Seismic Activity Notes PDF

Seismic Activity  Seismic Activity The Earth’s Interior Structure The Earth's interior is composed of several layers, each with its own physical and chemical properties. These layers can be categorized into the Crust, Mantle, Outer Core and Inner Core. Sketch and la...

Seismic Activity  Seismic Activity The Earth’s Interior Structure The Earth's interior is composed of several layers, each with its own physical and chemical properties. These layers can be categorized into the Crust, Mantle, Outer Core and Inner Core. Sketch and label a diagram of the Earth’s Interior Structure. 1. Crust: The Earth's outermost layer is called the crust. It is relatively thin compared to the other layers and is divided into two types: the continental crust and the oceanic crust. The continental crust is thicker and less dense, consisting mainly of rocks like granite. The oceanic crust is thinner and denser, primarily made up of basalt rocks. The crust is where we live and where most geological processes, like erosion, weathering, and human activities, occur. 1 | Page  Seismic Activity 2. Mantle: Beneath the crust lies the mantle, which is the thickest layer of the Earth. The mantle extends to a depth of about 2,900 kilometers (1,800 miles) and is composed of solid rock. The mantle can be further divided into the upper mantle and the lower mantle. The upper mantle has a relatively rigid layer called the lithosphere, which includes the crust and a portion of the uppermost mantle. The asthenosphere, a partially molten region, lies just below the lithosphere and plays a crucial role in plate tectonics and the movement of the Earth's crustal plates. 3. Outer Core: Beneath the mantle is the outer core, which is composed mainly of liquid iron and nickel. The outer core's extremely high temperature and pressure prevent the liquid metal from solidifying. The movement of molten metal within the outer core generates the Earth's magnetic field. This magnetic field is responsible for protecting the planet from harmful solar radiation and guiding compass needles. 2 | Page  Seismic Activity 4. Inner Core: The Earth's innermost layer is the inner core, which is solid and primarily composed of iron and nickel. Despite the immense pressure, the inner core remains solid due to the even higher temperatures. It is believed that the inner core's solid structure is maintained by the intense pressure from the surrounding layers. The inner core's temperature is estimated to be around 5,700 degrees Celsius. Overall, the Earth's interior is a complex system with dynamic interactions between its layers. Heat from the core drives the movement of the mantle and the motion of tectonic plates on the Earth's surface, resulting in earthquakes, volcanic activity, and 3 | Page Seismic Activity the formation of mountains and ocean basins. Studying the Earth's interior provides valuable insights into the planet's geological history, its current processes, and its potential future changes. Convectional Currents Convection currents are like heat-driven motions in a fluid, where hot stuff rises and cool stuff sinks. They happen because hot things are lighter and want to go up, while cooler things are heavier and want to go down. Inside the Earth, convection currents occur in the mantle, beneath the hard outer crust. When the heat from the Earth's core warms up parts of the mantle, these areas become less dense (less heavy) and start to rise. As they rise, they carry heat with them. When they get closer to the surface, they start to cool down, become denser, and then sink back down. This movement of rising warm material and sinking cool material creates a cycle of convection currents. 4 | Page Seismic Activity These convection currents in the mantle are like giant "magma rivers" flowing beneath the Earth's surface. They are responsible for moving the tectonic plates, which are like puzzle pieces that make up the Earth's crust. These moving plates can cause earthquakes, create mountains, and even lead to the formation of volcanoes. So, convection currents are a way that the Earth's interior moves heat around, and they play a major role in shaping the world we live on. Label the diagram with the following: Crust Mantel Inner Core Outer Core Convectional Currents 5 | Page  Seismic Activity Continental Drift The concept of Continental Drift, proposed by German meteorologist and geophysicist Alfred Wegener in the early 20th century, suggests that the Earth's continents were once part of a single supercontinent called Pangaea. Over time, Pangaea broke apart, and the individual continents drifted to their current positions. This theory laid the foundation for modern plate tectonics. Wegener's Continental Drift Theory was based on several lines of evidence: 1. Jigsaw Puzzle Fit: Wegener noticed that the coastlines of continents seemed to fit together like pieces of a jigsaw puzzle, especially when considering the continental shelves beneath the ocean. He found this similarity particularly striking when looking at the coastlines of South America and Africa. 