ENERGY FROM EARTHQUAKES TRAVEL THROUGH EARTH Throw a rock into a pond and waves ripple outward from the spot where the rock hits.
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH Energy released by an earthquake travels like ripples in a pond except the energy travels outward in all directions-up, down, and to the sides.
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH The energy from earthquakes travels as seismic waves. Seismic waves are vibrations caused by earthquakes.
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH Earthquakes start beneath Earth’s surface. The focus of an earthquake is the point underground where rocks first begin to move. Seismic waves travel outward from the focus.
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH The epicenter is the point on Earth’s surface directly above the focus. Earthquakes are often named after the city that is closest to its epicenter.
GREAT ALASKAN EARTHQUAKE, 1964 MAGNITUDE: 9.2 (SECOND STRONGEST EARTHQUAKE IN RECORDED HISTORY)
VALDIVIA, CHILE 1960 MAGNITUDE: 9.5 STRONGEST RECORDED EARTHQUAKE IN HISTORY
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH In general, the shallower the focus, the more damage caused by the Earthquake.
ENERGY FROM EARTHQUAKES TRAVELS THROUGH EARTH The depths of earthquakes along plate boundaries depends on what type of plate boundary it is. Divergent boundaries tend to have shallow foci. Subduction zones can have very shallow or very deep foci.
WAVES AND ENERGY As waves move through a material, each particle briefly shifts out of and back into position. In this way, energy moves through the material, but matter does not.
WAVES AND ENERGY All waves carry energy from place to place. https://www.youtube.com/watch?v=THUMdToh WkI https://www.youtube.com/watch?v=THUMdToh WkI
WAVES AND ENERGY Earthquakes produce 3 types of seismic waves. Each type moves through materials differently.
PRIMARY WAVES Primary waves (also called P waves) are the fastest seismic waves, with an average speed of 5 km/s (3 miles per second!) Primary waves travel with a push and pull motion through a material (like a slinky pulled back and released)
SECONDARY WAVES Secondary seismic waves (also called S waves) are the second type of wave to arrive at a location after an earthquake. They move at half the speed of primary waves. S waves move through a material by either an up- down or side-side motion.
SECONDARY WAVES Secondary waves can travel through solids (like rock), but cannot travel through liquids or gases. Scientists learned that the outer core of the Earth is liquid by observing that secondary waves do not travel through it!
SURFACE WAVES Surface waves move along the surface of the Earth only, not through its interior. They make the ground roll up and down or shake from side to side. Surface waves cause the most damage.
SEISMIC WAVES CAN BE MEASURED Scientists measure earthquakes using seismographs. A seismograph is an instrument that constantly records ground movements.
SEISMIC WAVES CAN BE MEASURED The recording of an earthquake on a seismograph looks like a group of wiggles. The height of the wiggles indicates the amount of ground movement.
LOCATING AN EARTHQUAKE To locate the epicenter of an earthquake, scientists need reading from at least 3 seismic stations.
LOCATING AN EARTHQUAKE Scientists can also locate the focus of an earthquake by calculating its depth in the Earth.
LOCATING AN EARTHQUAKE Scientists can also measure the magnitude (strength) of an earthquake. The more energy an earthquake releases, the greater the ground movement recorded.
REVIEW 1. Earthquakes release energy in the form of A. Seismic waves B. Faults C. Stress lines D. seismograms
REVIEW 2. Most damage from an earthquake usually occurs A. Below the focus B. Far from the epicenter C. At the focus D. Near the epicenter
REVIEW 3. To locate the epicenter of an earthquake, scientists need seismograms from at least ____ seismic stations. A. 2 B. 3 C. 4 D. 5
REVIEW 4. The seismic waves that usually cause the most damage are A. Surface waves B. Tsunami waves C. Primary waves D. Secondary waves