2 Reasons Why Nepal Can’t Expect Stronger Aftershock

We Nepalese learnt a big lesson on 12th May. It was really a surprised tremor for us that taught us whether we should remain cautious all the time as earthquake is natural and random process. This event has verified the scientific concept that the frequency of aftershocks decreases with time but intensity does not decline permanently. But it does not mean that chances are higher for another 12th May.  In my views, there is less than 0.01% probability of another stronger aftershock in Nepal.

2 reasons why we can’t expect stronger aftershock

General Patterns of Aftershocks
Though every earthquake is different, the average statistics accepted worldwide are 1 aftershock 1 M and 10 aftershocks 2 M less than the mainshock. Following this rule, Nepal is expected to experience 1 aftershock of around 6.6 Ml and 10 aftershocks of around 5.6 Ml. Because the mainshock was 7.6 Ml. According to the NSC, Nepal has already experienced about 3 aftershocks of 6.6 Ml or more than 6.6 Ml and about 9 aftershocks of 5.6 or more than 5.6 Ml. Similarly we faced 7 aftershocks of 5.5 Ml which are much closed to 5.6 Ml. Besides, 4 weeks average period to decrease aftershocks of a mainshock recommended by an analysis of USGS also has ended. Now we can freely say that we have already passed this level.

Aftershocks of the Aftershock
Though mainshock releases maximum strained energy, rest of the energy still remains stored till they reach their threshold. So, aftershocks of different magnitude happen for some days, weeks, months and sometimes even years. When strongest aftershock occurs, it triggers its own aftershocks sequences which we call aftershocks of aftershock. So we can estimate that as aftershocks can’t be stronger than the mainshock, aftershocks of aftershock also are weaker than the main aftershock. This is the reason we can’t expect another aftershock more than 6.8 Ml because this is the exact intensity of the earlier strongest aftershock.

Ok, we are not going to be hit by stronger aftershock. Then do we have to face aftershock around the size of 6.8 Ml? As aftershock more than 6 Ml is enough to cause damage, this question may arise on your mind.

Though it’s my personal analysis, l am trying to link it with the rule of the general pattern of the earthquake. Once again, the rule is 1 aftershock less than 1 M and 10 aftershocks less than 2 M of the mainshock. As you know that the size of the strongest aftershock was 6.8 Ml, we can expect 1 aftershock of 5.8 Ml and 10 aftershocks of around 4 Ml.  Now once again let’s check the record of NSC in its official website. After 12 May, we faced 3 aftershocks of 5.8 or more than 5.8 Ml and 21 aftershocks between 4.5 to 5 Ml. Haven’t we passed the next level too?

 I  believe that time also could be estimated as less than 15 second for that strong aftershock as first mainshock was around 52 seconds and the strongest aftershock was about 30 seconds, declining with around half percent. Also we can consider 2 weeks periods for another strong quake {but less than 5.8 Ml} because these aftershocks were decaying more exponentially in comparison of the aftershocks of the mainshock. And I am very happy to remind you that we have passed 2 weeks {12 May to 26 May} period too.


Actually strongest aftershock like 12 May was not totally abnormal according to some scientists. As we may expect 1 M less aftershock exactly after 24 hours of the mainshock, the strongest aftershock after some days was also inevitable. For instance, Haiti experienced 5.9 M strongest aftershock after 8 days of 7 M mainshock. There are many other examples. Nepal has already faced strongest aftershock of 6.8 Ml after 17 days of the mainshock on 12th May. Aren't we safe now?
Discovered by Don Prince

{Disclaimer: This post has been created to give relief to the people of Nepal who are fearful to the earthquake. It does not guarantee that there won’t be another large earthquake or strong aftershock in Nepal.  Common people and the concerned authorities should be cautious towards the earthquake and its aftershocks.}

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  1. Thanks once again for this and no more questions, waiting for next one.