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Science Forum Index » Geology - Earthquakes Forum » Allow this question please..........
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| CunnyBuster |
 Posted: Tue May 29, 2007 10:47 am |
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If the Mercalli scale ranks the effect of an EQ on the surface, and
the effect it has on the inhabitants of the area that gets rattled,
can the Mercalli scale be applied to subterranean EQ's that don't
shake people, but cause Tsunami's, the size of which will affect
people. If you read the Mercalli scale closely, it pertains to surface
disturbance. The Dec. 26, 2004 quake shook the Island of Sumatra, and
judging from video clips, I would venture a guess of about 10 on the
Mercalli, but the effect of the shaking was a non-event in Thailand
and other countries that were hit by the Tsunami, but the resulting
effect was devastating to humanity. Just some food for thought. But,
an opinion/answer would be read. |
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| Timberwoof |
| Posted: Tue May 29, 2007 12:59 pm |
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In article <s0io539g3dskttq0f6p9e9cn79ccv2hmjb@4ax.com>,
CunnyBuster <CunnyBuster@home.tv> wrote:
Quote: If the Mercalli scale ranks the effect of an EQ on the surface, and
the effect it has on the inhabitants of the area that gets rattled,
can the Mercalli scale be applied to subterranean EQ's that don't
shake people, but cause Tsunami's, the size of which will affect
people. If you read the Mercalli scale closely, it pertains to surface
disturbance.
The Mercalli scale is, as you say, dependent on observations of extent
and severity of damage to structures. It is a scale, not a measurement.
A more formal way to measure and record the energy of an earthquake is
its magnitude (popularly called the Richter scale): that is,
logarithm of the combined horizontal amplitude of the largest
displacement from zero on a seismometer output.
I suppose you could characterize the effects of the Christmas Tsunami on
the Mercalli scale, but the number would be relatively large. Measuring
the destruction resulting from an earthquake's side effects (such as
tsunamis) is probably best done in lives, Dollars, and Euros.
Quote: The Dec. 26, 2004 quake shook the Island of Sumatra, and
judging from video clips, I would venture a guess of about 10 on the
Mercalli, but the effect of the shaking was a non-event in Thailand
and other countries that were hit by the Tsunami, but the resulting
effect was devastating to humanity.
No, it wasn't. It was devastating to a lot of people, yes. But not to
all of us; not to humanity.
Quote: Just some food for thought. But,
an opinion/answer would be read.
--
Timberwoof <me at timberwoof dot com> http://www.timberwoof.com |
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| Gautam Majumdar |
| Posted: Tue May 29, 2007 1:52 pm |
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On Tue, 29 May 2007 16:47:30 +0100, CunnyBuster wrote:
Quote: If the Mercalli scale ranks the effect of an EQ on the surface, and the
effect it has on the inhabitants of the area that gets rattled, can the
Mercalli scale be applied to subterranean EQ's that don't shake people,
but cause Tsunami's, the size of which will affect people. If you read
the Mercalli scale closely, it pertains to surface disturbance. The Dec.
26, 2004 quake shook the Island of Sumatra, and judging from video
clips, I would venture a guess of about 10 on the Mercalli, but the
effect of the shaking was a non-event in Thailand and other countries
that were hit by the Tsunami, but the resulting effect was devastating
to humanity. Just some food for thought. But, an opinion/answer would be
read.
Mercalli scale does not explicitly exclude tsunami or other secondary
effects of an earthquake. However, Rossi-Forel scale on which the original
Mercalli scale was based and it various modifications, latest being the
Modified Mercally Scale introduced by Richter in late 30s, refers
exlusively to the effects of shaking. Thus the destrcution caused by
tsunami or landslide, etc. are implicitely excluded.
--
gautam |
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| Susan |
| Posted: Wed May 30, 2007 11:32 pm |
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On May 29, 8:47 am, CunnyBuster <CunnyBus...@home.tv> wrote:
Quote: If the Mercalli scale ranks the effect of an EQ on the surface, and
the effect it has on the inhabitants of the area that gets rattled,
can the Mercalli scale be applied to subterranean EQ's that don't
shake people, but cause Tsunami's, the size of which will affect
people.
One can always try to estimate the Mercalli intensity in an area, even
in the absence of the effects on structures/people. But if I'm
reading your question right, what you are suggesting doesn't really
make sense. Intensity scales use damage indicators to gauge the
severity of shaking -- they really aren't a scale of damage/
devastation per se. As you note, there can be a huge disconnect
between MMI values and devastation if an earthquake generates a
damaging tsunami. Other disconnects are possible -- for example, big
landslides can be very deadly, and are not necessary caused by severe
shaking.
Not sure if that helps -- just a few thoughts.
