The US cities of Los Angeles, San Francisco and Sacramento have all been rattled by large earthquakes 1.5 magnitude or greater in the past day.
The largest quake measured 2.6 magnitude and struck 4.30am local time at a depth of 23km near Tuolumne City, around 213km from San Francisco.
Eleven of the tremors were over 2.0 magnitude, while the rest were between 1.0 to 2.0 magnitude, according to Earthquake Track.
Although relatively small, the wave of earthquakes will entrench fears that a massive tremor measuring 7.0 or above could strike the region.
Scientists believe the US state is overdue a “big one” magnitude 7 or over earthquake by around 50 years.
Last week a magnitude 3.6 earthquake rattled northwest Los Angeles after striking in the Santa Monica mountains.
It struck in the same week a colossal 7.1 magnitude virtually flattened Mexico City, causing widespread damage and killing more than 300.
Over the weekend Mexico was shaken by more quakes, including a 6.2 tremor that caused people to flee their homes.
Since then experts have issued warnings that a powerful earthquake akin to the one that hit Mexico is “inevitable”.