1. Engineering Geology CE1011 Earthquakes Dr. SaMeH Saadeldin Ahmed Associate Prof. Mining and Environmental Engineering Email: s.mohamed@mu.edu.sa

2. Engineering Geology CE1012 Contents 1. Causes of Earthquakes a) Elastic rebound Theory b) Volcanic Theory c) Landslides 2. Distribution of Earthquakes 3. Types of Waves 4. Focus and Epicentre 5. Size of Earthquakes 6. Earthquakes in Arab world 7. Constitution of the Earth

3. Engineering Geology CE1013 An earthquake is the result of a sudden release of energy in the Earth’s crust that creates seismic waves. Some of these vibrations are severe and destructive, others are too low to be recorded unless very sensitive instruments are used for this purpo se (Seismograph). Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe.

4. Engineering Geology CE101 4 1. Causes of Earthquakes a) Elastic rebound theory The elastic rebound theory is an explanation for how energy is spread. As rocks on opposite sides of a fault are subjected to force and shift, they accumulate energy and slowly deform until their internal strength is exceeded. At that time, a sudden movement occurs along the fault, releasing the accumulated energy, and the rocks snap back to their original unreformed shape during earthquakes.

5. Engineering Geology CE1015 b) Volcanic theory One of the most causes of earthquakes is volcanoes. As volcanoes occurs due to great explosives or sudden movements of magma inside the earth, it reflects movements in the earth’s crust that causes earthquake. c) Landslides Earthquakes are a major cause of landslides. Landslides, in turn, are a major contributor to the damage and causalities associated with earthquakes.

6. 6 2. Distribution of Earthquakes Earthquakes take place or have taken place in all parts of the world. 80% of all seismic energy is generated from a belt that is found at the border of the Pacific Ocean. A great deal of volcanoes is also found there, and volcanoes set off many earthquakes. Japan, the Philippine Islands, New Guinea, and New Zealand. A second seismic belt produces 15% of seismic activity. It goes through southern Asia to the region of the Mediterranean Sea. The final 5% of seismic energy comes from parts of the Atlantic, and Indian Oceans.

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8. 8 This map shows the distribution of earthquakes around the world

9. Engineering Geology CE101 9 3. Types of Waves a)P rimary waves (P) Primary waves (P-waves) are compression waves that are longitudinal in nature. It has the highest velocity and is therefore the first to be recorded by seismographs. These waves can travel through any type of material, including fluids, and can travel at nearly twice the speed of S waves. Typical speeds are 330 m/s in air, 1450 m/s in water and about 5 000 m/s in granite.

10. Engineering Geology CE10110 b) Secondary waves (S) Secondary waves (S-waves) are shear waves that are transverse in nature. These waves arrive at seismograph stations after the faster moving P waves. S -waves are slower than P waves, and speeds are typically around 60% of that of P waves in any given material.

11. Engineering Geology CE10111 c) Surface or Longitudinal waves (L) Surface waves (L-waves) are similar to water waves and travel along the Earth's surface. They travel slower than body waves. Because of their low frequency, long duration, and large amplitude. They can be the most destructive type of seismic wave. They are called surface waves because they diminish as they get further from the surface.

12. Engineering Geology CE10112 Surface waves Body waves

13. Engineering Geology CE10113 4. Focus of Earthquake An earthquake's point of initial rupture is called its focus or hypocenter. وتصنف الزلازل اعتمادا على عمقها البؤري إلى: –ا–الز زل الضحلة: وهي الز زل التي يزيد عمق بؤرتها عن 50 كيلومترا. –ا–الز زل المتوسطة: وهي الز زل التي يقع عمق بؤرتها بين 50 – 250 كيلومترا. –ا–الز زل العميقة: وهي الز زل التي يقع عمقها البؤري بين 250 – 700 كيلومترا.