Susan |
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| John |
| Posted: Fri Jun 01, 2007 1:22 am |
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On May 29, 8:47 am, CunnyBuster <CunnyBus...@home.tv> wrote:
Quote: If the Mercalli scale ranks the effect of an EQ on the surface, and
the effect it has on the inhabitants of the area that gets rattled,
can the Mercalli scale be applied to subterranean EQ's that don't
shake people, but cause Tsunami's, the size of which will affect
people. If you read the Mercalli scale closely, it pertains to surface
disturbance. The Dec. 26, 2004 quake shook the Island of Sumatra, and
judging from video clips, I would venture a guess of about 10 on the
Mercalli, but the effect of the shaking was a non-event in Thailand
and other countries that were hit by the Tsunami, but the resulting
effect was devastating to humanity. Just some food for thought. But,
an opinion/answer would be read.
As the other said, intensity is meant to record the strength of
shaking, not the extent of tsunami or landslide damage. It can be
measured from either ground disruption, perceptions of people, or
damage to buildings.
The intensity varies across a region. I suspect directly above this
magnitude 9.2 event, the intensity was high, X is a good guess (roman
numeral for ten). Farther away, the shaking is less intense. At the
distance of Thailand, the shaking might not even be felt for a very
low intensity. |
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| Michael |
| Posted: Fri Jun 01, 2007 8:15 am |
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On May 31, 11:22 pm, John <john.vid...@gmail.com> wrote:
Quote: On May 29, 8:47 am, CunnyBuster <CunnyBus...@home.tv> wrote:
....
The intensity varies across a region. I suspect directly above this
magnitude 9.2 event, the intensity was high, X is a good guess (roman
numeral for ten). Farther away, the shaking is less intense. At the
distance of Thailand, the shaking might not even be felt for a very
low intensity.
I may be wrong but I understood that shaking intensity maxed out at
around Richter 6. That is, someone on top of a R6 epicenter would feel
as intense a quake as someone at the top of a Richter 9 quake
epicenter (ignoring refraction issues). The difference between the two
quakes is measured by both duration of the quake and the area affected
so more people would feel the maximum shaking from an R9 quake for a
longer period than they would for a R6 quake.
So wouldn't someone near the Moment 9.2 event feel the maximum
Mercalli 12 shaking? |
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| John |
| Posted: Fri Jun 01, 2007 9:07 am |
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On Jun 1, 6:15 am, Michael <google...@greenes.com> wrote:
Quote: On May 31, 11:22 pm, John <john.vid...@gmail.com> wrote:
On May 29, 8:47 am, CunnyBuster <CunnyBus...@home.tv> wrote:
...
The intensity varies across a region. I suspect directly above this
magnitude 9.2 event, the intensity was high, X is a good guess (roman
numeral for ten). Farther away, the shaking is less intense. At the
distance of Thailand, the shaking might not even be felt for a very
low intensity.
I may be wrong but I understood that shaking intensity maxed out at
around Richter 6. That is, someone on top of a R6 epicenter would feel
as intense a quake as someone at the top of a Richter 9 quake
epicenter (ignoring refraction issues). The difference between the two
quakes is measured by both duration of the quake and the area affected
so more people would feel the maximum shaking from an R9 quake for a
longer period than they would for a R6 quake.
So wouldn't someone near the Moment 9.2 event feel the maximum
Mercalli 12 shaking?
I'm reading two different answers in your post - that the intensity
might be VI or it might be XII right on top of an M9.2 event. (By the
way, M9.2 would be a moment magnitude, all the other common magnitude
scales, including Richter magnitude, saturate at lower levels).
The quantity that clearly saturates in ground motion is acceleration -
if an M7 can make half a g, an M9.2 cannot generate that much more
acceleration. As you note, however, the M9.2 can have strong shaking
for much longer.
In the case of Sumatra, as I recall, there is some evidence that the
ground motions were somewhat more gentle than might be expected from
such a monster quake, but also there were few big fragile buildings
around to shake down. Another factor is that the tsunami was so much
more destructive than the shaking that is has been the primary focis
of attention. A third factor is that there were few or no
seismometers in the near-field to directly measure the shaking.
So a short answer would be I'm not sure if the intensity of the
Sumatra quake has been directly estimated, but a peak intensity around
X would be about what I'd expect. |
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| David Oberman |
| Posted: Fri Jun 01, 2007 10:35 am |
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John <john.vidale@gmail.com> wrote:
Quote: In the case of Sumatra, as I recall, there is some evidence that the
ground motions were somewhat more gentle than might be expected from
such a monster quake, but also there were few big fragile buildings
around to shake down.
There is video -- probably still out there on the Web -- of the actual
shaking in Banda Aceh. Among other things, you can see what look like
big amplifiers rock & tumble over, & people appear to be experiencing
stronger shaking than, say, I'm used to experiencing here in
California.
Some Web sources say the felt shaking lasted about five minutes, &
another source reported that the Banda Aceh water system & electrical
utilities sustained no damage from the actual quake
(http://snipurl.com/1mz3l).
More: http://snipurl.com/1mz3v
____
There always seems to be a propensity for sulphur-bearing layers in areas of volcanic activity.
-- Weatherlawyer |
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