Earthquakes

Michael Thomas mike at mtcc.com
Wed Mar 24 15:32:49 CDT 2010


Something to keep in mind is that raw magnitude isn't the whole story. The
ground composition is *much* more important when it comes to destructiveness.
A 5.0 earthquake in the Netherlands might be extremely damaging because of
liquifaction. Also: California since we get quakes all the time, our rock is
more "shattered" which damps the seismic waves. Back east, on the other hand,
the bedrock is more solid which is why the New Madrid earthquakes traveled
so far (ringing bells in Boston, IIRC). Of course New Madrid were huge
earthquakes by any standard.

Mike

On 03/24/2010 01:20 PM, Owen DeLong wrote:
> In California, 4s are a regular occurrence and we have 2-3s every day.
>
> I rarely notice anything less than  a 5, and, often do not notice up to a 5.5 in my area.
>
> The worst quake I have personally experienced was the 1989 Loma Prietta quake
> which was a 7.9 IIRC.  It caused some significant damage to some substandard
> (by modern measure, not when they were built) structures, most notably the bay
> bridge and the cypress and embarcadero elevated freeways and a brick-and-morter
> (literally) mall in Santa Cruz.  Other than that, the damage from the 7.9 was minimal
> outside of a relatively contained zone rather close to the epicenter.
>
> I've been through more than one quake in the 5.2-5.5 range, so, perhaps they are
> rare in the Netherlands (6 million years or so), but, in California they are much more
> frequent, perhaps 5-7 years or so.
>
> Owen
>
> On Mar 24, 2010, at 12:31 PM, Jeroen van Aart wrote:
>
>> I saw a recent(-ish) short thread about a mag. 4 quake in the SF Bay Area. This http://earthquake.usgs.gov/earthquakes/recenteqsus/Maps/US2/36.38.-123.-121.php
>> should provide with everything you need to know.
>>
>> I check it on a daily basis and it's been rather quiet the past week or 2 or so. Actually I guess it's been rather quiet ever since the 1989 quake, but then a year or so ago I woke up in the morning from some rattling doors so I guess it all depends on your perspective.
>>
>> So far the "worst" quake ever I experienced was in the Netherlands back around 1988. Magn. 5.2 or something. Which is interesting considering these happen like once every 6 million years or thereabouts ;-)
>> Actually I slept through it so I don't know if one can call it "experiencing".
>>
>> Greetings,
>> Jeroen
>





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