G08 Science: Earthquakes and Faults

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Questions and Answers

What is a fault in geological terms?

A tension zone between tectonic plates

A type of earthquake

A layer of sedimentary rock

A defect in rocks where movement occurs (correct)

Which of the following statements about earthquakes is true?

Only tectonic activity generates earthquakes.

They occur only on the surface of the Earth.

They are completely preventable.

They result from sudden motions along faults. (correct)

What happens when blocks of rock on either side of a fracture move?

The rocks become smoother.

An earthquake occurs. (correct)

They create new fault lines.

Volcanic activity is triggered.

Which fault is known for its significant geological activity?

The San Andreas Fault Signup and view all the answers

What design feature was mentioned regarding the bridge over the San Andreas Fault?

It can slide on its foundation. Signup and view all the answers

Along which type of fault did the Nepal earthquake of May 2015 occur?

Thrust fault Signup and view all the answers

What causes the energy release that results in an earthquake?

Sudden movements along faults Signup and view all the answers

What is the movement along a fault commonly associated with?

Breakage and shifting of rocks Signup and view all the answers

What indicates a right-lateral fault in the offset of the dyke?

The far side moves to the right Signup and view all the answers

How is slip defined in the context of faults?

The distance rocks move along the fault Signup and view all the answers

What determines the type of fault based on the angle relative to the horizontal surface of the Earth?

The dip of the fault Signup and view all the answers

What do the arrows within the rupture surface represent?

The relative amounts of displacement Signup and view all the answers

What can be said about the movement of rocks along a fault?

Only one side can show movement Signup and view all the answers

What characterizes a dip-slip fault?

The fault's dip is inclined relative to the horizontal Signup and view all the answers

What does the rupture surface refer to?

The part of the fault along which displacement occurred Signup and view all the answers

Why is slip considered relative?

It's unclear which side of the fault moves Signup and view all the answers

What movement occurs in a normal fault?

The hanging wall moves down relative to the footwall. Signup and view all the answers

What type of forces create normal faults?

Tensional forces Signup and view all the answers

In a reverse fault, how does the hanging wall move in relation to the footwall?

It moves up relative to the footwall. Signup and view all the answers

What feature is associated with both normal and reverse faults?

They are both types of dip-slip faults. Signup and view all the answers

What is the key characteristic of a reverse fault?

Hanging wall moves up relative to the footwall. Signup and view all the answers

Which of the following examples represents a location of normal faults?

The Wasatch Fault Signup and view all the answers

Why can understanding dip-slip faults be helpful for miners?

It allows for better tunnel construction. Signup and view all the answers

What type of fault is characterized by a fault plane with a low dip angle of less than 45°?

Thrust fault Signup and view all the answers

What is characteristic of thrust faults in relation to rock layers?

They can cause repetition of rock units in the stratigraphic record. Signup and view all the answers

What type of fault is formed at convergent plate boundaries with subduction zones?

Megathrust fault Signup and view all the answers

Which characteristic describes a thrust fault?

The fault plane angle is nearly horizontal. Signup and view all the answers

What is a klippe in the context of thrust faults?

The hanging wall remnant after erosion. Signup and view all the answers

What significant geological events are commonly caused by megathrust faults?

Largest magnitude earthquakes and tsunamis Signup and view all the answers

What does the term 'window' refer to in thrust fault terminology?

Where the footwall is exposed by erosion of the hanging wall. Signup and view all the answers

Which of the following statements about thrust faults is true?

They can slip many miles. Signup and view all the answers

What is the typical angle of the fault plane in a thrust fault?

Nearly horizontal Signup and view all the answers

What characterizes a thrust fault?

It is a vertical fault where rock layers are thrust over one another. Signup and view all the answers

What type of fault occurs under shear stress with a vertical fault plane?

Strike-slip fault Signup and view all the answers

What happens during a reverse fault?

Rock layers are thrust over each other due to compression. Signup and view all the answers

What is the nature of flower structures formed by strike-slip faults?

