R OCKS M OVE A LONG FAULTS Fault: fracture or break in Earth’s lithosphere along which blocks of rock move past each other. Stress: Force exerted when an object pushes or pulls on another object. Earthquake: shaking of the ground caused by the sudden movement of large blocks of rock along a fault
R OCKS MOVE ALONG F AULTS Most faults are located at tectonic plate boundaries 80% of all earthquakes occur in the belt around the pacific ocean. pacific ocean. San Andreas fault is best known fault in U.S.
F AULTS ARE CLASSIFIED BY HOW ROCKS MOVE Normal Faults: occur as rocks are pulled apart common in the Great Rift Valley of Africa
R EVERSE F AULTS Occur near collision-zone boundaries Block of rock above the fault plane moves up relative to the other block.
S LIP S TRIKE F AULT Blocks of rock move sideways on either side of the fault plane Horizontal movement of rock
E NERGY FROM EARTHQUAKES TRAVELS THROUGH E ARTH Seismic Waves: energy waves that travel as vibrations caused by earthquakes Focus: point underground where rocks first begin to move, start of earthquake Epicenter: point on Earth’s surface directly above the focus Earthquakes are usually named for the city closest to the epicenter
E NERGY FROM EARTHQUAKES TRAVELS THROUGH E ARTH
W AVES AND E NERGY What are some examples of waves in your world? All waves including seismic waves carry energy from place to place
P RIMARY W AVES Fastest seismic waves Also known as P-waves Travel at 3mi/sec Particles are pulled apart and pushed together in the direction the waves’ travel
S ECONDARY W AVES Second seismic waves to arrive at a location after an earthquake Also known as S-waves Half the speed of primary waves Particles of materials move at right angle to the direction of the wave’s travel
S URFACE W AVES Seismic waves that move along Earth’s surface Slowest seismic wave Cause the most damage
S EISMIC W AVES CAN BE MEASURED Seismograph: instrument that constantly records ground movements.
U SING S EISMOGRAPHS Record side-to-side and up-and-down movements. SeismographsSeismographs measure thousands of earthquakes around the world every year By studying seismogram, scientists can determine the locations and strengths of earthquakes.
L OCATING AN E ARTHQUAKE 1. Scientists find the difference between the arrival times of the p and s waves at each of three stations 2. The time difference is used to determine the distance of the epicenter from each station 3. A circle is drawn around each station with a radius corresponding to the epicenter’s distance from that station
E ARTHQUAKES CAN CAUSE SEVERE DAMAGE AND LOSS OF LIFE Every year on average an earthquake of magnitude 8 or higher strikes somewhere on Earth. Most injuries and deaths are not caused by the movement of the ground but by collapsing buildings and fires.
E ARTHQUAKE MAGNITUDE First scale developed by Charles Richter, the Richter scale. Newer scale is called the moment magnitude scale Each step up is an increase of 32 times the previous value.
D AMAGE FROM EARTHQUAKES Aftershock: smaller earthquake that follows a more powerful earthquake in the same area. Liquefaction: a process in which shaking of the ground causes soil to act like a liquid. Tsunami: Tsunami: water wave triggered by an earthquake, volcanic eruption or landslide. 2004 Sumatra tsunami killed nearly 300,000 people
S CIENTISTS WORK TO MONITOR AND PREDICT EARTHQUAKES PREDICT EARTHQUAKES
S TRUCTURES CAN BE DESIGNED TO RESIST EARTHQUAKE DAMAGE Best to be outdoors far from buildings during an earthquake Use base isolators to insulate building from shock Shear walls add strength to a building Cross braces add structure
S TRUCTURES CAN BE DESIGNED TO RESIST EARTHQUAKE DAMAGE