Earthquakes! **Adapted from

What is an earthquake? Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip Caused by volcanic or magma activity, Caused by other sudden stress changes in the earth.

Three Types of Faults Strike-Slip Thrust Normal

What causes earthquakes? Tectonic plates move past each other causing stress. Stress causes the rock to deform, break, and/or move

Elastic Rebound – deformed rock goes back to its original shape

Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus

How Seismographs Work Normally everything would move, but…. the pendulum remains fixed as the ground moves beneath it …this mass, like the pen, has inertia and so resists motion. It’s a weighted pen writing on a rolling drum of paper.

Typical Seismogram

Primary Waves (P Waves) PUSH-PULL PATTERN! – A type of seismic wave that pushes & pulls the ground The FIRST wave to arrive from an earthquake—travels the fastest! Travels Parallel to the direction the wave travels

Secondary Waves (S Waves) A type of seismic wave that moves the ground up and down or side-to-side (perpendicular) to the direction the wave travels Slower! More destructive to buildings

Comparing Seismic Waves **P & S Wave song:

Surface Waves Move along the Earth’s surface – ROLL OUT! Motion can be up and down, around & back & forth Travel more slowly than S and P waves – Last to arrive Most destructive to structures

How do scientists calculate how far a location is from the epicenter of an earthquake? Scientists calculate the difference between arrival times of the P waves and S waves The further away an earthquake is, the greater the time difference between the arrivals of the P waves and the S waves

Locating Earthquakes Distance (km)  Difference in arrival times  Question: Where could the EQ be? P-wave S-wave Answer: Anywhere along the blue line. (not much help) 2. Find the distance to the EQ using the lag time and this Time/Distance graph. 3. Use the distance from the EQ as the radius (r) for this circle. r 1.Find the difference in the arrival times, or lag time ( t ), of the P & S waves. Time ( t)

Locating Earthquakes \  Arrival diff.  \ Question: Where could the EQ be, now?  Difference in arrival time  **Let’s get someone else that has readings for this EQ to help out… (Same procedure) Answer: Where the green and blue circles cross. (Better, but still a change of going to the right place to find the EQ.)

Locating Earthquakes Answer: Where all 3 circles intersect  Difference in arrival time  \  Arrival diff.  \ \  Arrival time diff.  \ So, no more guessing– Question: where is the actual EQ ? **If you get 3 people working on this puzzle, now you can triangulate.

How are Earthquakes Measured? Richter Scale-measures energy

How are Earthquakes Measured? Mercalli Scale-measures damage Click Link for Interactive Demo

Earthquake Waves & Earth’s Interior **See how seismic waves move through the Earth’s layers here (Shadow zone):

Seismic Waves in the Earth

Tsunamis

Formation of a tsunami

Tsunami Warning System