Scientists for the first time have detected a slow slip earthquake in motion during the act of releasing tectonic pressure on a major fault zone at the bottom of the ocean.

The slow earthquake was recorded spreading along the tsunami-generating portion of the fault off the coast of Japan, behaving like a tectonic shock absorber. Researchers from The University of Texas at Austin described the event as the slow unzipping of the fault line between two of the Earth’s tectonic plates.

Their results were published in Science.