Geological Aspects of Earthquake PDF

⁎ Seismic Regions in the World ⁎ Earthquake Genesis ⁎ Earthquake Propagation ⁎ Measurement of Earthquakes MODULE 2 CEnS 152 GEOLOGICAL ASPECTS OF EARTHQUAKE...

⁎ Seismic Regions in the World ⁎ Earthquake Genesis ⁎ Earthquake Propagation ⁎ Measurement of Earthquakes MODULE 2 CEnS 152 GEOLOGICAL ASPECTS OF EARTHQUAKE EARTHQUAKE 10/10/2024 10:14 am ENGINEERING CEnS 152 1  LEARNING OUTCOMES After discussing this module, the students must be able to: Identify the major seismic regions in the world. Describe the process of earthquake genesis related to tectonic plate movement. Explain how seismic waves propagate through the Earth's layers. Identify the instruments and scales used to measure earthquakes. Analyze the relationship between earthquake magnitude and intensity, and their implications on infrastructure. EARTHQUAKE 10/10/2024 10:14 am 2 ENGINEERING CEnS 152 2  Seismic Regions in the World ▪ Identify the major seismic regions in the world. EARTHQUAKE 10/10/2024 10:14 am 3 ENGINEERING CEnS 152 3  SEISMIC ZONES Earthquakes do not occur in all geographical locations around the world. Rather, they take place within certain limited areas. Earthquakes have been recorded instrumentally since the beginning of the twentieth century at a large number of seismographic stations distributed throughout the world. These seismic zones are located through numerous seismic data collected worldwide. EARTHQUAKE 10/10/2024 10:14 am 4 ENGINEERING CEnS 152 Earthquakes are not random events but occur within specific regions around the world, known as seismic zones. Thanks to seismographic data collected since the early 20th century, we can now track where and when earthquakes have happened, their magnitude, and where future ones might occur. This information is summarized in seismicity maps, which display the locations and intensities of past earthquakes. These maps are crucial for planners, engineers, and officials involved in earthquake mitigation, and they have also been instrumental in the development of plate tectonic theory. 4  SEISMIC ZONES GLOBAL SEISMOGRAPHIC NETWORK (GSN). The U.S. Geological Survey (USGS) operates in cooperation with a consortium of many universities, an international network of seismographic stations named the Global Seismographic Network (GSN). This network, designed to obtain high quality data in digital form and be able to access these data by computer via the World Wide Web, monitors and records earthquakes, volcanic eruptions, and nuclear explosions throughout the world. The GSN provides near-uniform, worldwide monitoring of the Earth, with over 150 modern seismic stations distributed globally. EARTHQUAKE 10/10/2024 10:14 am 5 ENGINEERING CEnS 152 Earthquakes are not random events but occur within specific regions around the world, known as seismic zones. Thanks to seismographic data collected since the early 20th century, we can now track where and when earthquakes have happened, their magnitude, and where future ones might occur. This information is summarized in seismicity maps, which display the locations and intensities of past earthquakes. These maps are crucial for planners, engineers, and officials involved in earthquake mitigation, and they have also been instrumental in the development of plate tectonic theory. 5  SEISMIC ZONES GLOBAL SEISMOGRAPHIC NETWORK (GSN) EARTHQUAKE 10/10/2024 10:14 am 6 ENGINEERING CEnS 152 There is one station in the country which is situated in Davao. (Station Code: DAV) There is also nearest which is in Taipei, Taiwan (Station Code: TATO) Link: https://earthquake.usgs.gov/monitoring/operations/network.php?virtual_n etwork=GSN 6  SEISMIC ZONES Therefore, it is now possible to know where and when earthquakes have occurred in the past, how large they have been, and where in the world earthquakes are likely to occur again. Seismicity is the description of the time, location, size, and frequency of the earthquakes that have occurred in a specific region and these are portrayed in a form of Seismicity Maps. Seismicity maps show the geographical location where earthquakes have occurred during a specified time interval and describe the intensity of these earthquakes by means of circles or dots of different sizes. EARTHQUAKE 10/10/2024 10:14 am 7 ENGINEERING CEnS 152 Earthquakes are not random events but occur within specific regions around the world, known as seismic zones. Thanks to seismographic data collected since the early 20th century, we can now track where and when earthquakes have happened, their magnitude, and where future ones might occur. This information is summarized in seismicity maps, which display the locations and intensities of past earthquakes. These maps are crucial for planners, engineers, and officials involved in earthquake mitigation, and they have also been instrumental in the development of plate tectonic theory. 7  WORLD SEISMICITY EARTHQUAKE 10/10/2024 10:14 am 8 ENGINEERING CEnS 152 This figure shows the distribution of earthquakes around the globe in the period between 1963 and 1988 collected by USGS. It may be seen from this map that the world’s areas of high seismicity are: 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacifi c side of Colombia, Ecuador, and Peru all the way down to Chile 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand 3. An east–west trans-Asiatic zone running from Burma through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea 4. A zone that follows the submarine Mid-Atlantic Ridge, which extends along the full length 5. of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and 6. Tristan da Cunhan 8  WORLD SEISMICITY 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacific side of Colombia, Ecuador, and Peru all the way down to Chile EARTHQUAKE 10/10/2024 10:14 am 9 ENGINEERING CEnS 152 This figure shows the distribution of earthquakes around the globe in the period between 1963 and 1988 collected by USGS. It may be seen from this map that the world’s areas of high seismicity are: 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacifi c side of Colombia, Ecuador, and Peru all the way down to Chile 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand 3. An east–west trans-Asiatic zone running from Burma through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea 4. A zone that follows the submarine Mid-Atlantic Ridge, which extends along the full length 5. of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and 6. Tristan da Cunhan 9  WORLD SEISMICITY 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand EARTHQUAKE 10/10/2024 10:14 am 10 ENGINEERING CEnS 152 This figure shows the distribution of earthquakes around the globe in the period between 1963 and 1988 collected by USGS. It may be seen from this map that the world’s areas of high seismicity are: 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacifi c side of Colombia, Ecuador, and Peru all the way down to Chile 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand 3. An east–west trans-Asiatic zone running from Burma through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea 4. A zone that follows the submarine Mid-Atlantic Ridge, which extends along the full length 5. of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and 6. Tristan da Cunhan 10  WORLD SEISMICITY 3. An east–west trans-Asiatic zone running from Burma (Myanmar) through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea EARTHQUAKE 10/10/2024 10:14 am 11 ENGINEERING CEnS 152 This figure shows the distribution of earthquakes around the globe in the period between 1963 and 1988 collected by USGS. It may be seen from this map that the world’s areas of high seismicity are: 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacifi c side of Colombia, Ecuador, and Peru all the way down to Chile 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand 3. An east–west trans-Asiatic zone running from Burma (Myanmar) through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea 4. A zone that follows the submarine Mid-Atlantic Ridge, which extends along the full length 5. of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and 6. Tristan da Cunhan 11  WORLD SEISMICITY 4. A zone that follows the submarine Mid- Atlantic Ridge, which extends along the full length of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and