4.14.17 Travel time, Shadow Zone, Intensity n Magnitude, IRIS Bill Nye? 4.14.17 Travel time, Shadow Zone, Intensity n Magnitude, IRIS Bill Nye? figure 7.22 figure 7.22 Region where seismic waves increase speed the most is: what depth? Because P waves travel faster what is here? than S waves, Distance to focus can be determined by difference figure 7.23 Seismic waves inside the earth in arrival time of P and S waves. reflected bouncing off layers fig 7.12 travel time graph Region where seismic waves increase speed the most is: what depth? what is here? Because P waves travel faster than S waves, we can use the difference in arrival times of seismic waves to determine the distance to a focus from a seismograph station. figures 7.11, 7.12, 7.21 fig 7.12 Travel time graph. refracted bent (like light waves air/water) absorbed S waves do not travel through the liquid outer core. Some parts of the earth do not receive seismic waves after an earthquake.... The path which seismic waves take is not straight... fig 7.23 and handout seismic waves get: reflected bounce off different earth layers (dotted line in handout) refracted bent/bend as they enter/leave layers of different densities/composition absorbed as in S waves encountering a layer (such as the outer core) which has a liquid composition. How are earthquakes measured? Intensity vs Magnitude How are earth quakes measured? Intensity is location specific. An earthquake can have several different intensities depending on the location where it is "sensed". Intensity vs Magnitude Mercalli scale is location specific. Any earthquake may result in people experiencing different intensities depending on distance away, ground conditions, for example. Richter scale (of earthquake Magnitude) identifies how much energy was released by the earthquake. Logarithmic (exponential) scale. Oct 318:24 AM Richter Scale measures magnitude. Magnitude is a single measurement of how much energy was released by a particular earthquake. Logarithmic/exponential scale... IRIS website see Links section of teacher page. Earth Models due for next class meeting... check grading sheet BEFORE you think you are done... Nov 48:05 AM 4.17.17 Travel time, Shadow Zone, Intensity & Magnitude, IRIS Bill Nye? figure 7.22 Region where seismic waves increase speed the most is: what depth? what is here? Section 7.2 and figure 7.11 Because P waves travel faster than S waves we can determine the distance between a focus and a seismograph station. The longer the interval between the P and S waves, the farther away the seismometer is from the focus. fig 7.12 Travel time graph P and S waves take different paths through the inside of the earth! fig 7.23 Seismic waves are: reflectedbounce off different layers refractedbent by different layers (changes in density) absorbedSwaves do not travel through liquid layers of the earth. Not all parts of the earth receive seismic waves after an earthquake! How do we measure earthquakes? 2 ways... Intensity vs Magnitude 1) Intensity: is location specific. Any given earthquake can have a range of intensity numbers/measurements. 2) Magnitude: a measure of how much energy was released at the focus. Bill Nye video: earth modeling, crust volcanoes, shadow zone, Oct 318:57 AM 1
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