Tangshan, China 1976Lisbon 1755 Earthquake is a sudden slip (rupture) on a fault and the resulting ground shaking caused by the radiated seismic energy generated by the slip (rupture) What is an Earthquake?

Earthquakes Alternate definition: A natural vibration of the ground caused when the stress built up between tectonic plates is suddenly released. There are three types of stress: Compression – caused by two plates being push together. Tension – Pulls plates apart. Shear – causes plates to twist.

Types of faults There are three types of Faults 1. Normal fault caused by tension. 2. Reverse fault caused by compression. 3. Strike-slip fault caused by shearing.

Three Types of Seismic Waves 1. Primary waves (p-waves) Longitudinal waves – these vibrate by the compression of material in the direction of the wave’s motion. These can travel through the core. 2. Secondary waves (s-waves) Transverse waves (Like in water) – these vibrate by moving the particles perpendicular to the direction of wave’s motion. These cannot travel through the core. 3. Surface waves (Love and Rayleigh waves) Vibrate in all directions.

Body Waves P waves are compressional (or longitudinal) body waves in which rock vibrates back and forth parallel to the direction of wave propagation –Fast (4 to 7 kilometers per second) wave that is the first or primary wave to arrive at a recording station following an earthquake –Can pass through solids and fluids (liquids or gases) Fig 10.7

Body Waves S waves are shearing (or transverse) body waves in which rock vibrates back and forth perpendicular to the direction of wave propagation –Slower (2 to 5 kilometers per second) wave that is the secondary wave to arrive at a recording station following an earthquake –Can pass only through solids Fig 10.7

Surface Waves Slowest type of seismic waves set off by earthquakes Love waves involve only side-to- side motion of the ground surface –Can’t travel through fluids Rayleigh waves behave like ocean waves, and cause the ground to move in an elliptical path opposite the direction of wave motion –Extremely destructive to buildings Fig 10.7

The Earth’s Interior Earthquakes (P and S waves) Were instrumental in the Study of the Earth’s Core S-waves can only propagate Through the Mantle, P-waves can propagate Through the core. This shows a density Difference inside the Earth Figs & & 10.26

Measuring Earthquakes Richter Scale Based on size of the largest seismic waves generated by the Earthquake. Each level increase represents an increase of energy by a factor of 32 and a wave size of 10 times.

Anatomy… Worst damage is not necessarily nearest to focus: it depends on ground type, time, magnitude, terrain, nature of structures… Fig 10.2

Measuring Earthquakes Moment of Magnitude Scale Based on the magnitude of seismic waves as well as the size of the fault rupture, amount of movement, and rock characteristics. More accurate than Richter scale. Modified Mercalli Scale Measures the amount of damage caused by the Earthquake.

Strongest Earthquakes of Chile (Feb 27 th ) Mag Indonesia (April 6 th ) Mag Vanuatu (May 27 th ) Mag Indonesia (May 9 th ) Mag Mexcali Valley, California (April4th) Mag Solomon Islands (Jan 3 rd ) Mag Haiti (Jan 12 th ) Mag Ryukyu, Japan (Feb 27 th ) Mag. 7.0 There have been 7460 earthquakes so far this year. Most are below a magnitude of 4.9.

Chile 7 th Strongest earthquake in History 130 after shocks over the next week. The focus ground at epicenter moved 3.0 up and 10 m west. 500 times more powerful than Haiti Called a megathrust quake because it is in a subduction zone

Earthquake Size and Strength… Modified Mercalli Intensity Map –1994 Northridge, CA earthquake, Richter magnitude 6.7 Los Angeles area…

Collapsed Cypress Freeway Copyright © Houghton Mifflin Company. All rights reserved. Source: Richards/Sipa Press

Japan (Tohoku) Earthquake and Tsunami CBC News Reports ws/world/story/2011/0 3/11/japan-quake- tsunami.html ws/world/story/2011/0 3/11/japan-quake- tsunami.html The Guardian o.uk/world/video/2011 /mar/14/japan- tsunami-amateur- footage-video o.uk/world/video/2011 /mar/14/japan- tsunami-amateur- footage-video

Tsunami The 9.0 magnitude earthquake and subsequent 40 m tsunami in Japan in March 2011, took nearly 20,000 lives and threatened many more with concerns over radiation from the damaged Fukushima Nuclear Power Plant. The Fukushima evacuation zone continues to displace thousands of residents of the region.

Generation of a Tsunami from EQ Copyright © Houghton Mifflin Company. All rights reserved.

Location of the Earthquake Focus The location in the Earth’s crust where the earthquake occurs. It can occur anywhere between the surface and a depth of 700 km. The closer to the surface it occurs, the more powerful the earthquake is. Epicenter The location on the Earth’s surface above the focus.

Finding the Epicenter Epicenters are found using triangulation from three or more seismograph stations. P-waves travel a lot faster than s-waves. The difference between the arrival time of each type of wave tells you the distance to the epicenter. The speed of each wave is a constant factor.

Steps for finding the Epicenter 1. Determine the difference in time between the arrival of the s & p waves.

Steps for finding the Epicenter 1. Use the travel-time graph at which the p-curve and s- curve have the same separation. 2. Record this distance.

Steps for finding the Epicenter 1. Repeat the steps #1-3 for two other stations

Steps for finding the Epicenter 1. Use a compass to draw a circle around each station with the radius in step #3. 2. The epicenter is located where all three circles intersect.

Locating Earthquakes P- and S-waves start out from the focus of an earthquake at same time P-wave gets farther and farther ahead of the S-wave with distance and time from the earthquake Travel-time curve can be used to determine the distance to the focus based on the time gap between first P- and S-wave arrivals –Plotting distances from 3 stations on a map, as circles with radii equaling the distance from the quake, will show the location of the epicenter TRIANGULATION OF DATA Fig 10.10

Earthquake Location Activity Class Activity: swf_earthquake_triangulation/p_activity_eqtriangulat ion.html swf_earthquake_triangulation/p_activity_eqtriangulat ion.html Class lab Activity

Homework P. 499 #1-4 p. 504 #2, 4 P. 510 #1-4