The “whiplash” effect: How earthquakes arrest and how to stop them

Kyoto University researchers have identified a “stopping phase” in seismic data that occurs when an earthquake hits a barrier and stops abruptly

This phase creates a violent “whiplash” ground motion that current anti-quake engineering isn’t fully designed to handle, highlighting a new priority for protecting buildings near fault lines.

While we often study how earthquakes start, a new discovery from researchers at Kyoto University, published in Science on April 23, 2026, focuses on how they end.

By analysing “strong-motion” data near fault lines, the team identified a distinct stopping phase—a violent, whiplash-like ground motion that occurs when a rupture hits a barrier and stops suddenly.

The mystery of the negative phase

The researchers noticed a consistent “negative phase” in seismic waveforms that didn’t fit existing models. By combining ground-motion recordings with satellite data and numerical simulations, they realised these dips represent the literal moment an earthquake “slams on the brakes.”

Key Discoveries:

• Abrupt vs. gradual arrest:

  • Earthquakes generate the most powerful stopping signals when they hit a barrier and stop abruptly. If a rupture simply slows down gradually, these signals are much weaker.

• The stopping phase signal:

  • This phase is characterised by a systematic “negative motion” at the end of the rupture.

• Whiplash motion:

  • The most dangerous finding is that this stopping phase creates a sudden, intense “whiplash” effect in the ground.

New challenges for engineering

This “whiplash” motion is particularly concentrated at the end points of a fault line or at internal boundaries where the earth’s crust changes. Because current earthquake-resistant engineering focuses primarily on the initial “shaking” phase, this new data presents a significant challenge.

Engineers will now need to account for these specific, high-intensity movements to protect structures located near the projected endpoints of major strike-slip faults. The team plans to continue building a global catalogue of these stopping phases to help refine seismic hazard models worldwide.