Tristan da Cunha EARTHQUAKE 10/10/2024 10:14 am 12 ENGINEERING CEnS 152 This figure shows the distribution of earthquakes around the globe in the period between 1963 and 1988 collected by USGS. It may be seen from this map that the world’s areas of high seismicity are: 1. A zone that extends from the Aleutian Islands through Alaska; the Pacific side of Canada, the United States, and Mexico; Central America; the Pacifi c side of Colombia, Ecuador, and Peru all the way down to Chile 2. A zone that goes from the Kamchatka Peninsula in Russia; through the Kuril Islands, Japan, Taiwan, the Philippines; to New Guinea, Indonesia, and New Zealand 3. An east–west trans-Asiatic zone running from Burma (Myanmar) through the Himalayan Mountains and the Middle East to the Caucasus Mountains and the Mediterranean Sea 4. A zone that follows the submarine Mid-Atlantic Ridge, which extends along the full length of the Atlantic Ocean and appearing above the surface in Iceland, the Azores Island, and Tristan da Cunha 12  WORLD SEISMICITY The first two zones constitute what is known as the circum-Pacific seismic belt or the Ring of Fire. Approximately 80% of the world’s largest earthquakes take place in this belt. The third one is called the Eurasian or Alpine– Himalayan Belt. Although it only accounts for ∼17% of the world’s largest earthquakes, some of the most destructive earthquakes have occurred in that belt. EARTHQUAKE 10/10/2024 10:14 am 13 ENGINEERING CEnS 152 The Earth's most significant seismic zones are concentrated in specific regions, with the circum-Pacific seismic belt, also known as the Ring of Fire, being the most active. This zone encircles the Pacific Ocean and accounts for approximately 80% of the world's largest earthquakes. The high level of seismic activity here is due to the complex interactions between multiple tectonic plates, including subduction zones where one plate is forced under another, leading to frequent and powerful earthquakes. The Eurasian or Alpine-Himalayan Belt is another major seismic zone, though it only accounts for about 17% of the world's largest earthquakes. Despite the lower percentage, this region has been the site of some of the most destructive earthquakes in history. The seismic activity in this belt is primarily due to the collision between the Indian Plate and the Eurasian Plate, which has created the Himalayan mountain range and led to significant seismic hazards in the region. 13  WORLD SEISMICITY EARTHQUAKE 10/10/2024 10:14 am 14 ENGINEERING CEnS 152 The Earth's most significant seismic zones are concentrated in specific regions, with the circum-Pacific seismic belt, also known as the Ring of Fire, being the most active. This zone encircles the Pacific Ocean and accounts for approximately 80% of the world's largest earthquakes. The high level of seismic activity here is due to the complex interactions between multiple tectonic plates, including subduction zones where one plate is forced under another, leading to frequent and powerful earthquakes. The Eurasian or Alpine-Himalayan Belt is another major seismic zone, though it only accounts for about 17% of the world's largest earthquakes. Despite the lower percentage, this region has been the site of some of the most destructive earthquakes in history. The seismic activity in this belt is primarily due to the collision between the Indian Plate and the Eurasian Plate, which has created the Himalayan mountain range and led to significant seismic hazards in the region. 14  WORLD SEISMICITY Earthquakes along the Mid-Atlantic Ridge are obviously not destructive, but they are important because they suggest a correlation between the occurrence of earthquakes there and the existence of the ridge. EARTHQUAKE 10/10/2024 10:14 am 15 ENGINEERING CEnS 152 Finally, the Mid-Atlantic Ridge is a less destructive but geologically important seismic zone. Earthquakes along this ridge are typically not as destructive because they occur under the ocean and are usually of lower magnitude. However, they are significant because they indicate a correlation between the occurrence of earthquakes and the presence of the ridge, which is a divergent plate boundary where new oceanic crust is formed as tectonic plates move apart. This helps to confirm the theory of plate tectonics, as the seismic activity along the ridge aligns with the process of seafloor spreading. We are going to talk more about this as we go along with this module later on. 15  WORLD SEISMICITY It may also be seen that many areas of the world are almost free from earthquakes. Notable examples are ▪ The eastern part of South America ▪ The central and northern regions of Canada ▪ Much of Siberia ▪ West Africa ▪ Large parts of Australia ▪ Northern Europe EARTHQUAKE 10/10/2024 10:14 am 16 ENGINEERING CEnS 152 16  PHILIPPINE’S SEISMICITY EARTHQUAKE 10/10/2024 10:14 am 17 ENGINEERING CEnS 152 This is the seismicity maps of the Philippines from the Spectral Acceleration Maps (SAM) of the Philippines published by DOST-PHIVOLCS in 2021. The seismicity map of the Philippines highlights the country as one of the most seismically active regions in the world due to its location along the Pacific Ring of Fire. This map reveals a pattern of frequent and sometimes devastating earthquakes, particularly along major fault lines such as the Philippine Fault Zone, the Valley Fault System, and the Manila Trench. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) monitors these regions closely, providing seismic data that helps in creating these maps. The maps are essential for understanding the distribution and intensity of past earthquakes, which in turn aids in disaster preparedness and mitigation efforts. Northern Philippines 17  PHILIPPINE’S SEISMICITY EARTHQUAKE 10/10/2024 10:14 am 18 ENGINEERING CEnS 152 Central Philippines 18  PHILIPPINE’S SEISMICITY EARTHQUAKE 10/10/2024 10:14 am 19 ENGINEERING CEnS 152 Southern Philippines Base on this seismicity maps, it is obvious that only Palawan and Sulu Places do not experience much earthqukes for past decades. That is why they belong to the Seismic Zone 2 as stipulated in our NSCP Seismic Zone 2 is an area with a lower seismic risk compared to Seismic Zone 4 (the highest risk) but still has a considerable risk of experiencing earthquakes. Link to Seismic Monitoring of Seismological Facility for the Advancement of Geoscience (SAGE) : https://ds.iris.edu/seismon/index.phtml 19  Earthquake Genesis ▪ Describe the process of earthquake genesis related to tectonic plate movement. EARTHQUAKE 10/10/2024 10:14 am 20 ENGINEERING CEnS 152 20  EARTHQUAKE: FROM MYTH TO SCIENCE “Theological preoccupations during the Middle Ages put a temporary end to speculation about the origin of earthquakes. The Wrath-of-God theory of earthquakes had its origin in Old Testament interpretations of natural disasters, such as the destruction of Sodom and Gomorrah, and the fall of Jericho, which may have been early instances of seismic activity in the Jordan Trough. Naturalistic explanations of earthquakes were formally banned as heresy by a father of the Church in the 5th Century.” Cinna Lomnitz, 1974 EARTHQUAKE 10/10/2024 10:14 am 21 ENGINEERING CEnS 152 During the Middle Ages, the dominant theological perspectives significantly influenced how people understood natural phenomena, including earthquakes. The statement by Cinna Lomnitz highlights how religious interpretations, specifically the "Wrath-of-God" theory, became the prevailing explanation for earthquakes during this period. This theory stems from Old Testament stories, such as the destruction of Sodom and Gomorrah and the fall of Jericho, which were believed to be divine punishments for human sin. Such interpretations were deeply ingrained in the medieval mindset, where natural disasters were often seen as direct acts of God's anger against human immorality. As a result, naturalistic explanations—those that sought to understand earthquakes through physical or scientific causes—were discouraged and even condemned. The Church's influence was so strong that in the 5th century, these naturalistic views were declared heretical by a prominent Church father. This effectively stifled any scientific inquiry into the origins of earthquakes for centuries, as the dominant religious doctrine did not permit challenges to its divine interpretations. 