The document discusses the internal structure of the Earth, detailing its layers: the crust (continental and oceanic), the mantle, and the core (outer and inner). Geophysical studies, particularly through seismic waves, reveal that the crust is thinner under oceans and that seismic wave speeds vary between crust types. It also notes key features like the lithosphere, moho boundary, and temperature characteristics of the core, highlighting that the outer core is liquid while the inner core is solid.

1. A Schematic view of interior of earth
CRUST MANTLE OUTER
CORE
INNER
CORE

2. Deep parts of Earth are studied indirectly, however,
largely through the branch of geology called geophysics.
 Geophysics includes the study of seismic waves
and Earth’s magnetic field, gravity, and heat.
 Together, they create a convincing picture of what
makes up Earth’s interior.
Introduction
 There are two important ways of learning about Earth’s
interior.
1.seismic reflection
2.Seismic refraction

3. By seismic study earth has following layers:
1-The crust
Continental crust
Oceanic crust
2-The mantle
Upper mantle
Lower mantle
3-The core
Outer core
Inner core

4. Studies of seismic waves have shown that the
crust is thinner beneath the oceans as compare
to the continents.
The uppermost layer of earth is called crust.
 Seismic waves travel faster in oceanic crust than in
continental crust.
On this basis crust is divided into two types.
Continental crust
Oceanic crust
 Seismic P waves travel through oceanic crust at about 7km/s
& about 6km/s through continental crust.

5.  Lithosphere
 The combination of uppermost mantle and crust above the
asthenosphere is called the lithosphere.
 The lithosphere is free to move over the weak asthenosphere.
 The tectonic plates are, in. fact, lithospheric plate
The boundary that separates the crust from the
mantle is called the Mohorovic˘ic´ discontinuity.
Moho Boundary:

7. Properties of the Crust:
Continental Crust:
►Depth 20 to 70 km, average 30 to 40 km
► Composition: felsic, intermediate, and mafic
igneous, sedimentary, and metamorphic rocks.
► Age: 0 to 4 B.y.
► Summary: thicker, less dense, heterogeneous,
 Oceanic Crust:
► Depth to Moho: ~7 km
► Composition: mafic igneous rock (basalt &
gabbro) with thin layer of sediments on top
► Age: 0 to 200 M.y.
► Summary: thin, more dense, homogeneous,

8. The Mantle:
 The next layer below the crust is mantle.
 Its thickness extended to a depth of 2890km.
 It is more denser than crust
 It consist of dense silicate rocks
both p-waves & s-waves travel through the mantle
 depths of around 100 km to 250 km arrive later than expected
(because pressure is increasing) indicating a zone of low seismic wave
velocity.

9. Velocity of seismic waves in mantle:
P-waves velocity:
Its velocity is about 8km/s in the upper
mantle and increases up to 13km/s in lower
mantle
 S-waves velocity:
S-waves velocity profile in the mantle is
similar to the p-wave profile. S-waves velocity
time cannot be measured as accurately as p-
waves travel time.

10. The core
The central or innermost portion of
earth below the mantle is core
 it lies at depth of 2900km up to
6370km
 the core is divided into two layers
outer core
inner core
Outer core:
The outer core begins at a depth of 2,890 to 5,150 km.
 The temperature at outer core is about 3700˚C
Inner core:
 The inner section begins at a depth of 5,150 to 6,360km.
 The temperature of inner core is about 4300˚C.

11. Seismologists first determined that the
back and-forth motion of S-waves does not
travel through liquid.
 Then, seismologists noticed that S-waves
do not travel through Earth’s center.
 This observation led to the discovery
that Earth’s core must be at least partly
liquid.