The year 2024 started off with a significant event – a magnitude 7.5 earthquake beneath Japan’s Noto Peninsula on New Year’s Day. This event resulted in the loss of over 280 lives and damaged more than 83,000 homes. Geologists studying this earthquake have discovered a rare “dual-initiation” mechanism where the seismic rupture began almost simultaneously at two different points on the fault, encircling and breaking through a resistant area known as a barrier. This intense pressure from both sides of the barrier led to a powerful release of energy and substantial ground shaking across the peninsula.
Leading up to the Noto earthquake, there were intense seismic swarms which are sequences of small earthquakes that can precede larger catastrophic events. Through the use of advanced seismic and geodetic technologies, researchers were able to analyze the movements within the Earth during these swarms that ultimately led to the earthquake. This study, published in the journal Science, offers valuable insights into the role of fault barriers in earthquake genesis and will assist in improving seismic risk assessments and future earthquake forecasting.
Earthquakes occur when faults in the Earth’s crust allow blocks of rock to move past each other. The movement is localized and not continuous due to the uneven and rough nature of fault lines, which dissipates energy and eventually stops the movement. Barriers on faults lock the two sides in place, absorbing energy until conditions are right for a violent rupture and strong shaking. While a swarm of small earthquakes may not be enough to break a barrier, stronger subsequent movement on the fault can lead to the barrier’s rupture and the release of stored energy.
An international team of researchers from the United States, France, China, and Japan, led by UCLA’s Lingsen Meng, UCLA graduate student Liuwei Xu, and UC Santa Barbara’s Chen Ji, analyzed geospatial data and seismic wave recordings to understand the relationship between the seismic swarm and the subsequent earthquake. They identified a previously unknown barrier in the region of the swarm and discovered that the New Year’s Day earthquake began almost simultaneously in two separate locations on the fault, leading to a violent rupture and strong shaking when the energy from both locations met at the barrier.
The discovery of the “dual-initiation” mechanism in the Noto earthquake was surprising as it is rarely observed in nature and requires specific conditions to occur. The use of seismic monitoring stations, GPS, and satellite radar data allowed the researchers to gather detailed information about the fault and better understand the fine details of the earthquake mechanics. While earthquakes with dual-initiation mechanisms may be more common than previously thought, the level of data collected for this event was extensive, making it easier to observe and analyze.
Moving forward, Meng’s group plans to explore future scenarios to better understand the conditions and probabilities of earthquakes with dual epicenters. The complexity of earthquake initiation and the critical conditions that can lead to large seismic events emphasize the importance of understanding these processes for predicting and mitigating the impacts of future earthquakes. The team’s findings highlight the need for continued research into the mechanisms behind earthquake initiation and the potential risks associated with dual-initiation earthquakes.