Your reports fill in gaps between instruments that record shaking. They also contribute to more complete earthquake assessments and provides valuable data for further earthquake research. There are two ways to describe the size of an earthquake.
Magnitude characterizes the amount of energy released by an earthquake at its source. The energy released is determined by measuring the amplitude or duration of earthquake waves recorded by a seismometer. Magnitude numerical values are calculated using a modern formulation of the Richter Scale. These values are assigned to an earthquake, independent of location.
Intensity describes the effects of shaking on people and structures. An earthquake's intensity is determined by collecting felt reports or by measuring the actual shaking of the ground. Intensity values are assigned using the Modified Mercalli Intensity Scale. Unlike magnitude, intensity may vary greatly from one place to another for a given earthquake.
Intensity values are usually, but not always, highest near an epicenter and decrease with distance from the source. The moment magnitude scale measures the movement of rock along the fault, and accurately measures larger earthquakes, which can last for minutes and affect a much larger area; the Richter scale did not accurately record such quakes, Jones said. The U. Geological Survey has a calculator that can help you make these calculations.
So, for instance, a magnitude 8. Magnitude is important, but a key factor is where a quake strikes. The ones most people care about strike under or near heavily populated areas. Generally, earthquakes of magnitude 6 and above are the ones for concern. When nearby, they can cause shaking intensities that can begin to break chimneys and cause considerable damage to the most seismically vulnerable structures, such as non-retrofitted brick buildings. Earthquakes of magnitude 7 and above can overturn heavy furniture and inflict considerable damage in ordinary buildings.
That earthquake was a magnitude 6. But the shaking intensity varied by where you were when it hit. Yet the downtown Los Angeles region got far less intense shaking from the same earthquake — intensity 6 or 7, where damage is negligible in buildings of good design and construction. Vast swaths of Southern California would feel intensity 10 shaking, or extreme shaking — an earthquake that no one alive today has experienced in this region.
Intensity Extreme — Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent. Intensity 9: Violent — Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations. Intensity 8: Severe — Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse.
Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Intensity 7: Very strong — Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.
Intensity 6: Strong — Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.
Intensity 5: Moderate — Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop. Intensity 4: Light — Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. What are those booms I sometimes hear before or during an earthquake?
Of course, most "booms" that people hear or experience are actually some type of cultural noise, such as some type of explosion, a large vehicle going by, or sometimes a sonic boom, but there have been many reports of "booms" At what magnitude does damage begin to occur in an earthquake?
It isn't that simple. There is not one magnitude above which damage will occur. It depends on other variables, such as the distance from the earthquake, what type of soil you are on, etc. That being said, damage does not usually occur until the earthquake magnitude reaches somewhere above 4 or 5. Learn more: Earthquake Magnitude, Energy Release, Filter Total Items: 5. Year Published: Shaking intensity from injection-induced versus tectonic earthquakes in the central-eastern United States Although instrumental recordings of earthquakes in the central and eastern United States CEUS remain sparse, the U.
Hough, Susan E. View Citation. Year Published: The ShakeOut Scenario This is the initial publication of the results of a cooperative project to examine the implications of a major earthquake in southern California. Jones, Lucile M. Year Published: Did you feel it? Wald, David J. Did you feel it? Boatwright, J. Year Published: Earthquake Shaking - Finding the "Hot Spots" A new Southern California Earthquake Center study has quantified how local geologic conditions affect the shaking experienced in an earthquake.
Field, Edward H. Filter Total Items: 6. Date published: April 24, Date published: March 28, Date published: March 1, Attribution: Science Application for Risk Reduction. Date published: October 17, Attribution: Natural Hazards. Date published: May 18, Date published: January 16, Filter Total Items: 9.
List Grid. January 25, Alerts could save lives and properties but several challenges remain. With millions at risk, why isn't full public alerting happening yet? February 13, May 20, March 30, Attribution: Region Alaska. March 15, September 25, Will the ground shaking in future earthquakes display similar patterns?
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