Module 1: Introduction to Seismology & Earthquakes - PDF

Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering...

Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Module # 1 INTRODUCTION TO SEISMOLOGY & EARTHQUAKES LEARNING OBJECTIVES: At the end of this module, students are expected to: 1. Define seismology and earthquakes. 2. Understand the causes and origins of earthquakes. 3. Determine and differentiate the types of earthquakes. CONTENTS: 1.1 Seismology 1.2 Earthquakes and its Origin 1.3 Causes of Earthquakes 1.4 Types of Earthquakes 1.1 SEISMOLOGY Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth, plays a crucial role in understanding the dynamic processes that shape our planet's geology. By analyzing seismic waves generated by natural events such as earthquakes and volcanic eruptions, seismologists can unravel the mysteries of Earth's interior and improve our ability to predict and mitigate the impact of these hazardous events. Figure 1. Seismologists studying a fault crack A seismologist is a scientist works in basic or applied Image Source: https://www.snexplores.org/article/scientists- seismology. say-seismology-definition-pronunciation It is the primary tool for the study of the earth’s interior because little of the planet is accessible to direct observation. The Earth’s interior was able to be mapped as well as the study of the distribution of its physical properties were made possible through this scientific discipline. Etymology: The term ‘seismology’ is made up of two Greek words, ‘seismos’ means earthquake and ‘logos’ mean study. Thus, this term refers to the study of earthquakes. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 1 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Historical Development of Seismology: Seismology has come a long way from ancient Chinese and Greek philosophers pondering about earthquakes to modern scientists using advanced technology to unravel the mysteries of the Earth's dynamic processes. Early speculations on the natural causes of earthquakes were included in the writings of Thales of Miletus (585 BCE), Anaximenes of Miletus (550 BCE), Aristotle (340 BCE), and Zhang Heng (132 Figure 2. A model of Heng’s Seismoscope Image Source: CE). https://collection.sciencemuseumgroup.org.uk/objects/ In 132 CE, Zhang Heng of China's Han dynasty co54055/model-of-the-zhang-heng-seismoscope designed the first known seismoscope. In the 17th century, Athanasius Kircher argued that earthquakes were caused by the movement of fire within a system of channels inside the Earth. Martin Lister (1638–1712) and Nicolas Lemery (1645–1715) proposed that earthquakes were caused by chemical explosions within the Earth. The Great Lisbon Earthquake of 1755, coinciding with the general flowering of science in Europe, set in motion intensified scientific attempts to understand the behaviour and causation of earthquakes. From 1857, Robert Mallet laid the foundation of modern instrumental seismology and carried out seismological experiments using explosives. He is also responsible for coining the word "seismology.” In 1897, Emil Wiechert's theoretical calculations Figure 3. A drawing of the Great Lisbon Earthquake Image Source: led him to conclude that the Earth's interior https://www.britannica.com/event/Lisbon-earthquake- consists of a mantle of silicates, surrounding a core of-1755 of iron. In 1906 Richard Dixon Oldham identified the separate arrival of P-waves, S-waves and surface waves on seismograms and found the first clear evidence that the Earth has a central core. In 1909, Andrija Mohorovičić, one of the founders of modern seismology, discovered and defined the Mohorovičić discontinuity. Usually referred to as the "Moho discontinuity" or the "Moho," it is the boundary between the Earth's crust and the mantle. It is defined by the distinct change in velocity of seismological waves as they pass through changing densities of rock. In 1910, after studying the April 1906 San Francisco earthquake, Harry Fielding Reid put forward the "elastic rebound theory" which remains the foundation for modern tectonic studies. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 2 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering An early scientific study of aftershocks from a destructive earthquake came after the January 1920 Xalapa earthquake. An 80 kg (180 lbs.) Wiechert seismograph was brought to the Mexican city of Xalapa by rail after the earthquake. The instrument was deployed to record its aftershocks. Data from the seismograph would eventually determine that the mainshock was produced along a shallow crustal fault. By the 1960s, Earth science had developed to the point where a comprehensive theory of the causation of seismic events and geodetic motions had come together in the now well- established theory of plate tectonics. Application of Seismology in Earth Sciences: Earthquake Monitoring and Prediction With seismology on their side, scientists can monitor seismic activity, assess earthquake risks, and work towards improving early warning systems to protect lives and property. Seismic Imaging of Earth's Interior Using clever techniques like seismic tomography, seismologists can create detailed 3D