ENV100Y5 Lecture Notes - Lecture 8: Seismic Wave, Oceanic Crust, Planetary Mass
Module 1: May 7-18
Date: Monday, May 14
SESSION 8: GEOLOGICAL SYSTEMS AND PLATE TECTONICS (II)
Readings: Chapter 2
How do scientists learn about the inside of the planet?
● Direct study of rocks:
○ Surface rocks - not representative of what is in the planet
○ Drill holes - 16 km deepest hole in Russia
○ Lava
○ Xenoliths - (xeno - foreign; lith - rock): foreign rock carried to surface
Scientists learn about the inside of Earth through several lines of inquiry
● Indirect methods
○ Astronomical & orbital measurements
■ Planetary mass and density
○ Meteorite analogy
■ Planetary composition
○ Gravity & magnetism measurements
○ Refraction of seismic waves (earth waves) - most important
An earthquake is a sudden release of built-up strain energy
● Earthquakes occur as a result of the build-up and release of strain energy in blocks of
rock subjected to tectonic forces
● Earthquake:
○ Ground shaking that accompanies the release of energy caused by fracturing of
rocks, due to the strain energy that builds up as a result of plate motion
○ Fault: rock fracture along which relative movement occurs
○ Focus: initial point of rupture along a fault
■ Focal depth influences earthquake impacts
○ Epicentre: point on the surface directly above
the focus
Seismic waves move outward
Body waves - moves through body of planet
● P-waves = fast, primary; compressional waves
alternately expanding and compressing
● S-waves = slower, arrives after P-waves, secondary;
shear waves
Surface waves will take longer
● Waves travel at different velocities through different
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ENV100Y5 Full Course Notes
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Document Summary
Session 8: geological systems and plate tectonics (ii) Surface rocks - not representative of what is in the planet. Drill holes - 16 km deepest hole in russia. Xenoliths - (xeno - foreign; lith - rock): foreign rock carried to surface. Scientists learn about the inside of earth through several lines of inquiry. Refraction of seismic waves (earth waves) - most important. An earthquake is a sudden release of built-up strain energy. Earthquakes occur as a result of the build-up and release of strain energy in blocks of rock subjected to tectonic forces. Ground shaking that accompanies the release of energy caused by fracturing of rocks, due to the strain energy that builds up as a result of plate motion. Fault: rock fracture along which relative movement occurs. Focus: initial point of rupture along a fault. Epicentre: point on the surface directly above the focus. Body waves - moves through body of planet.
