This enables them to calculate the distance the earthquake is from the seismograph.įirst slide details. Then they compare the difference in arrival times of the S waves. To locate the epicenter of an earthquake, we need to look at seismograms from three different recording stations.Įxperts compare the difference in arrival times of the P waves at the different stations. The resulting pattern, or seismogram, reveals to experts: Measures the total energy released by an earthquake. Modern versions are all computerized and instantly record activity at the seismic station. The Richter and moment magnitude scales often give very similar measurements. An increase in one integer means that 30 times more energy was released, while two integers means that 1,000 times the energy was released released. Older versions are anchored to the ground and have a pen attached to them, so when the Earth moves during a quake the device moves and the pen makes zigzag tracings on paper. Like the Richter scale, the moment magnitude scale is logarithmic. ![]() The waves are measured on sensitive instruments called seismographs. It accurately measures larger earthquakes, which can last for minutes, affect a much larger area, and cause more damage. MMS measures the movement of rock along the fault. Seismologists compare the arrival times of P waves and S waves at seismic stations to determine a quake's location. Step 1: calculate moment Step 2: convert moment to magnitude Give other features for the moment magnitude scale Other features are that there is a Logarithmic scale: increase of 1 on scale signifies a 10x increase in energy Magnitude 2.5 or lower cannot be felt by humans Largest recorded instrumentally: M 9.5 in S. Today, earthquake magnitude measurement is based on the Moment Magnitude Scale (MMS). Surface waves follow at the slowest speed, causing intensive damage as they move along the Earth's surface. It was defined in a 1979 paper by Thomas C. Secondary waves (S waves) move slower than P waves and vibrate at right angles to the direction of wave travel. The moment magnitude scale ( MMS denoted explicitly with Mw or Mw, and generally implied with use of a single M for magnitude 1) is a measure of an earthquake 's magnitude ('size' or strength) based on its seismic moment. ![]() Primary waves (P waves) travel at the fastest speeds and spread through the crust from the hypocenter, alternately squeezing and stretching the rock as they travel through it. When the quake begins, seismic waves travel rapidly outward in all directions. The epicenter is the point on the surface directly above the hypocenter. The hypocenter (or focus), the place where the movement first occurred on the fault, can be hundreds of kilometers below the Earth's surface or just beneath it. Sorry, your browser doesn't support embedded videos.
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