images of the Earth's interior, unveiling the mysterious landscapes hidden beneath our feet. Earthquake Early Warning Systems When the ground starts shaking, wouldn't it be nice to get a heads-up? Earthquake early warning systems use seismology to detect earthquakes and send alerts seconds before the shaking hits. It's like your very own earthquake psychic predicting when to duck and cover. Seismic Hazard Assessment Seismologists play a crucial role in assessing seismic hazards to predict the potential impact of earthquakes on buildings, roads, and communities. It's like being the Sherlock Holmes of shaking ground, piecing together clues to make informed decisions and keep people safe. 1.2 EARTHQUAKES AND ITS ORIGIN An Earthquake is a sudden release of energy (seismic waves) in the earth’s crust causes the shaking on the Earth’s surface. This is due to the pressure build up on each plate that causes each to give in and slip. The intensity of each shaking varies in speed and motion depending on the location’s distance from the fault. Figure 4. Anatomy of an Earthquake Earthquakes are natural phenomena Image Source: https://www.calacademy.org/explore- that have captivated scientists and the public science/anatomy-of-an-earthquake alike for centuries. These powerful geological This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 3 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering events, characterized by sudden shaking of the ground, stem from complex processes deep within the Earth's crust. Understanding the origin of earthquakes requires delving into the intricate interplay of plate tectonics, fault movements, and seismic waves. The earth’s land masses move at approximately 1.5 centimeters away or towards each other per year. Through the combination of gravity and heat rising from the Earth’s core or the epicenter, which is the origin of these waves, large pieces of crusts also known tectonic plates were able to form. These large pieces of crusts move in relation with each other along the fault zones which, in turn, can trigger an earthquake. Geological Processes Leading to Earthquakes: Stress Accumulation in Earth’s Crust Just like humans, the Earth can also get stressed out. Over time, the tectonic plates that make up the Earth's crust push and pull against each other, building up stress like a coiled spring ready to snap. Figure 5. Diagram of a Stress in the Earth’s Crust Image Source: https://geophile.net/Lessons/Earthquakes/Earthquakes_02.html Rupture along Fault Lines When the stress becomes too much to handle, the Earth's crust can't take it anymore and gives in. This leads to a rupture along fault lines, where the built-up energy is released in the form of seismic waves. It's like the Earth's way of letting off steam. Figure 6 (right). Rupture along Fault Lines Image Source: https://geophile.net/Lessons/Earthquakes/Earthquakes_02.html Sequences of an Earthquake: Earthquakes do often occur in sequences, with smaller quakes before and after the largest event. They are classified as foreshocks, mainshocks, and aftershocks. Foreshocks – These are the smaller earthquakes that occur before the largest quake in a sequence, called the mainshock. Foreshocks are related to the mainshock in both time and space. About 40% of moderate to large earthquakes have foreshocks, increasing to 70% for M>7.0 events. The time between a foreshock and mainshock can range from minutes to days, or even years in rare cases. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 4 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Mainshocks – They are the largest earthquake in a sequence. Mainshocks are caused by sudden slip on a fault, releasing built-up tectonic stress. The rupture begins at the hypocenter (depth) and spreads along the fault plane. Aftershocks – These are smaller earthquakes that occur after the mainshock, usually near it. Aftershocks are caused by stress changes on the mainshock fault and nearby faults. Larger mainshocks produce more and larger aftershocks. The rate of aftershocks decays quickly, with about half as many the day after compared to the first day. Aftershocks can continue for weeks, years or even centuries after the mainshock Figures 7, 8, 9 and 10. Sequence of a 2020 Magnitude 6.6 Masbate Earthquake Image Source: https://www.phivolcs.dost.gov.ph/index.php/news/10465-foreshock-mainshock-aftershock-sequece-of-the-18- august-2020-mw-6-6-masbate-earthquake This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 5 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering 1.3 CAUSES OF EARTHQUAKES What Happens if an Earthquake Occurs? When an earthquake occurs, it releases a massive amount of energy in the form of seismic waves that travel through the Earth's crust. Seismic Waves are the shockwaves of energy released during an earthquake. Seismic waves are the rockstars of the underground world, traveling through the Earth's layers and revealing crucial information about its composition and structure. There are two main types of seismic waves: Body Waves and Surface Waves. ❖ Body Waves - travel through the interior of the Earth along paths controlled by the material properties in terms of density and modulus (stiffness). The