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.

PGA_i (g)

Required list in g. Anchor amplitudes in g (ascending).

λ_i (1/yr)

Required list in 1/yr. Annual exceedance probabilities at anchors.

a* (g)

Required number in g. Target amplitude.

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

Log-log interpolation of annual exceedance probability between hazard-curve anchors. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

λ(a*) (1/yr)

Returned number in 1/yr. Interpolated annual probability.

w

Returned number. Normalized position within the anchor segment.

• 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.
• 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.

• Annual Rate To T Years Exceedance Converter

  Convert an annual exceedance rate to the probability of exceeding at least once in T years.

• Tau-P Travel Time Anchor Interpolation Calculator

  Linearly interpolate P travel time between supplied distance anchors.

• Uniform Hazard Spectrum Interpolation Calculator

  Log-log interpolated UHS ordinate at an arbitrary period from anchor ordinates.