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

• 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”

• Elastic strain energy is stored

Where Do EQ Occur?• Faults

– Fracture in the Earth’s crust where one side moves with respect to another

Types of Fault

Fault Terminology

– Fault block above the fault – Fault block below the fault

• Footwall• Hanging wall

Normal Fault

• Hanging wall moves down relative to the footwall• Exhibits lengthening or extension of the crust• Associated with fault block mountains

– Basin and Range

– Horst – uplifted block– Graben – down dropped block

Basin and Range

Reverse Fault

• 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

– Right lateral – As you face the fault, opposite side of plate moves right

• Types of Strike Slip:

– 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 – 1994M=6.7; 61 killed

Destruction from EQTsunami

• 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’sFires

• 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’sLandslides

• 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