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Earthquake Magnitude Calculator for the AS-1 Seismograph

Introduction:

Magnitude is an estimate of the energy release or size of an earthquake. The estimates are calculated from the amplitude of wave energy on a seismograph adjusting for the magnification of the seismograph and the distance of the seismograph station from the earthquake. Click here for more details and examples of magnitude calculation using the AS-1 seismograph. A detailed discussion about the different kinds of magnitudes can be found at the USGS site.

This earthquake magnitude calculator is designed for the AS-1 Seismograph. Specifications of the instrument can be found at web.ics.purdue.edu/~braile/edumod/as1mag/as1mag.htm. The description and examples presented here are for the AS-1 vertical component seismograph and the AmaSeis Software. The AmaSeis program connects the AS-1 seismograph to a computer running Windows, provides a continuous seismic record on the monitor, and includes several display and analysis tools. The seismograph records shown here were recorded using an AS-1 seismograph at West Lafayette, IN (Latitude 40.484°N, Longitude 86.881°W). Results of earthquake monitoring with an AS-1 seismograph and AmaSeis software, including epicenter-to-station distance calculations from S-P times and magnitude calculations, are illustrated at:

web.ics.purdue.edu/~braile/edumod/MagCalc/AS1Results.htm.

AS-1 Seismometer

Things to know before using the Calculator:

The calculator needs three inputs to measure the desired magnitude. The user must supply the Amplitude (in digital units; this amplitude is converted by the calculator to microns of ground displacement using seismometer characteristics determined by calibration of the seismometer), the Period (in seconds) and the Distance (in degrees, geocentric angle). The terms are briefly explained here. For more details, please visit the links shown above.

Epicentral Distance vs. Surface Distance

Click on the type of Magnitude to calculate:

Body Wave Magnitude (mb)

Surface Wave Magnitude (MS)

mbLg Magnitude - (1) 0.5°< D < 4° (2) 4°<= D <30°

(D=Distance in degrees)

Last modified October 19, 2004

Download an MS Word version of the entire AS-1 Magnitude Calculator document

Download a folder (~2.4MB) that contains a version of the AS-1 Magnitude Calculator that can be run locally on your computer. Last modified October 14, 2003. The download files will be called MagCalcLocal.exe.zip. It is a self-extracting executable file. Double click to open and unzip (of you don't have a zip program, go to http://www.winzip.com/ where you can download a free evaluation version). A folder called MagCalcLocal will be created. After placing this folder on your desktop and opening the folder, double click on MagCalc.htm and you will be able to perform all the magnitude calculations without being connected to the Internet. Of course to access links that are to Internet locations, you will need to be connected. The folder also contains an MS Word file that includes the entire AS-1 Magnitude Calculator document (instructions and examples).

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Developed by Lawrence W. Braile and Saptarshi Dasgupta, Purdue University, May, 2003. Funding for this development provided by IRIS and the National Science Foundation.