Seven-time Olympian Seiko Hashimoto replaces Yoshiro Mori, the former Japanese prime minister forced to resign over sexist comments about women.
One expert said Saturday's temblor was an aftershock of the devastating 2011 earthquake.
The quake, which had a preliminary magnitude of 7.1, shook buildings but no tsunami warning was issued.
It's another problem for the postponed Olympics, which have made the risky choice of trying to open on July 23 in the middle of a pandemic.
Yoshiro Mori apologized for saying that meetings with women participants "take a long time," but public outrage appears far from assuaged.
The Tokyo Games were postponed 10 months ago at the outbreak of the coronavirus pandemic, and now the event appears threatened again.
Scientists hope the samples will provide insight into the origins of the solar system and life on Earth.
The postponed Olympics are scheduled to open on July 23, 2021, and are set to include the full complement of 11,000 athletes. The Paralympics will add 4,400 more.
Solar and wind are more reliable in catastrophes –– and we need them to slow the worsening climate crisis.
The Tokyo Olympics are set to open on July 23, 2021, after being postponed eight months ago because of the COVID-19 pandemic.