DICTIONARY OF GEOPHYSICS, ASTROPHYSICS, and ASTRONOMY

liquefaction
behaves like an incompressible fluid, that is for
an observer moving with the flow, the phase
space density is constant. Liouville’s theorem
is a consequence of the equation of continuity
(see equation of continuity) in phase space
∂f
∂t +∇6
fC = 0
with f being the phase space density, C the
speed in phase space, and ∇6 the divergence in
phase space. If there are collisions,
df/dt= f,t +F i f ,pi+p i
f ,xi = Coll ,
where Coll represents the collision of particles
located at the same position in physical space,
which diminish or replenish particles of momentumpi,
and the subscript commas denote partial
differentiation.
liquefaction When loosely accumulated alluvial
sandy ground is shaken by strong earthquake
motion, friction acting among sand particles
decreases due to increase of pore water
pressure, and the ground loses shear resistance,
causing loss of the supporting force. This
phenomenon is referred to as liquefaction. To
generate liquefaction, necessary conditions are:
the ground is saturated with water; the sand is
loosely accumulated; the average diameter of
sand particles ranges from about 0.02 to 2 mm.
At the time of liquefaction, a large amount of
underground water sometimes springs up with
sand.
LISA (Laser Interferometric Space Antenna)
A proposal to put an array of several laser devices
forming an interferometric gravitational
wave detector on a heliocentric orbit. The sensitivity
of gravitational wave amplitude h ≈
10 −23 will be achieved in the frequency range
10 −2 to 10 −3 Hz. See GEO, LIGO, Virgo.
lithophile Elements that display a strong
affinity to combine with oxygen. Such elements
are concentrated in the crusts of the terrestrial
planets and in stony meteorites.
lithosphere The outermost rigid layer of a
terrestrial planet is called the lithosphere. The
Earth’s lithosphere is comprised of the crust and
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the upper part of the mantle. It is the region of
a planet where stress and strain result in fracturing
of the brittle rocks. The lithosphere is
the portion of the Earth that is broken up into
plates (see plate tectonics) and the motions of
these plates give rise to most of the earthquake
and volcanic activity on our planet. On Earth
the lower boundary of the lithosphere is defined
by the temperature below which rocks behave
rigidly, typically 1400 K. The typical thickness
of the lithosphere is 100 km although it will be
much thinner in zones of active volcanism such
as ocean ridges. On other planets, such as Venus
and Mars, the lithosphere is not apparently broken
up into plates, but extensive fracturing indicates
that these surfaces also experience tectonic
processes.
lithostatic pressure The lithostatic pressure
pl(y) is the pressure within the earth as a function
of depth y taking into account the variation of
local gravitational acceleration and density ρ as
a function of depth.
little ice age A period between about 1550
and 1860 during which the climate of the middle
latitudes became generally colder and there was
a world-wide expansion of glaciers. However, it
was not always colder during this period. There
were three cold subperiods. At 55 ◦ N Europe,
they are 1541–1680, 1741–1770, 1801–1890.
In China, they are 1470–1520, 1620–1720, and
1840–1890. An explanation for the little ice
age is very low solar activity during the Maunder
Minimum period. Little ice age effects have
been recorded in the Alps, Norway, and Iceland,
where farm land and buildings were destroyed.
There were times of especial severity during the
early 1600s when glaciers were particularly active
in Chamonix valley, in the French Alps.
littoral A term used to refer to the coastal
region that is affected by wind and wave-driven
sediment transport.
littoral barrier A physical barrier to longshore
sediment transport. A groin, placed to try
to stabilize a shoreline, represents such a barrier.
littoral cell A littoral region that does not
receive or lose sediment to adjoining upcoast