Mrs. Richardson's homepage
http://dsc.discovery.com/convergence/pompeii/interactive/interactive.html or try this link: http://kids.discovery.com/games/build-play/volcano-explorer
Types of Faults
Normal= when the hanging wall (wall above the fault line) moves down, from tension at Divergent boundaries
Reverse=when the hanging wall moves up, at Convergent boundaries from compression
Thrust= special kind of reverse fault when the fault is almost horizontal
Strike-slip (left or right lateral)= when rocks slide past each other parallel to the fault, at transform boundaries from shear stress
How seismograms are used
-first determine thetime inerval from first P wave arrival to first S wave arrival. The longer the time interval, the farther away the quake is. Only the distance can be determined from one seismogram. Using the data from 3 seismograms the scientists can use triangulation to find the epicenter (point on the surface above the focus).
-Using the amplitude (height) of the highest S wave scientists can determine the magnitude (strength) of the earthquake. This is calibrated to the richter scale or magnitude moment scale. the scale is exponential. each whole number on the scale represents 10 times more ground shaking or 32 times more energy released from the earthquake.
Waves-what's the difference?
P waves=Primary waves, they travel he fastest with a push-pull motion and are compresion waves. They can travel through solids or liquids
S Waves= Secondary waves. These are shear waves and have an up down motion. They can only travel in solids
L waves= Long waves, arrive last. hey are surface waves and have an oscillatory motion. These waves cause the most shaking and most damage.
Why do some earthquakes cause more damage than others?
Damage or intensity is measured by the Mercali scale (uses roman numerals). The amount of damage depends on a number of factors including 1) population of the area 2) structural materials of the buildings 3) length of the earthquake 4) depth of focus 5) substrate (whether the area is on rock or unconsolidated material)
Photo by D. Little
Photo by R. McGimsey 1990
Photograph by J.P. Lockwood on 1 December 1975