Lessons 3-5 Notes L3: Recording Earthquake Waves L4: Plotting Earthquakes L5: Using Earthquakes to Study the Earth’s Interior

Lesson 3: Recording Earthquake Waves A seismograph is an instrument that detects, records, and measures the vibrations produced by an earthquake. A seismogram is the record made by a seismograph; the paper on which earthquake waves are recorded.

Reading a Seismogram Prince William Sound, Alaska (1964) earthquake – magnitude 9.2 The Alaska earthquake shook the earth for more than 9 minutes. The longer the earth shakes, the more energy is released and the more violent the earthquake is. Aftershock – an earthquake that follows a larger earthquake, or main shock, that originates along the main fault (or break in the surface) as the main shock.

Locating the Epicenter The location within the earth where the earthquake rupture occurs and where the energy is released is the focus. The point on the earth’s surface directly above the focus is the epicenter.

Seismologists use data from three seismograph stations in order to determine the location of the epicenter. First, seismologists determine at what time the p-wave arrived at each seismograph station. Second, seismologists determine at what time the s-wave arrived at each seismograph station. Seismologists determine the lag time (the time between p-wave arrival and s-wave arrival). The seismograph station with the least amount of lag time is the one closest to the epicenter.

The lag time and the time each earthquake wave arrived at each station was different because they are different distances away from the epicenter.

The direction of the vibrations also affected the seismogram. In the model seismograph lab, the harder we hit the table and the closer the seismograph was to the vibrations, the larger the waves were on the seismogram. The larger the earthquake  larger waves on the seismogram The closer the earthquake  larger waves on the seismogram. The direction of the vibrations also affected the seismogram. This is why seismologists need recordings from several seismograph stations so that they could get an accurate reading.

Lesson 4: “Plotting Earthquakes” Earthquakes and volcanoes occur in a pattern because many occur on plate boundaries. The Ring of Fire, the Mid-Atlantic Ridge, and Mediterranean-Himalayan Belt are areas of intense earthquake activity. Ring of Fire: around edges of Pacific Ocean Mid-Atlantic Ridge: runs down the middle of the Atlantic Ocean floor Mediterranean-Himalayan Belt: extends from west Indonesia through the Himalayas in Asia and the Mediterranean region.

Intensity vs. Magnitude Intensity is the measure of damage done by an earthquake. Magnitude is the measure of the total amount of energy released at the focus of an earthquake.

Lesson 5: “Using Earthquakes to Study the Earth’s Interior”   Crust Mantle Outer Core: Liquid Inner Core: Solid

Lithosphere vs. Asthenosphere Lithosphere – made up of the crust and the solid part of the mantle. It is the solid outer shell of the earth that is broken up into plates. Asthenosphere – made up of the liquid part of the mantle. Directly below the lithosphere and flows like taffy. The asthenosphere is the reason why the plates move.

How seismologists use earthquakes to study the earth’s interior: Earthquake waves travel through some substances, but not others. Earthquake waves travel at different speeds depending on the substance. For example, s-waves do not travel through liquids. Patterns of earthquakes and their waves provide information about plate boundaries and the interior structure of the earth.