Japan Earthquake and TsunamiEarthquake. What happened? Large earthquake Earthquake hazards: –...
-
Upload
moses-banks -
Category
Documents
-
view
214 -
download
0
Transcript of Japan Earthquake and TsunamiEarthquake. What happened? Large earthquake Earthquake hazards: –...
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