Week 10
Earthquakes
Week 10
Earthquakes
Introduction
Earthquakes represent one of the most frightening and spectacular geologic phenomenon with which we have contact. Earthquakes release energy equal to more than 100 atomic bind of the type dropped at Hiroshima in 1945.
Earthquakes occur as a result of the buildup of stress in the crust until failure occurs, the rock fractures, and energy is released as a result of the failure.
Original state
Stress build-up and deformation
Failure and release of energy
Earthquakes release energy in the form of waves that are recorded by instruments called seismographs.
Earthquakes release two major types of waves, P waves and S waves.
P-Waves are waves in which the particle movement is in the same direction as the movement of the waves.
S Waves are waves in which the particle movement is perpendicular tot he movement direction of the waves.
Seismographs and waves. P waves travel faster than S waves as can be shown below.
Seismic wave arrivals can be used to determine the location of an earthquake, if we look at the data from three seismographs for the same earthquake.
Virtual Field Trip
One of the best known faults systems in the world is the San Andreas fault, which forms part of the tectonic boundary between the Pacific Plate and the North American Plate. In this virtual field trip you will look at the San Andreas Fault as it moves out into the Pacific Ocean, at its northern edge.
First let us look at an animation of the fault.
Now, let's look at a virtual panorama of the fault line. To move around the VR panorama, simply place your cursor in the image field, hold the mouse down, and move the mouse.
Can you see any physiographic evidence of the fault? Where do you think the fault line is located?
You may want to examine a 3D terrain map of the area. This terrain model may
tilted and rotated with your mouse, much like a VR panorama.
Stress states and faults
Compression
Extension/tension
Shear
The Earth's Interior
The evidence for the structure of the Earth's interior comes from two sources. Gravity data and seismic data.
