Chapter 10 Earthquakes and Earth’s Interior.ppt

Chapter 10: Earthquakes and Earth’s Interior Introduction When the Earth quakes, the energy stored in elastically strained rocks is suddenly released. The more energy released, the stronger the quake. Massive bodies of rock slip along fault surfaces deep underground. Earthquakes are key indicators of plate motion. How Earthquakes Are Studied (1) Seismometers are used to record the shocks and vibrations caused by earthquakes. All seismometers make use of inertia, which is the resistance of a stationary mass to sudden movement. This is the principal used in inertial seismometers. The seismometer measures the electric current needed to make the mass and ground move together. How Earthquakes Are Studied (2) Three inertial seismometers are commonly used in one instrument housing to measure up-down, east-west, north-south motions simultaneously. Earthquake Focus And Epicenter The earthquake focus is the point where earthquake starts to release the elastic strain of surrounding rock. The epicenter is the point on Earth’s surface that lies vertically above the focus of an earthquake. Fault slippage begins at the focus and spreads across a fault surface in a rupture front. The rupture front travels at roughly 3 kilometers per second for earthquakes in the crust. Seismic Waves (1) Vibrational waves spread outward initially from the focus of an earthquake, and continue to radiate from elsewhere on the fault as rupture proceeds. Seismic Waves (2) There are two basic families of seismic waves. Body waves can transmit either: Compressional motion (P waves), or Shear motion (S waves). Surface waves are vibrations that are trapped near Earth’s surface. There are two types of surface waves: Love waves, or Rayleigh waves. Body Waves (1) Body waves travel outward in all directions from their point of origin. The first kind of body waves, a compressional wave, deforms rocks largely by change of volume and consists of alternating pulses of contraction and expansion acting in the dir