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Another earthquake

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Faerie
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« on: March 11, 2011, 11:53:35 AM »

Another one - this one hitting Japan (well the Tsunami did) - 8.9 on the scale.

http://edition.cnn.com/2011/WORLD/asiapcf/03/11/japan.quake/index.html?hpt=T1

Further to this, I went cruising the interwebs and came across this site:

http://www.emdat.be/natural-disasters-trends


which makes for some fascinating reading.

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GCG
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« Reply #1 on: March 11, 2011, 12:18:50 PM »

my problem with those graphs, is that, today, our reporting skills are better, and every sneezing hamster gets news coverage.
as technology and connectivity increases, the disasters increase.  me feeling is, back  in the day, if there was a tsunami in japan, who knew, there was no cnn or sky news.  and during the war, who had time worry about a volcanic eruption in where-eversville?
i wonder, if the lack of reliable information was factored into those stats they have?
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GCG
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« Reply #2 on: March 11, 2011, 12:30:28 PM »

the site says:
Quote
The information on natural disasters presented here is taken from EM-DAT: The OFDA/CRED International Disaster Database. In order for a disaster to be entered into the database at least one of the following criteria has to be fulfilled:

• 10 or more people reported killed
• 100 people reported affected
• a call for international assistance
• declaration of a state of emergency

a whole bunch of problems right there.

im assuming their point was, that there is an increase in disasters of late. 

i searched south africa, and found a few distaster in the 80's, 90's and naughties.  and two in the 50's.  so, nothing happened in between?  no floods, no droughts, no earthquakes?
i hardly feel they should be calling it a 'trend' when they have only accessed 1900-2009 worth of data. and very sketchy data in the early days.  and i dont much about the earth and climates, but im sure that to draw up graphs and charts based on 110 odd years worth of data, and calling it a trend, is a bit much.

i can just see how a woo would latch onto this, and tote the increae of disasters as a results of 'morality of the times'.  pish.
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Rigil Kent
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« Reply #3 on: March 11, 2011, 12:37:30 PM »

GCG, I would be surprised if reporting skills played anything more than a minor role in explaining the upward trend. The time line only goes back as far as 1900. At the time there would have been precious few very isolated countries left. Its unlikely that a large natural disaster would go unnoticed by statisticians keen on populating their ANOVA spreadsheets, or whatever the equivalent was back in Pluto's planetary days.

The criteria in your second post of what constitutes a disaster seems heavily dependent on population density, which is known to change over time. One should probably consider correcting the data for population growth to gain better insight into a true escalation of disaster.

Mintaka
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Lurkie
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« Reply #4 on: March 11, 2011, 13:39:05 PM »

Two good places to find reliable earthquake info are the USGS and IRIS websites:

http://neic.usgs.gov/neis/qed/
http://www.iris.edu/hq/

This data is recorded by the global seismic network, which has a network sensitivity of approx magnitude = 5 (meaning that ALL earthquakes having magnitudes of 5 or more will be recorded reliably, whereas only a subset of those having magnitudes less than 5 will be recorded).

As a matter of interest, Japan has had over 30 aftershocks today, following the M = 8.9 earthquake this morning.

Regarding reporting trends. The public definitely has the impression that worldwide seismicity rates are increasing because of increased media reporting. However, if you look at the data, no such trend is evident.

Whenever a new geophone/accelerometer is connected to the global network, the sensitivity of the network is increased and smaller and smaller seismic events recorded. So, if you look at the sheer numbers of events recorded per year, it looks like the planet has cranked up its yearly earthquake quota. However, if you only look at those magnitudes above the network sensitivity (i.e. all events that are reliably recorded), you'll see that, on average, the same number of events per magnitude range is generated each year. As an example, the Earth experiences about 1400 events in the magnitude range 5 - 5.9 each year; about 125 in the range 6 - 6.9; and about 14 in the range 7 - 7.9.

If you plot the log of the average number of events generated each year for each of the magnitude ranges, you get a straight line with a slope that stays relatively constant on a yearly basis. This indicates that worldwide seismcity rates are not increasing and seismic Armageddon is not around the corner

The global seismic monitor makes for an interesting visit (not quite real time!):

http://www.iris.edu/dms/seismon.htm

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GCG
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« Reply #5 on: March 11, 2011, 13:41:43 PM »

what he said  Cheesy
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Faerie
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« Reply #6 on: March 11, 2011, 14:01:45 PM »

Thanks Lurkie, some interesting links there.

I just had to give the lot here at work a geography lesson, NONE of them knew the reference "ring of fire" nor had ever heard about tectonic plates.

How deep in a hole does your head have to be not to be at least familiar with the words/phrases?

*facedesk*
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Hermes
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« Reply #7 on: March 11, 2011, 14:03:25 PM »

An global analysis of seismic activity makes much more sense than lumping "natural disasters" that are unrelated together, unless of course you hold the view that they are "acts of God".  I would imagine that the insurance industry is aware of this and assesses the various risks individually in order to arrive at a collective risk level.
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Mefiante
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« Reply #8 on: March 11, 2011, 14:24:36 PM »

It is also well within statistical expectation that there will be occasions when several large seismic events occur within a short period of time.  The public’s attention will naturally be drawn to these, especially when they happen in populous locations.  On the other hand, longer periods of relative quietude do not receive the same attention.  It’s plain old bias, Confirmation ably helped along by its cousin, Selection.

'Luthon64
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Lurkie
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« Reply #9 on: March 12, 2011, 13:57:53 PM »

Hermes, you raise an interesting point about disasters, insurance & acts of god.

In the case of insurance claims related to damage caused by seismicity associated with mining, insurers try their best to classify the damaging seismic event as mining-induced (because there are exclusion clauses precluding/reducing payment in the case of mining-induced events), whereas the mining guys blame the gods of natural disasters (because this will result in a bigger insurance payout).

There was a case some years ago where the mining guys ignored their in-mine seismic data and quoted the USGS calculated depth of the event (10km) because it was way below the depth of active mining (3km). They even went as far as classifying the event as a "natural" rather than mining-induced - strange that, when the event occurred in the plane of the reef where active mining is taking place! The mine conveniently forgot to mention that the USGS seismic location algorithm fixes the depth to 10km if the data are too poor to compute a reliable depth, which often happens because mining-induced events are generally below the sensitivity of the global seismic network ...
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Hermes
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« Reply #10 on: March 14, 2011, 20:25:58 PM »

This issue has been raised before by Julian.  From the insurer's perspective, it would be easier to recover damages from a mining house than from God, considering that the latter does not have much respect for the rule of law, as is evidenced by Mefiante in replies 60 & 61 here.
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