Vocabulary 6/28/2016Chapter 19: Earthquakes1 SeismometerSeismographMagnitude Richter Scale Moment Magnitude Scale Modified Mercalli Scale

Chapter 19 Section 2: Seismic Waves and Earth’s Interior

6/28/2016Chapter 19: Earthquakes3 Seismology The study of earthquake waves Used to predict future quakes Used to study Earth’s internal structure

6/28/2016Chapter 19: Earthquakes4 Seismometers and Seismograms Seismograph or seismometer –Instrument that detects and records vibrations Seismogram –Recording made by a seismograph

6/28/2016Chapter 19: Earthquakes5 Travel-Time Curves P waves travel fastest S waves arrive next –Gap between arrival of the two waves increases with distance from epicenter

6/28/2016Chapter 19: Earthquakes6 Clues to Earth’s Interior Seismic waves change speed and direction when they pass through different materials P and S waves travel straight through the mantle P waves refracted by core –Gap where they do not show up is the P-wave shadow S waves cannot travel through liquid, so cannot enter core Analysis of these paths have led scientist to conclude that the outer core is liquid and the inner core is solid

Chapter 19 Section 3: Measuring and Locating Earthquakes

6/28/2016Chapter 19: Earthquakes8 Earthquakes Over 1 million per year More than 90% are not felt and do no damage We only hear about major seismic events or local minor events

6/28/2016Chapter 19: Earthquakes9 Earthquake Magnitude and Intensity Magnitude –The amount of energy released on an earthquake –Rated according to a numerical scale (Richter scale) Based on the largest seismic waves generated Each number represents an increase in amplitude of wave size by a factor of 10 –Magnitude-8 is 10 times larger than a magnitude-7 –Magnitude-8 is 100 times larger than a magnitude-6 The energy released increases by 32 –Magnitude-8 is 32 times greater than a magnitude-7 –Magnitude-8 is over 1000 times greater than a magnitude-6

6/28/2016Chapter 19: Earthquakes10 Classifying Earthquakes Moment Magnitude Scale –Used by most seismologists –Takes into account: Size of the fault rupture Amount of movement along the fault The rock’s stiffness –Estimated from several different types of waves

6/28/2016Chapter 19: Earthquakes11 Modified Mercalli Scale Measured by amount of damage to structures –The intensity of an earthquake Rates types of damage and other effects observed during and after an earthquake Uses the Roman numerals I – XII –The worse the damage, the higher the numeral –Damage can be mapped by connecting lines of the same intensity

6/28/2016Chapter 19: Earthquakes12 Depth of Focus Factor that determines intensity of earthquake Can be shallow, intermediate or deep The closer to the surface, the more intense they generally are

6/28/2016Chapter 19: Earthquakes13 Calculated using seismograms and travel-time curves Using a seismogram you find the P-wave, then measure how long it took for the S-wave to arrive You need readings from at least 3 seismic stations to pinpoint the epicenter Exact time of earthquake can be determined using this technique Locating an Earthquake

6/28/2016Chapter 19: Earthquakes14 Seismic Belts Using recorded sites of epicenter locations, patterns have been found Most are associated with plate boundaries –80% Circum-Pacific Belt –15% Mediterranean-Asian belt –<4% mid-ocean ridges –>1% random

6/28/2016Chapter 19: Earthquakes15

6/28/2016Chapter 19: Earthquakes16 Section Assessment 1.Explain how a seismometer works. 2.What is a seismogram? 3.What is a seismic travel-time curve, and how is it used to study earthquakes? 4.What is the P wave shadow zone and what causes it?