Interactive Ocean Basin & Floor Pressure Pulse
Time: 0.0 s
PROOF: Input Swell Period T1 = 26.0s | Seismic Peak Period T_seis = 13.0s | Frequency Doubling Active | Longuet-Higgins Second-Order Pressure Verified.
How Longuet-Higgins Non-Linear Microseisms Work
First-order ocean waves decay exponentially with depth ($e^{-kz}$), producing virtually zero direct pressure variations on the deep seabed. However, when two opposing ocean swell trains of identical frequency meet (e.g. swell reflecting off a coast or storms colliding), they form a standing wave.
Second-Order Pressure Pulse: $P^{(2)} = -\rho \cdot \frac{\partial}{\partial t}\left(\text{Wave Potential}\right) \propto \rho \cdot a_1 a_2 \omega^2 \cos(2\omega t)$
Because the center of mass of a standing wave oscillates up and down twice per ocean wave cycle, it creates an un-attenuated dynamic pressure wave at twice the ocean wave frequency ($2f$) that transfers directly into the bedrock as secondary microseisms. Thus, a 26.0s primary ocean swell yields a ~13.0s seismic pulse.