Japan Earthquake and Tsunami

What happened?

• Large earthquake• Earthquake hazards:

– Tsunami– Ground shaking – Liquefaction– Landslides

• People and structures in the way of the hazards = catastrohe

Note:

• Japan is a developed country: per capita income is $32,433

• Well prepared for earthquakes in terms of monitoring, education, and preparedness

• 8,000 fatalities and 12,000 missing

Japan was prepared. The earthquake and tsunami caused so much destruction that emergency services and education of population were not enough to save many lives.

Today’s lecture

• What is an earthquake?– Causes of earthquakes– Foreshocks and aftershocks– Earthquake terminology– Fault classification

What is an earthquake?

Release of stored energy

• Elastic rebound theory explanation to how earthquakes occur

• Plate movement concentrates energy in crust• When the stored energy exceeds the strength

of the crust, the crust ruptures• The rupture generally occurs along faults

because this is the weakest point• Japan’s earthquake was produced on a plate

boundary

Japan moved eastward 8 feet

How Faulting Generates Earthquakes

• Movement on the fault causes a release in energy

• As the energy passes through an area, the vibration is felt

• The energy is transferred through the earth and man-made structures

• The bigger the amount of slip the more energy released and therefore, the more vibrations are produced

Causes of Earthquakes• Tectonic stress (most

common)• Water added under

pressure• Geothermal gradient

(variation due to boundary)

• Rock type• Fast/cold versus

slow/warm rate and temperature

Causes of Earthquakes• Stress accumulation and energy release at

plate boundaries.

Types of Stress (think of plate boundaries)

• Compressional stress- crust shortens• Tensional stress- crust thins• Shear stress- one piece of crust slides past

another piece of crust

• Strain measures the amount of deformation

Permanently deformed

Maximum strength before rupture or failure

If stress is released the material will return to the original shape

Stress: causes rock to change volume or shape

Response to stress

Brittle : rock breaks Ductile: rock folds

Geothermal gradient

• Quartz makes a transition from brittle to ductile at about 350 degrees centigrade

• This is to a depth of about 12 miles in California

Fast/cold versus slow/warm

Fast/cold versus slow/warm

1906 San Francisco Earthquake: fast movement causes offset

Marin County, 16 feet of offset

Offset: amount of displacement

Calaveras Fault: creep causes deformation

Elastic Rebound Theory

• Stress is added to the crust• Strain is accumulated and deformation occurs• Stress exceeds the frictional strength of the

fault plane then rupture occurs

Elastic Rebound Theory: Reid, 1906 earthquake

Strike-slip Fault Example

1906 San Francisco Earthquake

The San Andreas fault: right lateral strike-slip (which way is the window relative to the manure pile?)

Fault scarp

Japan is part of the Ring of Fire

Ring of Fire: trenches and associated subduction zones that surround the Pacific

Ocean

Tectonic Plates

Tectonic plates may be composed of oceanic crust, continental crust or both types of crust. Describe the extent of the North American plate and the Pacific plate.

Tectonic Setting: complex

This earthquake was the result of thrust faulting along or near the convergent plate boundary where the Pacific Plate subducts beneath Japan.

This map also shows the rate and direction of motion of the Pacific Plate with respect to the Eurasian Plate near the Japan Trench. The rate of convergence at this plate boundary is about 83 mm/yr (8 cm/year). This is a fairly high convergence rate and this subduction zone is very seismically active.

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANMagnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC Friday, March 11, 2011 at 05:46:23 UTC

Japan Trench

This earthquake occurred 130 km (80 miles) east of Sendai, Honshu, Japan and 373 km (231 miles) northeast of Tokyo, Japan.

Images courtesy of the US Geological Survey

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANMagnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC Friday, March 11, 2011 at 05:46:23 UTC

What does the pink line represent?

The map on the right shows historic earthquake activity near the epicenter (star) from 1990 to present.

As shown on the cross section, earthquakes are shallow (orange dots) at the Japan Trench and increase to 300 km depth (blue dots) towards the west as the Pacific Plate dives deeper beneath Japan.

Images courtesy of the US Geological Survey

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANMagnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC Friday, March 11, 2011 at 05:46:23 UTC

Seismicity Cross Section across the subduction zone showing the relationship between color and earthquake depth.

Globally, this is the 4th largest earthquake since 1900.

Magnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANMagnitude 9.0 NEAR THE EAST COAST OF HONSHU, JAPANFriday, March 11, 2011 at 05:46:23 UTC Friday, March 11, 2011 at 05:46:23 UTC

Chile 1960

Alaska 1964

Sumatra 2004

Chile 2010

Japan 2011

Russia 1952

Ecuador 1906Alaska 1965

Foreshocks and aftershocks• Relative measurement• Foreshocks: smaller

earthquakes before the main event; – a portion of the fault

moves

• Aftershocks: larger earthquakes after the main event; – Adjustment of the fault

plane

Worldwide Seismicity

Classification of Faults• Based on relative movement

along the fault plane

Fault plane: described by an area; length x width; where movement occurs

Fault scarp: a portion of the fault plane exposed after an earthquake

Focus or hypocenter: point of movement initiation

Epicenter

• Point on the Earth’s surface directly above the hypocenter or focus

• The earthquake is generally named after the epicenter

USGS

Phil Stoffer, USGS geologist

Cold, brittle crust breaks and moves

• Compressional stress causes reverse faults• Extensional stress causes normal faults• Shear stress causes strike-slip faults• Oblique movement on strike-slip faults occurs

when there is also vertical slip along the fault plane

Thrust Fault

A close-up of the thrust plane at this location. The rocks underlying the fault plane are intensely deformed

Waterton Lakes National Park, Alberta, Canada

Alps

Older rocks on top of younger rocks

Strike-slip faults

North Anatolian Fault, Turkey

Identification of faulting• Rocks along fault may be ground up or

polished• Ground up rocks are easier to erode so

often depressions on the Earth’s surface are indicative of active faults.

Identification of faulting

• Rocks along fault may be ground up

• ground up rocks are easier to erode, so linear gullies or valleys form

Fault trace of the San Andreas Fault

LIDAR image, similar location

Prince William Sound, 1964 Alaska earthquake, marine terrace exposed

Flat surface formed by wave action below sea level. Uplifted above sea level during the earthquake.

Uplifted marine terraces, California coast north of Santa Cruz

Michael Rymer, USGS

Identification of faulting

• Offset is the distance of displacement along the fault plane

• Offset features such as offset streams, roads, fences are indicative of movement

• Changes in topography

Identification of faulting

• Fault Scarp produced by fault movement

• When fault plain rises higher than the Earth’s surface

• Hector Mine Earthquake, 1999

• Mojave Desert

Understand the relation between tectonic setting, stress, and fault type

Tectonic setting Stress Fault