![]() how is earthquake magnitude measured?Īn earthquake has one magnitude unit. The seismograph produces a digital graphic plotting of the ground motion of the event. The digital recording is called a seismogram.Ī network of worldwide seismographs detects and measures the strength and duration of the earthquake’s waves. The seismograph produces a digital graphic recording of the ground motion caused by the seismic waves. A seismograph is the primary earthquake measuring instrument. ![]() When the Earth trembles, earthquakes spread energy in the form of seismic waves. Now, scientists use earthquake measurements that describe the physical effects of an earthquake rather than measurements based only on the height of a waveform recording. But for very large earthquakes, some magnitudes underestimated the true earthquake size. Years ago, all magnitude scales were based on the recorded waveform lengths or the length of a seismic wave from one peak to the next. Seismographic networks measure earthquakes by their magnitude, energy release and intensity. Practice Questions 2.You may not always feel the earth shaking, but California has earthquakes occurring all the time. Return to the main article: The Ultimate Earth Science Reviewer Download Article in PDF Format Test Yourself! 1. Spillage of hazardous chemicals from factories and chemical containment facilities is also a possible threat, such as the leakage of radioactive water from the Fukushima nuclear power plant during the 2011 Japan Earthquake. Coupled with broken water pipelines, even small fires can quickly spread and cause massive damages. Fires can also break out due to severed gas and electrical lines. Damage to Man-made Structuresĭepending on the material used and the way they were constructed, structures such as buildings, bridges, roads, dams, and others are susceptible to damage.ĭamage can range from cracks on the walls to the total destruction of property. Related: Midnight Shocker of ’76: Remembering The Deadliest Tsunami In Philippine History 3. Tsunamis are giant waves that are produced when a fault displaces a large slab of the ocean floor They are nearly undetectable in the open ocean, but once tsunamis reach shallow waters, wave height increases dramatically and can reach up to 30 m, like what happened in the 2004 Indian Ocean M w 9.1 Megathrust Earthquake in Sumatra, Indonesia. One of the most dangerous effects of earthquakes that originate offshore are tsunamis. These are oscillating waves that produce major fluctuations in the water level, depending on the strength of the earthquake. In enclosed bodies of water such as lakes or reservoirs, waves called seiches may occur. These can cause flooding in populated areas which may result in property damage and harm to life. Flooding and Water-related Hazardsĭuring and after an earthquake, large water pipes underground and dams may be damaged and fail. While these events can occur naturally, they are usually aggravated by earthquakes. Liquefaction is similar to subsidence but occurs when sediments are saturated with water. Subsidence is the sudden sinking of the Earth’s surface due to the movement of the earth underneath. They can have devastating effects especially in heavily populated areas near hillsides or mountain slopes. These are caused by ground shaking during an earthquake.Ī landslide is a form of mass wasting where large amounts of earth move down a slope under the influence of gravity. Depending on the destructive force of the earthquake, it can cause the following events: 1. Earthquake-related HazardsĪs we all know, major earthquakes can have devastating effects on both living and nonliving things. The Moment Magnitude scale proves to be more effective in measuring stronger earthquakes (M w 5 and above) than the Richter scale.Ī combination of shearing forces and tensional or compressional forces would result in an oblique-slip fault, pictured above. Now, seismologists use the Moment Magnitude (M w) scale which measures the total amount of energy released by an earthquake. The magnitude refers to the quantitative measurement of the amount of energy released at the earthquake’s source.īefore, the most commonly used scale for measuring the magnitude is called the Richter Scale, which measures the amplitude of the largest seismic wave on a seismogram. This scale was developed by the Philippine Institute of Volcanology and Seismology (PHIVOLCS) as a response to the devastating 1990 Luzon Earthquake. In the Philippines, however, the PHIVOLCS Earthquake Intensity Scale (PEIS) is used. In countries like the United States, the Modified Mercalli Intensity Scale is used. The intensity refers to the qualitative measurement of the amount of ground shaking at a certain location, depending on the amount of damage to property, life, and nature.ĭifferent intensity scales are used in different countries.
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