The seismic activity that caused the Santa Maria quake on Wednesday was so powerful it was described as the strongest in at least 80 years, the U.S. Geological Survey said.
But it also revealed that some parts of the Santa Cruz County area were spared the worst of the disaster.
“The epicenter of this earthquake was in the Santa Clara Valley, about 20 miles (32 kilometers) southeast of San Jose, California,” the USGS said in a statement Thursday.
“We do not have a high degree of confidence that this earthquake is related to any natural or man-made event.”
The USGS added that the quake was centered about 30 miles (48 kilometers) west of San Francisco.
It wasn’t immediately clear how many people were killed or injured.
The US Geological Survey says it will conduct a broader review of the earthquake’s seismic activity in the coming days and weeks.
The quake triggered the worst disaster in the US since the Great Depression.
The Santa Maria fault is the result of a fault line that ran from Siberia, down to the Pacific Ocean, the fault line runs through California, and the Santa Barbara mountains.
Scientists said the quake had a magnitude of 6.3, about 3.5 times stronger than the magnitude of the 2011 magnitude-5.3 quake that killed more than 800 people in San Francisco and injured more than 2,000.
The U.K.’s National Earthquake Centre said the earthquake, which was centered near the village of San Rafael, was centered at a depth of 4.5 miles (6 kilometers), which was less than half the length of the fault.