Download - Seismicity
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SeismicitySeismicity
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Seismic Image of Venezuela BasinSeismic Image of Venezuela Basin
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Seismic wavesSeismic waves
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Seismic wave travel in a Seismic wave travel in a homogeneous Earthhomogeneous Earth
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Seismic wave travel in which density Seismic wave travel in which density increases monotonouslyincreases monotonously
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Seismic wave travel in a layered Seismic wave travel in a layered EarthEarth
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The P-wave shadow zoneThe P-wave shadow zone
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The S-wave shadow zoneThe S-wave shadow zone
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P and S-wave velocitiesP and S-wave velocities
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The Earth InteriorThe Earth Interior
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The Earth InteriorThe Earth Interior
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The distribution of landThe distribution of land
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Hypsographic CurveHypsographic Curve
Extreme elevations are rare
Two common elevations Ocean basins
(abyssal plains)
Continental interiors
Why??
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The weight of an Object is determined The weight of an Object is determined by its mass and the force of gravityby its mass and the force of gravity
F = the force of gravity (weight)F = the force of gravity (weight)
g = the gravitational constant (6.672 x 10g = the gravitational constant (6.672 x 10-11-11 N N · m· m22 · kg · kg-2-2))
mm11 = the mass of the object = the mass of the object
mm22 = the mass of the Earth = the mass of the Earth
r = the distance between the object and the center of the Earthr = the distance between the object and the center of the Earth
1 22
m mF g
r
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Weight varies due to three factorsWeight varies due to three factors
1. Altitude1. Altitude
As altitude increases r increases, so F decreasesAs altitude increases r increases, so F decreases
1 22
m mF g
r
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Weight varies due to three factorsWeight varies due to three factors
2. Latitude2. Latitude
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Weight varies due to three factorsWeight varies due to three factors
3. Local variations in rock density3. Local variations in rock density
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Geographic Survey of IndiaGeographic Survey of India
Mid-19Mid-19thth century century
Sir George EverestSir George Everest
Triangulation systematically Triangulation systematically disagreed with astronomical disagreed with astronomical near the Himalayasnear the Himalayas
Why? Why?
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Archdeacon Pratt’s theory of IsostasyArchdeacon Pratt’s theory of Isostasy
Water density 1.0
0.5 0.50.3 0.30.2 0.2
density= 0.1
Each block weighs 2 g
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Astronomer Royal Airy’s theory of IsostasyAstronomer Royal Airy’s theory of Isostasy
Water density 1.0
0.5 0.50.3 0.30.2 0.2
density= 0.1
Each block weighs 2 g
Water density 1.0
Wood density 0.5
2 g 2 g3 g 3 g5 g 5 g
8 g
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Uncorrected gravity profile at 20,000 ft.Uncorrected gravity profile at 20,000 ft.
Free-Air correction to 0 ft.Free-Air correction to 0 ft.
Bouguer Corrected profileBouguer Corrected profile
1 22
m mF g
r
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Free-air and Bouguer gravity Free-air and Bouguer gravity anomaly map of the Alpsanomaly map of the Alps
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Isostasy Isostasy and and
ErosionErosion