They can create either basins or mountains depending on relative movement. Signup and view all the answers

Where are most strike-slip faults commonly found?

At transform boundaries. Signup and view all the answers

What is a distinguishing feature of normal faults?

They result from extensional forces. Signup and view all the answers

What is depicted in the thrust fault example with the Athabasca Glacier?

Trailing ice being thrust over leading ice. Signup and view all the answers

What is the primary cause of reverse faults?

Compression. Signup and view all the answers

Study Notes

Course Information

Course: G08-SCI-L10
Revision: 0, updated May 1, 2021

Learning Outcomes

Students will use models or illustrations to explain how movements along faults generate earthquakes.

Earthquakes and Faults

(A visual aid or video linked to the presentation) should help with this topic.

Fault

"Fault" refers to a defect (a structural weakness or fracture in the rock).
The San Andreas Fault is an example, though there can be greater defects.
If the rock blocks on either or both sides of a fracture move, it is called a fault.
Sudden movement along faults causes rocks to break and shift, releasing energy (creating an earthquake).

San Andreas Fault (Example)

In central California.
People standing on either side of a bridge crossing the fault. Bridge is designed to move/slide with the fault.

India-Asia Convergent Boundary (Example)

Shows different fault types (thrust faults).
The Nepal earthquake of May 2015 was along a thrust fault.

Fault (Example)

Intrusive rocks (Quadra Island, BC).
The offset (displacement) is shown in the visualization by an arrow (about 10 cm).
The fault movement is described as right lateral.

Slip

Slip is the distance rocks move along a fault.
The movement can be up or down (the fault plane).
Movement is relative. Either one or both sides can move.
Faults are at an angle to the Earth's horizontal surface. This angle is the fault's dip.

Dip-Slip Faults

Two types of dip-slip faults:
- Normal fault: the hanging wall moves down relative to the footwall
- Reverse fault: the footwall moves down relative to the hanging wall
Dip-slip motion is relative up-and-down movement on a dipping fault.
The footwall is beneath the fault and the hanging wall is above the fault.
Consider a tunnel running along the fault. The hanging wall is where a miner hangs a lamp; the footwall is at the miner's feet.

Normal Faults

Normal faults move vertically (hanging wall moves down compared to the footwall); along the fault dip.
Created by tensional forces in the Earth's crust (stretching forces).
Common at divergent plate boundaries (where the crust is being stretched).
Examples in Utah include the Wasatch and Hurricane Faults and other fault features in the Basin and Range province.
Horst and graben are associated features of normal faults.

Reverse Faults

Compressional forces cause hanging wall to move up relative to foot wall.
Thrust fault: a reverse fault where the fault plane has a low-dip angle (less than 45 degrees).
Thrust faults can move older rocks on top of younger rocks, potentially reversing the expected rock sequence.
Megathrust faults: a special type of reverse fault at convergent plate boundaries (subduction zones) involving denser oceanic crust moving beneath less dense overlying crust.
These cause large earthquakes and significant destruction/tsunamis.

Thrust Fault

A type of reverse fault with a nearly horizontal fault plane.
Rocks can slip many miles along thrust faults.
A klippe is a remnant of the hanging wall (nappe) material after erosion.
A window is an area where the footwall (autochthon) is exposed after erosion.

Strike-Slip Faults

Dip-slip fault with a vertical fault plane.
Result from shear stress (forces that cause movement parallel but opposite directions).
Reverse and normal faults can be visualized across a strike-slip fault.
Often occur on transform boundaries.
Flower structures can be created by strike-slip faults (basins or mountains depending on the relative movement).

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Description

This quiz explores the concepts of earthquakes and faults, focusing on how movements along faults result in seismic activity. Students will learn about specific fault types, examples like the San Andreas Fault, and the impact of tectonic boundaries on earthquakes. Visual aids will enhance understanding of these geological phenomena.