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Frequency Tables and Histograms

Create and read data from histograms

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Credit: Masahiko Ohkubo
Source: http://www.flickr.com/photos/mah_japan/4478740217/
License: CC BY-NC 3.0

How many earthquakes do you think occur during one calendar year? According to the United States Geological Survey (USGS), the answer is several million. That is a lot of earthquakes! On the news, we only hear about a small fraction of these earthquakes. Millions of tremors go undetected or unreported because they do not cause much damage to human lives or property.

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Seismologists are scientists who study earthquakes. They measure the magnitude of earthquakes using the Richter scale or the moment magnitude scale. The numbers along the scale increase with the magnitude of the quake. To help people understand seismological data, scientists often use visual aids. For example, the USGS website features a frequency table displaying the average annual frequency of earthquakes by magnitude. The table shows that an estimated 1,300,000 earthquakes of magnitude between 2.0 and 2.9 occur annually. On average, only about one earthquake of a magnitude of 8.0 or higher occurs in a single calendar year. One glance at the table reveals that average frequency decreases as magnitude increases and that earthquakes of strong magnitude are extremely rare.

Credit: USGS
Source: http://earthquake.usgs.gov/earthquakes/eqarchives/year/graphs.php
License: CC BY-NC 3.0

To report the estimated number of deaths caused by earthquakes per year, the USGS website uses bar graphs, such as the one colored red above, which depicts data from 2010-2012. You can see that the year 2010 has the highest bar. Do you remember hearing about a deadly earthquake that year? On January 12, 2010, the country of Haiti experienced a disastrous magnitude-7.0 quake that claimed more than a hundred thousand lives. Research by seismologists is essential to understanding and better preparing for the devastating effects of earthquakes around the world.

See for yourself: http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

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The other (non-red) bars in the chart above report the number of earthquakes per year at different magnitudes from 2010-2012. Use the graph’s data to create a histogram that shows the total number of earthquakes in each magnitude interval (6.0-6.9, 7.0-7.9, and 8.0-8.9) during this time period.

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Image Attributions

  1. [1]^ Credit: Masahiko Ohkubo; Source: http://www.flickr.com/photos/mah_japan/4478740217/; License: CC BY-NC 3.0
  2. [2]^ Credit: USGS; Source: http://earthquake.usgs.gov/earthquakes/eqarchives/year/graphs.php; License: CC BY-NC 3.0

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