21  EARTHQUAKE: FROM MYTH TO SCIENCE Early human explanations for earthquakes were largely based on superstitions and mythologies. Ancient Japanese believed earthquakes were caused by a giant catfish under the islands. The Algonquin Indians thought a giant tortoise that supported the Earth caused it to shake when it moved. In ancient Mexico, earthquakes were attributed to the movements of a divine being with reptile and fish features. Other cultures blamed earthquakes on a frog (Asia), a giant mole (India), or an ox (China). EARTHQUAKE 10/10/2024 10:14 am 22 ENGINEERING CEnS 152 Throughout history, humans have sought to explain the causes of earthquakes, often resorting to superstitious beliefs. Various cultures attributed earthquakes to mythical creatures or divine beings, such as the Japanese catfish, the Algonquin tortoise, or the Greek god Poseidon. These explanations were often linked to moral judgments, with earthquakes seen as punishments from angry gods. However, the first scientific attempt to explain earthquakes came from Aristotle, who proposed that they were caused by winds trapped within the Earth. Modern understanding of earthquakes, based on extensive geological and seismological studies, now explains them through the mechanisms of plate tectonics. This chapter introduces these modern theories, exploring the correlation between earthquake-generating mechanisms and specific geological features, and discusses ongoing efforts to predict earthquakes more accurately. 22  EARTHQUAKE: FROM MYTH TO SCIENCE Earthquakes were also seen as divine punishment; for example, Poseidon in Greek mythology caused earthquakes when angry. Even in the 18th century, earthquakes were often viewed through a moralistic lens, with some clergy interpreting them as punishment for human sins. Aristotle made an early scientific attempt, theorizing that winds trapped inside the Earth’s interior caused earthquakes. EARTHQUAKE 10/10/2024 10:14 am 23 ENGINEERING CEnS 152 Throughout history, humans have sought to explain the causes of earthquakes, often resorting to superstitious beliefs. Various cultures attributed earthquakes to mythical creatures or divine beings, such as the Japanese catfish, the Algonquin tortoise, or the Greek god Poseidon. These explanations were often linked to moral judgments, with earthquakes seen as punishments from angry gods. However, the first scientific attempt to explain earthquakes came from Aristotle, who proposed that they were caused by winds trapped within the Earth. Modern understanding of earthquakes, based on extensive geological and seismological studies, now explains them through the mechanisms of plate tectonics. This chapter introduces these modern theories, exploring the correlation between earthquake-generating mechanisms and specific geological features, and discusses ongoing efforts to predict earthquakes more accurately. 23  EARTHQUAKE: FROM MYTH TO SCIENCE Modern science, through geological and seismological studies, has led to a clear understanding of the causes of earthquakes, their locations, and their frequency. Current studies focus on understanding earthquake- generating mechanisms and efforts to predict the size, time, and location of future earthquakes. EARTHQUAKE 10/10/2024 10:14 am 24 ENGINEERING CEnS 152 Throughout history, humans have sought to explain the causes of earthquakes, often resorting to superstitious beliefs. Various cultures attributed earthquakes to mythical creatures or divine beings, such as the Japanese catfish, the Algonquin tortoise, or the Greek god Poseidon. These explanations were often linked to moral judgments, with earthquakes seen as punishments from angry gods. However, the first scientific attempt to explain earthquakes came from Aristotle, who proposed that they were caused by winds trapped within the Earth. Modern understanding of earthquakes, based on extensive geological and seismological studies, now explains them through the mechanisms of plate tectonics. This chapter introduces these modern theories, exploring the correlation between earthquake-generating mechanisms and specific geological features, and discusses ongoing efforts to predict earthquakes more accurately. 24  TYPES OF EARTHQUAKE Earthquake a phenomenon that involves the motion or shaking of the earth’s crust. In this general sense, an earthquake may be, therefore, caused by: ▪ Tectonic forces. The forces involved in the formation of the earth’s features ▪ Volcanic Activity ▪ Conventional and nuclear explosion ▪ Landslides/ Collapse of mines ▪ Meteorite Impact ▪ Filling of reservoirs and wells EARTHQUAKE 10/10/2024 10:14 am 25 ENGINEERING CEnS 152 However, the earthquakes produced by volcanic activity, a soil or rock mass collapse, a conventional explosion, a meteorite impact, or the filling of reservoirs and wells are, for the most part, of a relatively small size and affect only an area of limi ted extent. Earthquakes generated by a nuclear explosion may be strong, but the factors that generate these earthquakes are known and may be controlled. In contrast, the earthquakes generated by tectonic forces may be exceptionally large and may affect a large geographical region at once. In fact, most of the catastrophic earthquakes that have occurred through historical times have been of the tectonic type. The discussion in this chapter will be, therefore, limited to the generation of tectonic earthquakes. 25  EARTH’S STRUCTURE The Earth is roughly spherical, with an equatorial diameter of 12,740 km and a polar diameter of 12,700 km. The difference is due to the Earth's rotation. Earth's mass is approximately 4.9 × 10²¹ kg, resulting in an average specific gravity of 5.5, indicating that the interior materials are denser than surface rocks (which have specific gravities of 2.7 to 3). EARTHQUAKE 10/10/2024 10:14 am 26 ENGINEERING CEnS 152 What is the shape of the earth? Spheroid The deep interior of the Earth remains somewhat of a mystery as we have only penetrated the very most outer portion with our deep drilling exploration. The deepest drilling exploration less than 5 km compare to almost 7000 km radius of the earth What knowledge we do have comes from seismic wave data or lava that has extruded onto the surface. What we do know is that the Earth's interior is somewhat like a concentric series of rings, progressing from the dense and intensely hot inner core toward the brittle outer shell of the crust. Meaning as we go deeper into the core, the density also increases. Base on your knowledge way back elementary, what are the layers of the earth? 26  EARTH’S STRUCTURE The shell of the increasing density are found towards the center of the earth is 80 g/cc. (SG= 8) Each shell is formed off different materials on the basics of seismic investigation the earth interior. Has been broadly divided into; crust, mantle and core. EARTHQUAKE 10/10/2024 10:14 am 27 ENGINEERING CEnS 152 27  EARTH’S STRUCTURE CRUST. The outermost solid layer of the earth where we can find all our landforms and life. It has two subdivision; the upper and lower crust MANTLE. Just below the crust is the Mantle. Just like the crust, it has also upper and lower layer. CORE. That is the central layer of the planet. Core is very hot that it may have the same temperature with the surface of the sun. Core is also composed of upper and EARTHQUAKE 10/10/2024 10:14 am lower core. 28 ENGINEERING CEnS 152 It is well known from deep mining operations that temperature increases downwards at an average rate of 300C per km. Challenger Deep in Marianas Trench And the deepest mine drilled below the earth is only about 2.5 miles. About 4 kms Seismology the gathering of information about the interior of the earth by recording, imaging, measuring variations of seismic waves caused by an earthquake or explosion. And this was first used by a Croatian Seismologist, Andrija Mohorovicic. 