111-37 - GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111 Lecture Note Series Faults Lecture Goals A) Fault terminology (recap of brittle deformation) B) Types of faults C) Faults on maps Reference: Press et al., 2004, Chapter 11; Grotzinger et al., 2007, Chapter 7; p 158-160 GY 111 Lab manual Chapter 7 A) Fault Terminology Last time we were discussing ductile deformation. Recall that this form of rock alteration results in folds. This time, we concentrate on the other type of permanent alteration; brittle deformation. Brittle deformation results in the breaking of rocks. It normally occurs in rocks that are near the surface of the Earth (and therefore in an environment of low confining pressure), or in rocks that are naturally strong and which therefore are less likely to "bend" (e.g., thick beds of quartz arenite sandstone, limestone or dolostone). Rocks that are prone to brittle deformation break when subjected to stress. When rocks break, one of 3 things can occur: 1) cracking/fracturing 2) jointing 3) faulting We've already discussed cracking/fracturing and jointing (at least as much as I think we need to in GY 111), but we really need to spend this lecture discussing faulting. Faulting occurs when there is movement along the plane of breakage induced by brittle deformation. This is an extremely important aspect of geology because the slippage is usually accompanied by the sudden release of "energy" which we call an earthquake . Earthquakes are one of the Earth's most destructive events with annual damage costs in the hundred of millions to billions of dollars. Even worse, hundreds to thousands of deaths per year can be directly linked to "slippage" along faults. We will devote an entire lecture to earthquakes very soon, but for today, I'd like to stick with just the geological "facts" about faults. Let's start with basic fault terminology. Consider the following block diagram cartoon:
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
GY 111 Lecture Notes D. Haywick (2007-08) 2 The first of the block diagrams shows a tranquil scene near a farmhouse in the middle of no where. The only excitement here is when the 9:15 express train passes by the farmhouse. But there is something stirring beneath the surface of the Earth. A crack (actually a plane of fracture) lies close to the farmhouse and underlies the railroad. Here, tensional stress is building up. All rocks have a certain amount of elasticity to them. Moreover, they are rather resistant to stress. You have to overcome inertia and friction along the plane of fracture before there is movement. This is true for all earthquakes; they only occur when the force of stress overcomes the forces of elasticity, friction and inertia. When it occurs (and eventually it will), there will be a sudden release of all the built up "energy" and movement will occur along the plane of fracture (now called the fault plane ). The point on the fault plane where the initial movement occurred is where most of the "energy" appears to radiate from. This is called the earthquake
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/04/2012 for the course GLY 111 taught by Professor Haywick during the Fall '11 term at S. Alabama.

Page1 / 7

111-37 - GY 111 Lecture Notes D. Haywick (2007-08) 1 GY 111...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online