Richter Scale

[CBL4]

Does anyone know if the Richter scale estimates from the past correspond well to the present? In other words, if an earthquake from 1932 is described as being 7.5 on the Richter scale, what are the chances it would now be described roughly the same?

The Economist had an article on earthquakes in the India, Pakistan area. They have chart of "Notable" earthquakes. From 1897 to 1950 there 10 earthquakes greater than 7 on the scale with 6 of these greater than 8. From 1951 to the present, there have only been 2 greater than 7 and none greater than 8.

The article says:

Across the Himalayas there is what seismologists call a “slip deficit”—a lack of earthquakes to release the stress that is known to be accumulating.

http://www.economist.com/displaystory.cfm?story_id=5019727
Clearly this is possible but it also possible that the older estimates are greater than the recent one.

CBL

 

[Iamme]

Does anyone know if the Richter scale estimates from the past correspond well to the present? In other words, if an earthquake from 1932 is described as being 7.5 on the Richter scale, what are the chances it would now be described roughly the same?

The Economist had an article on earthquakes in the India, Pakistan area. They have chart of "Notable" earthquakes. From 1897 to 1950 there 10 earthquakes greater than 7 on the scale with 6 of these greater than 8. From 1951 to the present, there have only been 2 greater than 7 and none greater than 8.

The article says:

http://www.economist.com/displaystory.cfm?story_id=5019727
Clearly this is possible but it also possible that the older estimates are greater than the recent one.

CBL

I'd say it has stayed the same just because of the name "Richter". There must have been something established with Richter...a specific meassured unit. I'd say the same would hold true with decibles, barametric pressure readings, inches in Hg, etc.

 

[GodMark2]

Does anyone know if the Richter scale estimates from the past correspond well to the present? In other words, if an earthquake from 1932 is described as being 7.5 on the Richter scale, what are the chances it would now be described roughly the same?
{...}
Clearly this is possible but it also possible that the older estimates are greater than the recent one.

CBL

Short answer: They will be roughly the same strength if they have the same Richter measurement.

Long Answer: There is some room for discrepancy. Richter numbers are calculated directly from sisemograph charts, involving the magnitude and frequency of the ground wave. Sisemographs have been much improved over the years, leading to more accurate readings, so the older strength values have a larger innaccuracy. As well, the Richter value is only accurate for a given location: the location of the sisemometer. The numbers from several locations are used to backtrace the location of the inital fault, and also the probable strength of the quake at that point. Now, if you use less accurate readings to try and do that backtracking, your results often have an even wider probable range.

So, assuming the instruments are perfectly accurate, the same Richter means the same strength, but we don't have perfect instruments now, and the older readings used even less perfect instruments.

 

[CBL4]

After posting, I tried to find more the Richter scale. I read that it is dependent on the geology of the land.

I assume that this mean it is possible that as we learn more about the underlying geology, we would learn that the strength of older earthquakes had been miscalculated. Is this correct? If so, would the older Richter values be revised?

CBL

 

[casebro]

I met Dr. Richter. I went to high school with his nephews. He died in 1985, sooo... he was not around to measure ancient earthquakes. Old figures are just estimates, based on damage, myths, etc.

I believe the Richter scale is merely the measurement of how far a pendelum swings, in centimeters, when an eathquake happens. But that must be a simplification, since seldom is a pendelum hanging at an epicenter.

I sleep in a water bed, in San Diego. If the TurfSurfin starts at night, I can usually guess which direction the epicenter is by which direction I get sloshed.

Maybe I'll make my own, just a weight with a pointer on the bottom, hanging over a bed of sand. In an earthquake, it will leave a track in the sand in the direction of movement, and the length of the track is the strength. I'd guess a network of these would triangulate the epicenter. Funny how simple things can be, after some genius figures out how to do it the first time.

 

[epepke]

Does anyone know if the Richter scale estimates from the past correspond well to the present? In other words, if an earthquake from 1932 is described as being 7.5 on the Richter scale, what are the chances it would now be described roughly the same?

The Economist had an article on earthquakes in the India, Pakistan area. They have chart of "Notable" earthquakes. From 1897 to 1950 there 10 earthquakes greater than 7 on the scale with 6 of these greater than 8. From 1951 to the present, there have only been 2 greater than 7 and none greater than 8.

I blame Global Warming.