Tectonics Revision Notes

These flashcards cover key vocabulary related to tectonics, including definitions and explanations of important concepts in geology and natural hazards.

1. Earth's Internal Structure

1.1 The Crust

What is the approximate thickness of the oceanic crust?

Between 5 and 10 km.

What is the approximate thickness of the continental crust?

Between 30 and 70 km.

What is the average density of oceanic crust?

Approximately 3.0 \text{ g/cm}^3.

What is the average density of continental crust?

Approximately 2.7 \text{ g/cm}^3.

What is the primary rock type that composes the continental crust?

Granite (often referred to as SiAl).

What is the primary rock type that composes the oceanic crust?

Basalt (often referred to as SiMa).

1.2 The Mantle

To what depth does the Earth's mantle extend?

Approximately 2,900 km.

What percentage of the Earth's total volume is comprised of the mantle?

About 84\% .

What is the maximum temperature reached at the mantle-core boundary?

Up to 4,000^{\circ}C.

What characterizes the 'Asthenosphere'?

A semi-molten, ductile layer located between 100 and 400 km deep.

1.3 The Core

What are the two primary elements found in the Earth's core?

Iron (Fe) and Nickel (Ni).

What is the temperature range of the Earth's outer core?

Between 4,400^{\circ}C and 6,000^{\circ}C.

Why is the inner core solid despite temperatures exceeding 6,000^{\circ}C?

Due to the immense pressure exerted by the weight of the overlying layers.

What is the estimated radius of the Earth's inner core?

Approximately 1,220 km.

Which part of the core is responsible for generating Earth's magnetic field?

The liquid outer core.

2. Plate Tectonics and Boundaries

2.1 Mechanical Layers

What parts of the Earth make up the lithosphere?

The crust and the uppermost solid portion of the mantle.

What is the depth range of the lithosphere?

0-100 km.

What is the name of the boundary between the crust and the mantle?

The Mohorovi\u010di\u0107 discontinuity (Moho).

2.2 Plate Movement Phenomena

What is 'Palaeomagnetism'?

The study of Earth's past magnetic fields as recorded in volcanic rocks.

How often do the Earth's magnetic poles flip?

Approximately every 200,000 to 300,000 years.

What is 'Seafloor Spreading'?

The process where new oceanic crust is formed at mid-ocean ridges and moves outward.

What is 'Mantle Convection'?

The movement of mantle rock in circular patterns caused by heat from the core.

What is 'Slab Pull'?

The driving force for plate movement where cold, dense oceanic plates sink into the mantle at subduction zones.

What is 'Ridge Push'?

A gravitational force where rising magma at ridges pushes plates apart.

2.3 Subduction and Seismicity

At what type of boundary does subduction occur?

Convergent boundaries (specifically where a dense oceanic plate meets a lighter plate).

What is the 'Benioff Zone'?

The inclined area within a subducting plate where high-pressure seismic activity occurs.

What is the maximum depth of earthquakes occurring in the Benioff Zone?

Up to 700 km.

3. Seismology and Measurement

3.1 Seismic Waves

What are 'P-waves' (Primary waves)?

Fastest longitudinal waves (8 km/s) that compress and expand the ground.

What materials can P-waves travel through?

Both solids and liquids.

What are 'S-waves' (Secondary waves)?

Transverse waves (4 km/s) that move the ground up and down or side to side.

Why do S-waves provide evidence that the outer core is liquid?

Because S-waves cannot travel through liquids.

What are 'Love waves'?

The fastest surface waves that move the ground side-to-side horizontally.

What are 'Rayleigh waves'?

Surface waves that create a rolling 'up and down' motion.

3.2 Measuring Hazards

What is the 'Moment Magnitude Scale' (MMS)?

A logarithmic scale measuring the total energy released by an earthquake.

In the MMS, how much more energy is released by a magnitude 7 earthquake compared to a magnitude 6?

32 times more energy.

What does the 'Modified Mercalli Scale' measure?

The intensity of an earthquake based on observable damage and human impact (I to XII).

What is the 'Volcanic Explosivity Index' (VEI)?

A logarithmic scale (0-8) measuring eruption size based on plume height and tephra volume.

How much more tephra is ejected in a VEI 5 eruption compared to a VEI 4?

10 times more.

4. Coastal and Tectonic Hazards

4.1 Tsunamis

What are the characteristics of a tsunami in the deep ocean?

Speeds of 500-800 km/h, wavelengths of 100-200 km, and amplitude < 1 m.

What is 'Wave Shoaling'?

The process where tsunami waves slow down and increase in height as they enter shallow coastal waters.

How high can tsunami amplitudes reach at the coast?

They can exceed 30 m.

4.2 Hazard Management Models

What are the three components of the Pressure and Release (PAR) Model?

1. Root Causes\n2. Dynamic Pressures\n3. Unsafe Conditions

Give an example of a 'Root Cause' in the PAR model.

Weak political or economic systems or lack of resources.

Give an example of a 'Dynamic Pressure' in the PAR model.

Rapid urbanization, heavy national debt, or high population growth.

Give an example of an 'Unsafe Condition' in the PAR model.

Lack of disaster warnings or poorly constructed infrastructure.

What is the simple 'Disaster Equation'?

Hazard \times Vulnerability = Disaster.

What defines a 'Tectonic Mega-event'?

High-magnitude, low-frequency events with regional or global impacts (e.g., the 2004 Indian Ocean Tsunami).

What is a 'Multiple Hazard Zone'?

An area vulnerable to two or more natural hazards, such as the Philippines.