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Science Notes / Geology, biology

Big quakes don't trigger other tremors far away

Here's some good news in the wake of Japan's disaster: A new study says big earthquakes don't set off other dangerous ones around the globe. Big quakes do trigger local aftershocks, but researchers found no sign of setting off moderate-sized events beyond about 600 miles away.

That won't surprise most experts, said lead study author Tom Parsons. But it's different from his prior research, which did find a global effect for setting off small quakes, said Parsons, of the U.S. Geological Survey in Menlo Park, Calif.

Parsons and Aaron Velasco of the University of Texas at El Paso reported the work online in the journal Nature Geoscience.

They looked at worldwide earthquake records for the 30 years ending in 2009. There were 205 big earthquakes, with a magnitude of seven or more, and 25,222 moderate ones with magnitudes between five and seven. The researchers did find an increase in moderate quakes, but only within about 600 miles of the initial event, and nearly all within 375 miles. At distances beyond 600 miles, the number of moderate quakes after a big event was no higher than normal.

-- Associated Press

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Space travel threatens reproductive organs

Ever dream about a honeymoon in space? You may want to think twice after you hear about Joe Tash's research.

The near-zero gravity of Earth's orbit may do serious harm to the male and female reproductive systems, the University of Kansas Medical Center biologist has discovered. Sperm counts drop. Egg-producing ovary cells waste away. At least that's been the case among the laboratory and space-traveling rodents that Tash has studied.

What prolonged exposure to microgravity does to an astronaut's fertility remains a big unknown. But Tash's hypothesis isn't reassuring: Long-term spaceflight renders people "reproductively compromised."

Scientists know plenty about how weightlessness impairs healing, weakens the immune system and causes muscles to atrophy and bones to lose calcium. His research suggests the reproductive system is at serious risk.

Tash studied the effects of weightlessness on earthbound male rats by using a harness to keep their hind legs elevated above the cage floor for six weeks, a duration more like the time astronauts spend on the International Space Station. His results were dramatic: The rats' testes shrank and their sperm counts dropped so low the rats were infertile. Tash's experiment with female mice that flew on the space shuttle Discovery showed effects that were equally devastating. "Fifteen days of spaceflight shuts down the ovaries," he said.

-- McClatchy Newspapers