Shear Wave Velocity Calculator — Vs & Vs30 Site Class
Calculate the shear wave velocity Vs from shear modulus and density, compute Vs30 from a multi-layer soil profile, and determine the ASCE 7-16 seismic site class (A through E).
MPa
kg/m³
m
m/s
m
m/s
m
m/s
m
m/s
Vs = √(G / ρ) — velocity of S-waves through the material
Average shear wave velocity over the top 30 metres of soil/rock profile
- 1
Convert G from MPa to Pa
30 × 10⁶ = 30,000,000 - 2
G ÷ ρ
30,000,000 ÷ 1,800 = 16,666.67 - 3
Shear wave velocity Vs = √(G ÷ ρ)
√(16,666.67) = 129.1Vs in m/s — stiffer or lighter material = faster S-waves.
How does this calculator work?
Vs = √(G/ρ) gives shear wave velocity from shear modulus G (Pa) and density ρ (kg/m³). Vs30 = 30 / Σ(dᵢ/Vsᵢ) is the harmonic-mean velocity over 30 m and determines ASCE 7-16 seismic site class: E (≤183 m/s), D (183–366), C (366–762), B (762–1524), A (>1524 m/s). Confirm with a geotechnical engineer for design use.
Formula
How this is calculated
A shear (S) wave propagates through a medium by oscillating perpendicular to its direction of travel. Its velocity depends entirely on the medium's shear stiffness and inertia: Vs = √(G / ρ), where G is the shear modulus (Pa) and ρ is the mass density (kg/m³). Stiffer, denser materials transmit S-waves faster — bedrock typically shows Vs of 700–3 000 m/s while soft clay may be as low as 50 m/s. This calculator converts G in MPa to Pa automatically before computing.
Vs30 is the time-averaged shear wave velocity over the top 30 metres of a soil profile: Vs30 = 30 / Σ(dᵢ / Vsᵢ), where dᵢ is the thickness of layer i and Vsᵢ is its shear wave velocity. This harmonic weighting gives more influence to slow (soft) layers because they consume disproportionately more travel time. If the defined layers total less than 30 m, the last layer's Vs is extended to the 30 m depth.
ASCE 7-16 (the US structural engineering reference standard) uses Vs30 to assign a seismic site class — Site A (hard rock, > 1524 m/s) through Site E (soft clay, ≤ 183 m/s) — which determines the site amplification factors that scale design ground motions. Site Class D is the default when subsurface data are lacking. Site Class F requires a site-specific analysis regardless of Vs30 and is not covered here. Values are based on ASCE 7-16 Table 20.3-1; verify against the applicable edition of the standard and local regulations.
Frequently asked questions
P-waves (primary or compressional waves) oscillate parallel to the propagation direction and travel faster; Vp = √((K + 4G/3) / ρ) where K is the bulk modulus. S-waves are slower and cannot propagate through liquids (liquids have no shear stiffness, G = 0). The ratio Vp/Vs for typical rock is about 1.7–2.0; ratios above 3–4 suggest near-saturation or liquefaction potential.
Common methods include: MASW (Multichannel Analysis of Surface Waves), which analyses Rayleigh wave dispersion from surface sources; seismic downhole or crosshole tests, which measure travel times between a surface source and borehole receivers; and SCPT (seismic cone penetration test), which combines cone penetration with a seismic source. Laboratory resonant column and bender element tests measure Vs on drill-core samples under controlled stress conditions.
ASCE 7-16 allows Site Class D to be used as a default when site-specific subsurface data are absent and the authority having jurisdiction does not require a more specific determination. Site D represents stiff soil with Vs30 of 183–366 m/s. Using Site D without investigation is conservative for most soft-soil sites but can underestimate amplification for very soft (Site E) conditions — a geotechnical engineer should evaluate whether a site-specific study is warranted.
Also known as
TG we-Calculate Editorial Team. (2026). Shear Wave Velocity Calculator — Vs & Vs30 Site Class [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/shear-wave-velocity-calculator
TG we-Calculate Editorial Team. "Shear Wave Velocity Calculator — Vs & Vs30 Site Class." TG we-Calculate. 2026. https://we-calculate.com/calculator/shear-wave-velocity-calculator.
TG we-Calculate Editorial Team, "Shear Wave Velocity Calculator — Vs & Vs30 Site Class," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/shear-wave-velocity-calculator
@misc{wecalculate_shear_wave_velocity_calculator, title = {Shear Wave Velocity Calculator — Vs & Vs30 Site Class}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/shear-wave-velocity-calculator}}, year = {2026}, note = {TG we-Calculate} }
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