Upload
isha
View
91
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Cascadia subduction zone and Mexico City. Similar size to the amount of crust that moved during the Sumatra earthquake. Cascade Subduction Zone. Dark red area indicates cooler crust storing energy Lighter red zone could possibly rupture Areas of silent earthquakes?. 1700 Cascadia earthquake. - PowerPoint PPT Presentation
Citation preview
Cascadia subduction zone and Mexico City
Cascade Subduction Zone
• Similar size to the amount of crust that moved during the Sumatra earthquake.
• Dark red area indicates cooler crust storing energy
• Lighter red zone could possibly rupture
• Areas of silent earthquakes?
1700 Cascadia earthquake
1700 Cascadia earthquake
• Drop in elevation
Vegetation exposed to sea water and dies
10:57
• Layers of sediment are shaken loose of the continental shelf
• Deposited on the ocean floor
1700 Cascadia earthquake
19 times in the past 10,000 years
• Organic layers are overlain by tsunami deposits
• 7 cycles the last 3500 years
1700 Cascadia earthquake
Silent earthquakes
• Creep events that release large amounts of strain energy without detectable seismic shaking
• Last 2-3 weeks, 14.5 month recurrence• A few centimeters at depths 30-50 KM• Equal to Mw 6-7
Silent earthquakes
• Movement is detected using Global Positioning Satellite technology
• Change in movement from compression to extension
• Significance– Understand how much silent earthquakes reduce overall
energy– Large earthquakes every 200-700 years
Silent earthquakes
Graph showing slip associated with silent earthquakes
Mexico
Silent earthquakes
• Yellow: GPS data– Slow slip or silent
earthquakes– Early- 2002, mid-2006
• Red/Green: seismic stations– Circled area,
earthquakes
Silent earthquakes: indicative of earthquakes
• Shallow and then becomes more steep under Mexico City
Mexican subduction zone
Mexico City Earthquake
• 50 x 170 kilometers of displacement along the subduction zone
• M 8.1 • Mexico city is 400 kilometers away• City was built on the sediments of Lake
Texcoco
Mexican subduction zone• Cocos tectonic plate is
subducting under the North American Plate
• Two plates lock• Stress builds and energy is
stored• Stress exceeds frictional
force• Release of energy in terms
of an earthquake
• Earthquakes are more shallow than other subduction zones
Mexican subduction zone
Mexico City
• Drained Lake Texcoco• Clay sedimentary layers• Low frequency surface
waves amplified• 1-2 second frequencies• Matched the periods of
buildings 6-16 stories
Common Building Failures
• Top floors fail-resonance• T-shaped structures• Flexible structures
between stiff structures
Building Failures
• Hammering
Soft story collapse
Not all subduction zones are created equally but are capable of producing
large earthquakes.