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97952 |
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Date: April 08, 2024 at 10:45:13
From: ryan, [DNS_Address]
Subject: Do we still use the Richter Scale to measure earthquakes? |
URL: https://thehill.com/changing-america/enrichment/science/4576713-do-we-still-use-the-richter-scale-to-measure-earthquakes/ |
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Do we still use the Richter Scale to measure earthquakes?
You might be surprised.
by Lara Bonatesta | Apr. 08, 2024
Story at a glance
One of the most commonly known earthquake-measuring tools is the Richter Scale, but the system is no longer used today.
The Richter scale was replaced in the 1970s by other magnitude scales that are more accurate.
Even though it’s outdated, the term is still used often when discussing earthquakes.
(WHTM) – Residents along much of the East Coast felt shaking Friday morning as a 4.8 magnitude earthquake struck New Jersey.
One of the most commonly known earthquake-measuring tools is the Richter Scale, but the system is no longer used today.
Earthquake reported in New Jersey, tremors felt in Pennsylvania
In fact, the Richter scale was replaced in the 1970s by other magnitude scales that are more accurate.
Even though it’s outdated, the term is still used often when discussing earthquakes.
According to the United States Geological Survey (USGS), the system was first introduced in the early 1930s by American seismologist and physicist Charles Richter — who collaborated with German-American seismologist Beno Gutenberg — to measure the size of earthquakes occurring in southern California.
The logarithmic earthquake magnitude scale used relatively high-frequency data from nearby seismograph stations, according to the USGS, but as more stations were installed around the world, scientists began to notice limitations.
Is a 4.8 earthquake big; how are earthquakes measured?
Among the problems was that the scale was only valid for certain frequencies and distances.
In response, a new magnitude system was developed, known as moment magnitude (Mw). This system, according to the USGS, is more reliable for determining earthquake size, particularly for bigger earthquakes.
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97955 |
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Date: April 11, 2024 at 19:47:19
From: eaamon, [DNS_Address]
Subject: Re: Do we still use the Richter Scale to measure earthquakes? |
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they changed to the moment magnitude in thee 1990s. this after the
great Alaskan quake was up graded to 10.3.
a year earlier a 10.5 was registered in South America.
it was a hundred miles deep.
no one felt it.
I still have the newspaper with the headlines.
it is my belief they changed it due to Y2K coming up and predictions of a
coming 10.5 would hit.
today nothing should go/could go above a 10.0, this to poo poo predictors.
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97953 |
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Date: April 08, 2024 at 13:04:17
From: Jeff/Lake Almanor,CA, [DNS_Address]
Subject: Interesting how Duration affects Magnitude |
URL: https://www.usgs.gov/faqs/what-was-duration-earthquake-why-dont-you-report-duration-each-earthquake-how-does-duration |
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What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?
The duration of an earthquake is related to its magnitude but not in a perfectly strict sense. There are two ways to think about the duration of an
earthquake. The first is the length of time it takes for the fault to rupture and the second is the length of time shaking is felt at any given point (e.g.
when someone says "I felt it shake for 10 seconds" they are making a statement about the duration of shaking). The duration of fault rupture is related
to both how long it takes for a spot on the fault to slip (which seems to be quite fast) and the time it takes rupture to proceed along a fault.
You have to think of an earthquake as an area on a fault rather than just a point. It starts at a point and then the rupture propagates along the fault at
around 2 kilometers or so per second. So the larger the area of the fault that ruptures, the longer the duration of the earthquake. And larger magnitude
earthquakes have larger fault areas. So there is a general relationship between duration and magnitude.
The reason we don't list this sort of duration on the Latest Earthquake website is that figuring out how long an earthquake took to rupture is still a
research project that takes some time rather than an automated process. The duration of shaking at a point on the ground depends on how long the
earthquake took to occur and how the waves move through the ground to that point. If there are a lot of reflections and resonances near the point (for
instance in a sedimentary valley), the shaking will last longer. In an area without resonances (for instance on a hard block of rock), it will last a shorter
time.
You must also specify a duration of shaking over a given level. We can actually detect the shaking from the very largest earthquakes for weeks after
they occur, but no one would say that they felt it for that long. So the duration of shaking is a very complex topic. We actually do use the duration of
shaking to estimate the magnitude for some small earthquakes. If you see a "Md" or "duration magnitude" on the Latest Earthquake webpages, this is
what has been done.
This is much like having someone yell, counting the echos, and then estimating how loud they yelled from how many echos you could hear. Finally, the
damage to a given structure will depend both on the amplitude of the shaking and its duration. How to best combine these quantities into an estimate
of the amount of damage is ongoing research.
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