Earthquakes As Evidence of Plate Tectonics

Earthquakes as evidence of plate tectonics

Introduction:

Strong supporting evidence for plate tectonics can be found in the patterns formed by mapping earthquake activity across the globe. In this exercise you will be asked to plot the occurrence of earthquakes during a 5 year period (1991-1996), the data for 25 years and the occurrence of major earthquakes in historic times. You will create maps showing the occurrence and depth/magnitude of each event. You will also manually create a plot showing the patterns of earthquake depth across different types of plate boundaries.

Data and Methods:

There a number of sites out on the web that provide records of global earthquake events. and

Take a look at the link below which provides a description of the time period of coverage for contributing seismic networks.

What locations on earth have the best early records of earthquake events? Why?

What was a significant driving factor for the development of global seismic recording stations?

Why do the records show significant increases in seismic activity between the years 1965 and 1975?

From the histograms or from the ‘fact’ sheet, describe the relationship between magnitude and frequency for earthquakes.

Plotting the data:

The data for this exercise are for earthquakes that occurred between 1991 and 1996 and 1979 and 2006. Shape files have been created and are available from the Dr. Gaston’sweb site (

The data of interest are

Equake_mag5 (events greater than magnitude 5)

Equake_gtm7 (events greater than magnitude 7… the really big ones)

And Equake_lt6 (events less than magnitude 6)

Historical_earthquake (large events that have been estimated from historical accounts)

25year_equakegt5 (all earthquakes magnitude 5 and greater for the most recent ¼ century 1979-2006)

Volcano (a map of active volcanoes around the world)

Use Arc Explorer along with the shape files CNTRY92 and world30 to display these files. Choose appropriate views to save and include in your write up.

Analysis:

How do the patterns observed in you map support plate tectonic theory?

What biases are evidenced in the historical earthquake data? What is the cause of this bias in the data?

How many earthquakes magnitude 5 and greater occurred in the last 25 years?

Use the field ‘depth’ to symbolize the earthquake data. Create a cross section of earthquake locations/depths from the Pacific Ocean into the interior of South America near the Peru/Bolivian border. Explain this pattern. What are you seeing in the data? How does this provide support for plate tectonic theory?

Create a cross section of earthquake depth from the Pacific Ocean into southern California… or across the North Anatolian fault in Turkey, is the pattern different here? How might you explain this difference? Does this also provide support to plate tectonic theory?

Plot the volcano shape file along with the earthquake data. Indicate on your map places of high correlation and low correlation. What explains the areas of low correlation?

Explain the term ‘ring of fire.