GEOL 108Lg 1st Edition Lecture 5Outline of Last LectureI. Surface Waves MotionII. Locating an EpicenterIII. Earthquake Magnitudes & IntensityIV. Empirical laws for aftershocksa. Omori’s Lawb. Bath’s LawV. Magnitude, Moment, IntensityVI. Gutenberg Richter RelationshipOutline Current Lecture I. Earthquake HazardsII. Ground Shaking EstimatesCurrent LectureEarthquakes IIIReview: 1. Intensity: this is a measure as to how much the earth moved due to an earthquake. Based on everyday observations (e.g. books falling off shelves, chandelier shaking, etc). It is typically measured in terms of the acceleration.a. % G force2. Magnitude: based on another way of measuring the effects of an earthquake—seismograph; defined as taking height of seismogram/amplitude of the seismogram at a certain frequency (corrected for distance)—take the log of the amplitude, magnitude increases linearly. Earthquakes come in huge sizes, so the magnitude is capable of havinga negative value as its magnitude. 3. Moment: slip of the earthquake x shear modulus x area of earthquake—this equation associated more with the physics of the rupture process. The units of moment are meters. The moment essentially analyses how material is deformed. Seismic moment equation listed above is required to learn for the exams. a. Shear Modulus: Larger the modulus, larger the velocity (the shear modulus is essentially how hard it is to deform a given material—how much stress you need to exert to shear; the deformation you induce by applying stress to the object is defined as shear strain. A brief review: stress it the amount of pressure on an object, greater surface area—spread stress—force per area. Force has units of N/Meters2 : Force x Length.-Intensity based on historical accounts, estimated magnitudes of past earthquakes and possible define if earthquake intensity could be recurrent over a certain periods of years. Gutenberg-Richter ScaleRichter Magnitude can be compared to TNT for Energy Yield to calculate an approximate seismicexample. The Richter scale is based on the amplitude of seismic waves – the stronger the earthquake, the stronger the seismic vibrations it causes. Geologists have found that the number of earthquakes of magnitude M is proportional to 10-bM. They call this law the Gutenberg-Richter law. It is represented by the equation below. One magnitude moment goes up by a factor of thirty—scary!—yields big earthquakes, however,they happen less frequently#earthquakes > MagnitudeSeismic hazard: the likelihood and intensity of strong ground motion and other damaging effects at any locationSeismic risk: the likelihood of seismically induced loss of life and property at any locationRisk = hazard x vulnerability(Risk = hazard x exposure x fragility / resiliency)Omori’s LawRate of aftershocks is inversely proportional to time from the main shock. In the simplest case, probability at day two is half that of day one, at day ten a tent of day one, etc. 30 x 109N/meters2You can measure the slip physically. For example if a stream is offset, the slip = the distance. Earthquake