Earthquakes

Anticipation Guide #4 Subduction occurs at divergent boundaries Seismic waves are measured by how fast they travel It takes 3 or more seismic stations to locate the epicenter of an earthquake Convection occurs when heat is transferred in waves All plate boundaries create volcanoes

VA SOL SOL 8 The student will investigate and understand geologic processes…... Key concepts include b. processes (faulting, folding, volcanism, metamorphism, …..) and their resulting features; and

Objective 4 Compare and contrast P, S, and L (surface) waves. 5 Identify how scientists locate an epicenter using earthquake data. 6 Evaluate the impact of earthquakes on human activities.

Enduring Understanding Geologic processes produce characteristic structures and features

Earthquakes One of nature’s most devastating occurrences is the earthquake. Earthquakes are capable of destroying entire cities and killing thousands of people in only a few seconds

Earthquakes Earthquakes are natural vibrations of the ground caused by movement along fractures in Earth’s crust.

Earthquakes Most earthquakes occur when rocks fracture deep within the Earth

Earthquakes Stress is the force per unit area placed upon the materials and there are three different types

Earthquakes Compression decreases the volume of a material

Earthquakes Tension pulls the material apart

Earthquakes Shear causes a material to twist

Earthquakes Strain is the deformation of materials in response to stress http://quake.wr.usgs.gov/research/deformation/modeling/animations/

Earthquakes Waves The vibrations in the ground during an earthquake are called seismic waves

Earthquakes Waves Primary Waves (P-waves) squeeze and pull rocks in the same direction along which the waves are traveling

Earthquakes Waves P-waves travel the fastest and CAN travel through liquids

Earthquakes Waves Secondary Waves (S-waves) cause rocks to move at right angles to the direction of travel

Earthquakes Waves S-waves travel slower than P-waves and CANNOT travel through liquids

Earthquakes Waves Surface Waves (L-waves) travel only on the surface in two directions causing an up-and-down and side-to side motion

Earthquakes Waves Most of the damage we see on the surface from earthquakes is caused by surface waves

Earthquakes Waves Most of our knowledge of Earth’s interior comes from the study of seismic waves. The relationship between P-waves and S-waves allows us to measure the size of the inner and outer cores

Measuring and Locating Earthquakes More than one million earthquakes occur each year. More than 9 0 percent of these are not even felt by humans.

Measuring and Locating Earthquakes Magnitude is the amount of energy released by an earthquake

Measuring and Locating Earthquakes Richter Scale is the numerical scale to measure magnitude based on the size of the largest seismic waves generated

Measuring and Locating Earthquakes Each number on the Richter scale represents an increase in amplitude by a factor of 10

Measuring and Locating Earthquakes 8 is ten times the amplitude of 7

Measuring and Locating Earthquakes Modified Mercalli Scale measures the amount of damage done by the earthquake in Roman numerals I - - X II

Measuring and Locating Earthquakes Earthquakes are located by tracking the seismic waves registered at different locations and plotting circles based on the speed of the waves and time elapsed

Measuring and Locating Earthquakes Seismometers are sensitive instruments used to detect and record even the slightest vibrations of the earth’s surface

Measuring and Locating Earthquakes Focus is the point of initial fault rupture and the location where the earthquake originates http://www.discoverourearth.org/student/earthquakes/index.html

Measuring and Locating Earthquakes Epicenter is the point on the surface directly above the focus

Impact of Earthquakes Earthquake activity has major impacts on human activities. Most of the damage caused by earthquakes comes from the prolonged shaking of the ground by surface waves, therefore structures in earthquake-prone areas are at risk.

Impact of Earthquakes Structures built of brittle-unreinforced materials will are at risk of tipping or pancaking”

Impact of Earthquakes Earthquake resistant buildings are now required in most advanced societies, but many poorer countries still allow tall structures to be built with substandard materials.. A recipe for disaster!

Impact of Earthquakes Another major hazard of earthquake activity is the Tsunami (not tidal wave) generated by vertical motions of the seafloor

Impact of Earthquakes Tsunami may appear as only one meter high in the open sea

Impact of Earthquakes but they are an entire vertical column of water that grows to tens of meters high traveling between 100-500 km/hr http://www.pbs.org/wnet/savageearth/animations/tsunami/index.html