20.1 - Classification of Earthquakes Based on Causes
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Tectonic Earthquakes
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Today, we're discussing tectonic earthquakes, which are the most common type. Can anyone tell me what causes them?
Is it because of the movement of Earth's plates?
Exactly! These earthquakes occur due to the movement of the lithospheric plates. Now, can anyone name the three types of plate boundaries?
Convergent, divergent, and transform!
Great! Let's remember that with the acronym 'CDT.' Now, which plate boundary do you think causes the largest earthquakes?
Convergent boundaries?
Correct! They produce significant stress that can lead to powerful earthquakes, like those in the Himalayas. To summarize: Tectonic earthquakes result from plate movements, particularly at convergent boundaries.
Volcanic Earthquakes
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Next, let's discuss volcanic earthquakes. What initiates these types of earthquakes?
Is it from magma movement beneath the Earth's surface?
Yes! The pressure from magma can fracture rocks and result in earthquakes. Can anyone think of a region known for volcanic earthquakes?
The Ring of Fire?
Exactly! That's a significant volcanic region. To help remember, think of volcanoes causing 'volcanic rumbles'. Summing up, volcanic earthquakes are caused by magma movement and are often precursors to eruptions.
Collapse and Explosion-induced Earthquakes
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Let’s now look at collapse earthquakes. What causes these, and can someone give an example?
They occur when caves collapse, right? Like in limestone areas?
Exactly! And such earthquakes typically have low magnitudes but can impact infrastructure. Now, what about explosion-induced earthquakes?
Are those caused by nuclear tests or mining?
Correct! They have a distinct seismic signature. Let’s remember this with the phrase 'Man-Made Shakes.' In summary, collapse earthquakes are local phenomena, while explosion-induced earthquakes are results of human activities.
Reservoir-induced and Isostatic Adjustment Earthquakes
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Now, let’s explore reservoir-induced seismicity. Who can explain what causes these earthquakes?
They result from water filling in large reservoirs? The weight of the water changes the stress in the earth?
Exactly! This can trigger seismic activity along faults. An example is the Koyna Dam earthquake. What about isostatic adjustment earthquakes? Can anyone explain that?
They happen because of changes in weight on the crust, like glaciers melting?
Yes! As land adjusts, it can trigger earthquakes. Let’s summarize: Reservoir-induced earthquakes come from water pressure, while isostatic adjustments are due to changing surface loads.
Induced Seismicity
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Lastly, we have induced seismicity. Who can give examples of human activities that lead to earthquakes?
Fracking and deep well injection?
Correct! These activities can alter the stress on faults, triggering earthquakes. Can you think of a location where this has been significant?
Oklahoma has had a lot of activity related to fracking.
Exactly! To remember, think 'Humans Shake too.' In summary, induced seismicity refers to earthquakes caused by our activities, affecting existing fault lines.
Introduction & Overview
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Quick Overview
Standard
This section categorizes earthquakes into various classes such as tectonic, volcanic, collapse, explosion-induced, reservoir-induced, and isostatic adjustment earthquakes, with a brief overview of each classification's characteristics.
Detailed
Classification of Earthquakes Based on Causes
Earthquakes are categorized according to their origin, which helps in understanding their mechanisms and implications for civil engineering and disaster preparedness. This section outlines the primary classifications:
- Tectonic Earthquakes: These are generated by the movement of Earth's tectonic plates. The interaction of these plates at their boundaries creates significant stress that, when released, results in seismic events.
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Types of Plate Boundaries:
- Convergent: Plates collide, leading to compression (e.g., Himalayas).
- Divergent: Plates move apart, creating tension (e.g., Mid-Atlantic Ridge).
- Transform: Plates slide past each other, leading to lateral stress (e.g., San Andreas Fault).
- Volcanic Earthquakes: Associated with volcanic activity, these occur as magma moves or pressure builds within the Earth.
- Collapse Earthquakes: Caused by the sudden collapse of underground structures like caves or mining tunnels. These are generally of low magnitude but can have localized effects.
- Explosion-induced Earthquakes: Results from human activity, such as nuclear detonations or large-scale mining explosions. They often have distinct seismic signatures.
- Reservoir-induced Earthquakes (RIS): Linked to the filling of large reservoirs, where increased water weight alters the stress in the surrounding rock.
- Isostatic Adjustment Earthquakes: Caused by the dramatic shifting of the Earth's crust due to changes in surface loads, such as glacial melting.
- Induced Seismicity: This arises from human activities like deep well injection and hydraulic fracturing, impacting natural fault lines.
Understanding the classification of earthquakes is crucial for civil engineers in designing resilient infrastructure and assessing seismic risks.
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Introduction to Earthquake Classification
Chapter 1 of 8
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Chapter Content
Earthquakes are classified based on their origin or causative factors. These include:
Detailed Explanation
This introductory statement explains that the focus of the section is on how earthquakes are categorized according to their causes. It indicates that various factors contribute to the occurrence of earthquakes, setting the stage for a detailed exploration of each type.
Examples & Analogies
Think of classifying books in a library. Just as books can be sorted by genre, author, or publication date, earthquakes can be categorized based on their causes. This helps scientists understand and study them better.
Tectonic Earthquakes
Chapter 2 of 8
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Chapter Content
- Tectonic Earthquakes
Detailed Explanation
Tectonic earthquakes are caused by the movement of the Earth's lithospheric plates. These movements happen due to the Earth's internal heat and lead to stress build-up at the edges of these plates. When the stress exceeds the strength of the rocks, it results in an earthquake. Tectonic earthquakes are the most common type and can be very destructive.