density and modulus, in turn, vary according to temperature, composition, and material phase. This effect resembles the refraction of light waves. Types of Body Waves: P-Waves – also known as primary waves or pressure waves. P-waves cause the ground to compress and expand, that is, to move back and forth, in the direction of travel. They are called primary waves because they are the first type of wave to arrive at seismic recording stations. P waves can travel through solids, liquids, and even gases. It travels faster than other seismic waves making it the first waves recorded during an earthquake. Figure 11. Graphical Illustration of a P-Wave Image Source: https://annex.exploratorium.edu/fault-line/activezone/slides/rlwaves-slide.html S-Waves – also known as secondary waves, are transverse in nature. It is a wave that comes after the pressure waves. It shakes the ground in a shearing, or crosswise, motion that is perpendicular to the direction of travel. These are the shake waves that move the ground up and down or from side to side. S waves are called secondary waves because they always arrive after P waves at seismic recording stations. Unlike P waves, S waves can travel only through solid materials. These shear waves displace the ground perpendicular to the direction of the propagation. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 6 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Figure 12. Graphical Illustration of an S-wave Image Source: https://annex.exploratorium.edu/fault-line/activezone/slides/rlwaves-slide.html ❖ Surface Waves - are waves that travels just under the Earth’s surface. These waves travel slower through Earth material and has a lower frequency than body waves. Although it is predominantly slower than an S-wave, they are much larger in amplitude making them the most destructive among the previous waves. Types of Surface Waves: After both P and S waves have moved through the body of Earth, they are followed by surface waves, which travel along Earth’s surface. Surface waves travel only through solid media. They are slower moving than body waves but are much larger and therefore more destructive. The two types of surface waves are named Love Waves and Rayleigh Waves, respectively, after the scientists who identified them. 1. Love Waves - have a horizontal motion that moves the surface from side to side perpendicular to the direction the wave is traveling. Love Waves were named for A.E.H. Love, a British mathematician, who discovered them in 1911. Of the two surface waves, Love waves move faster. Figure 13. Graphical Illustration of a Love Wave Image Source: https://annex.exploratorium.edu/fault-line/activezone/slides/rlwaves-slide.html 2. Rayleigh Waves - cause the ground to shake in an elliptical pattern. This motion is like that observed in ocean waves. Rayleigh Waves were named for John William Strutt, known as This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 7 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Lord Rayleigh, who mathematically predicted the existence of this kind of wave in 1885. Of all the seismic waves, Rayleigh waves spread out the most, giving them a long duration on seismograph recordings. Figure 14. Graphical Illustration of a Rayleigh Wave Image Source: https://annex.exploratorium.edu/fault-line/activezone/slides/rlwaves-slide.html CAUSES OF AN EARTHQUAKE: Long-term deformation and pressure buildup causes movements on the surface. It is a general knowledge that the yearly movement of tectonic plates, even with the smallest displacement could cause a huge amount of deformation on the plate’s boundary which later results in an earthquake. The Earth’s crust is fragmented into 15 major slabs called Tectonic Plates which is comprised of continental and oceanic crust and the upper part of the mantle. However, beneath those slabs lies the Earth’s asthenosphere that has a consistency of a fluid which drives the plates to move FIVE MAIN CAUSES OF EARTHQUAKE 1. Tectonic Plate Movements Plate tectonics is like a giant jigsaw puzzle where the Earth's outer shell, called the lithosphere, is broken into large pieces, or "plates." It is a scientific theory that explains how major landforms are created as a result of Earth’s subterranean movements. Figure 15. The San Andreas Fault The Earth's outer layer is broken into large, Image Source: rocky plates that float on top of a partially melted https://en.wikipedia.org/wiki/San_Andreas_Fault layer of rock called the asthenosphere. These plates, made up of the crust and upper mantle, This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 8 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering move very slowly, about 1-6 inches per year, due to the movement of the asthenosphere and lithosphere. As they move, they interact with each other, creating different geological formations, such as mountains like the Himalayas and faults like the San Andreas Fault, shaping the Earth's surface over time. Continental Drift Theory: Alfred Lothar Wegener (1880-1930) was a German scientist who is best known for proposing the theory of continental drift, which laid the groundwork for the modern theory of plate tectonics. He suggests that 200 million