In Escondido, we do not pray to the gods of stability. We measure the earth's breath against our bones.
Every structure has a heartbeat—a natural period determined by its height and stiffness. When the ground shakes, it does not shake randomly. It sweeps through frequencies like a choir testing pitch. If your building's period matches the quake's dominant frequency, resonance occurs. Amplitude multiplies. Walls remember what they were taught to forget.
Sa(T) = SDS × (0.4/T)^2/3 for T ≤ Tc
where SDS = Site Coefficient × Peak Ground Accel
This calculator uses the NEHRP response spectrum approximation for Site Class C (typical San Diego foothills). Adjust the sliders. Watch the period lengthen as your tower rises. See the spectral acceleration spike as your damping vanishes. You are not designing for the average shake. You are designing for the one that finds your frequency.
Download the constants (.json) — machine-readable proof of every coefficient used.