28  EARTH’S STRUCTURE The layers of the earth are separated by two sharp breaks known as major discontinuities. The crust has an average thickness of about 33 km. The mantle extends from below the crust to a depth of ~2900 kms The core extends below the mantle at ~3500 kms up to the center of the earth. EARTHQUAKE 10/10/2024 10:14 am 29 ENGINEERING CEnS 152 29  EARTH’S STRUCTURE Direct observation of earth is not possible due to fact that the interior became hotter. The deepest whole in the earth is only about 11km , this is quite negligible in comparison with radius of the earth The internal structures of earth is based on the existence yield at by indirect geophysical method (seismic method) EARTHQUAKE 10/10/2024 10:14 am 30 ENGINEERING CEnS 152 It is well known from deep mining operations that temperature increases downwards at an average rate of 300C per km. Challenger Deep in Marianas Trench And the deepest mine drilled below the earth is only about 2.5 miles. About 4 kms Seismology the gathering of information about the interior of the earth by recording, imaging, measuring variations of seismic waves caused by an earthquake or explosion. And this was first used by a Croatian Seismologist, Andrija Mohorovicic. 30  EARTH’S STRUCTURE The interior of the earth has been obtained from the study of earthquakes waves through the earth (seismology) Andrija Mohorovicic (1857-1936) was a pioneer of the developing science of seismology in the early twentieth century. When seismic waves pass between geologic layers with contrasting seismic velocities, a sudden jump in seismic velocities across a boundary will occur. This scenario is called as Seismic discontinuities. EARTHQUAKE 10/10/2024 10:14 am 31 ENGINEERING CEnS 152 It is well known from deep mining operations that temperature increases downwards at an average rate of 300C per km. Challenger Deep in Marianas Trench And the deepest mine drilled below the earth is only about 2.5 miles. About 4 kms Seismology the gathering of information about the interior of the earth by recording, imaging, measuring variations of seismic waves caused by an earthquake or explosion. And this was first used by a Croatian Seismologist, Andrija Mohorovicic. 31  EARTH’S STRUCTURE: CRUST It is the uppermost shell of the earth which has varying thickness in different areas: ▪ 25 – 60 km under the continent ▪ 4 – 6 km under the ocean Subdivided into two layer: ▪ Upper Layer (continental crust). Predominantly continents and land surface ▪ Lower Layer (oceanic crust). Basically the ocean floor EARTHQUAKE 10/10/2024 10:14 am 32 ENGINEERING CEnS 152 It is again brittle in nature Materials in the crust are the least dense compare to those materials at the center of the earth 32  EARTH’S STRUCTURE: CRUST (CONTINENTAL) The upper crust is predominantly continents and land surface. This layer is rich in Silica and Aluminum (SIAL layer) The density of SIAL is 2.4 g/cc (SG~ 2.4). The boundary between the Upper and Lower Crust is called the CONRAD Discontinuity. EARTHQUAKE 10/10/2024 10:14 am 33 ENGINEERING CEnS 152 It consists of all types of rocks (Igneous, Sedimentary, and Metamorphic) The rocks are granitic and granodiotic composition. That is the combined name of Silica and Aluminum which is the most abundant element in this layer 33  EARTH’S STRUCTURE: CRUST (OCEANIC) The lower crust is basically the ocean floor. This layer is rich in Silica, Iron and Magnesium (SIMA layer) The density of SIMA is 2.4 g/cc (SG~ 2.4). The continental crust float above the oceanic crust because it is less dense. EARTHQUAKE 10/10/2024 10:14 am 34 ENGINEERING CEnS 152 Composed of magma that erupts on the seafloor. The types of rock are basalitic in nature. The continental crust is floating above the oceanic crust because it has much lower density compare to the oceanic crust. 34  EARTH’S STRUCTURE: MANTLE The second part of the earth is the source region of the earth internal energy and of forces responsible for ocean floor spreading and continental drift and earthquake. The boundary between the crust and mantle is called the MOHOROVICIC Discontinuity. EARTHQUAKE 10/10/2024 10:14 am 35 ENGINEERING CEnS 152 35  EARTH’S STRUCTURE: MANTLE Subdivided into two layer: ▪ Upper Mantle. Predominantly molten magma. Also called ASTHENOSPHERE (“weak”) layer of the mantle where the crust is drifting. ▪ The layer of both the crust and the upper part of the mantle is called the LITOSPHERE (Greek: lithos = stone). ▪ Lower Mantle. Solid state EARTHQUAKE 10/10/2024 10:14 am 36 ENGINEERING CEnS 152 36  EARTH’S STRUCTURE: MANTLE The lower mantle is the one responsible for all the earth seismic and volcanic activities due to its very spacious area for such natural catastrophes. The boundary between the upper and lower mantle is called the REPETTI Discontinuity. EARTHQUAKE 10/10/2024 10:14 am 37 ENGINEERING CEnS 152 In our future discussion, we will be able to discuss the concept of continental drift. That is because our continents are just floating above the upper mantle thus they converge or diverge during earth movements. 37  EARTH’S STRUCTURE: CORE The central layer and extends up to the very center of the earth. ▪ S-Waves do not pass in this layer ▪ Pressure and temperatures are very high. The layer is mostly made up of Nickel (Ni) and Iron (Fe) This is also called as the NIFE Layer or the BARYSPHERE. EARTHQUAKE 10/10/2024 10:14 am 38 ENGINEERING CEnS 152 38  EARTH’S STRUCTURE: CORE The boundary between the core and the mantle is called the GUTTENBERG Discontinuity. ▪ There is a sudden decrease in the speed of seismic waves, indicating a transition from solid (mantle) to liquid (outer core). ▪ This discontinuity also marks where S-waves (shear waves) disappear, as they cannot travel through the liquid outer core. EARTHQUAKE 10/10/2024 10:14 am 39 ENGINEERING CEnS 152 39  EARTH’S STRUCTURE: CORE Subdivided into two layer: ▪ Outer Core - molten rocks - made up of nickel and iron ▪ Inner Core - crystalline or solid - magnetic field - made up of iron The boundary between the outer and inner core is called the LEHMANN Discontinuity. EARTHQUAKE 10/10/2024 10:14 am 40 ENGINEERING CEnS 152 Found between the outer core and the inner core, at a depth of about 5,150 km.Seismic waves increase in velocity, suggesting a transition from the liquid outer core to the solid inner core.Named after Inge Lehmann, who first proposed the existence of the Earth's inner core in 1936. That due to extremely high pressure in the inner core that is why it became a solid. Magnetism which is necessary in the survival of life here on the surface of the earth especially gravity. 40  CONTINENTAL DRIFT THEORY In the early 1900s a German explorer and scientist (Alfred Wegener) proposed the continental drift theory. He proposed that there was once a single “super continent” called Pangaea. He believed that the continent floated on the oceanic crust (like an iceberg in the ocean). Most scientist rejected his theory due to lack of evidence. EARTHQUAKE 10/10/2024 10:14 am 41 ENGINEERING CEnS 152 Although the theory of continental drift was received with contempt when it was originally proposed, today this theory and that of plate tectonics have become widely accepted and acknowledged as one of the greatest advances in the earth sciences. Their acceptance has come as a result of studies conducted after the 1960s, which, with the help of a modern worldwide network of earthquake-recording instruments, the developing of new techniques such as deep-water echo sounding, and a detailed exploration of the ocean floor, have provided a strong supporting evidence of the historical movement of the continents postulated by the theory of continental drift. Moreover, precise geodetic measurements have shown that the plates identified by the plate tectonics theory are indeed moving relative to one another and that this motion is between 1 and 13 cm/year. 41  CONTINENTAL DRIFT THEORY EARTHQUAKE 10/10/2024 10:14 am 42 ENGINEERING CEnS 152 Although the theory of continental drift was received with contempt when it was originally proposed, today this theory and that of plate tectonics have become widely accepted and acknowledged as one of the greatest advances in the earth sciences. Their acceptance has come as a result of studies conducted after the 1960s, which, with the help of a modern worldwide network of earthquake-recording instruments, the developing of new techniques such as deep-water echo sounding, and a detailed exploration of the ocean floor, have provided a strong supporting evidence of the historical movement of the continents postulated by the theory of continental drift. Moreover, precise geodetic measurements have shown that the plates identified by the plate tectonics theory are indeed moving