Examples & Analogies
Imagine two cars bumping against each other at a traffic light; the pressure builds as they push against one another until one moves. Similarly, tectonic plates push against each other, leading to seismic activity when stress is released.
Volcanic Earthquakes
Chapter 3 of 8
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Chapter Content
- Volcanic Earthquakes
Detailed Explanation
Volcanic earthquakes occur in areas with volcanic activity. They can result from the movement of magma beneath the Earth's surface, sudden fracturing of rocks due to pressure from magma, or the collapse of volcanic structures. While often localized, these events can indicate impending volcanic eruptions.
Examples & Analogies
Think about how bubbles form in a boiling pot of water. When the pressure builds up from the heat, bubbles burst to the surface, similar to how volcanic activity can create tremors as magma moves and pressure builds.
Collapse Earthquakes
Chapter 4 of 8
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Chapter Content
- Collapse Earthquakes
Detailed Explanation
Collapse earthquakes are generally minor and occur when underground caves or mine tunnels collapse. They can also happen due to sudden failures of rock strata or roof falls in mines. Although these quakes usually have low magnitudes, they can still impact local structures and communities.
Examples & Analogies
Picture a sandcastle that suddenly collapses when too much water erodes its base. Just as sand collapses, so too can underground structures lead to minor seismic events when they give way.
Explosion-induced Earthquakes
Chapter 5 of 8
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Chapter Content
- Explosion-induced Earthquakes
Detailed Explanation
These earthquakes are man-made and result from activities like nuclear detonations or large chemical explosions. Construction activities using heavy blasting can also induce such earthquakes. They typically last for a short duration and have a distinct seismic signature that differentiates them from natural earthquakes.
Examples & Analogies
Think of throwing a rock into a pond. The ripples created are temporary and localized, similar to the way explosion-induced earthquakes behave — quick and distinct without causing widespread effects.
Reservoir-induced Earthquakes
Chapter 6 of 8
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Chapter Content
- Reservoir-induced Earthquakes
Detailed Explanation
These earthquakes occur when large reservoirs behind dams are filled. The added weight of the water increase stress on underlying faults and can lead to slippage. Changes in pore pressure from water infiltration can also reduce friction on faults, causing earthquakes.
Examples & Analogies
Imagine sitting on a seesaw: if a friend jumps on one side suddenly, it can flip. Similarly, when water is added to a reservoir, it increases stress on fault lines, which can result in minor earthquakes.
Isostatic Adjustment Earthquakes
Chapter 7 of 8
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Chapter Content
- Isostatic Adjustment Earthquakes
Detailed Explanation
These earthquakes are connected to isostatic rebound, where land masses rise or fall due to the removal (like melting glaciers) or addition of surface loads (like sediment deposits). This adjustment of crustal weight can trigger seismic activity.
Examples & Analogies
Think of a sponge that is compressed when squeezed; once you let go, it slowly expands back to its original shape. As the land adjusts to changes over time, it may also 'release' energy in the form of small earthquakes.
Induced Seismicity due to Human Activities
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Chapter Content
- Induced Seismicity due to Human Activities
Detailed Explanation
This type of seismicity arises from activities such as deep well injection, hydraulic fracturing, mining, and geothermal extraction. These actions alter stress and pore pressure in the Earth's crust, potentially triggering earthquakes.
Examples & Analogies
Picture a tightly packed crowd in a concert; when a few people push towards the exit, it can set off a chain reaction of movement in the crowd. Similarly, human interventions can disrupt stress balance in the Earth, leading to earthquakes.
Key Concepts
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Tectonic Earthquakes: Caused by plate movements.
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Volcanic Earthquakes: Related to volcanic activity.
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Collapse Earthquakes: Occur from underground structure failures.
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Explosion-induced Earthquakes: Result from human-made detonations.
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Reservoir-induced Seismicity: Due to stress from large reservoirs.
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Isostatic Adjustment Earthquakes: Result from shifts in Earth's crust.
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Induced Seismicity: Triggered by human activities.
Examples & Applications
The 1906 San Francisco Earthquake, a tectonic earthquake resulting from the movement along the San Andreas Fault.
Koyna Dam earthquake in India (1967) caused by reservoir-induced seismicity.
Memory Aids
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Rhymes
When tectonic plates collide, earthquakes will reside.
Stories
Once upon a time, Earth's plates danced around, sometimes colliding, causing tremors that could be found, making local ground shake, with volcanic eruptions as well, to tell how Earth behaves, there's much more to tell.
Memory Tools
Remember the acronym 'TVCEIR' to recall the earthquake types: Tectonic, Volcanic, Collapse, Explosion-induced, Reservoir-induced, and Induced seismicity.
Acronyms
For 'Types of Earthquakes', think 'T-V-C-E-I-R' (like a train Traveling Very Close to a city Edge (I-R).
Flash Cards
Glossary
- Tectonic Earthquakes
Earthquakes caused by the movement of Earth's tectonic plates.
- Volcanic Earthquakes
Seismic events associated with volcanic activity.
- Collapse Earthquakes
Minor earthquakes resulting from the collapse of underground structures.
- Explosioninduced Earthquakes
Seismic events caused by human activities like nuclear detonations or mining blasts.
- Reservoirinduced Seismicity
Earthquakes caused by the filling of large reservoirs affecting stress in the Earth.
- Isostatic Adjustment Earthquakes
Seismic events resulting from the crust adjusting to changes in surface loads.
- Induced Seismicity
Earthquakes triggered by human activities that alter natural stress on fault lines.
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