In an earthquake, both S (transverse) and P (longitudinal) waves propagate from the focus of the earthquake. The focus is in the ground radially below the epicenter on the surface. Assume the waves move in straight lines through uniform material. When waves arrive the seismograph detect the arrival times. (a) How can we find the distance to the focus of the earthquake? (b) How many seismograph stations would we need to locate the focus unambiguously?
The three-dimensional waves that travel out from a point under the Earth’s surface at which an earthquake occurs are of both types, transverse and longitudinal. The longitudinal waves are the faster of the two, traveling at speeds in the range of 7 to 8 km/s near the surface. They are called P waves, with “P” standing for primary, because they travel faster than the transverse waves and arrive first at a seismograph (a device used to detect waves due to earthquakes). The slower transverse waves, called S waves, with “S” standing for secondary, travel through the Earth at 4 to 5 km/s near the surface.
In an earthquake, both S (transverse) and P (longitudinal) waves propagate from the focus of the earthquake. The focus is in the ground radially below the epicenter on the surface. Assume the waves move in straight lines through uniform material. When waves arrive the seismograph detect the arrival times. (a) How can we find the distance to the focus of the earthquake? (b) How many seismograph stations would we need to locate the focus unambiguously?
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