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Questions and Answers
What term describes the point on the ground surface where an earthquake is estimated to be centered?
Which classification pertains to earthquakes with a focal depth greater than 300 km?
What is the angle called that the fault plane makes with respect to the north direction along the surface?
What process leads to the buildup of strain energy at fault interfaces that results in an earthquake?
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What causes tectonic earthquakes in a broad sense?
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What effect does the friction at fault interfaces have on tectonic plate movement?
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Which term refers to the long crack in the surface of the Earth associated with tectonic activity?
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Which of the following is NOT a cause of earthquakes?
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What is the point directly above the hypocenter on the Earth's surface called?
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Which type of body wave transmits energy via push-pull motion?
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In which tectonic boundary region is earthquake activity particularly frequent?
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What type of fault motion occurs in the horizontal plane, parallel to the strike of the fault?
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Which type of wave is analogous to S body waves and oscillates horizontally?
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What term refers to the direction of slip in an earthquake and the orientation of the fault?
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Which type of fault involves two sides moving away from each other?
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What kind of hazard can earthquakes trigger aside from ground shaking?
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Study Notes
Earthquake Engineering Overview
- Earthquakes are broad-banded vibratory ground motions caused by tectonic activity, volcanism, landslides, rock bursts, and man-made explosions.
- Understanding earthquake engineering involves grasping key terminologies, causes, and the nature of faulting.
Earthquake Terminologies
- Epicenter: The surface point directly above where an earthquake is centered.
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Focal Depth: Distance below the earth's surface where the earthquake originates, classified as:
- Shallow: Less than 70 km (43 miles)
- Intermediate: 70-300 km (43-186 miles)
- Deep: Greater than 300 km (186 miles)
- Dip Angle: The angle at which a fault plane slips with respect to the ground surface.
- Strike Angle: Angle that the fault plane makes with the north direction along the surface.
- Fault Line: A long crack in the earth's surface where movement occurs.
- Fault Plane: The plane along which rupture and slip occur.
- Epicenter Distance: The distance from the epicenter to a specific ground point.
Causes of Earthquakes and Faulting
- Most earthquakes result from the movement of large tectonic plates (approximately 15 major plates) in the earth's lithosphere.
- Tectonic plate movement is driven by convection currents in the mantle, fueled by heat from the Earth's core.
- Strain energy accumulates at fault interfaces until it surpasses frictional resistance, leading to sudden slips (elastic rebound), which trigger earthquakes.
- Initial rupture point is called the hypocenter, while the direct surface point above it is the epicenter.
Wave Types in Earthquakes
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Body Waves: Travel through the Earth's interior, consisting of:
- P waves: Fastest, push-pull motion.
- S waves: Slower, shear action at right angles to motion.
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Surface Waves: Travel along the Earth's surface, including:
- Love waves: Horizontal oscillations.
- Rayleigh waves: Vertical oscillations.
Tectonic Activity and Earthquake Frequency
- Earthquakes frequently occur at tectonic plate boundaries, especially along the Ring of Fire, which includes Japan and the U.S. west coast.
- The interiors of tectonic plates experience low seismicity but can still produce minor to significant earthquakes.
- These movements build forces over time, culminating in sudden, damaging motions that can cause secondary hazards, such as landslides and tsunamis.
Fault Classification
- Faults are categorized based on their motion:
- Transform/Strike-Slip: Horizontal motion along the fault line.
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Dip-Slip: Vertical motion relative to the fault's strike:
- Normal: Tension causes sides to move apart.
- Reverse: Compression results in sides moving toward each other.
- Thrust: A type of low-angle reverse faulting.
Focal Mechanism
- Refers to the slip direction during an earthquake and fault orientation.
- Detected through seismograms and visually represented as a "beach ball" symbol on maps.
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Description
This quiz provides an overview of earthquake engineering, discussing essential terminologies and the fundamental concepts of earthquakes. You will learn about the causes of earthquakes and the science behind faulting. Perfect for students aiming to grasp the basics of this critical field.
