Lecture 17 // Earthquakes: EQ Hazards & Seismology

Question 1

Ground shaking can cause:

Answer 1

• Building collapse and damage
e.g., The 2009 Haiti Earthquake
• Infrastructure collapse and damage (bridges, roads, rail, power lines, gas lines, water pipes, etc.). Also causes ruptured gas lines (fire) and broken water pipes (can’t fight the fire).
e.g., The 1995 Kobe Earthquake
• Landslides
e.g.,2005 Kashmir, Earthquake (Pakistan, India), 86,000 deaths (M7.6, Maximum Mercalli Intensity VIII (severe))

Question 2

Seismic retrofitting

Answer 2

• Done in an attempt to strengthen buildings and infrastructure. (Many old structures were designed well below the current seismic code.)
• Seismic retrofit of the Surrey approach to the Pattullo Bridge.

Question 3

Tsunami

Answer 3

• Generated when a large volume of water is displaced at a subduction zone during a mega-thrust EQ.
• The overriding plate is displaced trench-ward as strain is released, pushing the water as it moves. A series of waves is set in motion.

Question 4

2011 Japan Tohoku MW 9.0

Answer 4

• Focal depth 30 km
• Tsunami height 5-25+m (20-80+ ft)
• 15,000+ deaths, 2,500+ missing
• Tsunami overtops a 7m seawall, the maximum height they expected for a tsunami…

Question 5

2004 Sumatra EQ MW 9.2

Answer 5

• Focal depth 30 km
• Tsunami height in northern Sumatra 25-30m (80-100ft)
• Tsunami height in Thailand up to 10m (30 feet)
• Deaths: 230,000+
(160,000+
in Indonesia)

Question 6

EQs in Canada occur along:

Answer 6

Old buried fault lines (eastern Canada)
• the Queen Charlotte Fault
• the Cascadia subduction zone

Question 7

Seismology

Answer 7

• The study of Earthquakes and seismic waves propagating through the Earth. Much information can be gathered about Earth’s interior.
• Large earthquakes generate seismic body waves capable of traveling through the entire Earth.

Question 8

Seismic discontinuities

Answer 8

• Seismic discontinuities are where sudden changes occur in body wave velocity. – They reflect abrupt changes in rock composition & density.

• Moho (Mohorovičić Discontinuity) @ the crust
• 400-km Discontinutity
• Gutenberg Discontinutity @ the core

Question 9

S-wave shadow zone

Answer 9

An S-wave shadow zone occurs on the opposite side of the Earth from the foci of a large EQ.
• S waves are not recorded by seismographs within the S wave shadow zone.

Question 10

P-wave shadow zone

Answer 10

A P-wave shadow zone also occurs. They are found within a portion of the S-wave shadow zone.
• P waves are not recorded
by seismographs within the P wave shadow zone.

Question 11

Seismic

tomography

Answer 11

Using seismic data to create ‘slices’ through the Earth. Red areas: warmer, low density rock
– deep mantle plumes
– spreading centres
Blue areas: cooler, high density rock
– subducting slabs
– slab graveyards