![]() ![]() Time is indicated on the horizontal portion (or x-axis) of the graph. The surface waves arrive just after the S-waves and are difficult to distinguish. If the earthquake has a shallow focus, the surface waves will be the largest ones recorded.įigure 7.40: These seismograms show the arrival of P-waves and S-waves. The surface waves arrive just after the S-waves. S-waves come in next and are usually larger than P-waves. The first waves to be recorded by the seismogram are P-waves since they are the fastest. First, there is a flat line, where there was no ground shaking. As with words on a page, the seismogram record goes from left to right. The wiggly lines that are produced in a seismogram clearly show the different arrival times of P- and S-waves (Figure 7.40). Seismograms contain information on how strong an earthquake was, how long it lasted, and how far away it was. This creates the squiggly lines that make up a seismogram (Figure 7.39).įigure 7.39: A seismograph that had recorded an earthquake is beginning to record another earthquake, likely an aftershock. As the earth shakes in an earthquake, the pen remains stationary but the drum moves beneath it. The pen is weighted so that it is suspended and not attached to the ground. Seismographs have a pen suspended from a stationary frame, while a drum of paper rotates beneath it. The data are then kept digitally on a computer. Modern seismometers record ground motions using electronic motion detectors. In the past, all seismometers were seismographs because they produced a graph-like representation of the seismic waves they received. Measuring Magnitude Ī seismometer is a machine that records seismic waves. Describe how earthquakes are predicted and why the field of earthquake prediction has had little success.Describe the different earthquake magnitude scales and what the numbers for moment magnitude mean.Describe how to find an earthquake epicenter.List the different types of seismic waves, their different properties and describe how seismologists can use them to learn about earthquakes and the Earth's interior.At this time, seismologists have not found a reliable method for predicting earthquakes. The currently accepted method is the moment magnitude scale, which measures the total amount of energy released by the earthquake. Over the past century, scientists have developed several ways of measuring earthquake intensity. ![]() At least three seismograms must be used to calculate where the epicenter is located. Seismograms tell seismologists how strong an earthquake is and how far away it is. ![]()
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