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Earthquakes PowerPoint PPT Presentation

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Earthquakes. Source: USGS. Source: NPS. Seismic Hazard. Source: USGS. California Tectonics: Present. Source: USGS. California Tectonics: Past. http:// What Is An Earthquake?.

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Source: USGS

Source: NPS

Seismic hazard

Seismic Hazard

Source: USGS

California tectonics present

California Tectonics: Present

Source: USGS

California tectonics past

California Tectonics: Past



What Is An Earthquake?






Types of earthquake waves

Types of Earthquake Waves

  • Surface waves

    • Complex motion

    • _________________________________

  • Body waves

  • 1. Primary (P) waves

    • Push-pull (__________________) motion

    • Travel through solids, liquids, and gases

    • ___________________of all earthquake waves

  • 2. Secondary (S) waves

    • "Shake" motion

    • Travel only through _____________

    • ____________________ than P waves

  • Seismic waves

    Seismic Waves

    A seismogram records vs

    A seismogram records ________________vs. _________

    Locating an from 3 seismograph stations

    Measure the difference in arrival of ____________ waves.

    Locating an ____________ from 3 seismograph stations

    Step 2 of locating the epicenter

    Step 2 of locating the epicenter

    2. Use a graph to determine the ______________ from the monitoring station to the epicenter.

    Steps 3 4 5 of locating the epicenter

    Draw a circle, centered around the monitoring station with a radius _________ to the distance from the epicenter.

    Repeat two more times.

    5. The point where all three circles intersect is the location of the ______________.

    Steps 3, 4 & 5 of Locating the Epicenter

    Measuring the size of an earthquake

    Measuring The Size of An Earthquake

    • ______________ – determined by effects on people, structures, and the environment

    • _______________ – measures energy released at the source of the earthquake.

    Magnitude from amplitude

    Magnitude From Amplitude

    Abbreviated modified intensity scale


    Witness observations


    Felt by very few people; barely noticeable


    Felt by a few people, especially on upper floors.


    Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake. Hanging objects swing.


    Felt by many indoors, by few outdoors. May give the impression of a heavy truck passing by.


    Felt by almost everyone, some people awakened. Small objects move. Trees and poles may shake.


    Felt by everyone. Difficult to stand. Some heavy items of furniture move, plaster falls. Slight damage to chimneys possible.


    Slight to moderate damage in well-built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall.


    Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse.


    Considerable damage to specially built structures, buildings shifted off foundations. Noticeable cracks in ground. Wholesale destruction. Landslides.


    Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction.


    Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground.


    Total damage. Waves seen on ground. Objects thrown up into air.

    Abbreviated Modified ________ Intensity Scale

    Did you feel it

    Did You Feel It?

    Earthquake hazards




    Ground shaking


    Ground Rupture

    Earthquake Hazards





    Niigata Earthquake, Japan, 1964:

    Tilting of apartment buildings


    Asian Earthquake and Tsunami of 2004What Happened and Why?

    Magnitude 9 earthquake

    • Largest earthquake since the 9.2 magnitude Alaskan earthquake (1964)

    • Energy release equivalent of 23,000 atom bombs such as the one that destroyed Hiroshima

    • Why did it occur here?

    Wind generated waves vs tsunamis

    Wind-generated Waves vs. Tsunamis

    Earthquakes and tsunamis

    Earthquakes and Tsunamis

    What, besides earthquakes, can cause a tsunami?

    Tsunami risk in california

    Tsunami Risk in California

    • California is at risk of tsunamis that are generated locally and from a distance.

    • 1964: 10 killed and 35 injured when tsunami from the 1964 Alaska earthquake reached Crescent City (Oregon/CA border).

    • A Cascadia earthquake (an earthquake up in ____________ or ____________ could bring a tsunami to Northern CA in ~ 15 minutes.

    Short term prediction

    Short-term Prediction

    • Precursors: May or may not occur

      • Uplift

      • Foreshocks

      • Anomalous animal behavior

      • Changes in water levels in wells

      • Release of radon gas

      • Changes in velocity of P waves

    Long range forcasting

    Long-Range Forcasting

    • Based on knowledge of when and where past earthquakes have occurred.

      • Paleoseismology –



      • Seismic gaps-



    Bay area eq probabilities

    Bay Area EQ Probabilities

    Hayward – Rodgers Creek Faults have the highest probabilities

    Forecasting (probability) vs. prediction

    Source: USGS

    Paleoseismology the study of prehistoric earthquakes

    Paleoseismology - the study of prehistoric earthquakes.

    M7 1868 hayward earthquake

    M7 1868 Hayward earthquake

    • 30 fatalities, 5 in San Francisco (12th most lethal US earthquake)

    • $350,000 (>$5-100M in 2007 dollars) in damage in San Francisco alone

    • Extensive damage in San Leandro, Hayward, and Fremont (total population less than 2000)

    • Bay Area population was 260,000 (it is now 27 times larger)

    Source: USGS


    1868 Hayward


    Source: USGS




    Earthquake of m 6 8 on the hayward fault

    Earthquake of M > 6.8 on the Hayward Fault?

    • A major earthquake today on the Hayward fault

    • would impact more than 5 million people and

    • Cause estimated total economic losses to residential and commercial properties would likely exceed $165 billion.

    • Other factors, such as fire, damage to infrastructure and related disruption would substantially increase the loss

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