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Diastrophism

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by

Bill Pasco

on 11 March 2014

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Transcript of Diastrophism

Types of Earth Movement
1. Uplift
2. Subsidence
3. Thrust

Structural Features of Earth Movement
Deformation of Rocks
Folds
Dip and Strike
Pitching Fold
Joints and Fissures
Faulting
Types of Faults
Normal Fault
Reverse Fault
Thrust Fault
Diastrophism
Diastrophism
is the large-scale deformation of Earth’s crust by natural processes
, which leads to the formation of continents and ocean basins, mountain systems, plateaus, rift valleys, and other features by mechanisms such as lithospheric plate movement (that is, plate tectonics), volcanic loading, or folding.

Theories of Diastrophism
Isostasy Theory
Contraction Theory
Convection Theory
Continental Drift Theory
Expansion Theory
States that as rock from higher region is removed by erosion and deposited on lower region, the higher region slowly rises while the lower region becomes heavier and slowly sinks.
Isostasy Theory
States that Earth is gradually shrinking. As the shrinkage occurs, the heavier blocks of the crust sink while the weaker strata are crowded and squeezed upward.
Contraction Theory
The Pushing and Folding of rocks through
Convection Currents
Convection Theory
Continental drift is the movement of the Earth's continents relative to each other by appearing to drift across the ocean bed.
Continental Drift Theory
States that the earth is gradually expanding. Expansion of the earth would change the continents' positions
Expansion Theory
The effects of diastrophism is more clearly seen in rocks. Any deformation of rocks is shown in tilts, bends, tweaks in the layer.
Deformation of Rocks
A bend or fissure in a rock can be likened to waves on the ocean. Each has a crust or upfold and a through or downfold.
Folds
Dip - is the between the Horizontal plane and a structural surface.
Strike - is the direction of a line along the edge of an inclined bed where it meets the horizontal plane.

The Strike is always at the right of the Dip
Dip and Strike
Folds whose
axes
slant downward at each end of an imaginary line running along the top of an anticline or along the bottom of a sycline are called the axes of the Fold. The angle between the axis and the horizontal is called
pitch
Pitching Fold
A
joint
is a fracture or a little separation between the rock walls while
fissures
are cracks or actual gaps between the rock walls.
Joints and Fissures
It refers to the surface along which a rock body has been broken and has been displaced.
Faults
A low angle fault (45 degrees or less) in which the hanging wall is moved upward in relation to the foot wall. It is characterized by the horizontal compression rather than by vertical displacement.
Thrust Fault
Also called gravity fault. a dip-slip fault in which the hanging wall moves downward relative to the footwall.
Normal Fault
Is the material above the fault plane that moves up in relation to the material below. It shows the surface area of the crust.
Reverse Fault
Earthquake
Is a ground displacement associated with the sudden release, in the form of seismic waves of built-up stress the
Lithosphere.

Causes of Earthquakes
Crustal Plate Movement
Man-made Quakes
Crustal Plate Movement
The plates are moving in slow, continual motion with respect to each other. Current within the hot, molten interior of the earth, produced by thermal convection and the earth's rotation are thought to underlie plate movement.
Man-made Quakes
Seismologists believe that both man-made reservoirs and deep wells lead to an increase in the pore-water pressure of underlying rocks, lessening their tensile strength. Also an increase in water content may lubricate already existing fracture zones and may lead to active faulting.
Seismic Waves
Seismic waves are sound waves traveling through and across the earth that are produced by earthquakes. Some waves travel down through the earth and other waves travel over the surface of the ground.
Primary Waves
These are a kind of longitudinal wave, identical in character to a sound wave passing through a liquid or gas.
The particles involved in these waves move forward and backward in the direction of wave travel, causing relatively small displacements.
Shear Wave or Secondary Wave
Particles oscillate back and forth at right angles to the direction of wave travel, Shear waves cause strong movements that can be recorded on seismographs.
Surface Waves
These are waves that travel along the outer layer of the earth.
This kind of wave is the last to arrive since it travels relatively slowly.
Particles involved in surface waves move in an orbit similar to the particles of water waves.
Effects of Earthquake
Soil Reaction
Seiches
Seismic Sea Waves or
Tsunami
Soil Reaction
Landslides
Liquification
Compaction
Soil Reaction
Seiches
These are long-period oscillations of the water level due to large and generally far distant earth tremors.
Seiches
Tsunami
A rapidly moving ocean wave generated by earthquake activity is capable of inflicting heavy damage in coastal regions.
Tsunami
Earthquake Predictions
Statistical Data
Earthquake Precursors Phenomena
Statistical Data
From the frequency of earlier recorded quakes in a given region, general statistical statements about future probabilities can be made.
Earthquake Precursors Phenomena
These are the things that happen or rock properties that change prior to an earthquake. From these, it may be possible to identify warning signs of an earthquake before it occurs.
Precursors
Seismicity
Subsidence and Uplift
Wave speeds
Water levels in wells
Geomagnetism
Geoelectricity
Strains
Radon content of ground water
Animal Behavior
Seismicity
A swarm of small tremors called foreshocks frequently, but not always precede a major earthquake.
Subsidence and Uplift
A vertical movement of surface of the land indicates a build-up of strains in the crust.
Wave Speeds
A change in the ratio of P and S waves. Velocity changes the strain of the rocks, as well as water content and other factors.
Water levels in wells
Underground water levels often rise or fall before earthquakes.
Geomagnetism
Changes in the earth's magnetic field have been measured prior to earthquakes in several places.
Geoelectricity
As water content in rock changes, so does the electrical resistance. When rocks become strained and microscopic cracks appear, more water can enter lowering electrical resistance.
Strains
The build-up of strain along fault lines can be measured by determining relative displacement between two points. Changes in rates of displacement could indicate a coming earthquake.
Radon Content of Ground Water
Radon is a slightly radioactive gas, found naturally in ground and well water.
Animal Behavior
Some animals have been claimed to show unusual and restless behavior just before an earthquake. The validity of this claim is not yet established.
The Philippines as an Earthquake Country
The Philippine Archipelago lies between two major tectonic plates of the world.
The Northwestward-moving Pacific Plate is presently pushing the Philippine Sea Plate beneath the eastern side of our archipelago at a rate of about 7cm per year.
Earthquake Generators in the Philippine Archipelago
Philippine Trench
East Luzon Trench
Manila Trench
Collisional Zone between Palawan and Mindoro
Negros Trench
Collisional Zone between Zamboanga Peninsula and Western Mindanao
Sulu Trench
Cotabato Trench
Davao Trench
Philippine Fault Zone
Many active faults (e.g. Lubang, Tablas, Casiguran, and Mindanao Faults)
Intensity versus Magnitude
Magnitude and Intensity measure different characteristics of earthquakes.
Magnitude measures the energy released at the source of the earthquake. Magnitude is determined from measurements on seismographs.
Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment.
Magnitude vs Intensity
Abbreviated Modified Mercalli Intensity Scale
I. Not felt except by a very few under especially favorable conditions.

II. Felt only by a few persons at rest, especially on upper floors of buildings.

III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.
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