Earthquakes & Subduction Zones Lab Report

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  • Topic: Plate tectonics, Convergent boundary, Subduction
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  • Published : March 27, 2013
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Earthquakes and Subduction Zones Lab
Amy Paret
Mrs. Igo
9th Grade
Periods 3 and 4 Even
Date: 2/14/13

Background Research:
This lab uses earthquake data to construct profiles of two convergent boundaries: the Tonga Trench and the Peru-Chile Trench. Where two tectonic plates converge, if one or both of the plates is an oceanic lithosphere, a subduction zone will form. When crust is formed at a mid-ocean ridge, it is hot and buoyant meaning it has a low density. As it spreads away from the ridge and cools and contracts, or becomes denser, it is able to sink into the hotter underlying mantle. When two oceanic plates collide, the younger of the two plates, because it is less dense will ride over the edge of the older plate. The density of the rock that makes up the subducting plate determines the way in which a plate behaves. A plate with a greater density subducts into the mantle faster and at a steeper angle than a plate with a lower density. The age of the crust involved in the subduction also affects the rate at which it subducts. Older crust is cooler and denser therefore it suducts at a steeper angle and faster than new crust at a subduction zone. The three key features associated with a subduction zone are a deep ocean trench, a volcanic arc on the overriding plate parallel to the trench, and a plane of earthquakes, shallow near the trench and descending beneath and beyond the volcanic arc. Most earthquakes occur at tectonic plate boundaries. The largest earthquakes are associated with subduction zones because they have long continuous fault lines. The depth of its focus can classify an earthquake. Earthquake depth range is divided into three zones: shallow, intermediate, and deep. Shallow earthquakes are between 0 to 70 km deep, intermediate earthquakes are between 70 to 300 km deep, and deep focus earthquakes have foci at more than 300 km.

Terms Introduced and Defined:
- Subduction zone: the place where two lithospheric plates come together, one riding over the other - Density: mass per unit volume
- Earthquake: the result of a sudden release of energy in the Earth's crust that creates seismic waves.
- Subduction: the process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other
- Plate boundaries: found at the edge of the lithospheric plates and are of three types, convergent, divergent and transform
- Deep ocean trench: a portion of the Earth's crust in which a tectonic plate is being sub-ducted (pushed down) below another plate
- Shallow earthquake: more damaging than deeper earthquakes due to there being less rock to absorb the shaking
- Deep focus earthquakes: occur within the subducting oceanic plates as they move beneath the continental plates

Hypothesis:
The East Pacific Rise Material at the two convergent boundaries: the Tonga Trench and the Peru-Chile Trench is older than the crust created at the East Pacific Rise but the Tonga Trench material is older than the Peru-Chili Trench material.

Materials:
- Earthquakes and Subduction Zones Lab
- Sharpened pencil with eraser
- Graphing Paper
- Ruler
- Calculator

Procedure:
1. Take out a sharpened pencil, ruler, blank sheet of graph paper, and a calculator. 2. Pick up the earthquakes and subduction zones lab from your teacher. 3. Read the background information.
4. Read the hypothesis information.
5. View Figure 1 at the top of the Lab.
6. Form a hypothesis about the relative ages of the East Pacific Rise material at the two convergent boudaries: the Tonga Trench and the Peru-Chile Trench. 7. View table 1.
8. Divide your graph paper into two sections.
9. Label the left section Tonga Trench and the right section Peru-Chili Trench 10. Draw a vertical line (y-axis) and a horizontal line (x-axis) on each section of the graph paper. 11. Label both vertical lines (y-axes) Focus Depth (km).

12. Label both horizontal lines (x-axes) Longitude...
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