EARTHQUAKES!

What causes earthquakes? What are earthquakes? What causes earthquakes? Natural vibrations in the ground caused by: Plate movement along giant fractures Volcanic activity Stress: the force applied to a rock exceeds its strength Strain: the deformation causes by stress 3 types: Compression, Tension, Shear

How do earthquakes travel? In seismic waves! Seismo- (Greek) “to shake” P-waves Primary (1st) Pulls rocks in the same direction as the wave Body waves (occur inside earth) Particle Movement Wave Direction

How do earthquakes travel? S-waves Secondary Causes rocks to move perpendicular to the wave Body waves (occur inside earth) Wave Direction Particle Movement

How do earthquakes travel? L-waves Third to arrive Move in two directions Up and down Side to side Surface waves (MOST destructive!) Wave Direction Particle Movement

How do earthquakes travel? Body waves spread out from the earthquakes origin, or focus On the surface above the focus, is the epicenter

How do we use earthquake data? Evenly though earthquakes can be destructive and even deadly, they also provide seismologists with valuable information… The body waves that penetrate Earth’s interior provide valuable information about its structure

How do we detect earthquakes? Seismographs: sensitive tools that can detect and record vibrations at great distances from epicenters…even though we can’t feel them!

How do we detect earthquakes? Many years of data from facilities around the world has allowed seismologists to construct global time-travel curves for P-waves and S-waves This allows us to predict earthquake patterns, no matter where in the world the epicenter is!

P-waves ALWAYS travel quicker than S-waves How do we detect earthquakes? Y-axis= Time X-axis= Distance P-waves ALWAYS travel quicker than S-waves Time lag= amount of time between P-waves and S-waves (increases with time)

Left-Side Math Practice Which wave travels 1000 miles first? About how many minutes does it take the P-wave to travel 1500 miles? What is the time lag at 2000 miles?

Earthquakes and Society Notes

How do we monitor seismic activity? Ground movements near a fault are a clue that an earthquake might happen. So, scientists measure ground movements near faults. They use tiltmeters, creep meters, laser-ranging devices, and GPS satellites.

Tiltmeters show how much the ground is tilting, or tipping. Works like a carpenter’s level—water inside a glass bulb shows how much tilting there is.

Creep meters show how far the sides of a fault have moved in opposite directions. Uses a wire stretched across a fault—gets longer when the two sides move apart.

Laser-ranging devices use a laser beam to detect horizontal fault movement. Device times a laser beam as it travels to a reflector and back and tracks change

To use the Global Positioning System, scientists put super-sensitive markers along both sides of the fault

How are earthquakes measured? By the amount of energy released or magnitude Measured on the Richter Scale By the amount of damage done or intensity Measured on the Mercalli Scale Some earthquakes aren’t even felt while others wipe out entire cities!

How much damage do earthquakes cause? Damage depends on strength of structures Severe Damage Unreinforced buildings Stone, concrete, and brittle materials Minimal Damage Rubber structures Steel-framed buildings Wooden structures

What types of damage do earthquakes cause? Structural Failure Walls collapse and cause “pancaking” Buldings between 5-15 stories sustain the most damage because of the affect of the natural sway Land Failure Sloping areas=landslide prone Soil liquefaction (quicksand affect) Softer soil=More violent quakes

What types of damage do earthquakes cause? Tsunamis Large wave generated by vertical motion of the ocean floor When waves move into shallow water, wave height grows exponentially Often larger death tolls than earthquakes themselves

Where do most earthquakes occur? Along plate boundaries in areas called seismic belts Probability of future damage is predicted using past damage Two Factors: History Amount of Strain Used to generate seismic-risk map

Where do most earthquakes occur?

Write a “T” for true or a “F” for false beside each statement about measuring earthquakes. Challenge: Try to change, add, or remove a word to make false statements true. Earthquakes that are a 1 on the Richter Scale and Mercalli Scale can only be felt at the epicenter. The Richter Scale measures the amount of damage done by an earthquake. The highest magnitude on the Mercalli Scale is 15. On the Richter Scale, each number represents a 10x increase in energy released.