How to Calculate Epicenter

••• Gary S Chapman/DigitalVision/GettyImages

The epicenter is the point on the Earth’s surface immediately above the center of underground movement sensed as an earthquake. This movement sends out shock waves of many kinds, which move at different speeds. The different waves can be detected by sensitive instruments called seismographs.

From the time difference between the first recorded occurrence of different kinds of waves of the same earthquake, a scientist studying the seismograph record can determine the distance to the earthquake’s epicenter but cannot determine the direction. By using three or more seismographs, however, a scientist can triangulate a location.

    Measure the difference in arrival times between the first shear (s) wave and the first compressional (p) wave, which can be interpreted from the seismogram. Multiply the difference by 8.4 to estimate the distance, in kilometers, from the seismograph station to the epicenter.

    Open the compass until the gap equals the calculated distance to the epicenter. Draw a circle on a world map, centered on the location of the first station. The epicenter can lie anywhere on this circle.

    Repeat the calculation process for the distance from the second seismograph station, and draw a circle of the calculated radius on the map, centered on that station. This circle and the first will intersect at two points. The epicenter can be at either point.

    Repeat the calculation and drawing process for the third seismograph station. The three circles will meet at a common point, which is the epicenter.

    Things You'll Need

    • Seismograms from three different seismograph stations
    • World map
    • Compass for making circles

    Tips

    • A seismograph is an instrument that measures ground movement continuously. A seismogram is the record, usually on paper, that a seismograph produces. In real life, scientists use many more than three seismograph records to locate an earthquake's epicenter.

Related Articles

What Are Some Differences Between P & S Waves?
All Types of Tsunamis
What Astronomical Instrument Measures the Brightness...
How to Figure a Delta Angle
How to Calculate Angles Without a Protractor
How to Calculate the Force of Moving Water
How to Find the Vertices of an Ellipse
How to Determine the Length of a Shadow
How to Measure the Intensity of a Flood
How to Find Mass in Weight
How to Figure the Diameter of a Circle
How to Convert DIN HP to SAE
How to Find Euclidean Distance
What are Latitude & Longitude?
How to Find the Radius of an Arc
How to Calculate the Diameter of a Circle From a Linear...
How to Calculate the Winter Solstice Sun Angle
How to Calculate Tangential Speed
How to Read Oscilloscopes
How to Calculate a Circular Area

Dont Go!

We Have More Great Sciencing Articles!