Introduction-to-Earthquakes.pptx environmental life science pdf

presentation done for earthquakes

1. Introduction to Earthquakes Earthquakes are one of the most awe-inspiring and destructive forces of nature. They are sudden, violent movements of the Earth's crust that can cause widespread devastation. Earthquakes can occur anywhere in the world, but they are most common along the edges of tectonic plates, where the Earth's crust is constantly shifting and colliding. The Earth's crust is made up of massive, interlocking plates called tectonic plates. These plates are constantly moving, albeit very slowly. When these plates collide, slide past each other, or pull apart, they cause a release of energy in the form of seismic waves that travel through the Earth. These waves shake the ground, causing the damage we associate with earthquakes. SS

2. Types of Earthquakes 1 Tectonic Earthquakes These are the most common type of earthquake, and they are caused by the movement of tectonic plates. The sudden release of energy along the fault line creates seismic waves that propagate through the Earth. 2 Volcanic Earthquakes These earthquakes are caused by the movement of magma beneath the Earth's surface. The movement of magma can cause pressure changes that trigger earthquakes. Volcanic earthquakes are often associated with volcanic eruptions. 3 Collapse Earthquakes These earthquakes are relatively small and occur when underground cavities collapse. This type of earthquake is often associated with mining or underground construction. They are typically localized and less destructive than tectonic earthquakes.

3. Tectonic Earthquakes 1 Convergent Boundaries At convergent boundaries, tectonic plates collide. This can result in the subduction of one plate beneath another, or the formation of mountains. The pressure and stress built up along these boundaries can lead to powerful earthquakes. 2 Divergent Boundaries At divergent boundaries, tectonic plates move apart. This creates new crustal material, often in the form of mid-ocean ridges. Earthquakes along these boundaries tend to be less powerful than those at convergent boundaries, but they can still cause significant damage. 3 Transform Boundaries At transform boundaries, tectonic plates slide past each other horizontally. This can cause large earthquakes, such as the San Andreas Fault in California. The movement of the plates can create a great deal of friction and stress, leading to sudden releases of energy.

4. Volcanic Earthquakes Magma Movement As magma rises toward the surface, it can cause pressure changes in the surrounding rocks. This pressure can trigger earthquakes, which may be a warning sign of an impending volcanic eruption. Eruption-Related Earthquakes During a volcanic eruption, the release of gas and ash can also trigger earthquakes. These earthquakes are often relatively small and localized, but they can still be felt near the volcano. Post-Eruption Earthquakes After a volcanic eruption, earthquakes can continue to occur as the volcano adjusts to the changes in pressure and stress. These earthquakes are often smaller than those that occurred during the eruption, but they can still be significant.

5. Collapse Earthquakes Mining Activities Underground mining can create large cavities in the Earth's crust. These cavities can become unstable and collapse, triggering earthquakes. This type of earthquake is often associated with coal mining and other extractive industries. Underground Construction Construction projects such as tunnels and underground storage facilities can also create underground cavities that can collapse. The collapse can trigger earthquakes, especially in areas with unstable rock formations. Natural Cave Collapse In some cases, natural caves can collapse, triggering earthquakes. This type of earthquake is typically small and localized, but it can still cause damage to nearby structures.

6. The Richter Scale Magnitude Description Less than 2.0 Micro earthquake, not felt 2.0-2.9 Very minor, felt by few 3.0-3.9 Minor, felt by many 4.0-4.9 Light, noticeable shaking 5.0-5.9 Moderate, damage to weak structures 6.0-6.9 Strong, significant damage 7.0-7.9 Major, widespread damage 8.0 or greater Great, catastrophic damage

7. Measuring Earthquake Magnitude Seismograph A seismograph is an instrument used to detect and record seismic waves. The seismograph produces a record called a seismogram, which shows the amplitude and frequency of the waves. Seismic Waves Seismic waves are the vibrations that travel through the Earth's crust during an earthquake. There are different types of seismic waves, including P-waves (primary waves) and S-waves (secondary waves), which are used to determine the epicenter and magnitude of an earthquake. Magnitude Calculation The magnitude of an earthquake is determined by measuring the amplitude of the largest seismic wave recorded on a seismogram. The Richter Scale is a logarithmic scale that assigns a numerical value to the magnitude of an earthquake.

8. Interpreting Richter Scale Readings Energy Released Each increase of one unit on the Richter Scale represents a tenfold increase in the amount of energy released by the earthquake. For example, a magnitude 6 earthquake releases ten times more energy than a magnitude 5 earthquake. Ground Motion The magnitude of an earthquake is directly related to the amount of ground motion caused by the earthquake. A higher magnitude earthquake will result in more intense shaking and greater potential for damage. Damage Potential The damage caused by an earthquake depends on several factors, including the magnitude of the earthquake, the distance from the epicenter, the geological conditions, and the vulnerability of the structures in the area.

9. Structural Mitigation Measures 1 Flexible Connections Flexible connections between different parts of a building allow the structure to move and sway during an earthquake without breaking. This helps to dissipate the energy of the seismic waves and reduce the risk of structural failure. 2 Cross Bracing Cross bracing is a structural system that uses diagonal beams to strengthen buildings. This helps to distribute the forces of an earthquake more evenly throughout the structure and prevent the walls from collapsing. 3 Shock Absorbers Shock absorbers are devices that are designed to absorb the energy of seismic waves. They are typically installed between the building and its foundation, and they help to reduce the shaking experienced by the building. 4 Foundation Design The foundation of a building must be designed to withstand the forces of an earthquake. This may involve using deep foundations, reinforcing the soil, or using special types of concrete.

10. Earthquake-Resistant Building Design 1 Site Selection Choosing a site with stable soil and geological conditions is crucial for minimizing earthquake damage. Avoid areas prone to liquefaction, landslides, or ground amplification. 2 Building Materials Selecting strong and durable building materials that can withstand seismic forces is essential. Reinforced concrete, steel, and timber are common choices for earthquake-resistant construction. 3 Structural System The design of the structural system should incorporate features that allow the building to move and deform during an earthquake without collapsing. This may involve using flexible connections, shear walls, or moment-resistant frames. 4 Non-Structural Elements Non-structural elements such as walls, ceilings, and windows should be designed to resist earthquake forces. This may involve using lighter materials, securing them to the building frame, or using shatterproof glass.