[Boatanchors] Some Shaking Going On??

[Richard Knoppow]

----- Original Message ----- 
From: "rbethman" <rbethman at comcast.net>
To: "boatanchors" <boatanchors at mailman.qth.net>
Cc: "Bill Stewart" <cwopr at embarqmail.com>
Sent: Tuesday, August 23, 2011 11:21 AM
Subject: Re: [Boatanchors] Some Shaking Going On??


> The Epicenter is about 40 miles South of here.
>
> It was a 5.9 4 miles SSE of Louisa, VA.
>
> Try here:
>
> <http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/US10/32.42.-85.-75_eqs.php>
>
> It definitely was more than a "little earth rattling"!
>
> However, I've been through them in Panama, CZ, and Kodiak, 
> Alaska.
>
> This is the strongest I've sat through.  No Hummel Plates 
> or pictures
> came off the walls.
>
> One picture frame fell off the dresser.
>

     Welcome to the wonderful world of earthquakes:-)
     The notice on the USGS mailing list says its depth was 
1 km but the map above shows 8 km, perhaps revised. The 
deeper center makes sense of the very wide area it was felt 
in and fairly low surface intensity. I have lived with 
earthquakes for some sixty years here but never really get 
used to them. Most are just jars like someone dropped 
something heavy but the bad ones are very frightening. Its 
not usually a heavy shake that tapers off but shaking that 
builds up for a time and then tapers off or, sometimes just 
stops abruptly. Depending one where you are they can also be 
noisy. Los Angeles is honeycombed with small faults; usually 
the first clue one is there is when it breaks loose and 
shakes. The quakes are usually near the surface so the 
intensity can be quite high but the area is limited. The 
"big one" the movies are so enamored of probably will never 
happen here because the big earth faults are fairly distant, 
mostly we have localized smaller quakes, but due to their 
proximity damage can be great.
     There is a limit on how strong any earthquake can be. 
It is established by the strength of the earth's crust. An 
earthquake can be likened to charging a capacitor: it takes 
a certain amount of energy to charge and then arcs over. The 
strength of the earth's crust is such that it will break 
when enough energy is stored for something less than a 
Richter 10 quake. I don't remember the record quake but 
think it was around a 9.8, which is close to the limit.
     Quakes on the East coast of the U.S. are fairly rare 
but do happen. Usually they are too weak to get much 
attention. Earthquakes, tornadoes, hurricanes, severe 
floods, volcanoes etc, are just little reminders of the 
power of nature. We like to pretend we are in control here 
but are really not.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com