GeologicalForces

ofthe

Earth

Diastrophism

It pertains to any movement of the solid part of the Earth.

• The movement may be strong and sudden that we feel the shaking of the Earth’s surface, we call this Earthquake

Tectonism

Leads to the formation of continents and ocean basins, mountain systems, plateaus, rift valleys, and other features.

Vertical movements in the crust are divided into two types—uplift and subsidence.

Uplift The rising of regions of the Earth’s crust to higher

elevations.Subsidence

The sinking of regions of the Earth’s crust to lower elevations.

Uplift and Subsidence

Uplifting of Depressed Rocks › Uplift can occur when large areas of land rise

without deforming. Areas rise without deforming is process known as

rebound.› When the crust rebounds, it slowly springs back to

its previous elevation.

Subsidence of Cooler Rocks › Rocks that are hot take up more space than cooler

rocks. The lithosphere is relatively hot at mid-ocean ridges, but

cools as it moves farther from the ridge. As it cools,

› The oceanic lithosphere takes up less volume and the ocean floor subsides.

Theory of Isostasy

Isostasy can be explained as the balancing of forces between the effects of gravity on the mass of a section of earth and the resistance of that mass to sinking into the mantle of the earth.

The simplest analogy of isostasy is icebergs (this is based on Archimedes’ Principal).

This explains why the wearing down of mountains and the filling up of the ocean basins have not resulted on a leveled surface over the whole earth.

As vertical adjustments take place, landmasses are folded, buckled and thrusted.

Simple Analogy:

Example:

North Greenland ford cliffs

TRIVIA: The general

term 'isostasy' was coined in 1889 by the American geologist Clarence Clarence Edward DuttonEdward Dutton..

› because it is cooling and the great pressure squeezes parts of the earth into a smaller volume.

› Gravity draws the crust inward causing it to buckle, bend and trench.

Theory of Contraction

Shrinking resulted in a reduction in the Earth’s diameter while the circumference remained unchanged due to folding and buckling of the crust

Theory of Convection

According to this theory, convection currents are set in the crust and heat comes from the disintegration of radioactive elements.

As heat accumulates, rocks become plastic and moves upward causing the surface of the earth to bulge.

convection within the Earth's mantle pushes the plates

movement of a fluid, caused by differences in temperature

Continental Drift Theory

Proposed by a German meteorologist and geophysicist, Alfred Wegener.

Wegener hypothesized that there was an original, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth".

Pangaea was a supercontinent consisting of all of Earth's land masses.

Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland, during the Jurassic period

Continents were joined in a super-continent, called Pangaea (all lands). Over a vast period of time, the continents drifted apart to their current locations.

Numerous geological similarities between South America and Africa.

TRIVIA: Continental

Drift theory was first presented by Alfred Wegener who died two days after his 50th birthday.

Theory of Expansion

Earth is physically expanding in diameter, mass, or both.

An Australian geologist who was an early advocate of the theory of continental drift. His work on plate tectonics reconstructions led him to develop the Expanding Earth hypothesis.

Changes in a rock’s shape due to stress De = “undo” Form = “shape” –tion = “process of”

Deformation of Rocks

Whether a material bends or breaks depends on:

1.How much stress is applied to the material.2.Process by which the shape of a rock

changes because of stress.3.Rock layers bend when stress is placed on

them.4.When enough stress is placed on rocks,

they can reach their elastic limit and break.

2 Major Types of Structural Deformation

Fold Fault

Folding

Folding › The bending of rock layers because of stress in the

Earth’s crust. Types of Folds

› Depending on how rock layers deform, different types of folds are made.

The major types of folds are1. Anticlines2. Synclines3. Monoclines.

Anticlines are upward-arching folds. Synclines are downward, troughlike folds. In a monocline, rock layers are folded so that

both ends of the fold are horizontal.

Anticline oldest rocks occur in the core of a fold Caused by compressional stress A-shaped

Syncline youngest rocks occur in the core of a fold Caused by compressional stress U-shaped

Monocline A fold that has both ends of the fold still

horizontal. There is a middle portion that bends

downwards.