relative to one another and that this motion is between 1 and 13 cm/year. 42  CONTINENTAL DRIFT THEORY Evidence of Continental Drift: ▪ Continents fit together like a jigsaw puzzle ▪ Fossils match across oceans ▪ Rock types and mountain ranges match across oceans ▪ Climate Evidence (Glacial Deposits) EARTHQUAKE 10/10/2024 10:14 am 43 ENGINEERING CEnS 152 Continents look like they could be part of a giant jigsaw puzzle 43  CONTINENTAL DRIFT THEORY Evidence of Continental Drift: ▪ Continents fit together like a jigsaw puzzle ▪ Fossils match across oceans ▪ Rock types and mountain ranges match across oceans ▪ Climate Evidence (Glacial Deposits) Glossopteris…seed much to large to be windblown Mesosaurus…lived in fresh water and could not have lived in salt water EARTHQUAKE 10/10/2024 10:14 am 44 ENGINEERING CEnS 152 Plant and animal fossils found on the coastlines of different continents 44  CONTINENTAL DRIFT THEORY Evidence of Continental Drift: ▪ Continents fit together like a jigsaw puzzle ▪ Fossils match across oceans ▪ Rock types and mountain ranges match across oceans ▪ Climate Evidence (Glacial Deposits) EARTHQUAKE 10/10/2024 10:14 am 45 ENGINEERING CEnS 152 Same rock patterns found in South America, India, Africa, Antarctica and Australia 45  CONTINENTAL DRIFT THEORY Evidence of Continental Drift: ▪ Continents fit together like a jigsaw puzzle ▪ Fossils match across oceans ▪ Rock types and mountain ranges match across oceans ▪ Climate Evidence (Glacial Deposits) Tropical plant remains (coal deposits) found in Antarctica Glacial deposits in Africa, South America, India, and Australia during the same time Warm weather plants have been found in the Arctic… but it’s not warm there! Glacier deposits have been discovered in tropical and desert locations…it’s not cold there, either! The continents had to have been at different locations in the geological past. EARTHQUAKE 10/10/2024 10:14 am 46 ENGINEERING CEnS 152 46  PLATE TECTONICS THEORY Most of these changes in the earth’s surface takes place so slowly that they are not immediately noticeable to the human eye. The idea that the earth’s landmasses have broken apart, rejoined, and moved to other parts of the globe forms part of the plate tectonics theory. EARTHQUAKE 10/10/2024 10:14 am 47 ENGINEERING CEnS 152 47  PLATE TECTONICS THEORY According to the theory of plate tectonics, the earth’s outer shell is not one solid piece of rock. Instead the earth’s crust is broken into a number of moving plates. The plates vary in size and thickness. EARTHQUAKE 10/10/2024 10:14 am 48 ENGINEERING CEnS 152 48  PLATE TECTONICS THEORY These pieces of Earth’s top layer are called tectonic plates. They are moving very slowly, but constantly. (Most plates are moving about as fast as your fingernails are growing -- not very fast!) Currently Earth’s surface layers are divided into eight very large plates and several smaller ones. EARTHQUAKE 10/10/2024 10:14 am 49 ENGINEERING CEnS 152 The importance of these interactions lead to significant geological phenomena, such as earthquakes, volcanoes, and mountain formation. 49  PLATE TECTONICS THEORY Major Plates: 1. North American Plate A N 2. Indian Plate G A 3. Antarctic Plate I O 4. South American Plate K 5. African Plate L L K M 6. Australian Plate M 7. Eurasian Plate N 8. Pacific Plate O I G EARTHQUAKE 10/10/2024 10:14 am 50 ENGINEERING CEnS 152 A. North American Plate - Type: Both Continental and Oceanic - Boundaries: - Convergent: Collision with the Pacific Plate (Aleutian Trench). - Divergent: Mid-Atlantic Ridge with the Eurasian Plate. - Transform: San Andreas Fault with the Pacific Plate. G. Indian Plate (sometimes considered part of the Indo-Australian Plate) - Type: Continental - Boundaries: - Convergent: Collision with the Eurasian Plate (Himalayas). - Divergent: Carlsberg Ridge with the African Plate. - Transform: Alpine Fault with the Eurasian Plate. I. Antarctic Plate - Type: Oceanic - Boundaries: - Divergent: Antarctic-Phoenix Ridge with the Pacific Plate, Antarctic-Indian Ridge with the Indo-Australian Plate. - Transform: No major transform boundary. - Convergent: Lesser known or minor boundaries with other plates. K. South American Plate - Type: Both Continental and Oceanic - Boundaries: 50  - Convergent: Collision with the Nazca Plate (Peru-Chile Trench and Andes Mountains). - Divergent: Mid-Atlantic Ridge with the African Plate. - Transform: No major transform boundary. L. African Plate - Type: Both Continental and Oceanic - Boundaries: - Convergent: Collision with the Eurasian Plate (Alps and Mediterranean region). - Divergent: East African Rift with itself, Mid-Atlantic Ridge with the South American Plate. - Transform: Boundary with the Arabian Plate. M. Australian Plate - Type: Both Continental and Oceanic - Boundaries: - Convergent: Collision with the Eurasian Plate (Himalayas), Subduction beneath the Pacific Plate (Tonga Trench). - Divergent: Carlsberg Ridge with the African Plate. - Transform: Boundary with the Eurasian Plate (Alpine Fault in New Zealand). N. Eurasian Plate - Type: Continental - Boundaries: - Convergent: Collision with the Indian Plate (Himalayas). - Divergent: Mid-Atlantic Ridge with the North American Plate. - Transform: Alpine Fault with the Indo-Australian Plate. O. Pacific Plate Type: Oceanic - Boundaries: - Convergent: Pacific Plate subducts beneath the North American Plate (Aleutian Trench), Indo-Australian Plate (Tonga Trench). - Divergent: Mid-ocean ridges with the Antarctic Plate (Pacific-Antarctic Ridge). - Transform: San Andreas Fault with the North American Plate. 50  PLATE TECTONICS THEORY Minor Plates: 1. Juan de Fuca Plate B 2. Cocos Plate C 3. Caribbean Plate D 4. Scotia Plate E B 5. Arabian Plate F J 6. Philippine Plate H D 7. Nazca Plate J H E C F EARTHQUAKE 10/10/2024 10:14 am 51 ENGINEERING CEnS 152 B. Juan de Fuca Plate - Type: Oceanic - Boundaries: - Convergent: Subduction beneath the North American Plate (Cascadia Subduction Zone). - Divergent: Juan de Fuca Ridge with the Pacific Plate. - Transform: No major transform boundary. C. Cocos Plate - Type: Oceanic - Boundaries: - Convergent: Subduction beneath the North American Plate (Middle America Trench). - Divergent: East Pacific Rise with the Pacific Plate. - Transform: No major transform boundary. D. Caribbean Plate - Type: Both Continental and Oceanic - Boundaries: - Convergent: Subduction beneath the North American Plate (Puerto Rico Trench). - Divergent: No major divergent boundary. - Transform: Boundary with the North American Plate. E. Scotia Plate - Type: Oceanic 51  - Boundaries: - Convergent: Subduction beneath the South Sandwich Plate. - Divergent: Scotia Sea with the South American Plate. - Transform: Scotia Transform Fault. F. Arabian Plate - Type: Continental - Boundaries: - Convergent: Collision with the Eurasian Plate (Zagros Mountains). - Divergent: Red Sea Rift with the African Plate. - Transform: Dead Sea Transform with the African Plate. H. Philippine Sea Plate - Type: Oceanic - Boundaries: - Convergent: Subduction beneath the Eurasian Plate (Philippine Trench). - Divergent: No major divergent boundary. - Transform: Philippine Fault. J. Nazca Plate - Type: Oceanic - Boundaries: - Convergent: Subduction beneath the South American Plate (Peru-Chile Trench). - Divergent: East Pacific Rise with the Pacific Plate. - Transform: No major transform boundary. 