2. Geological Matching: Similar rock formations, mountain ranges, and geological features were found on continents that were now widely separated by oceans. For instance, the Appalachian Mountains in North America were geologically similar to the Caledonian Mountains in Scotland and Scandinavia. 3. Fossil Evidence: Fossil evidence supported the idea of connected continents. Fossils of the same plants and animals were found on continents that are now separated by oceans, suggesting that these landmasses were once joined together. 6 | Page  Seismic Activity 4. Climate Clues: The distribution of ancient climate indicators, such as glacial deposits and coal beds, was puzzling if continents were in their current positions. For example, evidence of glaciation was found in regions that are now too warm for glaciers, implying that these areas were once in different positions relative to the poles. Wegener proposed that the continents moved due to the movement of the Earth's crust over a semi-fluid layer beneath it. However, his theory was met with skepticism because he couldn't provide a convincing mechanism for the movement of continents. It wasn't until the mid-20th century that advancements in geophysics and seismology provided more substantial evidence for the movement of continents. The discovery of mid-ocean ridges, deep ocean trenches, and the mapping of Earth's magnetic field patterns on the ocean floor suggested that the Earth's crust was divided into tectonic plates that moved slowly over the semi-molten mantle beneath them. This evidence eventually led to the development of the theory of plate tectonics, which integrated Wegener's ideas into a more comprehensive and scientifically supported framework. 7 | Page Seismic Activity In summary, Wegener's Continental Drift Theory proposed that continents were once connected in a supercontinent and drifted to their current positions. While his original theory faced skepticism, subsequent advancements in scientific knowledge, particularly the development of plate tectonics, have validated and expanded upon many of his ideas. Plate Tectonics The process of a plate, part of the crust, moving above the mantle is known as Plate Tectonics. The boundary between two plates is kown as Plate Boundary. Every piece of land is part of a particular plate. There are many plate forming the crust. Because of the convection currents in the Mantle, these different plates moves in different directions. 8 | Page Seismic Activity These are the three types of Plate boundaries: Divergent plates Convergent plates Transform plates (Destructive) (Constructive) (Conservative) The map below shows the major Tectonic Plates forming the crust of the world: Plate Tectonics can cause an earthquake, a volcanic eruption or the formation of mountains.  When plates move sideways the result is an earthquake. 9 | Page Seismic Activity  When plates move away from each other the result is an earthquake and/or a volcanic eruption.  When plates move towards each other the result is an earthquake, a volcanic eruption and the formation of mountains. Places, which frequently experience earthquakes, are found close to the plate boundaries as is shown in the map below. Most volcanoes and mountain ranges are also found along these plate boundaries, where two plates are next to each other. Mark with an X the correct answers: Earthquakes Volcanoes Mountains Divergent Convergent Transform 10 | P a g e Seismic Activity Plate tectonis have transformed ‘Pangaea’ into today’s continents while enclosing the ‘Tethys Sea’ and also forming today’s Mediterranean basin. The Mediterranean Sea formed because the two plates surrounding it, the African Plate and the Eurasian Plate are moving towards each other. The result of this movement is the formation of mountain ranges such as the Alps, Atlas, Pyrenees, Apennines and the Dinaric Mountains. The region also has many volcanoes such as Etna, Vesuvius and Stromboli. It also experiences frequent earthquakes especially in Italy, Turkey and Greece. On the map of the Mediterranean