years ago, a single supercontinent called Pangaea began to break apart, with its fragments moving away from each other to form the continents we see today. Wegener supported his theory by pointing out matching rock Figure 16. Alfred Wegener formations and similar fossils found in Brazil and West Africa, as well as Image Source: the puzzle-piece-like fit of South America and Africa, challenging the https://www.britannica.com/b prevailing views of his time and laying the groundwork for modern plate iography/Alfred-Wegener tectonics. Figure 17. Diagram of Wegener’s Continental Drift Theory Image Source: https://www.insightsonindia.com/world-geography/physical-geography-of-the-world/geomorphology/first- order/continental-drift-theory/ This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 9 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Figure 18. Gondwana, showing Fossil Patterns across Continents Image Source: https://www.geolsoc.org.uk/Plate-Tectonics/Chap1-Pioneers-of-Plate-Tectonics/Alfred-Wegener/Fossil-Evidence- from-the-Southern-Hemisphere Furthermore, the tectonic plates’ movements vary. There are the types of plate boundary that testifies with the statement. Three Types of Tectonic Plate Boundaries: Convergent Plate Boundary – Convergent boundaries occur when plates collide. This collision can result in one plate sliding beneath the other (subduction) or the plates crumpling and pushing against each other. The intense pressure and movement at these boundaries can trigger earthquakes. Figure 19: Graphical Illustration of There are 3 possible outcomes of Convergent Boundaries: Convergent Plate Boundary Image Source: https://www.bgs.ac.uk/wp- content/uploads/2020/04/ This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 10 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering ❖ Continental-Continental Convergence - When two continental plates collide, they crumple and form mountains. Example: The Himalayan Mountain Range, where the Indian plate collided with the Eurasian Plate. Figures 20 & 21 (left to right). Graphical Illustration of Continental-Continental Convergence & The Himalayas Image Source: https://www.slideshare.net/slideshow/convergent-boundaries/45154531, https://www.britannica.com/place/Himalayas ❖ Oceanic-Continental Convergence - When an oceanic plate meets a continental plate, the denser oceanic plate sinks beneath the continental plate, a process called subduction. Example: The Andes Mountain Range, where the Nazca plate is being subducted beneath the South American Plate. Figures 22 & 23 (left to right). Graphical Illustration of Oceanic-Continental Convergence & The Andes Image Source: https://www.slideshare.net/slideshow/convergent-boundaries/45154531 https://en.wikipedia.org/wiki/Andes ❖ Oceanic-Oceanic Convergence - When an oceanic plate meets another oceanic plate, the older, denser oceanic plate subducts under the younger oceanic plate. Example: Aleutian Islands, where the Pacific Plate is subducting beneath the North American Plate. Figures 24 & 25 (left to right). Graphical Illustration of Oceanic-Oceanic Convergence & The Aleutian Islands (highlighted) Image Source: https://www.slideshare.net/slideshow/convergent-boundaries/45154531 https://en.wikipedia.org/wiki/Aleutian_Islands#/ This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 11 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Divergent Plate Boundary – At divergent boundaries, plates move away from each other, creating rifts and mid- ocean ridges. The tension and fracturing of the Earth's crust at these boundaries can lead to earthquakes. This happens when new materials forms in between causing the fault to rupture farther. Transform Plate Boundary – Transform boundaries involve plates sliding past each other horizontally. The friction between the plates can cause them to become stuck, building up stress until it is suddenly released, causing an earthquake. Figures 26 and 27 (above right). Graphical Illustrations of Divergent and Transform Plate Boundaries Image Source: https://www.bgs.ac.uk/wp-content/uploads/2020/04/ 2. Volcanic Activity Earthquakes can trigger volcanic eruptions through severe movement of tectonic plates. Similarly, volcanoes can trigger earthquakes through the movement of magma within a volcano. Examples of Volcanic Induced Seismicity: Figure 28. A Volcanic Eruption 1. Magma Movement and Volcanic Tremors Image Source: https://www.mshslc.org/activity/volcano- 2. Volcanic Eruptions seismicity/ 3. Fault Lines Fault Lines are fractures in the Earth's crust where movement occurs. When stress builds up along fault lines, the rocks on either side are pushed and bent until they suddenly break, releasing energy in the form of seismic waves. Faults can form in response to any one of the three types of forces: compression, tension and shear. The type of fault produced, however, depends on the type of force exerted. