[meteorite-list] Quake as related to the Moon and Mars

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon, 5 Apr 2010 01:17:17 -0500
Message-ID: <AFDCAA3767B94DC2ACD0675B2DD78084_at_ATARIENGINE2>

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
---------------------------------------------------------------------------
----- Original Message -----
From: "Shawn Alan" <photophlow at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
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&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;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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Received on Mon 05 Apr 2010 02:17:17 AM PDT