51  PLATE TECTONICS THEORY: PLATE BOUNDARIES As mentioned earlier, those tectonic plates are always moving. ▪ pulling away from each other (Divergent) ▪ crashing head-on (Convergent) ▪ or sliding past each other. (Transform) The plates spread apart at rates of 1 cm to 20 cm per year. EARTHQUAKE 10/10/2024 10:14 am 52 ENGINEERING CEnS 152 52  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY Boundary between two plates that are moving apart or rifting. → RIFTING causes SEAFLOOR SPREADING EARTHQUAKE 10/10/2024 10:14 am 53 ENGINEERING CEnS 152 53  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY Sea-Floor Spreading was a theory proposed by Harry Hess in the 1960’s which is the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge EARTHQUAKE 10/10/2024 10:14 am 54 ENGINEERING CEnS 152 54  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY Ocean floor moves like a conveyor belt carrying continents with it. ▪ New ocean floor forms along cracks in the ocean crust as molten material erupts from the mantle spreading out and pushing older rocks to the sides of the crack. New ocean floor is continually added by the process of sea-floor spreading. EARTHQUAKE 10/10/2024 10:14 am 55 ENGINEERING CEnS 152 55  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY When two plates diverge, a rift is developed, creating a condition where molten basaltic magma from the asthenosphere rises to lift the plate edges and create new crust. Most of the known plate divergence occurs in what is now ocean area. EARTHQUAKE 10/10/2024 10:14 am 56 ENGINEERING CEnS 152 56  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY Features of divergent boundary. ▪ Mid-ocean ridges ▪ Rift valleys ▪ Fissure volcanoes EARTHQUAKE 10/10/2024 10:14 am 57 ENGINEERING CEnS 152 Mid-Ocean Ridges: Underwater mountain ranges formed by the divergence of oceanic plates and continuous new crust formation. Rift Valleys: Large depressions on continents formed by the divergence and stretching of continental plates. Fissure Volcanoes: Volcanoes that erupt through long cracks in the Earth's crust, producing wide, low-profile lava flows. 57  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY The mid-ocean ridge system is the most extensive chain of mountains on earth, but more than 90% of this mountain range lies in the deep ocean. The mid- ocean ridge wraps around the globe for more than 65,000 km like the seam of a baseball. EARTHQUAKE 10/10/2024 10:14 am 58 ENGINEERING CEnS 152 58  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY Examples are the Mid-Atlantic Ridge, East Pacific Rise, and South Indian Rise. Earthquake and volcano activity is involved along the boundaries of these diverging plates, although the earthquakes that occur there are usually of low magnitude. Earthquakes are triggered when the tensional forces that produce the plate divergence fracture the newly formed crust. EARTHQUAKE 10/10/2024 10:14 am 59 ENGINEERING CEnS 152 59  PLATE TECTONICS THEORY: DIVERGENT BOUNDARY When plates pull away from one another they form a diverging plate boundary, or spreading zone. Thingvellir, the spreading zone in Iceland between the North American (left side) and Eurasian (right side) tectonic plates. January 2003. EARTHQUAKE 10/10/2024 10:14 am 60 ENGINEERING CEnS 152 60  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Boundaries between two plates that are colliding. → The 3 types of convergent boundaries are: ▪ Ocean to Continent ▪ Ocean to Ocean ▪ Continent to Continent EARTHQUAKE 10/10/2024 10:14 am 61 ENGINEERING CEnS 152 61  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Oceanic vs. Continental Plate EARTHQUAKE 10/10/2024 10:14 am 62 ENGINEERING CEnS 152 62  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Oceanic vs. Continental Plate Ocean plate colliding with a less dense continental plate forming subduction zone Subduction. Process by which the ocean floor sinks beneath a deep- ocean trench and back into the mantle; allows part of the ocean floor to sink back into the mantle. Causes formation of deep-ocean trenches, powerful earthquakes, and volcanic activity EARTHQUAKE 10/10/2024 10:14 am 63 ENGINEERING CEnS 152 The creation of new crust where plates diverge is thus balanced by an equivalent loss at a subduction zone, which together complete a continuous cycle that replaces the ocean floor every 200 million years or so. Plate subduction also gives rise to some of the world’s most powerful earthquakes. In fact, almost 90% of the seismic energy released by tectonic plate movement comes from earthquakes generated in subduction zones. Earthquakes occur above the subducting plate in regions of the continental plate and at the interface between the subducting and overriding plates. The latter occurs along a well-defined area, known as the BENIOFF ZONE, which outlines the subducting plate. Earthquakes in these zones are known to take place at depths as great as 700 km. It is believed that earthquakes cannot occur at depths >700 km because beyond this depth a subducting plate melts. 63  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 64 ENGINEERING CEnS 152 Location: The Andes Mountain Range stretches along the western edge of South America, spanning seven countries: Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile, and Argentina. 5 Facts About the Andes Mountains: Longest Continental Mountain Range: The Andes is the longest continental mountain range in the world, extending over 7,000 kilometers (4,300 miles). Home to the Highest Volcanoes: The Andes hosts some of the world's highest volcanoes, including Ojos del Salado, the highest active volcano at 6,893 meters (22,615 feet). Biodiversity Hotspot: The Andes is one of the most biologically diverse regions on Earth, home to unique species like the Andean condor, vicuña, and spectacled bear. Incan Civilization: The Andes were the cradle of the Incan Empire, one of the most advanced civilizations in pre-Columbian America, with Machu Picchu as its iconic site. Climate Variations: The Andes exhibit a wide range of climates, from tropical rainforests in the Amazon basin to glaciers in the southern Patagonian region. 64  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 65 ENGINEERING CEnS 152 Location: The Peru-Chile Trench, also known as the Atacama Trench, lies off the western coast of South America, stretching from southern Chile to northern Peru, along the Pacific Ocean. About the Peru-Chile Trench: 1. Extremely Deep: The Peru-Chile Trench reaches depths of up to 8,065 meters (26,460 feet), making it one of the deepest oceanic trenches in the world. 2. Tectonic Activity Hub: The trench is a site of intense tectonic activity, where the oceanic Nazca Plate subducts beneath the continental South American Plate, leading to frequent earthquakes and volcanic activity in the region. 65  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 66 ENGINEERING CEnS 152 Location: The Philippine Trench is located in the western Pacific Ocean, east of the Philippines, stretching from the northern part of Luzon down to the island of Mindanao. About the Philippine Trench: One of the Deepest: The Philippine Trench plunges to a maximum depth of approximately 10,540 meters (34,580 feet), making it one of the deepest trenches in the world. Formation: The trench was formed by the subduction of the Philippine Oceanic Sea Plate beneath the Eurasian Continental Plate, which also contributes to the region's high seismic activity and frequent earthquakes. Subduction zones exist off the coasts of Mexico and Chile, south of the Aleutian Islands, off the eastern coast of Japan, and off the coasts of Washington and Oregon. 66  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Oceanic vs. Oceanic Plate EARTHQUAKE 10/10/2024 10:14 am 67 ENGINEERING CEnS 152 67  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Oceanic vs. Oceanic Plate When two oceanic plates collide, the denser or older plate is forced beneath the other into the Earth's mantle. This process is known as subduction. Causes formation of deep-ocean trenches, powerful earthquakes, and volcanic island arcs EARTHQUAKE 10/10/2024 10:14 am 68 ENGINEERING CEnS 152 When both are oceanic plates, one slides under the other. Often an island group forms at this boundary. 68  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 69 ENGINEERING CEnS 152 Deep-Sea Trenches: Example: Mariana Trench, the deepest part of the ocean, formed by the collision of the Pacific and Philippine Plates which are both oceanic plates. Volcanic Island Arcs Example: Some references say that the Japanese Archipelago, formed by rising magma from subducted plates. Japan is found near the boundary of 4 tectonic plates (Eurasian (C), Philippine (O), North American (C), and Pacific (O)). Also, the Marianas Islands are volcanic island arcs. Seismic Activity: Powerful earthquakes and tsunamis result from stress release along subduction zones. About the Mariana Trench Location: Western Pacific Ocean, east of the Mariana Islands. Depth: Approximately 10,994 meters (36,070 feet) Significance: The Mariana Trench is the deepest part of the world's oceans. The Challenger Deep, the trench's deepest point, is the deepest known point in Earth's seabed. 