Aftershock
An aftershock is a smaller earthquake which comes after a large earthquake (called the main shock) in the same area. An aftershock is the opposite of a foreshock, which a small earthquake comes before the large earthquake.
Omori's Law
There are many laws which refer to aftershocks, but the most famous is Omori's Law. In 1894, Fusakichi Omori did some works on aftershocks, and firstly he came up with this rule:
[math]\displaystyle{ n(t) = \frac {K} {c+t} }[/math]
- "t" is time.
- "n(t)" is the rate of earthquakes in a time after the main shock
- "c" is a constant
- "K" is the size of the earthquake.
By 1961, Utsu wanted to change the rule.[2][3] His rule looked like this:
[math]\displaystyle{ n(t) = \frac {k} {(c+t)^p} }[/math]
where "p" changes the rate, this mainly has a number between 0.7 and 1.5.
Aftershock Media
- Sichuan 2008 Aftershocks.jpg
Distribution of aftershocks associated with the May 12th 2008 Sichuan earthquake through to 28th May
- Neic slav fig72.gif
Aftershocks of the 2004 Indian Ocean earthquake, with data up to January 10, 2005.*This is an updated version of :Image:Neic slav fig72.jpg, with more recent data and smaller file size. Note USGS original is a GIF; file size is 60 kB vs 285 kB Source* *
- 2016 Central Italy earthquake (magnitude).svg
Magnitude of the Central Italy earthquake of August 2016 (red dot) and aftershocks (which continued to occur after the period shown here)
References
- ↑ F. Omori (1894) "On the aftershocks of earthquakes," Journal of the College of Science, Imperial University of Tokyo, vol. 7, pages 111–200.
- ↑ Utsu, T. (1961) "A statistical study of the occurrence of aftershocks," Geophysical Magazine, vol. 30, pages 521–605.
- ↑ Utsu, T., Ogata, Y. ,and Matsu'ura, R.S. (1995) "The centenary of the Omori formula for a decay law of aftershock activity," Journal of Physics of the Earth, vol. 43, pages 1–33.