Earthquake, another violent tremor right here… More…

To understand why earthquakes like this occur, it helps to visualize what is happening beneath the ocean floor.

A subduction zone forms when one tectonic plate is forced beneath another. In this case:

The oceanic plate is denser and thinner
The continental plate is thicker and more buoyant
The oceanic plate sinks into the mantle at a shallow angle
But this motion is not smooth. Instead, the interface between the two plates often locks due to friction. When stress builds up beyond the strength of the rocks, the locked zone suddenly slips, releasing energy in the form of seismic waves.

This slip can happen in different ways:

3.1 Shallow crustal earthquakes
These occur within the upper plate or very near the interface. They are often moderate in size.

3.2 Megathrust earthquakes
These occur when a large portion of the subduction interface ruptures at once. These are the most powerful earthquakes on Earth.

3.3 Slow-slip events
These are gradual movements that occur over days or weeks and release energy without strong shaking.

The reported earthquake fits into the shallow category, likely associated with stress adjustments near the plate interface.

4. Why a Depth of 9 km Is Significant
Depth is one of the most important parameters in seismology.

Deep earthquakes (70–700 km): less damaging at surface
Intermediate depth: moderate surface effects
Shallow earthquakes (0–20 km): strongest surface shaking potential
At ~9 km beneath the ocean floor, this earthquake is firmly in the shallow category.

Shallow earthquakes matter because:

Seismic waves travel shorter distances to the surface
Energy is less attenuated (less absorbed by surrounding rock)
They can trigger secondary hazards like submarine landslides
They are more clearly recorded by coastal and ocean-bottom sensors
However, in offshore environments like this one, the energy often dissipates before reaching heavily populated coastal areas.

5. The Cascadia Subduction Zone: A Sleeping Giant