Engineering Seismology seminar or presentation presentation
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29-05-2010, 12:50 PM
Engineering Seismology.ppt (Size: 1.12 MB / Downloads: 432)
Introduction to Engineering Seismology
Dr. G. Madhavi Latha
Dept. of Civil Engineering
Indian Institute of Science
Seismology is the branch of Geophysics concerned with the study and analysis of Earthquakes and the science of energy propagation through the Earth's crust.
Engineering Seismology is concerned with the solution of engineering problems connected with the Earthquakes. Seismology is extremely important because:
Study of earthquakes gives us important clues about the earthâ„¢s interior
Understanding earthquakes allows us to minimize the damage and loss of life
What is an earthquake
An earthquake is the vibration of Earth produced by the rapid release of accumulated energy in elastically strained rocks
Energy released radiates in all directions from its source, the focus
Energy propagates in the form of seismic waves
Sensitive instruments around the world record the event
What causes an earthquake
Movement of Tectonic Plates
Earth is divided into sections called Tectonic plates that float on the fluid-like interior of the Earth. Earthquakes are usually caused by sudden movement of earth plates
Rupture of rocks along a fault
Faults are localized areas of weakness in the surface of the Earth,sometimes the plate boundary itself
The Focus and Epicenter of an Earthquake
The point within Earth where faulting begins is the focus, or hypocenter
The point directly above the focus on the surface is the epicenter
Elastic Rebound Theory
Rocks bend under stress while storing elastic energy. When the strain in the rocks exceeds their strength, breaking will occur along the fault. Stored elastic energy is released as the earthquake. Rockssnap back, or rebound to their original condition.
Foreshocks and aftershocks
Adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks
Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years
Study of earthquakes
The study of earthquake waves, Seismology, dates back almost 2000 years to the Chinese Seismographs, instruments that record seismic waves. The first seismograph called Di-Dong-Di was invented by Cheng Heng (132 A.D.).
The ancient Chinese seismograph consist of a special vase that had eight sculpted dragons mounted around the vase in eight primary directions. Each dragon held in its mouth a metal ball. When the ground shook, some of the balls would fall from the mouths of the dragons into the waiting mouths of the sculpted frogs to show how the ground had moved.
The energy released during the earthquake travels as waves
Modern Seismograph can measure the intensity and duration of these waves in different directions.
Seismogram is visual record of arrival time and magnitude of shaking associated with seismic wave, generated by a seismograph.
Location and Intensity of Earthquake
seismographic stations around the World work together to
record earthquake location
determine earthquake strength
Earthquakes usually occur at some depth below the ground
Surface. The depth can also be calculated from seismograph
Earthquake foci are described as:
Shallow: less than 70 km depth
Intermediate: 70 - 300 km depth
Deep: 300 - 700 km depth
90% of earthquake foci are less than 100 km deep
Large earthquakes are mostly at < 60 km depth
No earthquakes occur deeper than 700 km
Strange Animal Behavior
stress in the rocks causes tiny hairline fractures to form, the cracking of the rocks evidently emits high pitched sounds and minute vibrations imperceptible to humans but noticeable by many animals.
unusual increase in the frequency of small earthquakes before the main shock
Changes in water level
porosity increases or decreases with changes in strain
based of the chronological distribution of major earthquakes
PROTECTING AGAINST EARTHQUAKE DAMAGE
Prepare a Seismic Risk Map for the globe which identifies rock types, liquefaction potential, landslide potential.
Extensive geologic surveying has to be done to identify all active faults, including hidden faults.
Earthquake Resistant Design of Structures
Enact building codes to design and build earthquake-resistant structures in high seismic risk areas. wood, steel and reinforced concrete are preferred as they tend to move with the shaking ground (unreinforced concrete and heavy masonry tend to move independently and in opposition to the shaking, battering one another until the structure collapses)
Critical facilities such as nuclear power plants and dams should be built on stable ground and as far as possible from active faults.
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01-10-2010, 09:41 AM
Seismograph design is discussed in the general terms of band pass, control of response characteristics through mechanical and electrical modifications of the system, and the limitations imposed on sensitivity when some seemingly innocuous numbers are ignored. Earth vibration amplitudes of one Angstrom or less, and power-sensing levels as low as 10-20 watts are considered, implying that instrumental noise levels should be even lower under some circumstances. A discussion of transducer elements leads to the conclusion that the incorporation of a galvanometer into the motion-amplifying system offers at least as good a system as can be devised by other means. The concept of a platform stabilized against seismic disturbances is outlined as an interesting and probably important sidelight on seismograph design. Remarks on mechanical construction are included as guidance to designers because certain details, such as spring proportions, lever systems, crossed flexure plate hinges and suspension members with controlled regions of bending have been found extremely effective while other details of design have produced elusive troubles. Some design features are illustrated in the construction of certain seismographs in whose design the authors have an interest. The problem of level sensitivity for horizontal component seismometers is outlined to show its basic nature, and some possible solutions. Earthquakes generate seismic waves which can be detected with a sensitive instrument called a seismograph. Advances in seismograph technology have increased our understanding of both earthquakes and the Earth itself. Perhaps the earliest seismograph was invented in China A.D. 136 by a m an named Choko.
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01-01-2011, 11:59 AM
ELEMENTS OF SEISMOLOGY.ppt (Size: 3.19 MB / Downloads: 475)
It is the study of the generation, propagation, and recording of elastic waves in the earth and the sources that cause them.
The word ,’seismic’ means with reference to earthquakes.
The study of causes and nature of earthquakes, seismic waves ,measurement of seismic vibrations ,form am major part of seismology.
Father of Earthquake-Winthrop
He says" It is a wave phenomenon with a train of oscillating waves radiating from an underground center and follows the laws of simple harmonic motion.”
Shaking of the Earth caused by a sudden movement of rock beneath its surface.
The release of stored elastic energy caused by sudden fracture and movement of rocks inside the Earth. Part of the energy released produces seismic waves, like P, S, and surface waves.
Causes of Earthquakes
Reservoir induced Earthquakes
Mining induced Earthquakes
Plate Tectonics Theory
The plate tectonics theory is a starting point for understanding the forces within the Earth that cause earthquakes.
Alfred Wegener is the Pioneer to study about plate tectonics.
Plates are thick slabs of rock that make up the outermost 100 kilometers or so of the Earth.
Plates are 120km thick in continental regions and 80km thick in oceanic regions.
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16-03-2011, 08:53 PM
plz can u send me the report of this as fast as u can