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DETERMINING GROUND SHAKING
In general, the larger the magnitude, the stronger the shaking and the longer the shaking will last. However, other factors influence the level of shaking as described in the following paragraphs. Table and descriptions from https://earthquake.usgs.gov/learn/topics/mag_vs_int.php
LOCATION AND DIRECTION
Closer earthquakes will inherently cause more shaking than those farther away. The location about epicenter and direction of rupture will influence how much shaking is felt. The direction that the rupture propagates along the fault influences the shaking. The path of greatest rupture can intensify shaking in effect known as directivity.
The nature of the ground materials affects the properties of the seismic waves. Different materials respond differently to an earthquake. Think of shaking jello versus shaking a meatloaf; one will jiggle much more to the same amount of shaking. The response to shaking depends on their degree of consolidation; lithified sedimentary rocks, and crystalline rocks shake less than unconsolidated sediments and landfill. This is because seismic waves move faster through consolidated bedrock, move slower through unconsolidated sediment, and move slowest through unconsolidated materials with high water content. Since the energy is carried by both velocity and amplitude, when a seismic wave slows down, its amplitude increases, which in turn increases seismic shaking. Energy is transferred to the vertical motion of the surface waves.
DEPTH OF FOCUS
The focus is the place within the Earth where the earthquake starts, and the depth of earthquakes influences the amount of shaking. Deeper earthquakes cause less shaking at the surface because they lose much of their energy before reaching the surface. Recall that most of the destruction is caused by surface waves which are caused as the body waves reach the surface.
Introduction to Physical Geography by R. Adam Dastrup is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.
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