![]() These two scales often give very similar measurements.How does the amplitude of the largest seismic wave of a magnitude 5 earthquake compare with the largest wave of a magnitude 4 earthquake? How does it compare with a magnitude 3 quake? The amplitude of the largest seismic wave of a magnitude 5 quake is 10 times that of a magnitude 4 quake and 100 times that of a magnitude 3 quake.Įach scale has their benefits. An increase in one integer means that thirty times more energy was released. The amplitude of the largest wave increases ten times from one integer to the next. Moment magnitude is calculated from the area of the fault that is ruptured and the distance the ground moved along the fault.The Richter scale and the moment magnitude scale are logarithmic. The moment magnitude scale measures the total energy released by an earthquake. Today, the moment magnitude scale has replaced the Richter scale. Developed in 1935 by Charles Richter, this scale uses a seismometer to measure the magnitude of the largest jolt of energy released by an earthquake. Today these maps are still important and various seismological stations will create shake maps of the surface damage.With the invention of the seismograph station, the Richter magnitude scale was created. ![]() This scale is more qualitative in information because it’s based on visual damage and not the actual energy released by the earthquake. Earthquakes are described in terms of what nearby residents felt and the damage that was done to nearby structures. Since early in the 20th century, there have been three methods The oldest of the scales is called the Mercalli Intensity scale. People have always tried to quantify the size of and damage done by earthquakes. Seismic stations record ten earthquakes in this animation. Although useful for decades, this technique has been replaced by digital calculations. A third circle will intercept the other two circles at a single point. Using data from two seismographs, the two circles will intercept at two points. The epicenter is somewhere along that circle. The scientist then draws a circle with a radius equal to the distance from the epicenter for that seismograph. This animation shows how distance is determined using P, S, and surface waves. So the difference in the P and S wave arrival times determines the distance between the epicenter and a seismometer. The longer the time between the arrival of the P-wave and S-wave, the farther away is the epicenter. The amplitude of the waves can be used to determine the magnitude of the earthquake, which will be discussed in a later section.In order to locate an earthquake epicenter, scientists must first determine the epicenter distance from three different seismographs. If a seismogram records P-waves and surface waves but not S-waves, the seismograph was on the other side of the Earth from the earthquake because those waves cannot travel through the liquid core of the earth. In an earthquake, body waves produce sharp jolts, while rolling motions of surface waves do most of the damage in an earthquake. Surface waves are the slowest of all seismic waves, traveling at 2.5 km (1.5 miles) per second. Surface waves travel along the ground, outward from an earthquake’s epicenter. P-waves travel through solids, liquids, and gases. The two types of seismic waves described in “Plate Tectonics,” P-waves and S-waves, are known as body waves because they move through the solid body of the Earth. Seismologists use seismic waves to learn about earthquakes and also to learn about the Earth’s interior. The energy from earthquakes travels in seismic waves, which were discussed in the chapter “Plate Tectonics.” The study of seismic waves is known as seismology. The distance between waves from crest to crest (or trough to trough) is its wavelength. ![]() The height of a wave from the center line to its crest is its amplitude. Every wave has a high point called a crest and a low point called a trough. Physics shows us that energy is always transmitted in waves.
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