20.8 - Induced Seismicity Due to Human Activities
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Deep Well Injection
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Today, we're going to talk about deep well injection. Does anyone know what that involves?
Is it about putting waste into deep holes in the ground?
Exactly! Deep well injection involves disposing of fluids deep underground. This can change pore pressure and stress in the Earth's crust. Can anyone guess why this might cause earthquakes?
Maybe the pressure buildup could make rocks break?
That's correct! When the pore pressure increases enough, it can cause existing faults to slip, leading to tremors. Remember the acronym DWI for Deep Well Injection to help you recall this process. Let's move on to a real-world example.
Were there any cases where this caused big earthquakes?
Yes, in Oklahoma, there was a marked increase in seismicity due to fracking and injection. This shows the impact of human activities on natural systems. Can anyone think of other examples?
What about places where they mine?
Great thought! Mining activities can also induce seismicity. Let's save that for our next session!
Hydraulic Fracturing (Fracking)
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Now let's talk about hydraulic fracturing, commonly known as fracking. Who can explain what fracking is?
It's when they pump fluid into rocks to make them crack for oil or gas, right?
Exactly! While it helps extract resources, it can lead to unintended larger seismic events, especially if not done carefully. What do we expect to see in terms of seismic activity during fracking?
I remember you said microseismicity is normal!
Yes! Microseismicity, or small quakes, occur regularly. But, improper control can lead to significant quakes. Can anyone think of a location where this has happened?
I think there were issues in Ohio related to that.
Excellent example! Always keep in mind the concept of pressure and how it relates to fault activity. Understanding these consequences is key for engineers working in seismic areas.
Mining and Quarrying
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Now, let's discuss mining and quarrying. Why might these activities create small earthquakes?
Maybe because they blast rocks and dig deep?
That's right! Blasting operations can lead to minor seismic events as the stress in the Earth changes. Over time, what other effects might this have?
They might change how stress is distributed underground?
Exactly! Changes in stress fields can trigger seismic activity, even long after mining has stopped. It's an important consideration in planning, isn't it?
Yeah, engineers have to account for that!
Great! So remember that mining adds to induced seismicity. Let's wrap up what we discussed today.
Geothermal and Oil Extraction
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Finally, let's explore geothermal and oil extraction. How might these practices induce seismicity?
They take fluids out, which can make the ground sink or change pressure?
Exactly! Extracting fluids can lead to voids underground and raise the risk of fault reactivation. What does this mean for areas around extraction sites?
There might be a higher risk of earthquakes occurring?
Yes! Understanding these risks is essential when designing infrastructure. Always consider the environmental impacts of resource extraction. Let's summarize what we learned today about human-induced seismicity.
Introduction & Overview
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Quick Overview
Standard
The section delves into various human-induced activities that can lead to seismic events, particularly focusing on deep well injection of fluids, hydraulic fracturing or fracking, mining operations, and geothermal or oil extraction. Each activity alters subsurface conditions and can trigger seismic events ranging from small tremors to larger earthquakes.
Detailed
Induced Seismicity Due to Human Activities
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Audio Book
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Deep Well Injection
Chapter 1 of 4
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Chapter Content
Deep Well Injection
- Disposal of industrial fluids, wastewater, or CO₂ in deep wells can alter pore pressure and stress regimes.
- Documented cases in Oklahoma, USA, where seismicity increased significantly due to fracking and injection.
Detailed Explanation
Deep well injection involves the disposal of fluids into the ground, often in deep wells designed for this purpose. When industrial fluids, wastewater, or carbon dioxide are injected, they can change the pressure in the surrounding rock layers. This change can, in turn, affect the stress on nearby faults which might eventually lead to earthquakes. Notably, there have been instances, particularly in Oklahoma, where this practice has been linked to increased seismic activity, indicating a correlation between human activity and natural seismic events.
Examples & Analogies
Think of the Earth's crust as a tightly sealed can of soda. When you shake the can and then pop it open, the pressure inside causes the soda to spray out. Similarly, injecting fluids into the ground can shake up the pressure in underground rocks, causing them to slip and create earthquakes.
