Moment Of Inertia

The time period of rotation of Earth did not decrease after the Japan 2011 earthquake. In fact, the earthquake caused a slight increase in the Earth's rotation period, resulting in a shortening of the day.

The calculations also show the Japan quake should have shifted the position of Earth's figure axis (the axis about which Earth's mass is balanced) by about 17 centimeters
During large-scale earthquakes, the distribution of mass on Earth can change. The Japan 2011 earthquake, also known as the Great East Japan Earthquake, was a massive undersea earthquake that occurred off the northeastern coast of Japan on March 11, 2011. This earthquake had a significant impact on the Earth's rotation due to the redistribution of mass caused by the shifting of tectonic plates.
The earthquake caused the Pacific tectonic plate to move and resulted in a redistribution of mass, primarily by shifting a significant amount of Earth's crust from the ocean floor to land. This shift of mass closer to the Earth's axis of rotation caused a slight increase in the planet's moment of inertia. To be more precise, the earthquake's effect on Earth's rotation was estimated to have shortened the day by approximately 1.8 microseconds (1.8 millionths of a second) by redistributing the Earth's mass closer to the axis. This change is relatively small and would not be perceptible to human experience.