Final answer:
The decision by the San Francisco postmaster following the 1906 earthquake and fire to allow people to send letters regardless of whether they had stamps or not is an example of an improvised response to a natural disaster.
Step-by-step explanation:
The decision by the San Francisco postmaster following the 1906 earthquake and fire to allow people to send letters regardless of whether they had stamps or not is an example of an improvised response to a natural disaster. In times of crisis, sometimes established rules and systems need to be adapted to meet immediate needs. In this case, the postmaster recognized that people needed a way to communicate and connect with their loved ones, so he made an exception to the usual stamp requirement.