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 12 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Types of Faults: Figures 29, 30 and 31 (left to right). Graphical Illustrations of Strike-Slip, Dip-Slip and Oblique-Slip Faults Image Source: https://www.researchgate.net/figure/Block-diagrams-schematically-showing-secondary-fractures-developed-above- steeply-dipping_fig8_276292586 Dip-Slip Fault - is a type of geological fault where the movement of the two sides of the fault is primarily up or down, parallel to the dip of the fault plane. This type of fault is caused by tensional or compressional forces in the Earth's crust that cause rocks to break and slide along the fault plane. Types of Dip-Slip Fault: 1. Normal Fault - is a type of geological fault that occurs when two blocks of the earth's crust are pulled apart, causing one block to drop down relative to the other. Normal faults occur in areas where the Earth's crust is being extended or stretched, often in areas of tectonic plate movement or rifting. 2. Reverse Fault - is a type of geological fault in which the hanging wall (the rock layer above the fault plane) moves upward relative to the footwall (the rock layer below the fault plane). Reverse faults are common in regions where tectonic forces cause compression, such as at convergent plate boundaries. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 13 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering 3. Thrust Fault - is a type of geological fault where the rocks on one side of the fault plane are pushed up and over the rocks on the other side of the fault plane. This type of fault is characterized by a low angle of dip, typically less than 45 degrees, and can result in the uplift of mountains and the creation of reverse faults. Thrust faults are often associated with convergent plate boundaries where two tectonic plates are colliding, and one plate is being pushed beneath the other in a process known as subduction. Figures 32, 33 and 34 (above right). Graphical Illustrations of Normal, Reverse and Thrust Faults Image Source: https://www.geological-digressions.com/faults-some-common-terminology/ Strike-Slip Fault - is a type of fault that occurs when two blocks of rocks slide past each other horizontally, parallel to the strike of the fault. This means that the movement of the blocks is predominantly horizontal, with relatively little vertical movement. Oblique-Slip Fault - a type of geological fault in which the movement of rock masses occurs at an angle to the orientation of the fault plane. In other words, the movement of the rocks is a combination of both vertical and horizontal movement, rather than just one or the other. 4. Induced Seismicity Human activities can also induce earthquakes by altering the stress distribution in the Earth's crust and weakening rock formations. Examples of Induced Seismicity: Hydraulic Fracturing - also known as ‘fracking’ is the process of injecting high-pressure fluid into the ground to extract oil and gas, can destabilize fault lines and trigger earthquakes. Similarly, injection wells used for waste disposal can increase pressure in underground rock formations, leading to seismic events. Reservoir-Induced Seismicity - The filling of reservoirs behind dams can induce earthquakes due to the added weight of the water, which can press down on the Earth's crust and reactivate dormant faults, causing seismic activity. This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 14 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Geothermal Plant Operations - Depending on the rock properties, and on injection pressures and fluid volume, the reservoir rock may respond with tensile failure, as is common in the oil and gas industry, or with shear failure of the rock's existing joint set. Intended Explosions - There are three main types of explosions: chemical, mechanical and nuclear. Each type of explosion can be equally devastating and serious, causing unprecedented harm to the surrounding people, atmosphere and infrastructure. Therefore, understanding different types of explosions and how they occur is important. Figures 35, 36, 37 and 38 (above right). Induced Seismicity Examples Image Source: https://www.researchgate.net/figure/Block-diagrams-schematically-showing-secondary-fractures-developed-above- steeply-dipping_fig8_276292586, https://www.geological-digressions.com/faults-some-common-terminology/, https://www.bgs.ac.uk/wp-content/uploads/2020/04/ 5. Collapses Collapse can induce earthquakes. The sudden failure of large rock formations or underground cavities shifts surrounding rocks, causing minor earthquakes. This occurs when the rock's structural integrity is compromised, releasing energy that generates seismic waves. Gradual subsidence from collapsing voids can Figure 39. A Collapsed Underground Quarry Image Source: also alter stress distributions in the crust, potentially https://www.flickr.com/photos/lionexploration/341 triggering seismic activity in nearby fault zones. 