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Quick start: using Easy HVSR

This page is for users who are not geophysics or HVSR experts: it explains in simple terms what Easy HVSR does and how to get a result in a few steps. Each step links to its detailed page.

What it is, in a nutshell

Easy HVSR analyses a recording of the ground's natural "noise" — the tiny vibrations always present in the soil (ambient seismic noise or microtremor) — recorded with a 3-component sensor (North-South, East-West, Vertical) kept still on the ground for a few minutes.

By comparing the horizontal vibrations with the vertical ones (the H/V spectral ratio, Nakamura's method), the software derives the fundamental resonance frequency of the site, f0: the "tone" at which the ground tends to vibrate.

What f0 is used for:

  • estimating the thickness of the soft covers above the rigid bedrock;
  • assessing the site's seismic response and the risk of soil-structure resonance;
  • supporting seismic microzonation.

No maths required

The software does the calculations: you just follow 5 steps — the tabs on the left, from top to bottom.

What you need

  • A 3-component ambient noise recording (e.g. from a tromograph/tromino or seismometer), in one of the supported formats: SAF, SEG-2, SEG-Y, SU, ASCII/TXT.
  • To practise, use the example files included: menu File → Open, Examples folder.

The 5 steps

1 · General data

Operator, date, location: optional, used only for the report header. Here you can also enter the coordinates of the measurement point. → General data

2 · Traces

  1. Click Read traces and choose the recording file.
  2. Check the Sampling frequency [Hz] (shown by the instrument; e.g. 128 Hz).
  3. The three traces over time appear on the right (North-South, East-West, Vertical). Click Apply.

→ Traces

A good recording

Lasts at least 15–20 minutes, on still ground, away from strong wind, heavy traffic or machinery.

3 · Selection (time windows)

The noise is analysed in "chunks" (windows). Easy HVSR splits the recording into windows and you choose which to keep:

  • keep the "quiet" windows (uniform signal);
  • exclude (untick) windows with obvious peaks/transients — a footstep near the sensor, a knock, a vehicle: they spoil the result;
  • you need at least 2 valid windows (the more, the better).

→ Selection

4 · Spectral analysis

  1. Set the frequency band (min/max) and the smoothing (Konno & Ohmachi): to start, leave the default values.
  2. Click Update: you get the average H/V curve and, at the bottom, the peak frequency f0.
  3. The colour maps (stationarity and directionality) show whether the peak is stable over time and independent of direction.

→ Spectral analysis

5 · H/V spectrum (result and model)

  • Read the fundamental frequency f0 and check the reliability indicators (international SESAME criteria): when you see "H/V curve reliability – VERIFIED" and "Peak reliability – VERIFIED", the result is robust.
  • (Optional, advanced) With the inversion ("Automatic search") the software estimates a shear-wave velocity (Vs) profile of the subsoil from the H/V curve.

→ H/V spectrum

How to read the result

  • High f0 (a few Hz) → thin covers; low f0 (fractions of a Hz) → thick covers.
  • A sharp peak indicates a strong contrast between soft layers (above) and rigid bedrock (below).
  • Quick estimate of the cover thickness \(H\): \(H \approx V_s / (4 \cdot f_0)\) (with \(V_s\) = average shear-wave velocity in the covers).

Common mistakes to avoid

Watch out

  • Recording too short or disturbed (wind, traffic, machinery).
  • Keeping windows with transients → "dirty" peak.
  • Trusting a peak when reliability is not verified.

Printing and export

  • File → Print: generates the report.
  • Export: saves charts and data.
  • First fill in the Technical office data (top bar) for the report header.

In short

Read traces → choose the good windows → Update → read f0 (and check that reliability is verified). This is the minimum workflow for a correct result.

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