Transcript Earthquake - Cal State LA - Instructional Web Server

Earthquakes
Movement
&
Destruction
What is an Earthquake?
• Shaking of the Earth produced by a sudden
movement of rock beneath its surface
How Do Earthquakes Occur?
Elastic Rebound Theory
• Deformation builds up and causes crust to bend
• Elastic strain energy is stored
• When strain exceeds strength of the rock, it will “snap”
into a new position
• In the process of rupturing, energy is released in the
form of “seismic waves”
Where Do EQ Occur?
• Faults
– Fracture in the Earth’s crust where one side
moves with respect to another
Types of Fault
Fault Terminology
• Hanging wall
• Footwall
– Fault block above the fault
– Fault block below the fault
Normal Fault
• Hanging wall moves down relative to the footwall
• Exhibits lengthening or extension of the crust
• Associated with fault block mountains
– Horst – uplifted block
– Graben – down dropped block
– Basin and Range
Basin and Range
Reverse Fault
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•
•
•
Hanging wall moves up relative to footwall
Exhibits shortening or compression of crust
Have dips > 45°
If dip’s < 45°, then thrust fault
Strike-Slip Fault
• Horizontal displacement
• Types of Strike Slip:
– Right lateral – As you face the fault, opposite side of
plate moves right
– Left lateral – opposite side of plate moves left
San Andreas Fault
Destruction from EQ
• Ground Shaking
• Tsunami
• Fire
•Liquefaction
Destruction from EQ
Ground Shaking
• Rapid horizontal movement of ground may shift
homes and cause them to collapse
• Shaking is exaggerated in water-saturated or
weak sediment
Northridge, CA – 1994
M=6.7; 61 killed
Destruction from EQ
Tsunami
• Giant Sea Waves generated by submarine EQ’s
• Tsunamis travel 1,000’s of miles
• Waves may reach 15 m (50 feet) in height
and travel up to 960 km/hr (600 mph)
Alaska - 1964
• M = 9.2; 125 died (110 tsunami, 15 EQ)
Alaska, 1964
• There was so much uplift that once-submerged
areas were exposed after EQ
Indonesia 2004
• M=9.0; 280,000 killed
Destruction from EQ’s
Fires
• Many gas lines may break from the severe shaking
• Unfortunately, many water lines may break as well
so that firefighting becomes impossible
San Francisco - 1906
• M = 7.8; 3,000 killed
Destruction from EQ’s
Landslides
• Mountains usually form in areas of convergent boundaries
• The steep slope are prone to landsides when shaken
• Landslides are common following EQ’s in California
Northridge - 1994
• Landslides prevalent in Santa Susana Mountains
Destruction from EQ’s
Liquefaction
• Occurs when water-saturated is reorganized
due to violent shaking
• Sediment collapses, expelling water, and
causes the ground to subside
U.S. Earthquake Hazards
San Andreas Fault
Southern California
Seismicity
Southern California
Faults
Earthquake Predictions