Earthquake Measurement Locating Earthquakes seismographs: instruments located at or near the surface of the Earth that record seismic waves. seismogram: a tracing of earthquake motion that is created by a seismograph.

Earthquake Measurement - seismologists find an earthquake’s start time and location by comparing the arrival of P waves & S waves. epicenter: the point on Earth’s surface directly above an earthquake’s starting point, or focus. focus: the point along a fault at which the first motion of an earthquake occurs.

Earthquake Measurement - the S-P time method is used to triangulate the location of an earthquake by comparing the distances both waves traveled from three seismic stations (Figure 3 – pg.137). Japan Seismic Station #3 Pakistan Seismic Station #1 2004 Indonesia Tsunami (230,000+ killed) Australia Seismic Station #2

Earthquake Measurement Measuring Earthquake Strength & Intensity - most seismologists use the Richter Scale to measure the magnitude of an earthquake. - magnitude is calculated by the amount of ground motion.

Earthquake Measurement - each increment is a factor of 10, so magnitude increases 10x per additional measurement. - for example, the ground motion by a 7.0 earthquake will be 1,000 times greater (10x10x10) than a 4.0 earthquake. - therefore, the difference between a 2.0 earthquake and a 9.0 earthquake can be calculated using the following formula: 10x10x10x10x10x10x10 = ___________________ 10,000,000x

Earthquake Measurement - the amount of damage an earthquake causes is referred to as intensity. - the Mercalli Scale is used to measure intensity by applying Roman Numerals to destruction