ABSTRACT
Most earthquakes occur due to the movement of faults. Faults slowly build up stresses that are suddenly
released during an earthquake. We measure the size of earthquakes using moment magnitude as defined
in Equation 18.1:
M ¼ 2 3
½logðM0Þ 16:05 ð18:1Þ
where M0 is the seismic moment as defined in Equation 18.2:
M0 ¼ GAD (in dyne cm) ð18:2Þ where G is the shear modulus of the rock (dyne/cm2), A is the area of the fault (cm2), and D is the
amount of slip or movement of the fault (cm).
