Use this seismology calculation to reproduce a stated convention, screen observations, or compare scenarios whose units, coordinate conventions, catalog selection, and model assumptions are known.

T_i

Required list. Anchor periods (ascending).

Sa_i

Required list. Anchor spectral accelerations (g).

T* (s)

Required number in s. Target period.

The cited overview of Seismic wave supplies background for the terminology and domain context used by this tool.^[1]

Log-log interpolated UHS ordinate at an arbitrary period from anchor ordinates. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Sa(T*) (g)

Returned number in g. Interpolated spectral acceleration.

Inside

Returned boolean. Whether the target lies inside the anchor range.

• Earth structure, source geometry, path effects, site response, instrument response, catalog completeness, uncertainty, and the fitted range can dominate the accuracy of simplified seismic calculations.
• T* must be at least 0.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

For analysis or hazard decisions, retain uncertainty and provenance and compare the result with waveform processing, calibrated regional models, and guidance from qualified seismologists or the responsible agency.

• Hazard Curve Probability Interpolation Log-Log

  Log-log interpolation of annual exceedance probability between hazard-curve anchors.

• Peterson Noise Model Low High Lookup

  Approximate NLNM/NHNM acceleration power (dB relative to 1 (m/s²)²/Hz) at a period, log-linearly interpolated from a reduced set of Peterson (1993) anchors.

• Response Spectrum Corner Period Band Lookup

  Acceleration- and velocity-controlled period bands scaled by magnitude class.