Surface Wave Magnitude VK20 Formula Calculator

Classic vertical-component Rayleigh surface-wave magnitude Ms = log10(A/T) + 1.66·log10(Δ°) + 3.3 with A in micrometres; nanometre input is converted to µm internally.

Description

Classic vertical-component Rayleigh surface-wave magnitude Ms = log10(A/T) + 1.66·log10(Δ°) + 3.3 with A in micrometres; nanometre input is converted to µm internally.

Surface Wave Magnitude VK20 Formula Calculator is a focused tool for the following task. Classic vertical-component Rayleigh surface-wave magnitude Ms = log10(A/T) + 1.66·log10(Δ°) + 3.3 with A in micrometres; nanometre input is converted to µm internally. It reports M_s, Valid Δ? from the values you provide rather than inventing measurements, coefficients, or professional judgment that are not part of the input.

When to use Surface Wave Magnitude VK20 Formula

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.

A (nm): Required number in nm. Vertical Rayleigh amplitude (converted to µm internally).
T (s): Required number in s. Wave period (18-22 s typical).
Δ (°): Required number in °. Epicentral distance.

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

How Surface Wave Magnitude VK20 Formula works

Classic vertical-component Rayleigh surface-wave magnitude Ms = log10(A/T) + 1.66·log10(Δ°) + 3.3 with A in micrometres; nanometre input is converted to µm internally. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

M_s: Returned number. Surface-wave magnitude.
Valid Δ?: Returned boolean. Whether distance lies in the 20-160 degree validity window.

Limitations and assumptions

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.
A must be at least 0.
T must be at least 0.
Δ must be at least 0.
Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Alternative or Complementary approaches

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.

References

Seismic magnitude scales — Wikipedia contributors

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