Intro to Earth’s structure and Plate Tectonics

Shape of the Earth Gravity Rotation Oblate Spheroid

Refraction and reflection of seismic body waves - ray paths Seismic ray paths if Earth were homogeneous Seismic ray paths in a layered Earth

Inside the Earth

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Plate Tectonics Unified the study of the Earth (geology,seismology, marine geophysics,…) Why is the Earth restless? (earthquakes, volcanoes, mountain ranges) Answers “old” questions: Why do earthquakes and volcanic eruptions occur in specific areas?

Mechanical Layers Lithosphere –Crust and mantle –~100 km thick –Hard –Crust floats on top Asthenosphere –Soft –~300 km thick the principle of isostasy

Tectonics is the term we use in geoscience to represent the formation of folds, fractures, faults, etc. in rocks. By plate we really mean a “shell” on Earth’s surface that is about km thick and includes all of the crust, and the uppermost part of the mantle.

Compare oceanic and continental crust mantle

Plate Tectonics Says that the earth’s crust and upper mantle are composed of several large, thin, relatively rigid plates that move relative to one another Plate Tectonics is the term for the processes associated with the creation, movement,and destruction of the plates.

Lithosphere plates are large slabs of the crust and upper mantle that move horizontally relative to one another. Velocities in cm/yr Keller, 2002

zoom in on U.S.-west coast

Keller, 2002 Plate tectonics is the overarching model which allows us to understand many global phenomena observed within, on, and above the solid earth

Plate boundaries and earthquakes Nasa cumulative earthquakes

3 types of plate boundaries 1: divergent plate boundary a) mid-ocean riftb) continental rift a continental rift turned mid-ocean rift Iceland = a mid-ocean rift above water!

Iceland: a mid-ocean rift above water! 1: divergent plate boundary

Krafla, 1980 Thingvellir: site of first parliament in 930 A.D. Iceland: a mid-ocean rift above water! 1: divergent plate boundary

Iceland: a mid-ocean rift above water! 1: divergent plate boundary

Oman Ophiolite A former mid-ocean ridge now on land

Oldoinyo-Lengai eruption, 1966 East-African Rift Zone: a continental rift 1: divergent plate boundary

Rifting earlier in Earth’s history The breakup (and rotation of Africa and S-America)

3 types of plate boundaries 2: convergent plate boundary subduction zone a) ocean-continent

Examples of subduction zone products Turrialba Volcano in Costa Rica Photo by Regina Small, student in this class (GEO 1001 Sec 002 – spring 2006)

Examples of ocean-continent subduction zone products Mt. St. Helens (January, 23, 2006 – Dave Sherrod, USGS) Mt. St. Helens, spring 1980 Cascades volcanism

East Depth of Earthquakes in subduction zones Cross-section through Japan area depth 200 km 400 km Pacific Plate Eurasia Plate 200 km400 km 0 km West

Limestone in the Andes In addition to subduction and volcanism there can be uplift of crust due to convergent plate motion

2: convergent plate boundary (continued) S N India Tibetan Plateau Mt. Everest b) continent-continent

Himalayas – the result of the convergence of two continental plate boundaries Mt. Everest

3.) Transform Boundary (Strike Slip Faults)

Strike-slip fault Alpine fault, New Zealand

Nasa Cumulative volcanic eruptions

Plate Boundaries also uplift