Seismic Risk Management in Bucharest | 24 comments (24 topical, editorial, 0 hidden)

Re: Seismic Risk Management in Bucharest (4.00 / 2)

I found a nice map:

Fig. 1:Top: Digital strong motion network of Kinemetrics K2 instruments in SE Romania and temporal stations during the Carpathian Arc Lithosphere Cross-Tomography (CALIXTO) experiment in 1999. Epicenters of Vrancea intermediate-depth earthquakes and shallow crustal events (since 1990) are marked by red circles and black crosses, respectively. Bottom: 3-component recordings of ground acceleration of the October 27, 2004 Vrancea earthquake (Mw=5.9) (epicenter marked in map by yellow star) at stations VRI (rock) and CFR (soil). Site effects at station CFR cause a significant higher level of ground shaking than expected from distant-dependent attenuation.

They also give what I sought after, the (significant) depths of the major earthquakes:

Four major events struck within this century:
Date Depth (km) Moment Magnitude
Nov. 10, 1940 155 7.7
March 4, 1977 95 7.4
Aug. 30, 1986 130 7.1
May 30, 1990 90 6.9

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Mon Jan 26th, 2009 at 05:01:55 AM EST
[ Parent ]

Re: Seismic Risk Management in Bucharest (none / 0)

Can anyone explain me the scientific reason why 1977 earthquake was a catastrophe and the one at 1990 was "little"... Not so much difference, apparently. The same between 1940 and 1986... The papers I found on the internet are either too technical for me or consider that so clear that don´t explain further... Thanks!

"If you don't want a man unhappy politically, don't give him two sides to a question to worry him; give him one. Better yet, give him none." (Fahrenheit 451)

by pereulok on Mon Jan 26th, 2009 at 08:50:09 AM EST
[ Parent ]

Re: Seismic Risk Management in Bucharest (none / 1)

My first reply would have been that the 1977 quake was 6-7 times stronger, which may make a difference. But then I Googled and found a few sources, from which the issue seems a still open question. I read that not only were there lots of dead, but even neighbouring blocks were very differently affacted.

Meanwhile, both theories advanced to explain it have holes: focussing (layers are aligned the wrong way for that) and the reactivation of an old fault line (no aftershocks and no damage along the entire length of the candidate paleo-fault).

<conspiracy theorist>
Maybe it was the Securitate...
</conspiracy theorist>

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Mon Jan 26th, 2009 at 01:38:46 PM EST
[ Parent ]

Re: Seismic Risk Management in Bucharest (none / 0)

Moment magnitude is measured on a logarithmic scale.

What that means is that a movement of +1 on the scale (say from 5.5 to 6.5) indicates that the earthquake is ten times larger.

So, to work out how many times bigger one earthquake is than another (say 1940 and 1986), you get yourself a scientific calculator (online version here) and calculate the difference between the numbers:

7.7-7.1 = 0.6

(OK, you didn't need a calculator for that bit)

and then press "INV" followed by "log". This converts the answer back into "regular" numbers, and in this case, gives an answer of 3.98. So the 1940 quake was about four times more powerful than the 1986 one.

For discussion, I'll just throw in the thought that whether or not an earthquake is a catastrophe is measured by loss of life (and property). Is it possible that the buildings that replaced those destroyed in the 1940 quake were built to a higher standard, leading to a lower rate of collapse next time?

by Sassafras on Mon Jan 26th, 2009 at 02:51:25 PM EST
[ Parent ]

Re: Seismic Risk Management in Bucharest (none / 0)

Actually, motion is one thing, power another: the multiplier for power is 30, not 10. So the 1940 quake was almost eight times more powerful than the 1986 one.

However, while I thought of the same as you, after some reading, the situation with the 1977 quake seems different, see my own reply to pereulok.

_{*Lunatic*, n.

One whose delusions are out of fashion.}

by DoDo on Mon Jan 26th, 2009 at 06:33:17 PM EST
[ Parent ]

Re: Seismic Risk Management in Bucharest (none / 1)

I´ll try to forget the killed for a minute. Yeah, meybe yoy´re right, standards are lowered. However, sometimes what happens also is that there´s an urgent need of housing to be solved, so many cheap buildings "prefabricados" (I think the word is pre-assembling estructures, but I´m not sure) are built. They are said to be temporal (3-5 years), but in practise they stay. I don´t know if that´s the case in Romania, I just remembered the case of the Soviet "Jrushovkas", 5-storey buildings built during the Khruschov years that never were rebuilt, and becoming a real danger in Russian cities of provinces. But in Romania I´ve heard complanis that standards were lowered after 1940 and after 1977, but not fully complied with until 1989...

Another issue in Bucharest is the consequences for the urban development in the city. Buildings that were built didn´t respect style, height or anything... In a context of disrespect (people blame Ceacescu, but Ceaucescu just made huge -because he was a megalomaniac- the kind of unrespectful development of Bucharest historical centre that was the habit in the 70s and is still the habit nowadays. If you look at the hedquarters of the Union of Arquitect you would imagine what they are doing around here... As this is not the only but one of many cocrete+glass let´s see if we change from being called little Paris to being called little Berlin buildings in city centre.

http://www.flickr.com/photos/pereulok/2281943859/in/set-72157612909967720/

And an example of the kind fo buildings that were bbuilt were the 1940s/1977s collapsed:

http://www.flickr.com/photos/pereulok/2251542375/

"If you don't want a man unhappy politically, don't give him two sides to a question to worry him; give him one. Better yet, give him none." (Fahrenheit 451)

by pereulok on Tue Jan 27th, 2009 at 04:10:25 AM EST
[ Parent ]

Seismic Risk Management in Bucharest | 24 comments (24 topical, 0 editorial, 0 hidden)

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