[PLUG-TALK] Italian Earthquakes

[Keith Lofstrom]

On Wed, Jun 13, 2012 at 9:48 AM, Rich Shepard <rshepard at appl-ecosys.com>wrote:
> http://quakeback.delegno.it/#45.223,10.415|44.2,12.406|2|20/05/2012|12/06/2012|5000
>   (press play button and look)

On Thu, Jun 14, 2012 at 09:27:46AM -0700, Denis Heidtmann wrote:
> That is quite impressive, both the software and the earthquakes.  Is it
> unusual to have such a large and prolonged cluster?  Are there details of
> the source of the quakes that a non-scientist would grasp?

Roughly:  The bottom of the Mediterranian between Italy and North
Africa is the boundary between the African and Eurasian tectonic
plates.  Not sure what the relative movement is, compression or
tension; since there are volcanos in southern Italy that would
imply some compression and subduction, pushing water down to
boil and push back up as volcanic steam megayears later.

The plates are pulled along on top of slow currents in the
mantle, which moves like very slowly churning molasses.  The
mantle churns because of radioactive heat slowly leaving the
earth by convection.  Planetary scale boiling.  The continents
are chunks of lighter scum floating on top of the mantle.  On
the planetary scale, continents are weak and easy to break. 
Earthquakes happen when the strain causes abrupt fractures.  

The earthquakes shown on the Italian website are mostly magnitude
2 and 3, with an occasional 4 and 5.  Seismometers can measure
very small quakes, most of which people never notice.  We've had
quite a few magnitude 5's in the Northwest, one or two per year
IIRC, and 2's and 3's daily.  The magnitude scale is logarithmic,
with a difference of 2 on the scale corresponding to a 1000x
increase in energy and a 100x increase in amplitude.  

When (not if) the Cascadia subduction zone goes (a 3% chance 
per decade), it may be a magnitude 9 or 10, a million times more
energy than the magnitude 5 quakes shown on the website.  Such
a quake will knock down hundreds of buildings in Portland, and
send most houses on steep slopes to the bottom of the hill. 
Have your sills bolted and water heater anchored, emergency
kits ready, and be prepared to pull many neighbors out of
the rubble.  Outside help may take weeks to arrive.

These map visualizations are useful.  Expect to see many more
GIS mashups like this in the future, hopefully informing our
fellow citizens about our fascinating and sometimes deadly
planet.  I would like to see some earthquake and structural
sims turned into photorealistic animated movies.  What will
it look like in downtown Portland when the buildings start
falling?  There are some interesting animations of a Cascadia
tsunami ripping through Seaside, but I don't recall the website.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs