A helicorder is a device which records signals from a seismometer. The traditional helicorder records the seismic signal on a piece of paper which is wrapped around a rotating drum. A pen draws the signal on this paper. Each line of data represents a specific, constant time interval: for example, 1 hour per line.

The seismogram is “read” like a book, from left to right and top to bottom (this is the direction that time increases). As with a book, the right end of any horizontal line “connects” with the left end of the line below it. Each line represents 15 minutes of data; four lines per hour.

An earthquake has just hit. A good seismograph can detect seismic waves from an earthquake thousands of kilometers away. In this activity, you will learn how to understand and get information from a seismogram.

to travel 5,000km? Go to the chart! Go to the chart! The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them.

For example, this graph tells you that if an earthquake epicenter is 4000 km away, the P-wave will take 7 minutes to get to you.

Instructor’s Copy

In a solid such as rock, the primary wave can travel at 5 km/sec; it would take 400 seconds, or about 6.7 minutes to travel 2,000 km. If traveling through water, the wave travels at about 1.45 km/sec and would need 1,379 seconds (23 minutes) to travel 2,000 km.

11 minutes