INTRODUCTION INTRODUCTION TO EARTHQUAKE EARTHQUAKE ENGINEERING Earthquake Engineering It can be defined as the branch of engineering devoted to mitigating earthquake hazards. In this broad sense, earthquake engineering covers the investigation investigation and solution of the problems created by damaging earthquakes, and consequently the work involved in the practical application of these solutions, i.e. in planning, designing, constructing and managing earthquake‐resistant structures and facilities.
Scope
Seismicity, Nature, Measures and Recording of earthquakes. Planning for Seismic Risk Assessment & Mitigation Analysis, Design and Construction of Earthquake Resistant Structures Evaluation of Buildings for Earthquake Resistance Retrofitting of Earthquake damaged Structures Earthquake Management and Security
Earthquake An earthquake is the motion or vibration, sometimes violent, of the earth’s surface that follows a follows a release of energy in the earth’s crust. This energy can be can be generated by a sudden movement of segments (plates) of the earth crust, by a volcanic eruption or even by manmade explosions.
Sources of Ground Movements
Tectonic Earthquakes Volcanoes Explosions Collapse of Mines & Large Reservoirs Tsunami
Earthquake Hazards
Failure of Slopes Occurrence of Fire Building Collapse Bridge Collapse Land Slide Disturbance
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History of Earthquakes In Pakistan
Major Earthquakes In Pakistan
1974 Earthquake Hunza, KPK
2005 Earthquake Muzaffarabad, AJK
Magnitude = 7.6
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2008 Earthquake Ziarat, Balochistan
2011 Earthquake Dalbandin, Balochistan
Causes of Earthquakes
Tectonic Earthquakes
These are caused by the sudden movement of large rock masses along geological faults within the earth's crust. The Earth is formed of several layers that have very different physical and chemical properties. The outer layer, which averages about 70 kilometers in thickness, consists of about a dozen large, irregularly shaped plates that slide over, under and past each ot her on top of the partly molten inner layer .Most earthquakes occur at the boundaries where the plates meet.
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Fault:
A fault is a fracture within some particular rocky mass within the earth's crust. Earthquakes are caused by active faults, that is, faults along which the two sides of the fracture move with respect to each other.
Earthquake Focus:
The point on the fault where rupture initiates is referred to as the focus or hypocenter of an earthquake. The hypocenter of an earthquake is described by its depth in kilometers, its map location in latitude and longitude, its date and time of occurrence, and its magnitude. The term epicenter is the point on the earth’s surface directly above the hypocenter.
Volcanic Earthquakes Explosions Collapse Earthquakes
Seismic waves: What happens during an earthquake? During an earthquake, seismic waves arise from sudden movements in a rupture zone (active fault) in the earth's crust. Waves of different types and velocities travel different paths before reaching a ENGR. ANEES KHAN
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building’s site and subjecting the local ground to various motions.The ground moves rapidly back and forth in all directions, usually mainly horizontally, but also vertically.
Two different types of seismic waves are generated by the sudden movement on a fault: P-waves (primary waves) and S-waves (secondary waves). A third type of seismic wave (Surface waves) is generated by the interaction of the P- and S-waves with the surface and internal layers of the Earth.
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Importance of ground conditions: What happens to the structures? If the ground moves rapidly back and forth, then the foundations of the structures are forced to follow these movements. The upper part of the structure however (would prefer) to remain where it is because of its mass of inertia.
In comparison with rock, softer soils are particularly prone to substantial local amplification of the seismic waves.
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Note that the ground displacement amplifies with decrease in soil stiffness.
Case Study
The 1.6 mile ling cypress freeway structure in Oakland, USA, was built in the 1950s. Part of the structure standing on soft mud (dashed red line) collapsed in the 1989 magnitude 6.9 Loma Prieta earthquake. Adjacent parts of the structure (solid red) that were built on firmer ground remained standing. Seismograms (upper right) show that the shaking was esp ecially severe in the soft mud.
The characteristics of each structure are different, whether in size, configuration, material, structural system, age, or quality of construction: each of these ch aracteristics affects the structural response. The ground motion parameters and other characteristic values at a location due to an earthquake of a given magnitude may vary strongly. They depend on numerous factors, such as the distance, direction, depth, and mechanism of the fault zone in the earth's crust (epicenter), as well as, in particular, the local soil characteristics (layer thickness, shear wave velocity).
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Earthquake Magnitude & Intensity: Magnitude: Earthquake magnitude is a quantitative measure of the size of the earthquake at its source. When an earthquake occurs, its magnitude can be given a single numerical value on the Richter Magnitude Scale. The Richter Magnitude Scale measures the amount of seismic energy released by an earthquake. Richter magnitudes < 2.0 2.0-2.9 3.0-3.9 4.0-4.9 5.0-5.9
Description
Earthquake effects
Micro Minor
6.0-6.9 7.0-7.9 8.0-8.9 9.0-9.9 10.0+
Strong Major Great
Micro earthquakes, not felt. Generally not felt, but recorded. Often felt, but rarely causes damage. Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings. Can be destructive in areas up to about 160 kilometres (100 mi) across in populated areas. Can cause serious damage over larger areas. Can cause serious damage in areas several hundred miles across. Devastating in areas several thousand miles across. Never recorded
Light Moderate
Epic
Intensity: Intensity is the way of measuring or rating the effects of an earthquake at different sites. The severity of earthquake shaking is assessed using a descriptive scale – the Modified Mercalli Intensity Scale. Category MM 1: Imperceptible MM 2: Scarcely felt MM 3: Weak MM 4: Largely observed MM 5: Strong
MM 6: Slightly damaging MM 7: Damaging MM 8: Heavily damaging
Definition Barely sensed only by a very few people. Felt only by a few people at rest in houses or on upper floors. Felt indoors as a light vibration. Hanging objects may swing slightly. Generally noticed indoors, but not outside, as a moderate vibration or jolt. Light sleepers may be awakened. Walls may creak, and glassware, crockery, doors or windows rattle. Generally felt outside and by almost everyone indoors. Most sleepers are awakened and a few people alarmed. Small objects are shifted or overturned, and pictures knock against the wall. Some glassware and crockery may break, and loosely secured door s may swing open and shut. Felt by all. People and animals are alarmed, and m any run outside. Walking steadily is difficult. Furnitur and appliances may move on smooth surfaces, and objects fall from walls and shelves. Glassware and crockery break. Slight non-structural damage to buildings may occur. General alarm. People experience difficulty standing. Furniture and appliances are shifted. S ubstantial damage to fragile or unsecured objects. A few weak buildings are damaged. Alarm may approach panic. A few buildings are damaged and some weak buildings are destroyed.
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MM 9: Destructive MM 10: Very destructive MM 11: Devastating MM 12: Completely devastating
Some buildings are damaged and many weak buildings are destroyed. Many buildings are damaged and most weak buildings are destroyed. Most buildings are damaged and many buildings are destroyed. All buildings are damaged and most buildings are destroyed.
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