Last Time Faults (Brittle Deformation) A) Types of Brittle Deformation B) Types of faults/terminology C) Faults on maps
Web notes 29: Lab Manual Chapter 7
Mechanical Behavior of Rocks Near-surface rocks that are under low T-P conditions behave as brittle material: – Fault fracture (slippage) – Joint fracture (no slippage) Deep rocks under elevated T-P conditions behave as ductile material: – Folding
Brittle Deformation Fractures are irregularly spaced cracks that cut across rocks
Brittle Deformation Joints are regularly spaced and parallel fractures that result from tension. Columnar jointing is caused by cooling
Brittle Deformation Faults are fractures that involve movement.
Fault Terminology All faults share some features. All active faults are subject to earthquakes
Fault Terminology Dip Slip Faults are subdivided into two types based upon the sense of motion along the fault plane and the type of stress involved
Tension = Normal Fault Compression = Reverse Fault
Fault Terminology Strike Slip Faults are also subdivided into two types based upon the sense of motion along the fault plane. Shear = Strike Slip Fault Left Lateral Strike Slip Fault Right Lateral Strike Slip Fault
Faults on Maps Strike Slip Faults (Right Lateral)
Faults on Maps Normal Faults
Faults on Maps There is a special class of reverse fault that is common in mountain belts Thrust Faults
Faults on Maps The Canadian Rockies are one of the best places to see thrust faults
Faults on Maps Trust faults usually occur in multiples (like in the Rockies) leading to complex geological maps
Today’s Agenda Earthquakes A) Earthquake intensity and magnitude B) Seismographs C) Case Studies
Web notes 29: GY 111 Lab Manual Chapter 7
Seismic Waves
P and S-waves are called body waves because they travel through the Earth. P-waves travel through all media and are the fastest (4+ km/s) S-waves cannot pass through liquids and are slower (3+ km/s)
Seismographs Seismic waves are recorded using seismographs.
Seismographs Seismic waves are recorded using seismographs. The traces are called seismograms.
More about seismograms shortly, but first… Earthquake magnitude.
Earthquake Magnitude The “intensity” of an earthquake can be measure through one of two ways. 1) A “people” method: Modified Mercalli Intensity Scale (I to XII) 2) A geophysical method: Modified Richter Scale (1 to 10)
Earthquake Magnitude
Earthquake Magnitude The Modified Mercalli Intensity Scale is most useful for historical earthquakes, but is subject to perception errors.
Earthquake Magnitude The Modified Richter Scale uses geophysical information recorded from seismographs.
You need to measure the amplitude, but also take into account the distance from the earthquake epicenter
Earthquake Magnitude
You need to measure the amplitude, but also take into account the distance from the earthquake epicenter
At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions.
1300
100
6
Can cause damage to poorly constructed buildings and other structures in areas up to about 100 kilometers across where people live. Substantial deaths, especially if epicenter is in a major city
150
1000
7
"Major" earthquake. Can cause serious damage over larger areas.
20
10,000
8
"Great" earthquake. Can cause serious damage and loss of life in areas several hundred kilometers across.
1
100,000
9
Rare great earthquake. Can cause major damage over a large region over 1000 km across.
