Question

If we observe 1 earthquakes of M>4 per year on average: How many earthquakes of M>3 can we expect in a year? How many earthquakes of M>5 can we expect in a years?

You should be able to give the result in terms of probability: For example, what is the probability of a M>5 in a year?

II. Know how to use the Omori law (Review slide 17):

If you are given the rate of occurrence of aftershocks on day 1 for example, you should be able to give the rate of earthquake on day 5.

Answer 1

According to the book 'Earthquakes' of Dr Brush Bolt, the number of earthquake occuring in worldwide manner is as shown below:

Magnitude of Earthquake	Number of Earthquake per year
>9.0 8.0 -8.9 7.0-7.9 6.0-6.9 5.0-5.9 4.0-4.9 3.0-3.9 2.0-2.9 <2 Total =	<1 1 25 120 1,000 6,000 49,000 300,000 600,000 ~956,147

Now, if we see this trend, and do same type of equivalent calculation, we will get earthquakes >3 magnitude will be 949,000.

Whereas, earthquakes >4 magnitude will be 7,146 and earthquakes >5 magnitude will be 1,146.

By, simple conversion formula, if we suppose earthquake >4 magnitude will be 1. Then, 132.80 number of earthquakes of M>3 can we expect in a year.

Similarly, 0.16 number of earthquakes of M>5 can we expect in a years.

Finally, the probability of a M>5 in a year is 0.119% (i.e. 0.00119 times probability)