25589222 Can A Meteorite Impact Cause an Earthquake? Meteorite impacts can produce earthquakes by generating significant seismic waves that cause ground shaking like tectonic earthquakes. The energy released during a large impact can exceed that of major earthquakes, leading to substantial crustal effects. Figure 40. An artist’ depiction of a meteorite that is believed to have caused the extinction of dinosaurs, now known as Chicxulub crater, located in Southeast Mexico Image Source: https://en.wikipedia.org/wiki/Chicxulub_crater This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 15 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering 1.4 TYPES OF EARTHQUAKES Earthquakes are classified into several types based on their causes and characteristics. Understanding the different types of earthquakes is crucial for assessing risks, developing mitigation strategies, and improving emergency response plans. Tectonic Earthquake – It is caused by sudden movement along faults in the Earth's crust as tectonic plates move and collide. Tectonic Earthquakes are the most common type, accounting for over 90% of all earthquakes. It can be further classified into normal, reverse, strike-slip, and oblique-slip faults based on the direction of movement. Figure 41. A Tectonic Earthquake Image Source: https://www.noaa.gov/sites/default/files/styles/default_ width_428/public/2022-11/ Volcanic Earthquake – It occurs in relation to volcanic activity, typically caused by the movement of magma beneath the Earth's surface. It has two main categories: volcano-tectonic earthquakes (result from stress changes in solid rock due to magma movement) and long period earthquakes (indicate pressure changes associated with magma transport and can serve as precursors to eruptions. Volcanic earthquakes can produce ground cracks, deformation, and damage to Figure 42. A Volcano structures and are often felt by people living near Image Source: https://www.shutterstock.com/image- active volcanoes vector/3d-volcano-eruption-educational-poster- 260nw-2289425123.jpg Explosion Earthquake - Explosion earthquakes are seismic events caused by the detonation of explosives, both man-made and natural (e.g. meteor impacts). Ground shaking may happen due to the explosion of chemical or nuclear devices. Explosion earthquakes are rare and distinct from the more common tectonic earthquakes caused by tectonic plate movement. Figure 43. Aftermath of the Beirut Explosion, an example of a man-made explosion which caused an They can be detected and distinguished from explosion earthquake tectonic earthquakes by their unique Image Source: characteristics and context. https://en.wikipedia.org/wiki/2020_Beirut_explosion#/m edia/ This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 16 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering Collapse Earthquake - Collapse earthquakes are small seismic events that occur in underground caverns or mines. They result from the shaking of the ground during surface earthquakes or from the collapse of mine roofs due to induced stress. Typically minor in magnitude, these earthquakes are linked to mining activities and occur when large rock masses are explosively removed. Collapse earthquakes can cause ground shaking and minor Figure 44. Graphical Representation of a Collapse Earthquake structural damage nearby, but are generally less Image Source: https://www.optimumseismic.com/wp- destructive than tectonic earthquakes content/uploads/2020/03/will-my-building-collapse-in- an-earthquake.jpg/ This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 17 of 18 | Introduction to Earthquakes & Seismology  Republic of the Philippines CAMARINES SUR POLYTECHNIC COLLEGES Nabua, Camarines Sur COLLEGE OF ENGINEERING AND ARCHITECTURE Bachelor of Science in Civil Engineering References: Earthquakes Booklet - How we measure them. (n.d.). https://earthquakes.bgs.ac.uk/education/eq_guide/eq_booklet_how_we_measure.htm Seth, S. (2009). An Introduction to Seismology, Earthquakes, and Earth Structure. John Wiley & Sons https://books.google.com.ph/books?id=z80yrwFsqoC&dq=seismology+earthquakes +and+earth+structure&lr=&hl=tl&source=gbs_navlinks_s Council, N. R. (2006). Improved seismic monitoring - Improved Decision-Making. In National Academies Press eBooks. https://doi.org/10.17226/11327 Anatomy of an Earthquake | California Academy of Sciences. (n.d.-b). California Academy of Sciences. https://www.calacademy.org/explore-science/anatomy-of-an-earthquake What is Tectonic Shift? (n.d.). https://oceanservice.noaa.gov/facts/tectonics.html What is a fault and what are the different types? | U.S. Geological Survey. (2011, September 30). https://www.usgs.gov/faqs/what-a-fault-and-what-are-different-types Michigan Technological University. (2021, August 11). Surface waves. https://www.mtu.edu/geo/community/seismology/learn/seismology-study/surface-wave/ Earthquake types: What you need to know. (2022, March 27). Unacademy. https://unacademy.com/content/nda/study-material/geography/earthquake-types/ Wikipedia contributors. (2024, July 12). Seismology. Wikipedia. https://en.wikipedia.org/wiki/Seismology Vedantu. (n.d.). Seismology. VEDANTU. https://www.vedantu.com/geography/seismology SE 412 – Earthquake Engineering Group 1 Members: Naomi Jorge V. Adorable John Timothy A. Babia Ma. Angelica M. Barreras Cybie S. Cervantes Hannah Aira C. Ibañez Daryl Angelo V. Mortera May-An S. Pentecostes Daryl Jane B. Portacio Harry E. Tiangco THANK YOU!!! This module is exclusive for the use of BSCE-4D Earthquake Engineering students of Camarines Sur Polytechnic Colleges only. Distribution, in any form, of this file is strictly prohibited. Made by Group 1 Page 18 of 18 | Introduction to Earthquakes & Seismology