Shawn, List,
Now I am wondering because of the low gravity
on the Moon's surface if in the past 4.5 billion years
if there has been a big enough quakes to project
the moons surface into space?
Thanks for all those fascinating references, but I can answer
the last question you posed about a quake powerful enough
to propel a piece of crust off the planet, or indeed any planet.
The energy required to accelerate a small piece of a planet,
say a pebble lying on the surface, up to escape velocity is
tremendous. Orders of magnitude greater than the greatest
quake imaginable.
Think about it. The piece of crust (or pebble) would have
to be accelerated to escape velocity. That is the same energy
per gram as is achieved by falling in from space. If an iron
object strikes the surface at or near escape velocity, it is
more energy than it takes to melt it, more energy than it
takes to vaporize it, enough energy to turn it to plasma,
and a lot of the crust with it.
If you tried to whack a piece of crust or pebble to escape
velocity, you would have to whack it harder than a whack
that would turn it to vapor. Not a good way to get into space.
To accelerate a pebble to escape velocity, the crust under it
would have to be moving up at escape velocity.
While it is true that seismic waves propagate through the
mantle of the Earth at speeds greater than Earth's escape
velocity (up to 13 km/s), no particle is moved at that speed,
or even a tiny fraction of it.
The energy requirements per gram to escape a small
planet are betwen 100,000 to 1,000,000 times greater
than the motion forces in the biggest never-happened
Richter Force 10 quake. Only kinetic energy events
(impacts) generate that kind of force, and then only
very rarely.
My conclusion? No way.
Sterling K. Webb
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----- Original Message -----
From: "Shawn Alan" <[email protected]>
To: <[email protected]>
Sent: Sunday, April 04, 2010 11:18 PM
Subject: [meteorite-list] Quake as related to the Moon and Mars
Hello Listers,
With the recent sizemic activites taking place in southern
Caliiforian, Mexico and China I thought I look up some information on
meteorites and quakes and here are some articals I got back from the
search.
First up is the moon
Title:
Shallow moonquakes - How they compare with earthquakes
Authors:
Nakamura, Y.
Abstract
Of three types of moonquakes strong enough to be detectable at large
distances - deep moonquakes, meteoroid impacts and shallow
moonquakes - only shallow moonquakes are similar in nature to
earthquakes. A comparison of various characteristics of moonquakes
with those of earthquakes indeed shows a remarkable similarity between
shallow moonquakes and intraplate earthquakes: (1) their occurrences
are not controlled by tides; (2) they appear to occur in locations
where there is evidence of structural weaknesses; (3) the relative
abundances of small and large quakes (b-values) are similar,
suggesting similar mechanisms; and (4) even the levels of activity may
be close. The shallow moonquakes may be quite comparable in nature to
intraplate earthquakes, and they may be of similar origin.
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1980LPSC...11.1847N&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
Title:
The MOON micro-seismic noise : first estimates from meteorites flux
simulations
Authors:
Lognonne, P.; Lefeuvre, M.; Johnson, C.; Weber, R.
Abstract
The Moon is considered to be a seismically quiet planet and most of
the time, the Apollo seismograms were flat when not quakes was
occuring. We show in this paper that this might not be the case if
more sensitive data are recorded by future instruments and that a
permanent micro-seismic noise is existing due to the continuous
impacts of meteorites. We perform a modeling of this noise by using,
as calibrated seismic data, those generated by the impacts of the
Apollo S4B or LEM, by taking care on the scaling law, necessary to
express the seismic force with respect to the mass and velocity of the
impactors. We also parametrize the dependence of the amplitude of the
seismic coda, associated to the maximum amplitude of the seismograms,
with respect to the epicentral distance and to the source geometry.
This enabling us to use the seismic data of the S4B impacts as
empirical waveforms for the modeling of the natural impacts. The
frequency/size law of
meteoroids impacting the Moon and the associated probability of NEO
impacts are however not known precisely. Uncertainties as large as a
factor of 3-5 remain, especially for the moderate-sized impacts which
are not observed on the Earth, due to the shielding by the atmosphere.
