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Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles. Photo: Wikipedia

Earthquake booms have been reported since the beginning of time.

But experimental and scientific explanations of this strange phenomenon were lacking.

Now it is done! For the first time ever, scientists were able to decipher in laboratory experiments with real rocks, how supershear earthquakes create sonic booms.

According to them, sonic booms are created during so-called supershear earthquakes.

During these strange events, the rupturing fault breaks faster than certain seismic waves can travel. This creates a seismic mach cone that fires out the end of a fault’s rupture zone.

Normal vs Supershear Earthquakes

The waves behind the weird phenomenon are called shear waves.

For most earthquakes, these slow seismic waves are felt as rolling and shaking motions after the initial shock.

In contrast, supershear earthquakes form in three steps and have two big wave arrivals:

  1. The initial shock followed by
  2. The formation of the powerful supershear mach cone instead of the rolling shear waves. This cone shakes the ground in a direction parallel to the fault zone that created it.
  3. Finally, and soon after, a second shear wave hit with ground motions at right angles to the fault zone. This change in the direction of the dominant ground motions is dramatic for buildings.

Which earthquakes create supershear quakes?

The San Andreas in California is a prime candidate for such strange seismic events.

Supershear quakes are not only produced by massive earthquakes. Already a moderately strong quake of a magnitude between 6 and 7 could produce supershear waves. And that is not a very unusual earthquake size along the San Andreas.

But don’t be too worry about supershear quakes. They are very rare.

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4 COMMENTS

  1. […] Earthquake booms have been heard and felt as a swarm of 12 small earthquakes has rattled the DFW area, all centered around the old Texas Stadium site in Irving. The latest one took place just before 10:00 a.m. and measured 2.7 in magnitude. Another quake about 90 minutes earlier registered in at a 2.6 in magnitude. […]

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