Dip and Strike

Pitching Fold

Joints and Fissures

Faulting

Fault› The surface along which rocks break and slide past

each other.› Some rock layers break when stress is applied.

Fault blocks › The blocks of crust on each side of the fault.

When a fault is not vertical, its two sides are either a hanging wall or a footwall.

Typesof

Faults

NORMAL FAULT - occurs when the crust is extended. Also called as extensional fault or gravity fault. The hanging wall moves DOWNWARD, relative to the footwall.

Dip Slip Faults - These are faults where the major movement is vertical.

• REVERSE FAULT - is the opposite of a normal fault — the hanging wall moves UPWARD relative to the footwall. Reverse faults indicate shortening of the crust.

Normal Faults

Tension forces in Earth's crust cause normal faults.

REVERSE FAULT

• STRIKE-SLIP FAULT - It is usually near vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are also known as SINISTRAL faults. Those with right-lateral motion are also known as DEXTRAL faults

•A special class of strike-slip faults is the transform fault, where such faults form a plate boundary. Transform faults runs along the boundary of a tectonic plate and are also referred to as conservative plate boundaries, as lithosphere is neither created or destroyed.

Oblique Faults – These are faults where the major movements are both horizontal and vertical.

For all naming distinctions, it is the orientation of the net dip and sense of slip of the fault which must be considered, not the present-day orientation, which may have been altered by local or regional folding or tilting.

Earthquakes

Vibrations (seismic waves) within Earth materials are produced by the rapid release of energy

Earth’s crust is in constant motion because of tectonic forces

Earth’s crust can store elastic energy When forces exceed the elastic limits and

structural strength of the rocks, the rocks will break and/or move producing vibrations that travel outward in all directions

What is an Earthquake?

Earthquakes happen because the ground is always moving

About 20 tectonic plates rub against each other, floating above a layer of molten rock

Move about 5 inches per year (about as fast as our fingernails grow!)

Causesof

Earthquake

• An aftershock is a small earthquake that follows the main earthquake.

• A foreshock is a small earthquake that often precedes a major earthquake.

Aftershocks and Foreshocks

Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to

great forces.

Short answer is that earthquakes are caused by “FAULTING” a sudden lateral or vertical movement of

rock along rupture (break) surface.

EARTHQUAKE provide direct evidence of crustal movement

Crustal Plates

Our planet's surface crust is relatively thin and extends to a depth of about 70 kms (40 miles) beneath the oceans to about

150 km (90 miles) beneath the continents.

The crust is now known to be discontinous-- that is, it is broken into a number of large fragments, called “PLATES”,

varying in width from few hundred to many thousands of miles.

Man-Made Quakes

Seismic Waves Are sound travelling through and across the

earth that are produced by earthquakes. Somes waves travel down through the earth and other waves travel over the surface on the ground. The surface waves travel faster than the interior waves. The waves from a large earthquake can be recorded on instruments on the opposite side of the world, having taken about 21 mins to pass right through the eath.

3Types

ofSeismic Waves

P wavesP waves (primary waves) Compressional wave

Particles move back and forth in the same direction as the wave

Travels the fastest Can pass through solids and liquids

(gases also) Does not cause damage

S waveS wave (secondary wave, shear wave) Particles move at right angles to the direction of

the wave Travels slower than P waves Can pass through solids only Does not cause damage Strong movements can be recorded through

seismographs

L waveL wave (long wave, surface wave, ground wave)

Travel along the outer layer of the earth. Two kinds of R (or Rayleigh) waves and L (or

Love) waves, named after the 2 scientist who first described them.

This kind of wave is the last to arrive since it travells relatively slowly.

How do we Measure Earthquakes?

Earthquake waves are recorded by a seismograph and the recording of waves on paper is called seismogram

Effect of

Earthquakes

Landslides

Fire

Seiches

Seismic Sea Wave of Tsunami for “bay wave”

TheEnd

Reported by: Kclyn Canonizado-PabellosaBEED-1