Measuring Earthquakes

This last quake was 7.2 by Japanese standards and 6.7 according to the scientists here in Taiwan. What gives? The Taipei Times continued to not answer this question this morning, and Will at the Early Bird Diner really wants to know.

I found out a few things, but nothing that resembles a complete answer to the question What's the root cause of this discrepancy?

First off, the Richter Scale was rendered obsolete in 1979 when Tom Hanks (the seismologist, I presume) and Hiroo Kanamori came up with the Moment Magnitude Scale.

Here's a short explanation from the USGS:

Q: What is moment magnitude?
A: Moment is a physical quantity proportional to the slip on the fault times the area of the fault surface that slips; it is related to the total energy released in the EQ. The moment can be estimated from seismograms (and also from geodetic measurements). The moment is then converted into a number similar to other earthquake magnitudes by a standard formula. The results is called the moment magnitude. The moment magnitude provides an estimate of earthquake size that is valid over the complete range of magnitudes, a characteristic that was lacking in other magnitude scales.

I may be missing something, but the Taiwan Weather Bureau is listing the quake as ML6.7, this is Local Magnitude, which according to Wikipedia is the same as the Richter Scale. It looks like the boys in Denver are using the moment magnitude calculations. So, "MagnitudeX" and "Y on the Richter Scale" are meant to be close, which now counts in horse-shoes, hand-grenades, nuclear war, and now, earthquakes.

The USGS also has an interesting summary of the quake.

We're All Ok

The earthquakes affected the southern part of the island. There is footage on TVBS of a collapsed building in Pingtong, apparently there's a little boy trapped inside. There are gas leaks and a rather large fire. There is a graphic at the top right of the screen that says "Live," however I've just seen the same fireman throw the same piece of debris onto the same pile three times. I have less and less faith in the local media. Well, I guess the talking heads are live.

In Taichung, some three hours to the north by car, we felt three quakes. I was in an office on the second floor for the first one, and we were all spooked by the rattling of the windows up and down the hall. I called Maggie immediately after the shaking stopped. She had been feeding Gretchen on the sixth floor at the PNCC and I could hear the other mothers in the room making their "Oh goodness that makes me nervous" noises. I felt the next quake in the car at the corner of Wenshin Rd and WuChuan Rd. To feel an earthquake in a car at ground level is quite an experience. The car did not go up on two wheels, but I could feel shock waves passing underneath me.

I have a flashlight ready to go in Franklin's backpack just in case. There was a third shock about three minutes before I started this post. It was more of a gentle shake that barely had any impact on the beaded curtains.

Coming two years after the Big One that set off the Asian Tsunami, I know a lot of folks must have been mighty nervous. Leica and Frankie are sound asleep.

Gretchen weighs 3766 grams (that's 3.76 kg for those keeping score) and is the favorite of all the nurses in the nursery. I've been keeping my distance as Franklin and I have been battling colds. More pictures before her first birthday, I promise.

More quake news here, and here.

Also, anyone know why there would be such a great discrepancy between the Richter reading from Taiwan and the one from the friendly folks at the USGS? I'm sure the cynical answer that the Taiwanese computer is not set up properly would not be the most accurate, but what gives? It seems to me that the USGS reading is usually quite a bit higher. The Taiwan News this morning acknowledged the difference by saying that no explanation was given for the wide variance. How bout it?