TEST THREE OUTLINES - 6Earthquakes ,onghastlydiagramsof...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
6 - Earthquakes 10/25/07 “We learn geology in the morning after the earthquake, on ghastly diagrams of  cloven mountains, upheaven plains, and the dry bed of the sea” – Ralph Waldo  Emerson  USGS estimates about 1 million quakes annually Most earthquakes are concentrated along plate boundaries Stress and Strain Stress: force exerted per unit area Strain: deformation caused by stress  o compressive   inward o tensile   opposite directions o shear   two different directions = tumbling Rock Strength: ability to withstand stress before rupture  EARTHQUAKE: GROUND-SHAKING CASUED BY THE SUDDEN RELEASE  OF STRAIN ENERGY CAUSED BY ROCK RUPTURE (FAULTING)   All  earthquakes occur on faults! Earthquake Cycles Drop in strain after event, takes time to rebuild Four Stages: (cycle can take hundreds to thousands of years) o Inactivity o Increase seismicity, accumulated strain o Foreshocks
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
o Major earthquake, aftershocks  Earthquake Focus and Epicenter Seismic waves propagate outwards from the focus  Epicenter, point on surface, directly above the focus of the earthquake Fault plain = As rupture grows bigger and grows up, it releases energy of  strain and releases it in all directions in form of seismic waves Seismic Waves P-Waves o Travels through all material o Faster in dense material S-Wave o Travels only through solids   dissipates in gases or liquids  o ½  the speed of P-Wave Surface Waves o Seismic waves that intersect with the surface o Travel much slower o Can cause more damage to buildings  Frequency As waves move out from the focus, high frequencies attenuated (lose their  power and disappear fast)
Image of page 2
High F = low building vibrates Low F = high building vibrates  Measuring Earthquakes Seismograph or seismometer Amplitude of seismic waves: ground vibration First arrival of seismic waves: o Time of earthquake o Distance to epicenter  Wave Speeds   As distance to the focus increases, so does the time gap  between the arrival of the first P-Wave and the first S-Wave An earthquakes occurs 500 km. from a seismometer.  The fist P-Wave arrives  after 70 seconds, the first S-Wave arrives in 150 seconds. Locating Epicenter Locating an epicenter depends on the different velocities of P and S Waves Compare P and S wave arrival times from a minimum of 3 seismic stations A circle with a radius = distance to the epicenter is drawn around each station Triangulation!
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern