Introduction:
After the earthquake in Calcutta, nerves remained on edge due to the frequent occurrence of aftershocks. This caused a continued sense of fear and anxiety among the residents of the city.

Explanation:
Aftershocks:
Aftershocks are smaller earthquakes that occur after a larger earthquake. They are caused by the movement and adjustment of the Earth's crust following the main earthquake. In the case of Calcutta, the initial earthquake would have caused significant stress and displacement of the Earth's crust, leading to aftershocks. These aftershocks can be just as unsettling and unnerving as the main earthquake, as they can continue to cause damage to already weakened structures and trigger fear among the population.

Frequency of Aftershocks:
One of the reasons why nerves remained on edge in Calcutta after the earthquake was the frequency of aftershocks. Aftershocks can continue to occur for days, weeks, or even months after the main earthquake. The residents of Calcutta would have been constantly reminded of the initial earthquake and its destructive power with each aftershock. This constant reminder and uncertainty can have a significant psychological impact on individuals, leading to heightened anxiety and fear.

Building Collapse:
Another reason for the heightened nerves in Calcutta was the continued collapse of buildings due to structural damage caused by the earthquake and aftershocks. The initial earthquake would have weakened the structural integrity of many buildings, making them more susceptible to further damage from aftershocks. The fear of buildings collapsing and the potential loss of life and property would have contributed to the anxiety and nervousness among the residents.

Trauma:
The initial earthquake itself would have been a traumatic experience for the people of Calcutta. The sudden shaking of the ground, the destruction of buildings, and the potential loss of life would have left a lasting impact on individuals. This trauma would have been further exacerbated by the aftershocks, as each occurrence would have triggered memories and fear associated with the initial earthquake. The cumulative effect of the trauma and constant reminders through aftershocks would have kept the nerves of the residents on edge.

Conclusion:
In conclusion, the nerves remained on edge in Calcutta after the earthquake due to the frequent occurrence of aftershocks. These aftershocks, along with the continued collapse of buildings and the trauma associated with the initial earthquake, contributed to the anxiety and fear experienced by the residents.