New earthquake rupture mode during the Mw7.5 earthquake that struck Central Japan in January 2024

05 Jul 2024 | EOS News

Author: Lauriane CHARDOT

On 1 January 2024, a magnitude-7.5 earthquake struck the Noto Peninsula, located north of the island of Honshu in Japan. The event generated strong shaking, numerous landslides and a local tsunami, and caused more than 200 casualties and significant damage to infrastructure.  

New research shows that the event uplifted the peninsula by up to about 5 metres, and caused the nearby areas to experience accelerations of up to 2.6 G. This acceleration, which is the third largest on record caused by earthquakes, posed a non-negligible threat to the power plant nearby. What the research also found is that the earthquake started in an area thought to have limited capability of initiating a devastating earthquake. These findings are pushing the frontiers of earthquake physics and identify a new earthquake rupture mode that early warning systems should account for.  

Fig1_0624Map showing the location of the magnitude-7.5 event and other past earthquakes, as well as the surface motion generated by the earthquake. The arrows depict the horizontal displacement and the colour scale represents vertical displacement. The triangles represent the peak ground acceleration (PGA) recorded at different locations; they show that large PGAs were observed near the nuclear power plant. (Source: Figure 1 of the study)

In the study, which was published in Science, scientists from Nanyang Technological University, Singapore (NTU Singapore) and their collaborators from the University of Tokyo, China Earthquake Administration, and Hohai University, explain what happened on this fateful day, and identify a new mode for a fault to break during an earthquake. They show that the strong earthquake had a complex rupture process, started with a slow rupture on a fluid-rich fault before breaking adjacent segments of the fault. “It is the first time that we observe a strong earthquake that generates so much shaking yet starts with such a slow rupture,” said Mr Hongyu Zeng, a Research Associate at the Earth Observatory of Singapore (EOS) and PhD student at the Asian School of the Environment (ASE) at NTU Singapore.

According to the scientists, the unusual slow phase of the event could be due to the presence of fluids that facilitated the rupture. Those fluids are thought to have migrated from depths, and related to the numerous small earthquakes that occurred in swarms over about three years preceding the 2024 event. “The 2024 devastating event that struck the Noto Peninsula represents the peak of restless in the region so far,” said Dr Haipeng Luo, an Associate Professor at the Department of Earth and Space Sciences, Southern University of Science and Technology, China, who worked on this study while being a Research Fellow at EOS.  

Mr Hongyu Zeng, Research Associate EOS and PhD student at ASE (left), and Dr Zhangfeng Ma, Research Fellow at EOS (right) are the two co-first authors of the paper. They are posing outside of the new office space dedicated to the ‘Integrating Volcano and Earthquake Science and Technology’ (InVEST) in Southeast Asia programme, an interdisciplinary research programme that will provide a holistic understanding of regional tectonics, volcanoes, the linkages between the two, and their cascading hazards and impacts. (Source: Earth Observatory of Singapore)   

The discovery has implications for the design of early warning systems because these rely heavily on how much the fault ruptures in the first few seconds of an earthquake to estimate the size of the event. In the case of the Noto earthquake, the slow rupture lasted for 15 to 20 seconds and ruptured a small patch of the fault – much smaller than the subsequent ruptures on other segments of the fault. An early warning system estimating the size of such earthquakes based on the initial slow rupture would therefore not be representative of the whole event. “Such a phenomenon where a slow rupture in a fluid-rich swarm zone initiates a large earthquake underscores a challenge in earthquake early warning and necessitates the re-evaluation of earthquake and tsunami hazards in areas near swarm zones,” said Associate Professor Shengji Wei, from NTU’s ASE and EOS.  

Although the initial rupture was slow and relatively small, it was accompanied by large accelerations that were comparable to those generated by later large rupture. Such signals are generally observed when the fault zone does not behave the same everywhere, and where different sections rupture differently. “Such a slow initial rupture accompanied with intense high frequency radiation has not been documented before. It can be due to a fault that has heterogeneities and a low strength due to the presence of fluids,” said Dr Zhangfeng Ma, a Research Fellow at EOS. 

To reconstruct what happened to such level of detail, the scientists analysed a complex set of data from satellites and ground stations. This analysis revealed that the best explanation for the observed ground deformation and seismicity patterns was an earthquake that ruptured at least three segments of the fault at different propagation speeds over more than 150 kilometres. “Thanks to the rapidly available high-quality space geodetic and seismic observations, we could conduct a comprehensive and interdisciplinary analysis shortly after the event with researchers from diverse backgrounds and expertise. Such fast, high-resolution results can bring benefit to earthquake hazard assessment and post-seismic reconnaissance,” said Assoc Prof Shengji Wei.    

“Understanding the many ways that earthquakes can be generated and cause damage is critical to enhancing seismic safety in our region. To build this understanding requires collaboration across scientific fields, as we have for our large, MOE-funded 'Integrating Volcano and Earthquake Science and Technology' (InVEST) in Southeast Asia programme,” said Professor Emma Hill, Chair of the ASE and Principal Investigator at EOS, who leads the InVEST programme. 

This research was supported by the Ministry of Education, Singapore, under its MOE AcRF Tier 3 award MOET32021-0002.



Geographic Area

Asia > Japan

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