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Abstract:
This article reports a significant breakthrough in earthquake science: the first-ever real-time detection of a slow-slip earthquake (SSE) in motion along the tsunami-generating portion of Japan's Nankai Fault. Scientists from the University of Texas at Austin, utilizing advanced offshore borehole sensors, observed these slow-motion seismic events, which unfold over weeks and involve movements as subtle as millimeters. The findings reveal that these SSEs act as a "tectonic shock absorber," safely releasing accumulated pressure. Crucially, the events were directly correlated with elevated geologic fluid pressures, providing strong evidence for fluids as a key ingredient in slow earthquakes. This discovery significantly advances the understanding of subduction zone fault behavior, offering insights into stress accumulation and release mechanisms that are vital for assessing seismic hazards globally, including a comparison to the potentially more hazardous Cascadia fault.
Summarizing the Transcript: Scientists Capture Slow-Motion Earthquake in Action
Discovery Announced: Scientists from the University of Texas at Austin have for the first time detected a slow-slip earthquake (SSE) in motion along the tsunami-generating portion of Japan's Nankai Fault.
Nature of Slow Slip Earthquakes: These events are slow-motion seismic occurrences that unfold over days or weeks, acting like "tectonic shock absorbers" by slowly releasing tectonic pressure.
Breakthrough Technology: The detection was made possible by highly sensitive borehole sensors placed offshore, capable of detecting movements as small as a few millimeters, which are invisible to land-based systems like GPS.
Observed Events: A slow slip earthquake was captured in the fall of 2015, followed by a second slow tremor in 2020, both traveling along the shallow, tsunami-prone tail of the Nankai Fault.
Fault's Shock Absorber Role: This discovery suggests that the observed part of the Nankai Fault releases energy harmlessly through these recurring slow slip events, rather than contributing to large, destructive earthquakes and tsunamis.
Critical Role of Fluids: The slow slip events occurred in areas with higher-than-normal geologic fluid pressures, providing strong evidence that fluids are a key factor in triggering slow earthquakes.
Historical Context of Nankai Fault: The Nankai Fault is historically known for generating large earthquakes, with the last significant one in 1946 (Magnitude 8), which caused extensive destruction and loss of life.
Global Implications: The findings will aid in understanding subduction zone faults across the Pacific Ring of Fire, informing hazard assessments for other regions.
Comparison to Cascadia Fault: Unlike Nankai, the Cascadia fault (facing the Pacific Northwest) appears to lack a similar "natural shock absorber" at its tsunami-generating trench, suggesting it may be strongly locked and a high priority for monitoring.
Data Sources: The research utilized data from borehole observatories installed by the Integrated Ocean Drilling Program and ocean floor cable observatories operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).