Geodesy, GE 202

Kutubuddin ANSARI

kutubuddin.ansari@ikc.edu.tr

Lecture 3, Oct 11, 2016Interior of the Earth

•The Earth's mass is about 5.98 x 1024 kg.

• Earth is the densest planet in our Solar System (mass/volume).

•Earth is made of several layers with different compositions and physical properties, like temperature, density, and the ability to flow.

Earth

CrustMantle Core

The Earth is divided into three main layers.

Earth Layers

Shell = crustEgg white = mantleYolk = core

How are the earth’slayers similar to anegg?

Earth Layers

Earth LayersCrust = 0 to 50 kmMantle= 50 to 2900 kmOuter Core= 2900 to 5100 kmInner Core= 5100 to 6371 km

Earth Layers

The Crust

The Earth’s crust is like the skin of an apple. It is very thin compared to the other three layers.

The crust makes up 1% of the Earth.

The crust of the Earth is broken into many pieces called plates.

CrustCrust

•Thinnest layer (0-50 km)•Two types of crust

Continental crustOceanic crust

The Crust

ContinentalAverage 30 km

OceanicAverage 5-8 km

The Crust

The Mantle

• The mantle is the layer below the crust.

• The mantle is the largest layer of the Earth.

• The mantle is divided into two regions: the upper and lower sections.

•Extremely Thick! (2,900 km)•It is too far down to drill

How do we know what it is made of?

•Like the mineral olivine •Large amounts of iron and magnesium

The Mantle

The Core

The core of the Earth is like a ball of very hot metals.

The outer core is liquid.

The outer core is made up of iron and is very dense

Outer Core

The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move.

The inner core is a

solid

Inner Core

Plate Tectonics

Plate Tectonics

• The Earth’s crust is divided into 12 major plates which are moved in various directions.

• This plate motion causes them to collide, pull apart, or scrape against each other.

• Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.

• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

• Plates are made of rigid lithosphere.

• The lithosphere is made up of the crust and the upper part of the mantle.

Plate Tectonics

Plate Tectonics

• Below the lithosphere which makes up the tectonic plates is the asthenosphere.

• “Plates” of lithosphere are moved around by the underlying hot mantle convection cells

Plate Tectonics

The lithosphere is broken up into plates that move horizontally across the Earth.

Earth’s Layered Structure

• Divergent

• Convergent

• Transform

Three types of plate boundary

Plate BoundariesConvergent

• Ocean-continent

• Ocean-ocean

• Continent-continent

Plates move away from each other

Plate BoundariesDivergent

• Plates move away from each other• New crust is being formed

Plate BoundariesTransform

• Plates slide past one another

• Crust is neither created nor destroyed

• The earthquakes are not randomly distributed over the globe

• At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.

Figure showing the distribution of earthquakes around the globe

Earthquakes and Plate Tectonics…

Length

Wid

th

DIP Angle

Slip

FaultRake Fault is a planar

fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of rock mass movement.

DIP Angle (δ )Rake (ψ)

Depth

Top Depth

LengthWid

th

Bottom DepthEarth Surface

( ) Bottom Depth Top DepthSin Dip AngleWidth

Fault

Strike-Slip Fault

•  The movement of blocks along a fault is horizontal.

•Rake zero (0o ) Slip

•If the block on the far side of the fault moves to the left, the fault is called Left-lateral (sinistral) Fault.

•If the block on the far side moves to the right, the fault is called Right-lateral (dextral) Fault.

Strike-Slip Fault

Dip-Slip Fault

•  The movement of blocks along a fault is vertical.

•Rake (90o )

Slip

•If the hanging wall moves downward relative to the footwall, the fault is called Normal (extensional) Fault.

•If the hanging wall moves upward relative to the footwall, the fault is called Reverse Fault. Reverse faults indicate compressive shortening of the crust.

• Reverse fault having dip angle less than 450 is called Thrust Fault.

Dip-Slip Fault

Normal Fault

Thrust Fault

Reverse Fault

Dip-Slip Fault

Oblique-Slip Fault

•A fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault.

• Rake will be (0 < ψ >90)

Slip

The Geometry of the fault having parameters (length, width, depth, dip angle) can be given by analytically by Green function (G):

2 2

1 1

AL AW

AL AW

G d d Len

gth

Wid

th

DIP

Slip

Length(AL) Wid

th(A

W)

LengthW

idt

h

cos sinx ALy d AW

(δ)

Dislocation Theory

S is Slip For Oblique Slip

S= s.cos ψ + s.sin ψ

d= sG(m)

Relationship between dislocation field (d) and the fault geometry G(m)

Dislocation Theory

Consider the case we have observed data d1, d2, ……. dn and the Green function of each observation data are G1, G2, ……. Gn respectively, Then:

Suppose we have n GPS Stations

Dislocation Theory

Richter magnitude scale

The Richter magnitude scale (Richter scale) assigns a magnitude number to quantify the energy released by an earthquake.

Seismic moment = μ* slip*rupture area MO= μ*s*A

MO= μ*s*L*Wμ = shear modulus of the crust (approx 3x1010 N/m2)L= Length of finite rectangular faultW= Width of finite rectangular faults = slip

μ = 3x1010 N/m2

L=400 kmW= 50 kms = 10 mmMO= μsLWMo=(3x1010 )x(10 x10-3 )x (400 x 103 )x(50 x 103 )Mo=(3x1010 )x(10-2 )x (2 x 105)x(1x105 )Mo=6x1018

1810log (6 10 ) 6.07

1.5wM Nm

Richter magnitude scale

1810

10

log (6 10 ) 6.071.5

log(6) 18log (10) 6.071.5

0.778+18 6.071.5

6.448

w

w

w

w

M

M

M

M Nm

Richter magnitude scale