McGuire was briefly alarmed by a swarm of small earthquakes about 12 miles away. When nothing serious followed, he and Lohman analyzed what had happened using radar imagery of the landscape (see photo). They discovered that the Earth’s surface had shifted as much as 12 cm (4 inches) during the month-long swarm of 1,000 quakes. That’s enough movement to have caused a magnitude 6 earthquake, but Lohman’s calculations suggested the whole swarm combined only added up to about a third as much energy.

Lohman, McGuire and their colleagues think the earth sometimes moves smoothly, without setting off earthquakes, in a phenomenon known as “deep creep.” Creeping movement is a comforting prospect for residents of earthquake zones because it dissipates stress peacefully. Even some notoriously violent faults can enter calm periods, despite continued movement at the fault, Lohman said. Studying swarms of small earthquakes like the ones near Palm Springs may help identify when a fault is likely to creep instead of quake.

Penguins, Pterosaurs on a Stroll through the Posters

I’ve been kept busy all week learning about WHOI research, but I set aside part of Thursday afternoon to prowl through the rest of the poster sessions. Here are a few posters I was glad I hadn’t missed:

BYOP: Bring Your Own Planetarium: Pat Reiff of Rice University has designed an inflatable planetarium that fits in a suitcase. It can hold up to 30 students at a time while it plays 20-minute planetarium shows. (Laser lights not included.)

Poop of the Penguins: Penguins eat lots of tiny, shrimp-like krill, which means that penguin poop (guano) contains lots of krill shells - along with special bacteria that digest the shells. Chinese scientists analyzed the bacterial genes found in mounds of accumulated guano and found they could estimate the colony size all the way back to the Dark Ages.

High-Powered Pterosaurs: Massive pterosaurs like Quetzalcoatlus flew over the prehistoric earth on 36-foot wingspans. Flapping those massive sails would have taken more energy than you’d expect from a cold-blooded lizard. A Duke University team used models of modern birds’ energy output to suggest that pterosaurs must have been warm-blooded to generate enough energy to fly.

The Telltale Teeth of Wanderers: Is there no limit to what geochemists can learn from isotope ratios? A Mexican team used strontium isotopes in teeth and bones to identify immigrants in the Aztec ruin Teotihuacan. Teeth record a strontium signature characteristic of where they were formed, during early childhood. The scientists compared that to strontium in bones, which reflect where the people lived during their last decade or so.


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Last updated February 15, 2006
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