69  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Continental vs. Continental Plate EARTHQUAKE 10/10/2024 10:14 am 70 ENGINEERING CEnS 152 70  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY Continental vs. Continental Plate A continental plate colliding with another continental plate Have Collision Zones: The plates push against each other, creating mountain ranges. EARTHQUAKE 10/10/2024 10:14 am 71 ENGINEERING CEnS 152 When two plates carrying continental crust converge, there is no subduction as it occurs at the ocean trenches. Being lightweight and thick, continental crust is too buoyant to sink into the asthenosphere. In this case, the plates simply collide head on and over time fold up like an accordion. Earthquakes are generated at these boundaries when rock blocks near the boundaries fracture under the high compressional forces between the colliding plates and slip. 71  PLATE TECTONICS THEORY: CONVERGENT BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 72 ENGINEERING CEnS 152 Earth’s highest mountain range, the Himalayas, was formed millions of years ago when the Indo-Australian Plate crashed into the Eurasian Plate. Even today, the Indo-Australian Plate continues to push against the Eurasian Plate at a rate of about 5 cm a year and is often referred to as the "Roof of the World“. The Himalayas span five countries: Bhutan, China, India, Nepal, and Pakistan. This mountain range is home to the world's highest peaks, including Everest. Mount Everest, the highest peak on Earth, stands at 8,848.86 meters (29,031.7 feet) above sea level. Located in the Himalayas on the border between Nepal and the Tibet Autonomous Region of China. 72  PLATE TECTONICS THEORY: TRANSFORM BOUNDARY Boundary between two plates that are sliding past each other. EARTHQUAKE 10/10/2024 10:14 am 73 ENGINEERING CEnS 152 Where plate edges slide past each other, crust is neither created nor destroyed, nor do changes occur on the surface of the earth. The boundaries where this type of interaction occurs are often called transform faults or transform boundary. 73  PLATE TECTONICS THEORY: TRANSFORM BOUNDARY The sliding of one plate against another generates earthquake activity but no volcanism. Only shallow earthquake occurs in this boundaries (5 to 40km below the surface). EARTHQUAKE 10/10/2024 10:14 am 74 ENGINEERING CEnS 152 74  PLATE TECTONICS THEORY: TRANSFORM BOUNDARY EARTHQUAKE 10/10/2024 10:14 am 75 ENGINEERING CEnS 152 For example: Here, the San Andreas Fault lies on the boundary between two tectonic plates, the north American Plate and the Pacific Plate. The two plates are sliding past each other at a rate of 5 to 6 centimeters each year. This fault frequently plagues California with earthquakes. Other important transform faults are the Motagua Fault that runs from the Caribbean Sea to the mountains west of Guatemala City, the Alpine Fault in New Zealand, and the Dead Sea Fault that connects the Read Sea to the Bitlis Mountains in Turkey. 75  CAUSE OF PLATE MOVEMENT Various theories exist to explain plate movement; the convection current theory is the most accepted. ▪ Heat generated within the Earth, mainly from radioactive decay, causes convection currents in the mantle. EARTHQUAKE 10/10/2024 10:14 am 76 ENGINEERING CEnS 152 Several theories have been proposed to explain the movement of tectonic plates, with the most widely accepted being the convection current theory. This theory suggests that heat generated within the Earth, primarily from radioactive decay, creates gigantic convection currents in the mantle. These currents, although the mantle is solid, move extremely slowly—possibly at a rate of 0.5 meters per century—mirroring the way heated air circulates in a cool room. 76  CAUSE OF PLATE MOVEMENT Various theories exist to explain plate movement; the convection current theory is the most accepted. ▪ These currents, although extremely slow (0.5 meters per century), move solid mantle material similarly to how heated air circulates in a room. EARTHQUAKE 10/10/2024 10:14 am 77 ENGINEERING CEnS 152 Several theories have been proposed to explain the movement of tectonic plates, with the most widely accepted being the convection current theory. This theory suggests that heat generated within the Earth, primarily from radioactive decay, creates gigantic convection currents in the mantle. These currents, although the mantle is solid, move extremely slowly—possibly at a rate of 0.5 meters per century—mirroring the way heated air circulates in a cool room. 77  CAUSE OF PLATE MOVEMENT Models show convection currents rising and separating beneath mid- ocean ridges. This movement creates tension, driving plates toward continental boundaries and contributing to mountain formation. EARTHQUAKE 10/10/2024 10:14 am 78 ENGINEERING CEnS 152 Different versions of the theory depict these convection cells in varying ways. A common model shows currents rising and separating beneath mid-ocean ridges, generating tension and driving the movement of plates toward continental boundaries, where they contribute to mountain formation. However, the complexity of the Earth's structure poses challenges in applying these models to explain all geological features like mountains, island chains, and mid-ocean ridges. No single convection model has yet successfully accounted for all these features. 78  CAUSE OF PLATE MOVEMENT However, the complexity of the Earth's structure poses challenges in applying these models to explain all geological features like mountains, island chains, and mid-ocean ridges. No single convection model has yet successfully accounted for all these features. EARTHQUAKE 10/10/2024 10:14 am 79 ENGINEERING CEnS 152 Different versions of the theory depict these convection cells in varying ways. A common model shows currents rising and separating beneath mid-ocean ridges, generating tension and driving the movement of plates toward continental boundaries, where they contribute to mountain formation. However, the complexity of the Earth's structure poses challenges in applying these models to explain all geological features like mountains, island chains, and mid-ocean ridges. No single convection model has yet successfully accounted for all these features. 79  INTRAPLATE EARTHQUAKES Most earthquakes happen at plate boundaries, but some occur far from these boundaries. These are called intraplate earthquakes. These earthquakes are caused by stress within the plate itself, which may result from forces acting on the plate from the boundaries or from weaknesses in the plate's structure. Because they occur far from plate boundaries, intraplate earthquakes can be less predictable and their causes are not as well understood as those of earthquakes at plate boundaries. EARTHQUAKE 10/10/2024 10:14 am 80 ENGINEERING CEnS 152 An intraplate earthquake is an earthquake that occurs within a tectonic plate rather than at the plate boundaries where most earthquakes happen. These earthquakes are caused by stress within the plate itself, which may result from forces acting on the plate from the boundaries or from weaknesses in the plate's structure. Because they occur far from plate boundaries, intraplate earthquakes can be less predictable and their causes are not as well understood as those of earthquakes at plate boundaries. Notable intraplate earthquakes include those in New Madrid, Missouri (1811–1812); Charleston, South Carolina (1886); Tangshan, China (1976); and Marathawada, India (1993). 