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
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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
