Seismology Lesson 01: Seismic Waves

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Questions and Answers

What type of wave travels through all three states of matter?

Rayleigh Wave

S Wave

P Wave (correct)

Love Wave

Which of the following is true about Secondary waves (S Waves)?

They move parallel to the direction of motion.

They can travel through both liquid and solid matter.

They are the fastest seismic waves.

They arrive after Primary waves. (correct)

Which seismic wave type has both perpendicular and parallel movement?

Rayleigh Wave (correct)

S Wave

Love Wave

P Wave

What is the primary responsibility of a seismologist?

To study seismic waves in geological material. Signup and view all the answers

What technique is used to determine the location of an earthquake's epicenter?

Triangulation Signup and view all the answers

What feature is considered the initial point of an earthquake?

Focus Signup and view all the answers

Which of the following statements about Pangaea is correct?

Pangaea existed over 200 million years ago. Signup and view all the answers

What is the purpose of a seismograph?

To record ground movement during earthquakes. Signup and view all the answers

Which geologist enhanced the understanding of continental drift by analyzing coastlines?

Antonio Snider-Pellegrini Signup and view all the answers

What characteristic of surface waves is true?

They can only travel along the Earth's surface. Signup and view all the answers

Which fossil evidence supports the idea of continental drift?

Mesosaurus found in both Brazil and Southern Africa Signup and view all the answers

What mechanism was proposed for plate tectonics but later deemed impossible?

Continents being pulled by tidal energy Signup and view all the answers

What evidence supports the process of seafloor spreading?

Pillow rocks formed during continuous eruptions Signup and view all the answers

What is a characteristic feature of young seafloor rocks?

Typically found closer to mid-ocean ridges Signup and view all the answers

How do mantle convection currents affect plate tectonics?

They drive the movement of tectonic plates. Signup and view all the answers

What type of plate boundary is formed when two plates move apart?

Divergent boundary Signup and view all the answers

Which of the following describes a characteristic of the lithosphere?

It is composed of a rigid, brittle layer. Signup and view all the answers

What is the primary reason for the rejection of Alfred Wegener's theory of continental drift?

Absence of a mechanism for movement Signup and view all the answers

What causes magnetic reversal in rocks as evidence for seafloor spreading?

Shifts in the Earth's magnetic field Signup and view all the answers

What is the estimated rate of movement for tectonic plates?

6-10 cm per year Signup and view all the answers

What type of plate boundary involves one oceanic plate subducting under another?

Oceanic-oceanic Signup and view all the answers

Which of the following is an example of a convergent boundary feature?

Himalayas mountain range Signup and view all the answers

What does the term 'sea-floor spreading' primarily describe?

Formation of new oceanic crust at divergent boundaries Signup and view all the answers

What discovery helped validate seafloor spreading and plate tectonics in the 1960s?

Sonar mapping of ocean ridges Signup and view all the answers

Study Notes

Seismic Waves

Waves are energy transmitters that travel through elastic materials like rock, primarily generated by earthquakes or explosions.
Seismology is the scientific study focused on earthquakes and the Earth's internal structure via seismic waves.
Seismologists, also called earthquake hunters, analyze seismic waves within geological materials.

Types of Seismic Waves

Body Waves travel through Earth's interior, divided into:
- Primary (P) Waves:
  - Move in a compression and dilation pattern, parallel to the motion direction.
  - Fastest seismic waves, capable of traversing all states of matter.
- Secondary (S) Waves:
  - Exhibit up-and-down movement, perpendicular to motion direction.
  - Slower than P Waves, capable only of traveling through solids.
Surface Waves:
- Only travel along the Earth's surface, arriving after P and S Waves.
- Love Waves:
  - Similar to S Waves but travel parallel to the surface and perpendicular to wave motion.
  - Exhibit a dispersive property where velocity and depth are frequency-dependent.
- Rayleigh Waves:
  - Show elliptical movement, combining perpendicular and parallel motion relative to wave direction.
  - Slightly slower than Love Waves and also frequency-dependent.

Locating Epicenter

Focus is the initial earthquake point beneath the surface; the epicenter is the point directly above this location, experiencing the most intense shaking.
Seismograms capture data from seismographs, which record ground movements during seismic events.
Epicenter location involves calculating lag time between P and S Wave arrivals; triangulation from at least three seismic stations intersects to identify the epicenter.

Seismic Stations

30 unmanned and 29 manned seismic stations distributed across different regions, including observatories and networks for monitoring seismic activity.

Continental Drift

Pangaea, a supercontinent existing around 240 million years ago, split into Laurasia and Gondwana, surrounded by the Panthalassic Ocean with the Tethys Sea nearby.
Early observations of continental shapes by figures like Francis Bacon (1600s) and enhanced comparisons by Antonio Snider-Pellegrini (1858) led to Alfred Wegener's (1915) hypothesis that continents drifted apart.
Initial skepticism arose due to the lack of mechanisms explaining drift, despite topographic, paleontological, and paleoclimatic evidence supporting the theory.

Evidence Supporting Continental Drift

Topographical evidence includes fitting coastlines, similar rock types, and aligned mountain ranges.
Paleontological finds of fossils like Mesosaurus indicate shared land areas across now-distant continents.
Paleoclimatic evidence shows ancient ice coverage in currently warm areas and the presence of coal deposits in Antarctica indicative of a historical warm climate.

Rejection of Continental Drift Theory

Lacked an accepted mechanism for movement, and proposed mechanisms such as tidal movements and sliding over rigid oceanic crust were deemed implausible.

Seafloor Spreading

Paleomagnetism maps magnetic directions aligned to the Earth's magnetic poles to track rock formation locations.
Mid-Ocean Ridge is a massive, 84,000 km chain of mountains indicating divergent plate boundaries where new oceanic crust forms.
Proposed by Harry Hess (1962), seafloor spreading describes crust creation at mid-ocean ridges and destruction at trenches through magma's movement.

Characteristics of Seafloor Spreading

Young rocks near ridges are hotter, less dense, and less sediment-laden; older rocks are colder, denser, and more sediment-rich.
Evidence of magnetic striping supports the theory, alongside discoveries of younger rocks closer to ridge regions.

Plate Tectonics

The theory of plate tectonics encapsulates Earth's dynamic activities, involving the creation, movement, and interaction of lithospheric plates.
Comprises 15 major tectonic plates that can hold both oceanic and continental crust, moving due to convection currents.
Plate Boundaries include convergent boundaries (where plates collide) leading to mountain formation or subduction, and divergent boundaries (where they separate) forming new crust.

Types of Plate Boundaries

Convergent Boundaries:
- Continental-Continental: Mountain ranges, e.g., Himalayas.
- Ocean-Continental: Subduction features forming volcanoes, e.g., Pacific Ring of Fire.
- Ocean-Ocean: Deep trenches and volcanic arcs, e.g., Mariana Trench.
Divergent Boundaries:
- New oceanic crust forms as magma rises, e.g., Mid-Atlantic Ridge.

John Tuzo Wilson

A pivotal figure in geophysics, Wilson integrated previous theories on continental drift and plate movement to formulate the modern understanding of plate tectonics.

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Description

Explore the fundamentals of seismic waves in this lesson quiz. Learn how these waves transmit energy through the Earth, their relation to earthquakes, and the role of seismologists. Test your understanding of body waves and their characteristics.