Free air gravity anomalies derived from radar altimetric determinations of geoid height

milligals

Bathymetry determined from satellite radar derived gravity plus shipboard measurements

Free Air gravity anomaly

Now consider an elastic plate which bends under the load

The flexural parameter, a

where

= flexural parameter

Deflection vrs x, for vertical line load on infinite plate and half plate

Distance, x/a (a = flexural parameter

( )m w

W

Fgaρ ρ

Δ

⎡ ⎤⎢ ⎥−⎣ ⎦

deflection,

Half plate, vertical line load on edge

Infinite plate, vertical line load at x =0

3/4

/2

1 2 3 4 502.0

1.6

1.2

0.8

0.4

0

-0.4

Bending of half plate

FF

Outer (oceanic side) slope of trenches associated with subduction zones

elastic plate model elastic-plastic model

Outer (oceanic side) slope of trenches associated with subduction zones

elastic plate model elastic-plastic model

strain

stre

ss

plastic

elas

tic

Venus Gravity, Topograph

y and Geoid

High correlation between gravity and topography

Anomaly amplitude similar to Earth

Data from Magellan spacecraft, Images from Wieczorek, 2006

Mars Gravity & Topography Maps

Free air gravity anomaly from Mars Global Surveyor (MGS)

Mars topography from MOLA on MGS

• Total amplitude of anomaly larger than on Earth Why?

Elysium volcano

Isidis impact crater

•From Goddard Space Flight Center Gravity maps

Gravity anomalies

from Martian features

LunarGravity & Topography Maps

Gravity data from lunar nearside from Lunar Prospector (Sugano and Heki, 2004)

Topography data from Clementine

• Again total amplitude of free-air anomaly larger than on Earth

Global map from Knopoliv et al., 1998

viscous fluid

Temperature, degrees C

0 1300

50

100

150

200

dep

th,

km

shea

r st

ress

shear strain

Slope = modulus of r

igidity

elastic

shea

r st

ress

shear strain

yield stress

plasticplastic

elastic

shea

r st

ress

Slope = coeff of v

iscosity

Viscousfluid

shear strain rate