Forces in the Earth – Seismic Waves! Physical Science Notes 10/8/2012
Seismic Waves • Seismic Waves Definition: Seismic waves are vibrations that travel through the Earth after an earthquake occurs at a fault. • Examples: • Compression waves • Transverse waves
Seismic Waves • Compression Waves Definition: Compression waves are waves through matter that is squeezed and stretched. Example: squeezing together multiple slinky coils and then releasing.
Seismic Waves • Transverse Waves Definition: Transverse waves cause matter to move at right angles to the direction the wave is moving. Example: moving a slinky up and down with your hand.
Focus & Epicenter • Focus • Epicenter Definition: The point in the Earth’s interior where seismic waves originate (below the surface). Seismic waves moves outward in all directions from the focus. Definition: The point on the Earth’s surface directly above the focus.
Surface Waves • Surface Wave Definition: Surface waves travel outward from the epicenter along the Earth's surface much the way ripples travel outward from a stone thrown into a pond.
Classwork – Monday 10/8/2012 Earthquake waves classwork (handout, due at the end of the class period)
Homework DUE 10/9/2012 Part 1: Compare and contrast epicenter and focus IN YOUR OWN WORDS (either in complete sentences or a Venn diagram or a labeled illustration) Part 2: Compare and contrast compression, transverse, and surface waves Study for vocabulary quiz tomorrow!
Tuesday 10/9/2012 Vocab Quiz! (turn in) For each term, please summarize the definition IN YOUR OWN WORDS • Fault (& list the three types) • Seismic Wave (& list the three types) • Epicenter
Compression & Transverse Wave Data • Take out a fresh sheet of graph paper. • Make sure your x & y axis are appropriately labeled (“Distance from focus (km)” on the x-axis and “Time of Arrival (hr: min: sec)” on the y-axis). • Put numbers on the x-axis: start at 250 on the left side of the x-axis and count by 1000s (250, 1250, 2250, 3250, 4250, 5250, 6250, 7250, 8250, 9250, 10250) OR count by 500s • Put numbers on the y-axis: start at 4 hours on the bottom of the y-axis and count a minute for each square.
Conclude & Apply:Answer questions under your graph • Based on your graph, which is faster – a compression wave or a transverse wave? • Do the waves remain the same distance apart as they travel? • Do they grow closer together or farther apart over time? • How could you use your graph to fill in the missing arrival times in the chart? • Use your observations to tell why compression waves are called primary waves and transverse waves are called secondary waves.