14. Engineering Geology CE10114 5. Epicentre The epicenter is epicenterthe point at ground level directly above the hypocenter Epicentre Focus

15. Engineering Geology CE10115 Hypocenter (Focus) and epicenter of an earthquake An earthquake's focus is the position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture. This occurs at the focal depth below the epicenter. strain fault epicenter

16. Engineering Geology CE10116 6. Size of Earthquakes The earthquakes are measured by two ways: its intensity and magnitude a) Intensity ( Mercalli) The Mercalli intensity scale is a seismic scale used for measuring the intensity of an earthquake. The scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale from I (not felt) to XII (total destruction).

17. Engineering Geology CE10117 b) Magnitude (Richter magnitudes) The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismograph. The scale is a base-10 logarithmic scale. The magnitude is defined as the logarithm of the ratio of the amplitude of waves measured by a seismograph to an arbitrary small amplitude. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0, and corresponds to an energy release of √1000 ≈ 31.6 times greater.

18. Engineering Geology CE10118 MagnitudeDescription Mercalli intensity Average earthquake effects Less than 2.0MicroI to II Micro earthquakes, not felt, or felt rarely by sensitive people. Recorded by seismographs. 2.0–2.9MinorI to IIIGenerally felt by few to many people up to several miles/kilometers from the epicenter. Weak shaking in the felt area. Recorded by seismographs. 3.0–3.9II to VOften felt in the area by at least many people, but very rarely causes damage. Can be felt tens of miles/kilometers from the epicenter, but at weak intensity 4.0–4.9LightIII to VIINoticeable shaking of indoor objects and rattling noises. Many people to everyone feel it with slight to strong intensity. Slightly felt outside. Generally causes none to slight damage. Moderate, heavy, major, or significant damage unlikely. Some falling of objects.

19. Engineering Geology CE10119 MagnitudeDescription Mercalli intensity Average earthquake effects 5.0–5.9ModerateIV to VIII Can cause moderate to major damage to poorly constructed buildings. At most, none to slight damage to well-designed buildings. Can be felt hundreds of miles/kilometers from the epicenter at low/lower intensity.. 6.0–6.9StrongVI to XCan be damaging/destructive in populated areas. Damage to many to all buildings; poorly designed structures. Most likely felt hundreds of miles/kilometers from the epicenter. Can be damaging further from the epicenter; up to tens of miles/kilometers away. Death toll between none and 25,000. 7.0–7.9MajorVII to XIICan cause great(er) damage over larger areas. Damage to most or all buildings. Most likely will be felt several hundred miles/kilometers away. Death toll is usually between none and 250,000.

20. Engineering Geology CE10120 MagnitudeDescription Mercalli intensity Average earthquake effects 8.0–8.9 Great VIII to XII Can cause major damage across very wide, large areas. Many to all buildings in epicentral area severely damaged. Very strong shaking up to a few hundred kilometers away. Death toll is usually between 100 and one million;. 9.0–9.9Destructive to very devastating in extremely large areas. Many to all buildings severely damaged or completely destroyed up to tens of miles from the epicenter. Effects will go for a long time. Ground changes. Death toll usually between 1,000 and over one million. 10.0+Massive/EpicIX to XIIHeavy, widespread, colossal damage/devastation across enormous areas. Will destroy buildings fairly easily and quickly. Death toll most likely will be over 25,000 people. Large ground changes. Effects will last for an extremely long time. It has never been recorded.

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22. Engineering Geology CE10122 7. Constitution of the Earth الأرض تتكون من قشرة Crustلا يزيد سمكها عن حوالي 35 كيلومترا، تقع على رداء Mantleيمتد حتى عمق 2900 كيلومترا. وتوجد تحت القارات صخور رسوبية وجرانيتية ومتحـولة Sialوهي غنية جدا بمادة السيليكــا (70 % تقريبا) والألومينا وتقع فوق صخور البازلت. ويوجد تحت المحيطات قشرة صخرية تتكون من الصخور البازلتية Simaوهي تمثل النطاق الداخلي من القشرة ا رضية حيث تقل فيها نسبة السيليكون وتزيد نسبة المغنسيوم.

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24. Engineering Geology CE10124 Quiz (4) Write your name, ID, and you have 3 minutes to answer online the following question A)Landslides is one of the theories explaining the earthquakes, what are the other famous two theories: 1) …………………………… 2) …………………………