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.

I₀

Required number. Epicentral intensity.

I

Required number. Isoseismal of interest.

h (km)

Required number in km. Focal depth.

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

Kövesligethy isoseismal radius: I(r) = I₀ − 3·log₁₀(√(r²+h²)/h), inverted for a target intensity. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

r_I (km)

Returned number in km. Radius of the target isoseismal.

Note

Returned string. Validity note.

• 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.
• h 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.

• Isoseismal Annulus Area Between Intensities Calculator

  Felt area of the annulus between two intensity contours using the Kövesligethy decay.

• Felt Radius Heuristic Log Scaling Calculator

  User-parameterized log-linear felt-radius screen R = R₀·10^(kM). The default R₀=0.1 km and k=0.5 are illustrative and must be calibrated for regional attenuation, depth, and reporting conditions.

• JMA Intensity From PGV Converter

  Japan Meteorological Agency instrumental intensity from PGV (cm/s): I_JMA = 2.68·log₁₀(PGV) + 2.29 (approx).