EARTH 20 Lecture Notes - Lecture 6: Keiiti Aki, Shear Modulus, Seismic Moment
Document Summary
D = ((vp vs)/(vp- vs)) x (ts-tp) (d= distance from seismometer; v= velocity) Determines radius of circle in center of which earthquake took place; use several different stations to determine intersection of circles and find epicenter. Magnitude of recent quakes: at each step up the scale, earthquakes are ten times as powerful as the earthquake one step below. Ex. difference between haiti (7. 0) and japan (9. 0) earthquakes: japan was 100x as powerful shaking, but amount of energy released = even bigger. Magnitude: relative size of an earthquake (charles richter, 1935) Records movement (amplitude of seismic wave) of a seismograph relative to a small earthquake of magnitude zero. Can have negative magnitudes (m-3 is detectible) Seismic moment: absolute size (aka energy release) of an earthquake (keiiti aki, 1966) Seismically radiated energy is proportional to seismic moment. Erg= amount of energy for a fly to do a pushup. Cumulative moment (cumulative energy released) by earthquakes from 1900-2011)
