Supershear Earthquakes: A New Threat to Buildings and Lives

Topic: Earth Science

Scientists have discovered that supershear earthquakes produce unique ground motion signatures. This could change building codes and our understanding of earthquake damage. Researchers at Caltech simulated supershear earthquakes to learn more.

A team of scientists from the California Institute of Technology (Caltech) has been studying a type of earthquake called a supershear earthquake.

Supershear earthquakes are different from regular earthquakes because the fault rupture itself moves faster than the earthquake's shear waves. This creates an intense shock front, similar to the sonic boom of a supersonic jet. The phenomenon causes strong shaking close to the fault.

In the past 15 years, researchers have found that nearly 36% of strike-slip earthquakes with a magnitude of 7 or greater contained supershear ruptures. However, observations of ground shaking near the fault in supershear earthquakes are rare. This led Mohamed Abdelmeguid, the lead author of the study, to ask: 'Do supershear ruptures produce ground motions that are distinctly different from subshear ruptures?'

Abdelmeguid and his team used computer simulations to model supershear earthquakes. They found that prolonged and sustained supershear ruptures consistently produced stronger ground-motion amplitudes than their subshear counterparts. The researchers also discovered that peak ground velocity (PGV) for supershear ruptures remained high even up to 20 kilometers away from the fault.

The study's findings have significant implications for building codes and ground-motion models. Existing codes do not explicitly separate rupture speed or sustained supershear propagation as design-relevant parameters. The researchers concluded that supershear earthquakes generate larger spectral accelerations, especially in the frequency range that affects buildings.

Why It Matters

This discovery is crucial for India because many parts of the country are prone to earthquakes. Understanding how supershear earthquakes behave can help us develop more effective building codes and emergency response plans.

Key Facts

• Supershear earthquakes occur when the fault rupture moves faster than the earthquake's shear waves.
• Nearly 36% of strike-slip earthquakes with a magnitude of 7 or greater contained supershear ruptures between 2011 and 2026.
• The study found that prolonged and sustained supershear ruptures produce stronger ground-motion amplitudes than subshear counterparts.
• Peak ground velocity (PGV) for supershear ruptures remained high even up to 20 kilometers away from the fault.
• Supershear earthquakes generate larger spectral accelerations, especially in the frequency range that affects buildings.

Key Terms

Supershear earthquake

An earthquake where the fault rupture moves faster than the earthquake's shear waves.

Peak ground velocity (PGV)

The maximum speed the ground moves during an earthquake.

Spectral acceleration

The maximum acceleration buildings experience during an earthquake.

Implications

This discovery is crucial for India because many parts of the country are prone to earthquakes. Understanding how supershear earthquakes behave can help us develop more effective building codes and emergency response plans.