Environmental Science Geology 1401410 Instructor: Don Thieme

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Environmental ScienceGeology 1401-410Instructor
Don Thieme

• 17th Lecture Plate Tectonics, Petroleum Traps,
  Earthquakes

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Lithosphere
Average density of the solid Earth 5.5 g/cm3
Continental Crust is 20-70 km thick (average of
35 km) with density of 2.7 g/cm3 Oceanic Crust
is 5-12 km thick with density of 3.0 g/cm3
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Earth's crust is divided into 7 major and 20
smaller plates
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divergent plate boundary
convergent plate boundary
transform faults/ triple junctions
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Divergence at Mid-Ocean Ridges
- most important area for creation of new crust -
sea floor spreading apart at gradual and constant
rate - ocean floor subducted at trenches, remains
geologically young
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Ocean-Continent Convergence
Archean ocean floor and volcanic arc
sediments accrete to the edges of
the craton Vishnu schist Ashe group
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Convergent Boundary - Oceanic-Oceanic
Aleutian, Mariana, and Tonga Islands
in Pacific Antilles in Caribbean
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Convergent Boundary - Continent-Continent
Himalayan Mountains in Nepal and India
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Thrust Faults
- low angle reverse faults (hanging wall moves
up) - convergent plate margins (Proterozoic, Ordov
ician, Devonian, Late Pennsylvanian and Permian)
Spring Mountain thrust fault from the Alleganian
orogeny in northeastern Pennsylvania
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Folds
Rocks fold under compressional stress at
convergent plate margins (Proterozoic,
Ordovician, Devonian, Late Pennsylvanian and
Permian)
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• Structural Trap
• upward folding of sedimentary rock strata
• impermeable layers overlie more permeable strata
• oil and gas are less dense than water and become
  trapped at the top of dome or anticline structures

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United States of America Energy Budget
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Petroleum (Crude Oil)

• liquid composed of hundreds of hydrocarbon
  compounds
• compounds are separated from one another by
  petroleum refining
• petrochemicals are used in the production of
  fertilizers, plastics, paints, pesticides,
  medicines, and synthetic fibers

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Synfuels

• synthetic fuels that can be used in place of
  natural gas and oil
• tar sands
• oil shales
• gas hydrates
• liquified coal
• coal gas

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Coal Gasification

• synfuel technology in which coal is used to
  produce methane (CH6), a combustible gas
• methane burns more cleanly than coal
• gasification removes sulfur

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Earthquake - a vibration produced by the rapid
release of stored energy. The focus is the
source of the quake, typically on a fault or
plane of slippage in the Earth's crust The
epicenter is the point on the Earth's surface
immediately above the focus, determined from the
seismic waves generated by the quake.
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Earthquake Magnitude

• Richter Scale (quantitative and based on
  amplitude of seismic waves)
• Mercalli Scale (Modified Mercalli Intensity
  Scale) is semi-quantitative and based on damage
  caused by the quake.

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J.C. Penney store destroyed in Anchorage, AK
destroyed by the "Good Friday" earthquake in
1964.
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Twisting of steel frames and disintegration
of concrete blocks
Local uplift of shorelines (up to 1 m)
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Large earthquakes in central Mexico (1985, 2003)
occur due to transform motion at a "Triple
Junction" situation like that in California.
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Mexico City was built on a drained lake basin.
Even though the city is over 400 km east of the
epicenter on the west coast, liquefaction of the
lake deposits resulted in subsidence and severe
shaking during the 1985 event.
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Shattered windows caused by twisting motion in
a Mexico City building, 1985
Undamaged buildings with vertical steel frames
next to completely demolished structures.
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Buildings vibrated against one another because
the seismic wave periods coincided with the
spacing of storeys.
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1989 Loma Prieta Earthquake
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Effects of 1989 Loma Prieta earthquake on the
Cypress Freeway in Oakland, CA
Seismic shaking is much greater in unconsolidated
sediment, in more saturated materials, and in
materials with laminar bedding.
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The earthquake of January, 1995 in Kobe, Japan
occurred near a "Triple Junction" where transform
plate motion occurs inboard of the plate
boundary.
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Landslide where faulting destabilized the
hillslope.
Paved roads cracked and offset several meters.
Offset of agricultural terraces
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Liquefaction of landfill and estuarine muds
Suspension Bridge pylon offset a meter.
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Intraplate Seismicity (New Madrid Zone)
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Prediction based on Past Frequency?
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Prediction based on "Gaps" with stored energy
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