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Continuation of geologic structures and natural process, Lecture notes of Geology

The causes of earthquakes and how they are detected and recorded. It also explains the design of a traditional seismometer and the different types of seismic waves. historical context by describing the world's first seismometer, constructed by Chinese scholar Zhang Heng in A.D. 132. This information is relevant to students studying geology, earth science, or natural disasters.

Typology: Lecture notes

2022/2023

Available from 02/10/2023

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Geology of National Parks 2/02/2023
Earthquakes and Earth Structure
Earthquakes and their causes
-Occurring every day, more than a million every year
-Sudden slip motion along a newly formed crustal fault
-Sudden slip along an existing g crustal fault
-Volcanic eruption or magma movement in a volcano
-Giant landslides, meteorite impacts, nuclear denotations, fracking, or
fluid injection
Movement (displacement) along a fault zone
-Releases seismic energy
-Transmitted through earth and along the surface
-Manifested as an earthquake
-
Detecting an earthquake: The World’s First Seismometer
-Constructed by Chinese scholar Zhang Heng (A.D. 78-139) In A.D. 132
-Bronze vessel, resembling a wine jar, 64’’ in diameter, with a domed cover
-Inside was a central column capable of displacement in eight directions
-On outside surface were 8 dragons holding bronze balls in mouth
-Below were 8 toads ready to catch the bronze balls
-During earthquake, the central column would vibrate and impact the dragons causing
them to “vomit” their bronze balls revealing the direction of the temblor
Recording an earthquake: Design of a Traditional Seismometer
-Mass, heavy weight, loosely coupled to the earth
-Pivot constrains mass to move up and down
-Spring constrains vertical movement of the mass
-Paper fixed to rotating drum
-Pen attached to mass draws signal from earthquake
-Instrument mounted securely to bedrock
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Geology of National Parks 2/02/ Earthquakes and Earth Structure Earthquakes and their causes

  • Occurring every day, more than a million every year
  • Sudden slip motion along a newly formed crustal fault
  • Sudden slip along an existing g crustal fault
  • Volcanic eruption or magma movement in a volcano
  • Giant landslides, meteorite impacts, nuclear denotations, fracking, or fluid injection Movement (displacement) along a fault zone
  • Releases seismic energy
  • Transmitted through earth and along the surface
  • Manifested as an earthquake

Detecting an earthquake: The World’s First Seismometer

  • Constructed by Chinese scholar Zhang Heng (A.D. 78-139) In A.D. 132
  • Bronze vessel, resembling a wine jar, 64’’ in diameter, with a domed cover
  • Inside was a central column capable of displacement in eight directions
  • On outside surface were 8 dragons holding bronze balls in mouth
  • Below were 8 toads ready to catch the bronze balls
  • During earthquake, the central column would vibrate and impact the dragons causing them to “vomit” their bronze balls revealing the direction of the temblor Recording an earthquake: Design of a Traditional Seismometer
  • Mass, heavy weight, loosely coupled to the earth
  • Pivot constrains mass to move up and down
  • Spring constrains vertical movement of the mass
  • Paper fixed to rotating drum
  • Pen attached to mass draws signal from earthquake
  • Instrument mounted securely to bedrock
  • Ground moves up or down, mass pivots according
  • Spring is stretched or compressed
  • Pen record’s the signal on the paper Seismic body waves P-Waves
  • Primary
  • Compressional
  • Particle motion parallel to the direction of propagation S-Waves
  • Secondary
  • Shear
  • Particle motion perpendicular to direction of propagation Surface Waves
  • Energy dissipates with depth
  • Maximum intensity at surface
  • Long waves (back and forth motion)
  • Rayleigh waves (retrograde rolling motion)

P-waves paths vs. S-waves paths Earth cross-section

  • Crust (silicate
  • Mantle (silicate
  • Core (Ni-Fe metal)
  • Earth’s outer core is fluid, responsible for magnetic field and, in part, drives mantle convection