region below: Label the Mediterranean Sea, the African Plate and the Eurasian Plate. Shade Italy, Turkey and Greece. Formation of Fold Mountains When two tectonic plates are moving towards each other, the land close to the plate boundary folds. As the process is repeated several times the folded land becomes 11 | P a g e Seismic Activity higher as the plates slowly pressed towards each other, thus forming mountain ranges. Every time the plates move towards each other the mountains uplift further. The Alps are Europe’s biggest mountain range and lie right at the heart of the continent. They stretch across eight countries: France, Switzerland, Italy, Monaco, Liechtenstein, Austria, Germany and Slovenia. This formation is caused by the convergent movements of the European and Adriatic plates. The Andes Mountains in Peru and Chile are another example of mountain folding caused by convergent plates. These mountains were formed because the Nazca Plate is colliding with the South American Plate. 12 | P a g e  Seismic Activity Formation of Volcanoes Volcanoes form through the process of plate tectonics primarily at convergent and divergent plate boundaries. These plates move and interact with each other, leading to various geological phenomena, including the formation of volcanoes. 1. Convergent Boundaries (Subduction Zones): At convergent boundaries, where tectonic plates move towards each other, one plate usually gets pushed beneath the other in a process known as subduction. The descending plate, called the subducting plate, sinks into the Earth's mantle. As it descends into the mantle partial melting (fractional melting) of the crust occurs. The molten (melted) material, called magma, is less dense than the surrounding rocks, so it rises through the overlying plate. This rising magma can eventually reach the surface, leading to the formation of a volcanic arc. Examples of this type of volcano formation include the Pacific Ring of Fire, where the Pacific Plate subducts beneath surrounding plates, creating a series of volcanic arcs. 13 | P a g e  Seismic Activity 2. Divergent Boundaries: At divergent boundaries, tectonic plates move away from each other, creating a gap in the Earth's crust. As the plates separate, magma from the mantle can rise to fill the void. This magma, which is relatively less dense than the surrounding rock, can solidify and accumulate over time, forming new crust. This process leads to the formation of underwater volcanoes, also known as seafloor spreading centers. If these volcanic activities continue for a long time, the accumulated lava and volcanic rocks can rise above sea level, forming islands or land-based volcanoes. The Mid-Atlantic Ridge is an example of a divergent boundary where new oceanic crust is continuously being formed through volcanic activity along the seam of the tectonic plates. In summary, volcanoes form through plate tectonics due to the movement and interactions of tectonic plates at convergent and divergent boundaries. Convergent boundaries involve subduction of one plate beneath another, leading to the ascent of magma and the formation of volcanic arcs. Divergent boundaries involve the 14 | P a g e Seismic Activity separation of plates, allowing magma to rise and create new crust, forming underwater and terrestrial volcanoes over time. Types of volcanoes Characteristics of volcanones Magma (molten rock) from deep inside the earth forces its way to the surface because of the great pressure found deep down in the mantle. When magma reaches the earth’s surface it is called lava. When it cools different types of rocks form like basalt, pumice and obsidian. 15 | P a g e Seismic Activity Crater A funnel shaped hollow at the top of a volcanic cone. Vent An opening in the planet’s surface from which magma passes through. Magma Chamber A store of molten rock deep inside the earth. Secondary vent Forms if the main vent is blocked and magma is forced to the surface by another route. Ash Cloud Small pieces of shattered rock thrown from the volcano. Pyroclastic flow A fast-moving current of super-heated gas and flow. Lava A flow of magma coming out of the volcano. Magma Molten rock beneath the earth’s surface. Secondary cone A small volcano, which form around secondary vents. Volcanic bombs A mass of molten rock formed when a volcano ejects large fragments of lava during an eruption. 16 | P a g e  Seismic Activity Describe what happens when a volcano erupts by sorting the phrases below in the correct order. Rescue service goes into action. A huge explosion followed. Lava destroyed restaurants, houses and vineyards. Volcano gently rumbles and steams. A patch of snow south of the main crater began to melt. Lava poured down the mountainside. Volcanic areas Volcanic areas offer both benefits and hazards to the surrounding environment and human populations. Benefits of Volcanic Areas: 1. Fertile Soil: Volcanic soils are rich in minerals and nutrients, making them highly fertile for agriculture. The eruption of volcanoes releases these nutrients into the soil, creating excellent conditions for the growth of crops. 2. Geothermal Energy: Volcanic regions often have access to geothermal energy, which is harnessed by tapping into the heat from the Earth's interior. Geothermal power plants can provide a consistent and renewable source of energy for electricity generation and heating. 3. Mineral Resources: Volcanic areas can contain valuable mineral deposits such as sulfur, gold, silver, and various other metals. These resources can be economically significant and contribute to local economies. 17 | P a g e  Seismic Activity 4. Tourism and Recreation: Some volcanic regions, especially those with iconic and accessible volcanoes, attract tourists and outdoor enthusiasts. Volcanic landscapes, hot springs, and geysers can be popular attractions for sightseeing, hiking, and adventure tourism. Hazards of Volcanic Areas: 1. Lava Flows: Erupting volcanoes can produce lava flows that destroy vegetation, infrastructure, and homes in their path. Lava flows can move slowly or quickly, depending on their viscosity, and can cover large areas. 2. Pyroclastic Flows: These are extremely hot and fast-moving mixtures of volcanic gases, ash, and rocks. Pyroclastic flows can be deadly and devastate everything in their way, often descending rapidly down the sides of volcanoes. 3. Ashfall: Volcanic eruptions can release large amounts of ash into the atmosphere. Ashfall can disrupt air travel, damage crops, contaminate water supplies, and pose health risks due to inhalation. 4. Volcanic Gases: Eruptions release gases such as sulfur dioxide, carbon dioxide, and others into the atmosphere. These gases can lead to air pollution, acid rain, and respiratory problems in humans and animals. 5. Lahars: Lahars are volcanic mudflows or debris flows that can be triggered by heavy rainfall, melting snow, or the collapse of accumulated volcanic material. They can flow down valleys and river channels, causing significant damage to communities in their path. 6. Tsunamis: Some volcanic eruptions, particularly those that occur underwater or near coastlines, can trigger tsunamis, which are large and destructive sea waves that can inundate coastal areas. 7. Disruption of Infrastructure: Volcanic eruptions can disrupt transportation networks, damage power lines, and cause disruptions to essential services such as water supply and communication systems. 18 | P a g e  Seismic Activity 8. Long-term Environmental Changes: Large volcanic eruptions can inject large amounts of ash and gases into the stratosphere, leading to temporary climate cooling. This can impact global weather patterns and lead to short-term changes in temperature and precipitation. 19 | P a g e Seismic Activity Formation of Earthquakes Major earthquakes occur at plate boundaries where the crust is subjected to enormous stress as the plates try to move. The rocks are forced to bend, building huge quantities of stored energy. As the crust is unstable, this energy is released in the form of an earthquake. The place underground where an earthquake starts is called the focus. This is where seismic waves called shock waves start. The area directly above the focus, at the surface of the crust, is called the epicentre. This is where the earthquake is felt most. Earthquakes are happening all the time. Some are so weak that they can hardly be felt and instruments called ‘seismographs’ are needed to detect them. Seismologists are scientists who study earthquakes. 20 | P a g e Seismic Activity ‘Seismologists’ use the Richter Scale (Forces 1 to 9) to measure the strength of an earthquake. Each level on the Richter scale is 10 times stronger than the previous. This means that an earthquake, which is ‘6’ on the Richter scale, is 10 times greater and stronger than an earthquake, which is ‘5’ on the Richter Scale. Usually an earthquake, which reaches ‘7’ onwards on the Richter scale, is catastrophic as a lot of building collapse. This is what happened in 2005 in Pakistan when an earthquake of Force 7.6 killed 73,000 people and left millions homeless. The Mercalli Scale measures the size of an earthquake depending on its aftermath, on a scale, which ranges from 1 to 12. In both scales forces under 3 are only felt by the seismograph. 