  During any unique crisis, panic sell-off leads to a massive stock market
crash that may continue for more than a day, termed as mainshock. The effect of
a mainshock in the form of aftershocks can be felt throughout the recovery
phase of stock price. As the market remains in stress during recovery, any
small perturbation leads to a relatively smaller aftershock. The duration of
the recovery phase has been estimated using structural break analysis. We have
carried out statistical analyses of the 1987 stock market crash, 2008 financial
crisis and 2020 COVID-19 pandemic considering the actual crash-times of the
mainshock and aftershocks. Earlier, such analyses were done considering an
absolute one-day return, which cannot capture a crash properly. The results
show that the mainshock and aftershock in the stock market follow the
Gutenberg-Richter (GR) power law. Further, we obtained a higher $\beta$ value
for the COVID-19 crash compared to the financial-crisis-2008 from the GR law.
This implies that the recovery of stock price during COVID-19 may be faster
than the financial-crisis-2008. The result is consistent with the present
recovery of the market from the COVID-19 pandemic. The analysis shows that the
high magnitude aftershocks are rare, and low magnitude aftershocks are frequent
during the recovery phase. The analysis also shows that the distribution
$P(\tau_i)$ follows the generalized Pareto distribution, i.e.,
$\displaystyle~P(\tau_i)\propto\frac{1}{\{1+\lambda(q-1)\tau_i\}^{\frac{1}{(q-1)}}}$,
where $\lambda$ and $q$ are constants and $\tau_i$ is the inter-occurrence
time. This analysis may help investors to restructure their portfolios during a
market crash.
