Biggest California Earthquake in 2 Decades Ruptures 24 New Faults

Many Americans live in fear that the 'big one' would happen; however, a new study suggests the 'small ones' might cause even a bigger problem.

Researchers from CalTech and NASA's Jet Propulsion Laboratory published the findings from a study regarding Ridgecrest earthquake - the biggest to hit California in 20 years - which caught many off-guard. The scientists analyzed seismographic information from the two satellites to try and explain what happened. 

The quake, according to a report on their research from the LA Times, was not the result of a single fault but at least 24 intersecting or adjacent faults causing a domino effect or earthquake swarm.

The tremor started on July 4 in the craggy desert town of Ridgecrest in California, with three smaller quakes, of magnitude 6.1, 6.2, and 6.2, causing few dozens of fault lines across the region to rupture.

The smaller ruptures in the town near Los Angeles and Death Valley caused a 7.1 magnitude earthquake on July 5 and added more than 100,000 aftershocks. Shaking was felt as far as Reno, San Francisco, San Diego, and Phoenix. 

Caltech's Egill Hauksson told the LA Times the earthquakes have connected segments that were deemed to be independent but have shown to unite in one massive shock.

Other smaller faults had been mapped beforehand and served to stretch the range of the area while forcing it to crate higher magnitudes than current modeling software would have predicted.

CalTech's Zachary E. Ross told LA Times the geometry of the fault network is "just incredibly complicated." He said the faults were unmapped before.

"Many of them [faults] are at right angles to each other; they're cross-cutting each other. They are spaced a few kilometers apart, like dominoes, in the central portion," Zachary explained.

The current system for assessing earthquake zones may undervalue the tremor risks - researchers

Researchers suggest that the current system for assessing the size of earthquake zones might significantly undervalue the area of risk. They based on how related set of mechanics drove the 2016 Kaikoura earthquake in New Zealand, where smaller fault ruptures started across more than 120 miles of the country's coastline.

Hauksson explained there were many ruptures over a wide area in the Kaikoura earthquake. He noted the importance of the earthquake since the surface rupture and the surface ground shaking spreading over a much wider area would affect the people.

The mainshock in Ridgecrest stopped a few kilometers away from California's main faultline - the Garlock Fault - the second-longest in the state, which spans 160 miles across the state's high desert region.

The Garlock Fault intersects with the San Andreas fault, California's longest fault, located in the Tehachapi Mountains that separate Los Angeles from San Joaquin Valley.

Researchers observed what they called 'fault creep' of almost an inch at the Garlock, which could have affected the San Andreas if activated. The quake could have affected a broader region if activated.

They pointed to the high number of smaller previously unmapped faults involved in the Ridgecrest quake as a 'challenging trial in quantifying topographic seismic hazards.'