After the first (main) earthquake, other smaller shocks may occur at times for:

Aftershocks can after the first (main) earthquake, other smaller shocks may occur at times for several weeks to months or even for few years.

Explanation:

Aftershocks are a series of lower intensity earthquakes which occur following a main higher intensity earthquake in the same location but at a short rupture distance from the main fault line.

The number and intensity of aftershocks decrease with time. Aftershocks result from changes in the internal stress taking place suddenly after the principle change by the main earthquake.

The rocks near the major fault line cause aftershocks. The damage caused by aftershocks also varies with the intensity of the main earthquake and sometimes aftershocks can bring down buildings or trees which were already weakened by the main earthquake