Monday, November 01, 2004

Shake it up Baby!

A few weeks ago, there was an earthquake centered about 20 miles from my house. Some folks back home got worried and wanted to check up on me. I explained to them that it wasn't even a 2.0 on the Richter scale. I didn't even know about it until they told me. For those not familiar with the Richter scale, it measures magnitude of seismic activity. It's a logarithmic scale, which means that each step up is exponentially larger than the previous step. The scale looks something like this...

This table comes right from the wikipedia entry.

DescriptorRichter MagnitudesEarthquake EffectsAverage Annually
MicroLess than 2.0Microearthquakes, not felt.About 8,000 per day
Very minor2.0-2.9Generally not felt, but recorded.About 1,000 per day
Minor3.0-3.9Often felt, but rarely causes damage.49,000 (estimated)
Light4.0-4.9Noticeable shaking of indoor items, rattling noises. Significant damage unlikely.6,200 (estimated)
Moderate5.0-5.9Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings.800
Strong6.0-6.9Can be destructive in areas up to about 100 miles across in populated areas.120
Major7.0-7.9Can cause serious damage over larger areas.18
Great8.0 or greaterCan cause serious damage in areas several hundred miles across.1

So, as you can see, a 2.0 is not significant. They happen all the time and are not cause for alarm. Another earthquake measurement scale is the Mercalli scale. This is not a seismic scale. It's a bit more judgement oriented and involves assessment based on the perceived effects of the quake.

(I) - Not felt except by a very few under especially favourable conditions.
(II) - Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing.
(III) - Felt quite noticeably by persons indoors, especially on the upper floors of buildings. Many do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibration similar to the passing of a truck. Duration estimated.
(IV) - Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
(V) - Felt by nearly everyone; many awakened. Some dishes and windows broken. Unstable objects overturned. Pendulum clocks may stop.
(VI) - Felt by all; many frightened and run outdoors, walk unsteadily. Windows, dishes, glassware broken... books off shelves... some heavy furniture moved or overturned; a few instances of fallen plaster. Damage slight.
(VII) - Difficult to stand... furniture broken..damage negligible in building of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars.
(VIII) - Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture moved.
(IX) - General panic... damage considerable in specially designed structures, well designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.
(X) - Some well built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.
(XI) - Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.
(XII) - Damage total. Lines of sight and level distorted. Objects thrown into the air.

Still, it would have to be hard to be back east, hearing about earthquakes and wonder what is going on. For those of you that would like to keep on top of the quake situation in my neck of the woods, I present the following link. Here is a link to the U.S. Geological Survey's earthquake site for Souther California. It contains breaking news as well as historical data. My favorite feature is the interactive map. It shows all quakes in So Cal from the past week. The square representing the quake varies in proportion to its magnitude.

So, if you hear about a San Diego area quake, call up the map and see how close it is to me and how big it is. Anything below a 5 and you can assume we are fine. :)