GEOL 110 1st Edition Lecture 11Outline of Last Lecture II. Global Patterns of VolcanismIII. Shield VolcanoesA. BasaltIV. Cinder ConesV. StratovolcanoesVI. Volcanic HazardsA. AshB. Pyroclastic FlowC. LaharD. Volcanic GasesOutline of Current Lecture VII. Force, Stress, and StrainVIII. EarthquakesIX. Locating EarthquakesX. Measuring the size of earthquakesXI. Intraplate earthquakesCurrent LectureI. Force, Stress, and StrainA. Force energy required to move an objectB. Stress is equal to the force over a particular area (more stress over smaller areasThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.C. Strain is how an object can be deformed when it is under stress1. When rock becomes deformed (usually happens at a fault line) strain occursII. EarthquakesA. Earthquakes occur when rock that is under stress suddenly breaks along a fault plane sending ground vibrations or seismic waves in all directions1. Types of wavesI. Body wavesa. P waves (primary) – compressional (like a slinky), shortens and then stretches apart. These velocities are greater than s waves. P-waves do no arrive in the ‘shadow zone’ because they refract at the core-mantle boundary.b. S waves (secondary/shear) – generally arrive after p waves. They are slower, cannot move through liquid. (think of the slinky being shaken up and down when held between two people) S waves have a much larger shadow zone because they are blocked through earthquakes liquid core. c. Both types of body waves are refracted when they encounter denser layers of rock at depth, thus they are first directed downward toward the interior of the earth and then often follow an upwardly curving path through the mantle that bring them back to the Earth’s surfaceII. Surface waves only travel on the surface of the earth, usually last to arrive (after p and s waves)a. Elliptical wavesb. Shaking waves2. Stick-slip-behavior/Elastic rebound theoryI. Think of a weight attached to a spring dragged along a rough surfaceII. The pulling of the spring results in a buildup of elastic strain (in the spring) when is eventually released when the weight suddenly slides along the rough surface. III. Results from the rough nature of fault surfaces, which get stuck on rock protrusions called asperities that eventually breakIV. Hypocenter/focus: where slippage actually happensV. Epicenter: immediately above the hypocenter (straight up above ground)III. Locating EarthquakesA. The location of an earthquake can be recorded if it is recorded by different seismographsB. Seismograph: instrument used to measure seismic waves created by earthquakesC. The basis for locating an earthquake is the difference in the arrival time between the first p-wave and the first s-wave. Bigger difference in time = bigger distance between epicenter and hypocenterIV. Measuring the size of earthquakesA. Magnitude – estimates the amount of energy released at the source of the earthquake. It is dependent on the distance between the epicenter and hypocenter, and the type of bedrock. 1. The Richter scale: used to measure magnitude (uses logarithmic scale, aka increases by a factor of 10)B. Intensity – a measure of the degree of earthquake shaking at a given locale based on the amount of damage. 1. Modified Mercalli Intensity Scale – more qualitative, based on interviews of many peopleC. Most earthquakes occur along plate boundariesV. Intraplate earthquakesA. Caused by old faults formed by plate boundaries, which form weak zones that concentrate
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