21 | P a g e  Seismic Activity Hazards associated with earthquakes Earthquakes can pose a range of hazards and risks to people, infrastructure, and the environment. The severity of these hazards depends on factors such as the magnitude of the earthquake, its depth, the distance from the epicenter, and the local geological conditions. Some of the main hazards associated with earthquakes include: 1. Ground Shaking: The primary hazard of an earthquake is the shaking of the ground. The intensity and duration of the shaking depend on the earthquake's magnitude and distance from the epicenter. Ground shaking can cause buildings, bridges, and other structures to collapse, leading to injuries and loss of life. 2. Surface Rupture: In some cases, the Earth's surface can crack and rupture along the fault line where the earthquake occurred. This rupture can cause displacement of the ground and damage to infrastructure built across the fault. 22 | P a g e  Seismic Activity 3. Landslides: The shaking from an earthquake can trigger landslides on steep slopes, especially in areas with loose soil or rock. These landslides can bury homes, block roads, and disrupt transportation. 4. Tsunamis: Underwater earthquakes, particularly those that occur along subduction zones, can trigger tsunamis— large sea waves capable of causing extensive damage when they reach coastlines. Tsunamis can inundate coastal areas, causing loss of life and property damage. 5. Liquefaction: In areas with loose, water-saturated soil, the shaking from an earthquake can cause the ground to behave like a liquid temporarily. This phenomenon, known as liquefaction, can lead to the sinking or tilting of buildings and infrastructure. 6. Aftershocks: Aftershocks are smaller earthquakes that follow the mainshock (the initial, larger earthquake). These aftershocks can cause additional damage to already weakened structures and infrastructure. 7. Building and Infrastructure Damage: The shaking from earthquakes can lead to structural damage to buildings, bridges, dams, and other infrastructure. Poorly constructed or older buildings are particularly vulnerable to collapse. 8. Fires: Earthquakes can disrupt electrical systems, gas lines, and water pipes, leading to fires. Fires can spread rapidly in urban areas where buildings are closely packed together. 9. Disruption of Utilities: Earthquakes can disrupt power and communication systems, as well as water and sewage networks. 23 | P a g e  Seismic Activity This can hamper emergency response efforts and make it difficult for people to access essential services. 10. Injuries and Loss of Life: The combination of collapsing structures, flying debris, and other hazards during an earthquake can result in injuries and loss of life, particularly in densely populated areas. 11. Psychological and Social Impact: Earthquakes can cause fear, trauma, and emotional distress among survivors. They can also lead to social disruption, displacement of populations, and long-term psychological impacts. 12. Economic Impact: The destruction caused by earthquakes can result in significant economic losses, affecting local economies, businesses, and government resources required for recovery and reconstruction. The Mediterranean region: A seismic prone area The Mediterranean region is a seismic-prone area due to its location at the convergence of several tectonic plate boundaries. Tectonic plate boundaries are zones where the Earth's lithospheric plates interact, leading to geological activities such as earthquakes and volcanic eruptions. The Mediterranean region is characterized by its complex tectonic setting, which contributes to the high seismic activity observed there. Some key factors that make the Mediterranean region seismically active include: Plate Tectonics: The Mediterranean region is situated at the boundary between several tectonic plates, including the African Plate, Eurasian Plate, Arabian Plate, and smaller microplates. The interactions between these plates create stress and strain in the 24 | P a g e Seismic Activity Earth's crust, leading to the accumulation of energy that is eventually released as earthquakes. Convergent Boundaries: The collision between the African Plate and the Eurasian Plate gives rise to various convergent boundaries in the Mediterranean region. One of the most significant is the boundary between the African Plate and the Eurasian Plate, where the African Plate is