Hydraulic Fracturing (Fracking)
Chapter 2 of 4
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Chapter Content
Hydraulic Fracturing (Fracking)
- High-pressure injection of fluid to fracture shale rocks.
- While microseismicity is expected, improper control can trigger larger seismic events.
Detailed Explanation
Hydraulic fracturing, commonly known as fracking, is a technique used to extract natural gas or oil from underground rock formations. In this process, high-pressure fluid is injected into shale rocks to create fractures, allowing oil or gas to flow more freely. While small earthquakes or microseismicity can occur as a normal part of this process, if the operation is not carefully controlled, it can lead to larger earthquakes. This highlights the need for stringent monitoring and regulation in fracking operations.
Examples & Analogies
Imagine trying to poke holes in a sponge with a straw. If you poke gently, small holes form where the liquid flows easily. However, if you push too hard, you could create a big tear, causing a larger mess. In fracking, if the injection pressure is too high without proper management, it can lead to significant seismic events like that larger tear in the sponge.
Mining and Quarrying
Chapter 3 of 4
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Chapter Content
Mining and Quarrying
- Blasting operations, excavation, and mine collapse can lead to small earthquakes.
- Long-term mining alters the stress field in the Earth's crust.
Detailed Explanation
Mining and quarrying involve removing materials from the ground through processes that often include blasting and excavation. These activities can disturb the Earth's crust, sometimes leading to small earthquakes, especially if the stress that builds up in the rocks exceeds their strength. Over time, as mining progresses, the stress distribution in the surrounding area can change, potentially triggering seismic events due to the altered stress conditions.
Examples & Analogies
Consider how digging a hole in the sand can cause the sand nearby to shift and collapse. If you dig too much in one area, the surrounding sand may no longer be stable and can give way, similar to how mining can disturb the ground and lead to small quakes.
Geothermal and Oil Extraction
Chapter 4 of 4
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Chapter Content
Geothermal and Oil Extraction
- Withdrawal of fluids can create voids or reduce subsurface pressure.
- Ground subsidence and fault reactivation may follow.
Detailed Explanation
When fluids such as water or oil are extracted from the ground through geothermal or oil extraction processes, it can reduce the pressure in the subsurface. Over time, this can create voids or spaces underground where the fluid used to be. The resulting changes in pressure can lead to ground subsidence, where the ground sinks, and also increase the likelihood of existing faults becoming active again, potentially resulting in earthquakes.
Examples & Analogies
Imagine a balloon filled with water. If you start to let the water out, the balloon’s shape changes and can even collapse in on itself. Similarly, when fluid is removed from underground, it can cause the land above to 'sink' and create stress on faults, increasing the risk of earthquakes.
Key Concepts
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Induced Seismicity: Seismic events caused by human activities.
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Deep Well Injection: A method that alters pore pressure and may trigger earthquakes.
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Hydraulic Fracturing: A resource extraction method that can lead to minor and major seismic activity.
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Microseismicity: Small quakes anticipated during activities like fracking.
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Mining and Quarrying: Practices that can disrupt subsurface structures leading to seismic events.
Examples & Applications
The increase in seismicity in Oklahoma linked with fracking and deep well injection.
Ohio cases where hydraulic fracturing caused notable seismic events.
Mining-related earthquakes from blasting operations in various regions showing the connection to induced seismicity.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Fracking cracks with pressure high, but too much can make the earth sigh.
Stories
Once, there was a town that used deep wells for waste. Over time, they felt quakes — little at first, but then they shook awake. The community learned that their actions could cause the ground to quake.
Memory Tools
RAMP for remembering: (R)esources, (A)ctivities, (M)ining, (P)ressure.
Acronyms
DWI
Deep Well Injection impacting seismicity.
Flash Cards
Glossary
- Induced Seismicity
Earthquakes that are directly caused by human activities.
- Deep Well Injection
The disposal of fluids into deep geological formations, affecting pore pressure and stress.
- Hydraulic Fracturing
A method of extracting hydrocarbons involving high-pressure fluid injection to fracture rocks.
- Microseismicity
Small seismic events that occur, often associated with fracking and other industrial activities.
- Geothermal Extraction
The process of extracting heat or hot water from the earth for energy production.
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