Earthquake Magnitude Experiment
Size vs Magnitude
Theory
In this lab we focused on two different schemes called magnitude scales, which is used by seismologists to measure the magnitude of an earthquake. We used Ms and Mb. Mb is the body wave magnitude scale and Ms is the surface wave magnitude scale.
Discussion
We calculated the Mb by taking the Log of a/l plus q. For the body wave magnitude I got 6.943. The Ms was calculated by the log of a/t plus 1.66log of D pus 3.3. I got 6.699 for surface wave magnitude.
For the MacQuerie Ridge earthquake these are the following measurements.
Ms and Mb waves from other stations
station locations Mb Ms COCO 64.3 6.943 6.699 SBA 28.7 6.770 6.11 CTAO 31.6 6.74 7.22 NWAO 36.5 6.421 6.689 PMSA 60.9 6.21 7.38 TATO 82.0 6.3 7.01 WBAB 36.4 6.2 7.2 PTCN 57.6 6.7 7.09 MATO 6.48 6.87
As you can see the Mb and Ms magnitudes are all different but similar. That is the result of the different locations of the stations. SBA is the closest station and TATO is the furthest, and we can see that there is a significant difference in the magnitudes of the earthquake. The Mb measurement is greater closest to the earthquake (SBA) and the Ms measurement is greater away from the earthquake (TATO). I'm guessing that the intensity of the Mb wave decrease away from the earthquake, and the intensity of the Ms increase or gains power as it gets to a shallow level. Measuring magnitude can be very complex; each type of magnitude does not yield the same number. However, each type of magnitude calculates a specific part of the earthquake. Some measuring method aside of Ms and Mb are Richter magnitude and moment magnitude.
We all know that the intensity of ground shaking and damage of an earthquake diminishes the farther you move away from the epicenter. The Sumatra earthquake in December 2004 was felt all around the world but the damage in south East Asia was much greater than what was felt in the USA. For this reason, it is good to measure all magnitudes to get an idea about the earthquake.
Questions:
I feel that the lab had a lot of direction and not a lot of information. Some questions that I have are;
1. Why have scientists developed so many different ways to calculate earthquake magnitudes, and how do you get the number that we all receive in the news?
2. We hear of the Richter scale whenever a large earthquake occurs on Earth. What exactly is the Richter scale? And if we use the Richter scale why do we have to use the different types of magnitudes?
3. What are the strengths and weaknesses of each of the different magnitude scales?
4. What do scientists need to take into account when they design a magnitude scale, and how do they figure out the formulas?
Published by Jeny Espinal
I am an undergraduate economics student at Binghamton University. View profile
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9 Comments
Post a Comment4. What do scientists need to take into account when they design a magnitude scale, and how do they figure out the formulas?
all magnitudes come form the first formula that Richter proposed wish is: ML = log10A - log10Ao , where Ao is the maximum amplitude for the "default" earthquake, and A the max. amplitude for the eartquakes you're studying.
Hope I could answer your questions
;)
Hails!!!
..sorry, my html isn't so good :(
3. What are the strengths and weaknesses of each of the different magnitude scales?
the principal weakness is the saturation of the scales, it means there are some "roof numbers", maximun in those scales that saturate. Example, Ms saturates around 8.5, mb, around 7..the best of all is Mw (moment magnitude), wich still doesn't saturate.
2. We hear of the Richter scale whenever a large earthquake occurs on Earth. What exactly is the Richter scale?
The Richter scale, or ML, is a local magnitud that Richter postuled in 1930. It was a formula for earthquakes in a radius smaller than 600 Km in California, and the parameters were obtained from the seismogram of a Wood Anderson torsion seismometer.
The idea was, knowing the distance from the sesimometer to the event, and having the signal's maximun amplitud , you can estimate the relative size of earthquakes (you compare to one "default" event)in an empiric way.
...And if we use the Richter scale why do we have to use the different types of magnitudes?
As I said, Richter scale is a LOCAL magnitud, so it's correcte for every region in the world. In most earthquakes, magnitudes are relatively liked, but not for large earthquakes (Sumatra, Loma Prieta, Valdivia-Chile, etc)
Hi Jeny!!!
I study seismology, so there are some answers to your questions :)
1. Why have scientists developed so many different ways to calculate earthquake magnitudes, and how do you get the number that we all receive in the news?
Magnitude is a way to show the size of the earthquake, and it's related qith the amount of energy released. There're different magnitudes because they are calculated from a diferent type of wave (the seismic event has three principal types of waves: body waves (compretional), shear waves and surface waves), and those different types of waves have different amounts of energy.
If you see the formulaes, they all have in common the period of the wave and the maximun amplitude.
The number is calculated from the seismogram, for Ms, mb and ML with those parameters basically.
please dont' follow the previous post.. :)
Hi Jeny!!!
I study seismology, so there are some answers to your questions :)
1. Why have scientists developed so many different ways to calculate earthquake magnitudes, and how do you get the number that we all receive in the news?
Magnitude is a way to show the size of the earthquake, and it's related qith the amount of energy released. There're different magnitudes because they are calculated from a diferent type of wave (the seismic event has three principal types of waves: body waves (compretional), shear waves and surface waves), and those different types of waves have different amounts of energy.
If you see the formulaes, they all have in common the period of the wave and the maximun amplitude.
The number is calculated from the seismogram, for Ms, mb and ML with those parameters basically.
2. We hear of the Richter scale whenever a large earthquake occurs on Earth. What exactly is the Richter scale?
The Richter scale, or ML, is a local magnitud that Richter
You have very good question!! the people int he new or something should explain this to the rest of the poeple because i didnt know what it meant.
It is reall informative!!!
This is very interesting. I didn't know any of this.