moving northward and being subducted beneath the Eurasian Plate. This subduction process leads to the formation of deep-sea trenches and volcanic arcs, along with strong seismic activity. Transform Boundaries: Transform faults are another common feature in the Mediterranean region. These boundaries occur where tectonic plates slide past each other horizontally. The movement along these transform faults can also generate earthquakes. One prominent example is the North Anatolian Fault, which runs across northern Turkey. Extensional Boundaries: Extensional boundaries occur where tectonic plates move away from each other. The rift zones in the Mediterranean, such as the Red Sea and the Gulf of Corinth, are experiencing extensional tectonics. The stretching of the Earth's crust in these regions can lead to the creation of faults and earthquakes. Subduction Zones: Subduction zones, where one tectonic plate is being forced beneath another, are common in the Mediterranean region. These zones are associated with the potential for large earthquakes due to the release of stress as the subducting plate sinks into the mantle. An example of this is the Hellenic Arc and the subduction of the African Plate beneath the Eurasian Plate. Complex Fault Systems: The Mediterranean region is characterized by intricate fault systems resulting from the interactions of different tectonic plates. These complex fault networks can lead to both localized and widespread seismic activity. 25 | P a g e Seismic Activity Given these factors, the Mediterranean region experiences a high degree of seismic activity and is prone to earthquakes of varying magnitudes. The seismicity in the region underscores the importance of earthquake preparedness, monitoring, and resilient infrastructure to mitigate the potential impacts of these natural events. Areas with frequent seismic activity ITALY has several active volcanoes and experiences disastrous earthquakes. In the past 30 years there have been around 5 major earthquakes that have caused thousands of deaths. The figure below shows a cross section of the earth’s crust. The African plate is pushing into the Eurasian plate forcing it against the Adriatic plate. The layers of rock are put under such pressure that they start to fold up in some places and down in other. The layers that have folded up have formed the Apennines. Near the plate boundaries where the crust is weaker, magma may escape to from volcanoes. This is how Mt. Etna and Mt. Vesuvius formed. GREECE has more earthquakes than anywhere else in Europe – in fact two percent of all earthquakes released by the earth each year are felt in Greece. On average Greece has an earthquake measuring 5 on the Richter Scale every 18 days, one measuring 6 every six 26 | P a g e Seismic Activity months and one measuring 7 every five years. The most powerful earthquakes they have had in Greece measured 7.8 and it occurred in 1810 in Crete. Greece’s most damaging earthquake was on the island of Khios in 1881 when 3550 people were killed. It measured 6.4 on the Richter Scale. The most powerful earthquakes that Greece has suffered in recent times occurred on 13th May 1995 when an earthquake measure 6.6 on the Richter scale struck the town of Kozani. Fortunately, there were no deaths although 2500 homes were damaged. Six weeks later on 15 June another earthquake measuring 6.1 occurred in Greece killing 28 people in Aegean city in Southern Greece. Most of TURKEY, (92%) is considered a seismic region. Most earthquakes nowadays are barely felt tremors to more detectable earthquakes measuring 5 on the Richter Scale. Turkey's most severe earthquake in the twentieth century occurred in Erzincan on the night of 27th December 1939; it devastated most of the city and caused an estimated 160,000 deaths. Earthquakes of moderate intensity often continue with sporadic aftershocks over periods of several days or even weeks. The most earthquake-prone part of Turkey is an arc-shaped region stretching from the general vicinity of Kocaeli to the area north of Lake Van on the border with Armenia and Georgia. Seismicity in Turkey is due to the Arabian, African, and Indian continental plates colliding with the Eurasian Plate. 27 | P a g e Seismic Activity Mention and explain TWO reasons why the Mediterranean region is so prone to seismic activities. Choose ONE of the areas mentioned in the case study (Italy, Greece or Turkey) and write a short paragraph on ONE seismic episode experience by this country. Imagine you are writing for a newspaper article the day after it happened. 28 | P a g e