We therefore use several meteoroid mass/frequency laws from the
literature to generate, with a random simulator, a history of impacts
on the Moon during a given period. The seismic signals generated by
succession of seismic sources and estimate the frequency/amplitude
relationship of such seismic signals. Our results finally provide an
estimate for the meteoritic seismic background on the Moon. This
background noise was not recorded by the Apollo seismic experiment due
insufficient resolution. Such an estimate can be used in designing a
new generation of lunar seismometers, for estimating the probability
of detecting proposed impacts due to nuggets of strange quark matter ,
and to
inform future lunar based experiments, which require very stable
ground, such as optical interferometry moon-based telescopes or
gravity waves detectors.
http://adsabs.harvard.edu/abs/2008AGUFM.P51D..08L
Title:
Why the next generation of Moon exploration needs a global seismic
network
Authors:
Neal, C. R.
Abstract
The 4-station Apollo Passive Seismic Experiment (APSE) network was
completed in April 1972, and operated until it was switched off on 30
September 1977. During this time, the network demonstrated that the
Moon exhibits seismic activity on a similar scale to that of an
intraplate setting on Earth. However, there are significant gaps in
our understanding of lunar seismicity and what it tells us about the
lunar interior. For example, collection of seismic data that pass
through the interior of the Moon are critical for determining the
size, state and composition of the lunar core, the nature of the deep
lunar mantle, determining the global extent of discontinuities, and
mapping the extent of crust/mantle heterogeneities. Additionally, with
the advent of a new era of lunar exploration and potential
colonization, understanding the nature and extent of lunar seismicity
is now required in terms of risk assessment for a permanent lunar
habitat. The data needed
to address all of these issues must be collected using a network of
seismometers that is global in coverage. Lunar Seismic Events. There
were four types of lunar seismic event defined by the APSE network. 1)
Thermal moonquakes - the smallest magnitude event (associated with
stresses induced by diurnal temperature changes at the lunar surface);
2) Deep moonquakes - magnitude =2 (>7,000 having been recognized
occurring 700-1,200 km within the Moon and associated with Earth's
tidal pull); 3) Meteoroid impacts (>1,700 events representing masses
of 0.1 to 1,000 kg were recorded); 4) Shallow moonquakes - strongest
type of event, with 7 of the 28 recorded events being magnitude 5 or
greater although the exact causes of such quakes are not known (focal
depths 50-200 km, but exact depths and locations are unknown as all
recorded events were outside the APSE network). Relevance. Apart from
a direct impact from a meteorite, shallow moonquakes offer the
greatest
potential seismic risk to a permanent lunar habitat, but the amount of
epicentral ground motion associated with such events is difficult to
estimate. Estimates of ground acceleration at the epicenter of a
magnitude 5.7 shallow moonquake is estimated to be ˜ 0.75 m s-2 for a
focal depth of 25 km and ˜0.22 m s-2 for a focal depth of 100 km.
However, the estimates could be meaningless because the calculations
were conducted using formulations for earthquakes and there are
distinct differences in seismic wave transmission between the Moon and
Earth. For example, the maximum signal from a shallow moonquake can
last up to 10 minutes with a 1 slow tailing off that can continue for
hours, indicating that damping is less efficient in the Moon than it
is in the Earth. In other words, seismic energy is more efficiently
propagated through the Moon, especially at higher frequencies. This is
particularly significant for shallow moonquakes as they contain more
energy at high frequencies than earthquakes of comparable total
energy. In addition, the scattering properties of the regolith need to
be fully evaluated. A Lunar Seismic Network: At this time, it is
suspected, but not known, that seismic events could seriously
compromise a permanent lunar habitat. In order to fully evaluate this
risk, as well as answer fundamental science questions regarding the
lunar interior, a long-lived, global lunar seismic network needs to be
established. In order to achieve this, technological issues such as
deployment and low mass power supplies that can supply consistent
power over a period of at least 6 years need to be addressed. 2
http://adsabs.harvard.edu/abs/2006epsc.conf..291N
Now lets move on to Mars
Title:
Floods on Mars released from groundwater by impact
Authors:
Wang, Chi-Yuen; Manga, Michael; Wong, Alex
Abstract
On Earth, large earthquakes commonly cause saturated soils to liquefy
and streamflow to increase. We suggest that meteoritic impacts on Mars
may have repeatedly caused similar liquefaction to enable violent
eruption of groundwater. The amount of erupted water may be comparable
to that required to produce catastrophic floods and to form outflow
channels.
http://adsabs.harvard.edu/abs/2005Icar..175..551W
Now I am wondering because of the low gravity on the Moon's surface if
in the past 4.5 billion years if there has been a big enough quakes to
project the moons surface into space?
Shawn Alan
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