Friday, April 13, 2007

Six Pointer (No not a hound with six ears...)

Last night, Alice and I heard at the beginning of the 11PM television news a "breaking news" item about a big earthquake in Mexico. The talking head said "....Mexico City.... power outages....six points on the Richter scale...." A few minutes later the news said epicenter was near Acapulco, a 6.1, and Alice knew it was bad, but not ohmigod bad.

Alice remembered instantly the 8.0 1985 earthquake in Mexico. Thousands died in Mexico City. Pika's people had family there who felt it but were all lucky to be in safe places during the quake. Randy, the family dog, was also safe. None were in buildings on the old lakebeds subject to dire liquifaction but in areas with solid basalt under them or in seismically safe buildings. A really wierd thing - many 8 and 18 story buildings had very bad damage. Scientists think that was due to the harmonics of that particular quake. Randy knew about the quake before the people felt it. If only people could talk to us!

Pika's people felt the one last night. One said the whole house creaked and shook. Alice had a look at the Shake Map from the USGS. The quake has a name at the USCG: 2007bcan. Mexican authorities call it a 6.3 and Atoyac de Alvarez, Guerrero.

People felt it as far away as Guadalahara. So far 357 people in Mexico City have reported to USGS what they felt. Anyone who feels an earthquake can tell the USGS how strongly they felt it. It's very important for scientists to have such info since not all the maps and sensors can tell what people connected to the Internet can. For example, lots of people think the 1906 San Francisco quake was worst in San Francisco. Not really. Santa Rosa was hit the hardest in that one thanks to where the San Andreas fault really is. But San Francisco got most of the disaster response help. Not Santa Rosa. Often new faults are detected only by people reporting unusual shaking.

Alice once felt a strong earthquake. The 7.1 Hector Mines quake in 1999. She was in a modern highrise hotel in Ontario, California. Shaken awake right after 2:30 AM. Very clearly felt the P and S waves arrive. Knew from the long lag between the wave types the epicenter was not very close by. Got out of bed to listen to how well the building was handling the quake. Thought if it got worse she'd have to take shelter in the tub or consider leaving the building, but then the rattling mirrored closet doors suggested she go back to the center of her room and think about the spot between the beds. But then the shaking stopped. She knew instantly from the first few jolts of the P, or compression, waves the direction from which the quake came and that there would be aftershocks because it was so strong. Clicked on the TV for CNN. Breaking News. A map with an epicenter was exactly along the line where Alice predicted. Amtrack's Southwest Chief train was derailed close to the epicenter. That was one of the few times her college degree in geophysics paid off. Clicked off the TV after five minutes and just let the aftershocks rock her back to sleep.