Page 254 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

with
add
the
over
plat-
Edtvés
certain
a
adds
value
237
1976):
that
represents
that
stations,
measurement
ship
velocity
the
so
al.,
Isostasy
a
the
accelerations
by
calibrated
adding
et
the
as
(Telford
(Ag)
ship’s
other
of
known
station
speed
by
gravity
the
the
at
is
computed
measurements
correction,
gravimeter
base
taken
causing
that
the
words,
in
rotation,
fact
the
change
then
other
down,
be
at
the
additional
measured
recorded. The
are
then
by
a
station.
Earth’s
in
gravity
represents
and
Measurements
complicated
acceleration;
can
up
(g)
base
marine
spring)
An
like
ship
acceleration
rotation.
(AL)
spring
the
Also,
the
is
to
of
outward
the
surveying
point.
move
length
added
gravity.
gravity
the
of
Earth’s
length
of
that
Waves
Gal). The
spring
therefore
an
length
absolute
the
Atsea, gravity
in
at
of
initial
unstable.
from
results
gravity
in
velocity
in
change
is
changes
the
(in
the
subtract
correction,
water
absolute
amount
to
is,
is
the
given
of Ag
(that
form
the
the
to
or
-L V? 0.004154 + sina cos V 7.503 = EC AL as where: of Mass (mGal) correction Eétvés = EC 2 and m/s) 0.5144 = km/hr 1.852 = knot | (knots; of ship speed = V (degrees) point observation the of latitude = & degrees). in (azimuth, ship direction of course = a ISOSTASY lead a suspending by instruments their leveled surveyors recently,
Le @« Weight 1 length of a spring (L), results (F,) at another station. The re-measurement at less weighing more
AL = Ag Stations at one station is by a or simply is (base station), 8.15c). The
= 14 more is there
Lag ita be F,, & at f Nyy Sta. (F,) force force of the spring (AL) Map of relative gravity survey. The 16 stations, followed (exert where point (Fig.
2 “freee 1% length less gravimeter starting station
>
L Station Fo 4 / 11 (g).b) A to L, because of a different in g=F/m or more (+AL) 8.15b). (Fig. a at that to
:
lsostasy ted aamoteaa ime seanenes 4L 4 ! : ; r / (mm ninen, sen Measurement of relative gravity. a) A gravimeter measures the the gravitational acceleration function of g: the change base station, then each of the mass will weigh the station. A at stretches spring less is gravity relative
and A 10 eS may change gravitational acceleration (Ag). c) (g) the gravity absolute points
Gravity Spring: Mass on Vibd we 9 ‘Sta, length mass is a the the of gravity stations; when the measure
a 1 cares F; to at pull (—AL) know to
8 Station is proportional (L,). The by the in measurement words, the If we
Chapter 8.15 spring length force exerted the change base station, that: other ing on different contracts gravimeter
b FIGURE which to a with the so In at
236