GLG101: Physical Geology Lecture Outlines for Exam#3:

G. Calderone- GLG101: Physical Geology Lecture Reviews, Exam#3, August 23, 2011 Page 12 of 20Measuring Seismic WavesSeismometers- device that can detect the passage of waves through the earth. Many typesof seismometers used to measure different periods of waves World-wide seismicnetwork (WWSN)- set up after W.W.II to monitor nuclear testing.Seismographs - seismometer with a recording mechanism to show passage of wavesSeismogram - graph from a seismograph- and the fundamental source of seismic data.Record of arrival of various waves and their times. Seismograms from all the stations ofthe WWSN are stored and archived by the National Earthquake Information Center inGolden Colorado and several other sites as well. Nowadays the seismograms are recordeddigitally for instant data dissemination all over the world.Locating Earthquakes from seismogramsDifference in p and S velocities allow construction of Travel time curves.Difference in wave type allow for easy recognition of p and S waves on seismograms. Thetwo combined allow us to Figure out from any given seismic station, how far away anEarthquake occurred. Triangulation is neeed to give real location of epicenter. Can also getdepth to focus.Shallow focus 0-70 kmIntermediate Focus 70-350 kmDeep focus 350-700 km.Can also determine type of faulting first motion studies (don't worry about how we do thisjustthat we can do it.)Distribution of aftershocks indicate fault plane.Distribution of EarthquakesPlate boundary quakes- most earthquakes occur on and help define plate boundariesShallow focusDivergent boundaryConvergent boundaryTransform boundaryDeep focus- Convergent boundary onlyBenioff zones- can determine which plate is subducting—know this.Subduction angles