West LA Times

The 7.5-magnitude earthquake beneath Japan’s Noto Peninsula on January 1, 2024, was caused by a “dual-initiation mechanism” that generated enough energy from two different locations to break through a fault barrier. This barrier is an area that locks two sides of a fault in place and absorbs the energy of fault movement, slowing it down or stopping it altogether.

An international team of researchers led by UCLA graduate student Liuwei Xu, professor Lingsen Meng, and UC Santa Barbara’s Chen Ji analyzed a preceding seismic swarm and identified a previously unknown barrier in the region. The team's data collection methods could aid future research into the conditions and probabilities of dual-initiation earthquakes.

The first seven months of 2024 have been eventful, overshadowing the magnitude 7.5 earthquake centered beneath Japan’s Noto Peninsula on New Year's Day. The earthquake resulted in over 280 fatalities and damaged more than 83,000 homes.

Geologists have discovered that the earthquake began almost simultaneously at two different points on the fault, allowing the seismic rupture to encircle and break through a resistant area known as a barrier. This rare “dual-initiation” mechanism applied intense pressure from both sides of the barrier, leading to substantial ground shaking across the Noto Peninsula.

The Noto earthquake was preceded by intense seismic swarms—sequences of many small earthquakes that can sometimes lead to larger events. Using advanced seismic and geodetic technologies, the research team meticulously analyzed movements within the Earth during this swarm leading up to the earthquake.

The study, published in Science journal, offers insights into the role of fault barriers in earthquake genesis and will help improve seismic risk assessments and future forecasting.

Earthquakes occur when fractures in the Earth’s crust allow blocks of rocks on either side to move past each other. This movement is localized due to unevenness along the fault line which dissipates energy eventually stopping it.

A barrier is a rough area that locks both sides of a fault in place. Barriers absorb energy from fault movement but can only hold so much before breaking violently under sufficient stress causing strong shaking. A swarm of small earthquakes might not be enough to break a barrier; however, stronger subsequent movements can cause its rupture releasing stored-up energy.

Led by Lingsen Meng, UCLA associate professor of earth sciences; UCLA graduate student Liuwei Xu; and UC Santa Barbara geophysics professor Chen Ji; an international team analyzed geospatial data and seismic wave recordings to understand relationships between smaller tremors and larger subsequent earthquakes identifying an unknown barrier in their study region.

Surprisingly, they found that New Year’s Day's earthquake began almost simultaneously at two separate locations on the fault with energies moving toward each other causing violent rupture resulting in extremely strong shaking.

“The earthquake started in two places and circled together,” Meng said. “The first one started waves that traveled fast triggering another epicenter then both parts propagated outward meeting where there was a barrier breaking it.”

This finding was surprising since dual initiation has been seen mainly in simulations but harder observed naturally requiring precise conditions set easier inside labs compared real-world unpredictability

“We were able observe because Japan has very good seismic monitoring stations also used GPS satellite radar data grabbing all available data! Only through combined data got high resolution faults fine details,” Meng said

Most earthquakes lack such extensive collected data making dual initiation mechanisms potentially more common than thought possibly identified better imaging resolution future

“It could be through better imaging resolution we’ll identify more like this future,” Meng said

Earthquakes with dual epicenters pose higher risks for stronger shaking due stronger movements; Meng’s group plans consider future scenarios learning about conditions probabilities these quakes

"Our findings emphasize complex nature earthquake initiation critical conditions leading large-scale seismic events," Meng said "Understanding processes vital improving ability predict mitigate impacts future earthquakes"