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UNM ENVS 101 - Earthquakes and the Earth's Interior

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ENVS 101 1st Edition Lecture 8 Outline of Last Lecture I. From Regolith to RockII. New Rock From OldIII. Metamorphic RocksIV. Introduction to EarthquakesOutline of Current Lecture V. EarthquakesVI. Earthquake Hazards and RiskVII. Earthquakes and the Earth’s interiorCurrent LectureAmong other things, Earthquakes end up releasing Seismic Waves: Elastically stored energy thatis carried outward from the focus of the earthquake by vibrations.Focus: Where an earthquake starts, with respect to the Earth’s interior. The epicenter is the pintdirectly above the focus, and is found on the surface of the Earth, rather than the interior.Additionally, Body Waves travel outward in all directions from the focus of an earthquake all throughout the Earth’s interior. There are two particular types of body waves:- P (Primary) Waves: Which consist of o Compression and Expansiono Are capable of passing through solid, liquid, and gaso And are recognized as pressure waves, much like sound waveso These waves can pass through both the inner and outer core of the Earth- S (Secondary) Waves: Which consist ofo A shearing motiono And are capable of passing through solidso These waves do not pass through neither the inner or outer core of the EarthThere are also Surface Waves, which only travel along the surface. A good visual example to consider is the ocean itself, where surface waves are always present. Although these waves are the slowest, and last to occur in an earthquake, they are also the waves that end up doing the most severe damage. These 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.In tracking how long it takes for the different types of waves to occur during an earthquake, and important time interval is that of the S-P time interval, which tells you how far you are from an earthquake. Magnitude: The amount of energy that was released from an earthquake. The Richter/ Moment Magnitude scale quantifies the magnitude of an earthquake, where it is compared to past events on Earth (man-made or natural disasters) where a comparable amountof energy was released.Richter Magnitude: Is calculated from the maximum recorded amplitudes of seismic waves witha correction for distance. Seismic Moment Magnitude: takes into account both fault length and area.*Both of the above scales are logarithmic.Earthquake intensity measures that damage that is done, by the Modified Mercalli intensity scale. For a better perspective on how these scales measure energy, think of this:An increase of just 1 on the Richter scale, is like a 10-fold increase in wave amplitude, and a 32-fold increase in the amount of energy released!The vast majority of seismically active areas on Earth are located along plate tectonic boundaries. In the occurrence of an earthquake, there are both primary and secondary effects:- Primary Effects: Ground motion which is capable of damaging, or destroying buildings.o Surface rupture: Occurs when the fault actually breaks the ground surface, whichcan also split buildings.- Secondary Effects: These include fires, landslides, liquefaction, and tsunamis. o Fires can be caused by the displaced stoves, gas lines, and wires, etc.o Landslides can occur in sloped regions where the earthquake hito Liquefaction occurs with a sudden disturbance of water saturated soils. This effect is problematic for people living near wet sediments, as it can cause sand boil, a movement of liquefied sand that goes through layers of silt and clay to reach the Earth surface.o Tsunamis are a seismic sea wave, and is initiated by a sudden movement of the seafloor.Earthquake forecasting news which determine the long-term likelihood of an earthquake striking a particular location are mainly the result of recurrence patterns, or seismic gaps.The overall speed of body waves is determined by the density, strength, and rigidity of the rocks that they are passing through. In general, the higher the density of the rock they pass through, the greater the speed of these waves will be.Earthquake locations, including both the epicenter and the focal depths, provide important information about the dimension of the tectonic plates, as well as their interactions, allowing for greater understanding of this particular Earth


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