A teacher and students practice the drop, cover and hold on technique during the "Great ShakeOut" earthquake drill at Marlton School in Los Angeles, Oct. 15, 2015. Reuters

A 6.5-magnitute earthquake that struck near the northern California city of Ferndale occurred near a massive geological formation known as the San Andreas Fault that potentially threatens major cities within the state, including Los Angeles. While Thursday morning's quake caused no reported damage, according to the town's mayor, it originated in the Pacific Ocean about 102 miles off the coast of Ferndale in one of California's most seismically active regions.

The area is the northern end of the San Andreas Fault, the boundary between the North American and Pacific tectonic plates that constantly scrape against one another, causing seismic activity such as Thursday's event. Experts have long said that increasing pressure could lead to a major earthquake along the 800-mile fault, causing significant destruction throughout the state.

Last month, data firm Core Logic reported that an unlikely rupture in both the northern and southern regions of the San Andreas fault could produce a 8-magnitude earthquake capable of damaging 3.5 million homes. While unlikely, the so-called "mega-quake" could cost over $289 billion in repairs.

Even in the more likely event that only the southern portion of the fault ruptured, major populated areas such as Los Angeles would be at risk. This powerful quake would kill an estimated 2,000 people and further injure 50,000 more while wreaking havoc on the state's infrastructure. With the collapse of at least 100 buildings, the disaster would cause about $200 billion in damage. The last time the southernmost part of the San Andreas Fault ruptured was in 1682 and scientists estimate a major earthquake should occur every 150 or 200 years, noting the region was long overdue.

California's deadliest natural disaster was the 1906 San Francisco earthquake, estimated at 7.8-magitude and responsible for over 3,000 deaths. It displaced about 225,000 people and caused $400,000,000 in damages at the time.