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A 75-kilometre tear, and a slab that has dropped five kilometres

Qurexa Editorial Team26 September 20265 min read 0 0
A 75-kilometre tear, and a slab that has dropped five kilometres

What happened

Scientists have worked out how a huge piece of the Earth's crust is coming to the end of its life, and the answer is stranger than expected. The research was carried out by a team at Louisiana State University and published in the journal Science Advances on 25 September 2026. The place they studied is the Cascadia subduction zone, off the coast of the Pacific north-west of North America. A subduction zone is where one slab of the Earth's outer shell slides underneath another and sinks. At Cascadia, two oceanic plates, the Juan de Fuca and the Explorer, are sinking beneath the North American plate. The team expected that, eventually, such a system simply stops. What they found instead is that it is coming apart in pieces. The sinking plates are slowly breaking into smaller fragments, called microplates, with new boundaries forming between them. They found a tear running 75 kilometres through the oceanic plate. At one fault, the slab has dropped by about 5 kilometres. The researchers built this picture by combining earthquake records with seismic reflection imaging. They towed a 15-kilometre-long underwater listening cable to catch echoes bouncing back from deep rock, during the 2021 Cascadia Seismic Imaging Experiment.

Why this matters

The Cascadia subduction zone has a reputation. It is capable of producing very large earthquakes, and it has done so in the past. So any headline about it tearing apart sounds alarming. It should not be read that way, and the researchers themselves are clear about this. The process they describe unfolds over millions of years. Not decades. Not centuries. Millions of years. On any human timescale, nothing is changing. Lead researcher Brandon Shuck described the mechanism simply: "Rather than shutting down all at once, the plate is ripping apart piece by piece, creating smaller microplates and new boundaries." He also explained what happens once a piece finishes breaking off: "Once a piece has completely broken off, it no longer produces earthquakes because the rocks aren't stuck together anymore." The real value of the finding is elsewhere. Geologists find odd fragments of ancient plates scattered around the world, and have long wondered where they came from. This offers an explanation: they may be leftovers from subduction zones that fell apart in exactly this way.

What the evidence actually says

The measurements are specific, which is a good sign in earth science. A 75-kilometre tear through the oceanic plate. A vertical offset of roughly 5 kilometres at one fault. Data gathered with a 15-kilometre seismic streamer during a dedicated 2021 imaging experiment, combined with earthquake records. The researchers state plainly that the discovery does not significantly change earthquake hazard assessments at Cascadia on timescales relevant to people. We want to repeat that, because it is the single most misreadable part of this story. It is worth being honest about the limits too. Seismic imaging produces a picture of deep structures from reflected sound. It is interpretation, not direct observation. Nobody has been down to look. And "millions of years" is an estimate of process, not a countdown. It does not mean a piece will detach on a schedule. What this study genuinely adds is a mechanism. It shows a subduction zone in the act of fragmenting, which had been proposed but not clearly imaged before.

Practical advice

If you live in the UK, this is interesting rather than useful. Britain gets small earthquakes, but nothing on this scale, and there is nothing to prepare for. If you are travelling to the Pacific north-west of the United States or Canada, the sensible steps are the ordinary ones, unchanged by this research. Check the FCDO travel advice for your destination before you go, and read the natural disasters section. Take note of any earthquake or tsunami guidance from your hotel or host. In coastal areas, find out where the evacuation route goes. It takes five minutes. Pack your regular medicines in your hand luggage, with a copy of your prescription list, and take more than you think you need. That advice applies to any trip, not just this one. Make sure your travel insurance covers medical treatment and repatriation. If you have a long-term condition, register for any local emergency alert system where one exists. And for the science itself, the useful habit is to check the date range in any earthquake headline. "Millions of years" and "imminent" are not the same sentence, however similar they look in a summary.

What to know

Researchers at Louisiana State University found that the Cascadia subduction zone is breaking apart into smaller microplates rather than shutting down all at once. They imaged a 75-kilometre tear through the oceanic plate, and a fault where the slab has dropped about 5 kilometres. The process takes place over millions of years, and the researchers say it does not significantly change earthquake hazard assessments for people living there now. The finding may explain fragments of ancient plates found around the world. The study was published in Science Advances on 25 September 2026, using data from a 2021 seismic imaging experiment. Sources: Louisiana State University via ScienceDaily, "Earth is tearing apart beneath the Pacific Northwest", 25 September 2026, https://www.sciencedaily.com/releases/2026/09/260924231343.htm; Science Advances, 25 September 2026, https://www.science.org/journal/sciadv; FCDO (GOV.UK), "Foreign travel advice", accessed 26 September 2026, https://www.gov.uk/foreign-travel-advice. This article is for general information. It is not medical advice, and it does not replace guidance from a doctor, pharmacist or other qualified healthcare professional on any health matter.

#earth science#earthquakes#geology#Cascadia#research#natural world

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