Lecture 10 28 Why S waves are the biggest waves for earthquakes within 100km Surface waves are the biggest waves for the distant earthquakes 1 Body waves spread as a sphere 4 r2 Surface area ENERGY SPREADS AS 1 r 2 so body waves lose energy faster than surface waves as distance increased Surface waves spread in 2D as a cylinder 2 r t surfacearea ENERGY SPREADS AS 1 r 2 Body waves tend to be high frequency short period whereas surface waves are low frequency long period Every time a wave goes through a cycle it loses some energy Always an inherent ambiguity as to which of the two possible fault planes actually slipped in the earthquake These two fault planes are perpendicular to each other This is a function of how earthquakes work Centre Hypocenter where earthquake strikes and faults slip Only look at the bottom half of the hemisphere of the focosphere Always looking straight down at it looking into your cereal bowl P Stations that are close to the earthquake that station will plot near the edge of the focal mechanism Stations that are distort to the earthquake that station will plot near the middle of the focal mechanism because they are almost going straight down