Geologists claim there were at least 200 smaller tremors recorded at the Coso Volcanic Field in Southern California.
They had magnitudes of between 3.0 to 4.0.
The United States (US) Geological Survey monitors micro-earthquakes daily throughout the US.
These earthquakes were happening around the same time as a significant one, measured at 6.0 to 6.4 at the Banda Sea, on Monday.
That sea is close to Timor-Leste and Indonesia.
These did not trigger any threat of a tsunami and there were no casualties reported.
But the death toll of a recent mega quake of 7,7 in Indonesia’s Flores Island, went up to 100 people.
Some 1,600 people were injured.