Earthquakes and Tectonics by luy15016


									                       Earthquakes and Plate Tectonics
                                Source: UAA GEOG 205 Lab Manual

     Name:                                                       Date:                    Per:


In this assignment, you will collect web-based earthquake data and link this data to plate tectonic
theory. You will then construct at least two charts to help analyze and interpret a fairly large data


Prepare a short report, summarizing your analyses and conclusions of the earthquake data you are
required to collect. In your report, discuss whether or not there are apparent relationships between
earthquake origins and earthquake depth and intensity. Make sure to include both of the charts
you are required to produce and a printout of the earthquake data and accompanying map.


Most earthquakes are the product of the movement of tectonic plates. The movement of these
plates is explained by the theory of plate tectonics. The theory of plate tectonics holds that the
crust is actually broken up into about 20 different crustal plates of various sizes. About 200
million years ago, most geologists believe, there was only one „super-continent‟, which has been
labeled by geologists as Pangaea. But, as the changing temperatures of the mantle caused large
„upwellings‟ of mantle to push against the underside of this continent it began to break up into
pieces. The continents are now „drifting‟ towards and away from one another. This drifting is all
powered by the upwelling of mantle towards the crust of the earth. When the various plates
collide, pull apart or push against one another, mountains are created.

According to the theory of plate tectonics, there are several key types of plate movement or
interaction that help to explain geology and earthquakes. The first of these movements is called
spreading (or divergent plate boundaries). This occurs where two plates are pulling away from
one another and forming a rift zone. These plates can be both continental and oceanic at their
point of spreading. The spreading of the North American plate away from the Eurasian plate has
formed the volcanic island of Iceland in the middle of the North Atlantic Ocean.

Subduction occurs where dense oceanic crust is slipping underneath continental crust or another
oceanic crust. Here the plunging crust is destroyed in the mantle. The Aleutian volcanoes are
created as the Pacific plate is „subducted‟ by the North American plate and melting crust rises to
the surface as magma.

Translation (also referred to as a transform fault plate boundary) occurs where two plates are
moving against each other in a lateral or sideways motion. The San Andreas Fault in southern
California is the margin between the Pacific plate and the North American plate where lateral
movement is taking place. And the Coastal Mountains are formed where plate grinding has
deformed the two plates.
Collision occurs where plate boundaries of continental crust collide and are driven upward by the
force of that collision. The Himalayan Mountains were formed by collision. In addition, there are
several other forms of movement that will not be addressed here.

The movement of tectonic plates directly causes most earthquakes. As plates move against one
another there are massive amounts of friction along the plate margins. Unless the plates slowly
„creep‟ against one another, thereby releasing friction energy constantly, energy is built up. The
seams along which this energy builds up are faults. Faults are the actual edges where plates come
together or the cracks in the plates themselves (these cracks are breaks in the plate, possibly
caused by plate movement). Occasionally, the built-up energy along one of these faults is too
much and the fault ruptures and the plates move, often quite violently, against one another. This
movement causes an earthquake. However, when we feel an earthquake what we experience is a
phenomenon known as elastic rebound: The movement of the plates causes the plates to vibrate
and shake after the rupture occurs. After a major rupture has taken place the plates settle
somewhat causing aftershocks.

Earthquake strength is determined by the Richter scale, which is based on the size of an
earthquake‟s waves. In addition to variation by strength, earthquakes can also vary by depth, due
in part to the type of plate movement that created the quake itself. In this lab you will explore the
relationship between earthquake strength, depth and tectonic origin.

How to proceed

For this lab, you will need your Geology textbook that has a map showing the tectonic plate
boundaries. You may also need to consult a basic world atlas (the library has a number of these).

At the National Earthquake Information Center‟s main web page (, click on
“Current Worldwide Earthquake List”. This will bring you to a list of all the recorded earthquakes
that took place during the last seven days. Note that it may have over 100 earthquakes listed!
Print this list and the map that accompanies it (bottom of page there is a link “Back to world
earthquake map”). Where are these quakes geographically? What parts of the world have the
most quakes?

Now, produce at least two charts. One of these charts will compare the tectonic origin of the earth
quakes to their depth. You will need to determine what the depth of each earthquake is and
compare that to whether it took place in a subduction, translation (ex: San Andreas), collision (ex:
Himalayas) or spreading zone. The chart will look something like this:

Depth           Subduction         Collision        Translation        Spreading         Unknown
0-33 km         # of quakes
33-70 km        recorded
70-150 km       in table
150-300 km
300-500 km
500-800 km
The second chart will compare Richter scale strength to tectonic origin

Richter        Subduction        Collision         Translation       Spreading       Unknown
0-3.9          # of quakes
4.0-4.9        recorded
5.0-5.9        in table

After you have constructed these charts, draw some conclusions as to the relationship between
earthquake depth, strength and the theory of plate tectonics. It may very well be that your
observations are inconsistent with what you know about plate tectonics.

Due: Monday, February 5

Worth 40 points

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