ERTH 2415 Chapter 4: Summary of chapter 4 pt 2.doc

• School: Carleton University
• Department: Earth Sciences
• Course: ERTH 2415
• Professor: Claire Samson

Document Summary

Magnitude of earthquakes: magnitude is an estimate of the relative size or energy release of an earthquake. It is commonly measured from the amplitude of seismic waves on a seismogram. Richter scale: devised by charles richter in 1935 at the california institute of technology. It is used to asses moderate size earthquakes. It uses waves with frequencies between 0. 5 to 10 hz that saturate for distant or truly large earthquakes. 2. 5 magnitude is the threshold of detection by humans: this scale is now restricted to measuring only local earthquakes with moderate magnitudes. 0. 05 hz: earthquakes generate different proportions of energy at different frequencies. It relies on the amount of movement along the fault that generated the earthquake. It equals the shear strength of the rock times the rupture area of the fault times the average displacement (slip) on the fault: moment is a more reliable measure of earthquake size.