80  EARTHQUAKES FAULT Faults are cracks or fractures in the Earth's crust where the sides have moved relative to each other. They are the visible evidence of tectonic plate boundaries on the Earth's surface. The San Andreas Fault is a well-known example, with a main fissure and a series of smaller, connected faults. EARTHQUAKE 10/10/2024 10:14 am 81 ENGINEERING CEnS 152 Faults can vary greatly in size, from a few meters to hundreds of kilometers long, and can extend deep into the Earth. They may show a single main crack or a complex network of smaller fractures branching off from the main fault. Also, here in the country, as mentioned awhile ago, the nearest tectonic boundary here is the subduction zone of the Philippine plate to the Eurasian plate. And as you can see from the hazardhunter map of DOST-PHIVOLCS, small fractures are branching off. And the longest fault found here is the Philippine Fault System. The Philippine fault is a ~1250-km-long. 81  EARTHQUAKES FAULT Faults indicate past movement between the Earth's plates. This movement can be gradual or occur in bursts when the rock along the fault breaks, causing an earthquake. Some faults are considered inactive if they haven't moved in tens of thousands of years. EARTHQUAKE 10/10/2024 10:14 am 82 ENGINEERING CEnS 152 Faults can vary greatly in size, from a few meters to hundreds of kilometers long, and can extend deep into the Earth. They may show a single main crack or a complex network of smaller fractures branching off from the main fault. Also, here in the country, as mentioned awhile ago, the nearest tectonic boundary here is the subduction zone of the Philippine plate to the Eurasian plate. And as you can see from the hazardhunter map of DOST-PHIVOLCS, small fractures are branching off. And the longest fault found here is the Philippine Fault System. The Philippine fault is a ~1250-km-long. 82  EARTHQUAKES FAULT TYPE 1. A STRIKE-SLIP FAULT (or transcurrent fault) is a type of fault where the two sides move horizontally past each other. ▪ Strike: The angle formed between a fault plane and the Earth's surface, measured relative to north. ▪ Slip: The horizontal movement along the strike of the fault. a. Left-Lateral Fault: If, from either side of the fault, the other side moves to the left. b. Right-Lateral Fault: If the other side moves to the right. EARTHQUAKE 10/10/2024 10:14 am 83 ENGINEERING CEnS 152 The Philippine fault is a ~1250-km-long, left-lateral strike-slip fault extending NNW parallel to the Philippine archipelago. This fault has been very active in the past 200 years with several destructive earthquakes accompanied by surface rupture. 83  EARTHQUAKES FAULT TYPE 2. A DIP-SLIP FAULT occurs when the two sides of a fault move vertically, either pressing together or pulling apart. ▪ Dip: The angle between the fault plane and the Earth's surface. ▪ Slip: The movement happens along the fault's dip. a. Normal Fault: The upper block (hanging wall) moves downward relative to the lower block (footwall). Occurs due to extensional strain, leading to the horizontal lengthening of the Earth's crust. EARTHQUAKE 10/10/2024 10:14 am 84 ENGINEERING CEnS 152 Scarp Formation: The vertical movement in a dip-slip fault can create a steep, exposed slope called a fault scarp. 84  EARTHQUAKES FAULT TYPE 2. A DIP-SLIP FAULT occurs when the two sides of a fault move vertically, either pressing together or pulling apart. ▪ Dip: The angle between the fault plane and the Earth's surface. ▪ Slip: The movement happens along the fault's dip. b. Reverse/Thrust Fault: The upper block (hanging wall) moves upward relative to the lower block. Caused by compressional strain, resulting in the horizontal shortening of the crust. EARTHQUAKE 10/10/2024 10:14 am 85 ENGINEERING CEnS 152 Scarp Formation: The vertical movement in a dip-slip fault can create a steep, exposed slope called a fault scarp. In most cases however, fault slip is a mixture of strike-slip and dip- slip and is called OBLIQUE FAULTING. 85  ELASTIC REBOUND THEORY Earthquakes often occur near tectonic plate boundaries, but the relative motion of plates alone doesn't fully explain earthquakes. The Elastic Rebound Theory, proposed by Harry F. Reid after the 1906 San Francisco earthquake, provides a more complete explanation. EARTHQUAKE 10/10/2024 10:14 am 86 ENGINEERING CEnS 152 86  ELASTIC REBOUND THEORY Reid's investigation of the San Andreas Fault showed that fences and roads had shifted up to 6 meters, leading him to propose that earthquakes result from the sudden release of stress in the Earth's crust. EARTHQUAKE 10/10/2024 10:14 am 87 ENGINEERING CEnS 152 Before 1906, scientists observed ground ruptures and displacements after earthquakes, but they thought these were caused by the earthquake itself. However, the 1891 Mino-Owari earthquake in Japan suggested that the rupture was actually responsible for the earthquake. Reid's investigation of the San Andreas Fault showed that fences and roads had shifted up to 6 meters, leading him to propose that earthquakes result from the sudden release of stress in the Earth's crust. 87  ELASTIC REBOUND THEORY Earthquakes occur when stress builds up along a fault due to the relative movement of tectonic plates. Initially, friction prevents the fault from slipping. However, once the stress exceeds the frictional resistance, the fault slips suddenly. This slip causes the rock on both sides of the fault to rebound to an unstressed state, releasing stored elastic energy as seismic waves. EARTHQUAKE 10/10/2024 10:14 am 88 ENGINEERING CEnS 152 88  ELASTIC REBOUND THEORY 1. Stress accumulates along a fault due to tectonic forces. 2. The stress overcomes friction, causing the fault to slip. 3. The fault ruptures and the rock rebounds to an unstressed state. 4. The release of energy creates seismic waves that propagate through the Earth. EARTHQUAKE 10/10/2024 10:14 am 89 ENGINEERING CEnS 152 Process of Earthquake Generation 89  EARTHQUAKE PARAMETERS Focus (Hypocenter): The initial point where the fault rupture begins underground. Epicenter: The point on the Earth’s surface directly above the focus. Rupture Surface: The area along the fault plane that experiences displacement during an earthquake. Fault Slip: The amount of relative displacement between the two sides of the fault. EARTHQUAKE 10/10/2024 10:14 am 90 ENGINEERING CEnS 152 According to the Elastic Rebound Theory, earthquakes occur when a fault suddenly ruptures. This rupture starts at a point below the Earth's surface and spreads across the fault plane, rather than happening instantaneously at a single point. The area affected by a rupture can range from a few to thousands of square kilometers. For example, the 1989 Loma Prieta earthquake in California had a rupture area of approximately 40 km long and 20 km deep. The velocity of the fault rupture is estimated to be between 2 and 3 km/s. 90  EARTHQUAKE PARAMETERS Earthquakes are classified based on their focal depth: ▪ Shallow: Depth < 60 km ▪ Intermediate: Depth between 60 and 300 km ▪ Deep: Depth between 300 and 700 km Focal depths can range from a few kilometers to 680 km. EARTHQUAKE 10/10/2024 10:14 am 91 ENGINEERING CEnS 152 Because usually, about 700 km, the rocks are already ductile or in some point melting in the mantle. 91  EARTHQUAKE PARAMETERS Slip rate is a parameter used to characterize earthquake faults, calculated by dividing the cumulative displacement of the fault by the age of the earliest displacement. This value gives an average rate over geological time. Active faults, such as the San Andreas Fault, exhibit higher slip rates compared to less active faults. EARTHQUAKE 10/10/2024 10:14 am 92 ENGINEERING CEnS 152 Because usually, about 700 km, the rocks are already ductile or in some point melting in the mantle. 92  FORESHOCK AND AFTERSHOCK Foreshocks: Smaller tremors that occur before a larger earthquake (main shock). Foreshocks are generally few and smaller, and not all earthquakes have them. Foreshocks are thought to indicate the impending rupture that leads to the main earthquake. EARTHQUAKE 10/10/2024 10:14 am 93 ENGINEERING CEnS 152 It can be difficult to determine which tremor is the foreshock and which is the main shock, especially when they are of similar size. 93  FORESHOCK AND AFTERSHOCK Aftershocks: Tremors that follow the main earthquake. Can be numerous and vary in size but typically decrease in frequency and magnitude over time. Result from adjustments to the stress changes caused by the main shock. EARTHQUAKE 10/10/2024 10:14 am 94 ENGINEERING CEnS 152 It can be difficult to determine which tremor is the foreshock and which is the main shock, especially when they are of similar size. 94  Earthquake Propagation ▪ Explain how seismic waves propagate through the Earth's layers. EARTHQUAKE 10/10/2024 10:14 am 95 ENGINEERING CEnS 152 95  SEISMIC WAVES Seismic waves are waves of energy that travel through the Earth, generated by the sudden release of energy during an earthquake. Think of it as throwing a stone into a pond—the ripples you see spreading out are similar to how seismic waves travel away from the earthquake’s epicenter. There are two main categories of seismic waves: body waves and surface waves. EARTHQUAKE 10/10/2024 10:14 am 96 ENGINEERING