2 FocusThe point on a fault where rocks “break” and energy is released.
3 EpicenterPoint on the surface of the Earth directly above the focus.
4 SeismographInstruments that register seismic waves and record horizontal and vertical ground movement.Produce a paper record of the seismic event that is called a seismogram.
5 MagnitudeThe height (or amplitude) of the lines on a seismogram indicate the magnitude or strength of an earthquake.Most commonly measured with the Richter magnitude scale.For each increase of 1.0 on the scale:The height of the line on the seismogram is 10x greater.The amount of released energy is 32x greater.A magnitude 9.5 earthquake is the largest ever recorded (southern Chile – 1960).
6 Locating an EpicenterBecause s and p waves travel at different speeds, they each reach a seismograph station at different times.The difference in time can be converted into a distance.Using three seismograph stations, the location of the epicenter can be determined through triangulation.
7 Tips for Your Assignment: Finding amplitude of S-wave:The distance between the center line and the highest peak on the seismogram.
8 Tips for Your Assigment: Finding S-P lag time:Time between the start of the p-wave and the start of the s-wave.
9 Tips for Your Assignment: Finding distance:Use the chart to convert s-p lag time into distance.
10 Tips for Your Assignment: Finding magnitude:Line up distance and s-wave amplitude to determine magnitude.
11 Tips for Your Assignment: Finding epicenter location:Draw a circle from each station with a radius equal to the distance of the station from the epicenter.Epicenter is located where the three circle cross.