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Producing a "Scattergram" Signature for Your Seismic Station

Determining the magnitude and distance of seismic events your seismic station can differentiate.

Indiana Earth and Space Science I Standards addressed in this project:

Tom Rademaker - Oak Hill High School

INTRODUCTION

This project is designed for schools which are currently operating their own digital seismic station or monitoring another station over the internet. Every seismic station is uniquely designed. The local geology, type of instrument, the presence and design of a supporting pier, and background "noise", all influence the ability of a seismic station to "pick up" seismic events. In addition, the direction and depth of a seismic event, may influence the ability of a seismic station to recognize those waves. This project will enable students to analyze how well designed their station is, how local geology influences the operation of their station, and compare their station to other stations. The results of this project could introduce many possible research possibilities as well.

DESCRIPTION

The project requires monitoring streaming seismic data on a regular basis, collecting event data, and possibly using a spreadsheet program to help analyze the collected data. Any seismic event recognized in the raw (unfiltered) data will be noted, the magnitude and distance from the station determined, this data will then be recorded in a spreadsheet program for later analysis, or placed on a classroom graph for immediate display.

PROCEDURE

(It is necessary that students be able to recognize a seismic event on the streaming data before they begin this project. This is best accomplished by pointing out the "signature" of a seismic event as they occur. The characteristic waveforms are not difficult to recognize if they are pointed out.)

1. A display of the streaming data from your station must be available on a daily basis. SCREAM! has the capability of displaying 24 hours of data from your station. A Drumplot display could be used but the waveforms are not displayed as well as in SCREAM!.

2. When a seismic event is recognized the students will then determine the magnitude, location, and depth of the event by noting the time of the event and looking at the NEIC list of recent events here. The distance of the event from the station can be determined by using the Java Script Calculator below.

Solving for Great Circle distance with VB Script

Great Circle distance Calculator Java Script

Coordinates must be entered in decimal degrees of longitude and latitude. Longitude for the western hemisphere and latitude for the southern hemisphere are expressed as negative values.

Point 1
Latitude
Longitude
Point 2
Latitude
Longitude

km

3. Either input all the data in a spreadsheet program for later analysis or use a large classroom graph constructed by hand to watch your station "signature" develop as you collect data. Initially we will be plotting magnitude on the vertical axis and distance on the horizontal axis. This should eventually create a scattergram consisting of data points in a diagonal area in the upper left area of the graph. The station "signature" then would be the line defining the lowest magnitude events seen at each distance.

EVALUATION

This project was designed as a long term cooperative group activity. As such, formal evaluation would be fairly limited. The project does allow the opportunity to reinforce concepts which are formally evaluated however. Examples include seismic wave identification, data collection and analysis, scientific tools and their uses, and many other areas.

EXTENSION

It is anticipated that deviations from the norm will be encountered during this project. Seismic events outside of the expected magnitude/distance range will probably be seen, and seismic events that should fall within the limits of a stations capabilities will be missed. These apparent anomalies present excellent research possibilities for individual students. Things such as the depth or direction of a seismic event, local geology, or even constructive or destructive interference of background "noise" could be investigated.

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