Determining Magnitudes of Historical Earthquakes

• Introduction
• Estimating the Magnitude of a Historical Earthquakes
• Useful Concepts
• Important Questions to Consider
• Historical Earthquakes

Introduction

There is a great deal of data on earthquakes that occurred too early in history to have been recorded by seismographs. These data include written accounts and drawings in newspapers, scientific journals of the times, and personal letters. People who experienced the quake directly often wrote accounts that describe the damage and their observations of changes in geography afterwards.

Can you determine the magnitude of a historic earthquake using this kind of information? Scientists have worked on this question for many years. Currently a group of seismologists at Boston College, Massachusetts, have been studying this question for New England.

Back to Table of Contents

Estimating the Magnitude of a Historical Earthquake

Choose a historic earthquake for which you believe you will be able to gather a great deal of anecdotal (narrative) information. One idea is to choose a local quake, so that your library will be able to provide accounts in old, local newspapers and in books on local history. If you cannot find a local quake strong enough to appear in newspaper articles, choose a stronger historical quake elsewhere in the country. At the end of this document we've listed a number of historical earthquakes that have occurred within New Zealand, and important historical quakes that occurred near large cities in the US. Perhaps a student in another PEPP classroom will be able to work with you on this project.

NOTE: The earthquakes listed are only suggestions. Research the history of your region/country to select an earthquake of your choice if you wish.

You will also need similar data from more recent earthquakes that were recorded by seismographs and whose magnitudes have been calculated (by seismologists or by you). From these data, you can get an idea of how the measured magnitudes of earthquakes tend to relate to anecdotal observations of the effects of the quakes.

Back to Table of Contents

Useful Concepts

You can use the PEPP Learning Library to help get you started on these concepts.

• The Modified Mercalli Intensity Scale, which rates earthquakes' intensity based on observed accounts, including damage reports.
• The Felt Area of an Earthquake, or the area of the earth's surface in which a given earthquake was felt by humans.

Back to Table of Contents

Important Questions to Consider

As you design your research, consider the following questions:

• Where will you look for anecdotal data? Your local library may have copies of old newspapers, histories of your town, and other documents such as letters and diaries.
• How will you determine whether enough data are available about a particular earthquake?
• How will you decide which more recent earthquakes you should use in the comparison group? Should they be similar to the historical quake in particular ways? If so, in what ways?

Back to Table of Contents

Historical Earthquakes

New Zealand earthquakes:
The source of these earthquakes is the 'Atlas of Isoseismal Maps of New Zealand Earthquakes,' by G.L. Downes (available from the Institute of Geological and Nuclear Sciences).

1848, Oct 15, Marlborough
1868, Oct 18, Cape Farewell
1888, Aug 31, North Canterbury
1893, Feb 11, Nelson
1904, Aug 08, Cape Turnagain
1914, Oct 06, East Cape
1931, Feb 02, Hawke's Bay
1934, Mar 05, Pahiatua
1942, Jun 24, Wairarapa
1953, Sep 29, Bay of Plenty

United Stated earthquakes:
The source of these earthquakes is USGS publication 41-1.

Northeastern US:
1884, Aug 10, Near New York city
1904, Mar 21, Southeastern Maine

Eastern US:
1886, Aug 31, Charleston SC

Central US:
1811, Dec 16; 1812, Jan 23, Feb 7, New Madrid (heavily researched already)
1891, Jan 8, Rusk, Texas

Western US:
1857, Jan 9, near Fort Tejon, Cal.

Back to Table of Contents