CIVTECH 3CS3 Chapter Notes - Chapter 2: Seismic Wave, Subduction, Epicenter

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Published on 19 Apr 2013
School
McMaster University
Department
Civil Engineering Infrastructure Technology
Course
CIVTECH 3CS3
Chapter 2
Earthquakes
2.1 Introduction
Earthquakes result from the rupture of rocks along a fault
Fault a fracture in the earth’s crust
Seismic Waves the energy formed when rocks on opposite sides of the fault move
Earthquake Magnitude
Epicentre the point on the surface directly above the fault rupture
Richter Scale a decimal number on a scale that represents the size or magnitude of a
quake
See Figure 2.3 on pg 33
Today, the most common unit to measure quakes is Moment Magnitude (Mw), which is
determined:
o From an estimate of the area that ruptured along a fault plane during the quake
o The amount of movement or slippage along the fault
o The rigidity of the rocks near the focus
Magnitude and Frequency of Earthquakes
o See Table 2.3 on page 34
Earthquake Intensity
The intensity depends on magnitude, distance from epicenter, and the nature of the ground
at the site
Modified Mercalli Intensity Scale
o Measures the degree to which an earthquake affects people, property, and the
ground
o Usually shown on maps
o Based on newspaper articles, reports of damage assessment teams, and
questionnaires to residents
2.2 Earthquake Processes
Process of Faulting
Compared to sliding two rough boards past each other two lithospheric plates move past
each other
This rupture produces vibrational energy called seismic waves
Fault Types
o Strike-Slip Faults: displacements are mainly horizontal
o Dip-Slip Faults: displacements are mainly vertical
Classified as a reverse fault or a normal fault (depending on how the earth’s
material moves)
Can also be called thrust faults, which are mostly located in deep-sea
trenches, where they are low-angle reverse faults
o See Figure 2.12 on pg 40
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Document Summary

Earthquakes result from the rupture of rocks along a fault. Fault a fracture in the earth"s crust. Seismic waves the energy formed when rocks on opposite sides of the fault move. Epicentre the point on the surface directly above the fault rupture. Richter scale a decimal number on a scale that represents the size or magnitude of a quake. Magnitude and frequency of earthquakes: see table 2. 3 on page 34. The intensity depends on magnitude, distance from epicenter, and the nature of the ground at the site. Modified mercalli intensity scale: measures the degree to which an earthquake affects people, property, and the ground, usually shown on maps, based on newspaper articles, reports of damage assessment teams, and questionnaires to residents. Compared to sliding two rough boards past each other two lithospheric plates move past each other. This rupture produces vibrational energy called seismic waves. Fault types: strike-slip faults: displacements are mainly horizontal, dip-slip faults: displacements are mainly vertical.

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