Less is more:

from van der Rohe to the 4-channel system

for the holistic analysis of surface waves

G. Dal Moro (1) (2), S.R. Moustafa (3) (4), N. Al-Arifi (3)

(1) Department of Seismotectonics, Institute of Rock Structure and Mechanics, Prague (Czech Republic)

(2) Eliosoft.it, Udine (Italy)

(3) Geology and Geophysics Department, Faculty of Sciences, King Saud University, Riyadh (Saudi Arabia)

(4) Seismology Dept., National Research Institute of Astronomy and Geophysics, Cairo (Egypt)

GNGTS (Gruppo Nazionale Geofisica della Terra Solida - gngts.ogs.trieste.it) 17-19 November 2015 – Trieste (Italy)

Ludwig Mies van der Rohe - Villa Tugendhat (Brno – CZ)

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Obtaining the maximum possible outcome out of an

extremely-light equipment and limited field effort.

The proposed system consists of:

- a (good quality) 4-channel seismograph;

- one 3-component (3C) geophone;

- four vertical geophones.

The system (after the van der Rohe’s motto “Less is More”):

minimalistic elements with multiple functional purposes

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

The acquired (active and passive) data, are used to determine

up to six (now actually seven) independent (but mutually

related and complementary) objective functions that, all

together, fully describe the surface-wave propagation.

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Questioning the multi-channel dogma:is the analysis of phase velocity (analyzed via multi-channel data) better with respect to the single-channel data useful for the analysis of group velocities?

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

the multi-channel dogma:here the group velocity spectra (Z and T components) for the most-distant trace

the multi-channel dogma:here the FVS analysis of the group velocity spectra (Z and T components)

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

“comparing” the field and the synthetic velocity spectra[no interpretation in terms of dispersion curve(s)]

“compact” FVS representation: background colors are the field data, overlaying black contour lines the synthetic

The FVS (Full Velocity Spectrum) approach: the point

The 4-channel (triggerable) system & the 6 (now 7) components

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

1) Horizontal-to-Vertical Spectral Ratio (HVSR) [3-channel passive

seismics] (e.g., Arai and Tokimatsu, 2004) [1 component];

All together 6 components (now actually 7 – stay tuned)

2) Active acquisitions recorded by means of the 3-component geophone

and used for the holistic analysis of the group velocities of Rayleigh and

Love waves also jointly with the RVSR [HS method] (Dal Moro et al.,

2015a; 2015b) [up to 4 components: ZVF + RVF + THF group velocity

spectra + RVSR].

3) Miniature Array Analysis of Microtremors (MAAM) [4-channel

(vertical geophones) passive seismics] (Cho et al., 2013) [1 component];

Onesource

Just onereceiver

(a 3-component geophone)

The active HS acquisition

The active data (Rayleigh- and Love-wave group velocities)

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Active seismics (HS approach): the components acquired in case a single 3C geophone is used

to record the signal(s) produced by both a Vertical and Horizontal Force (VF and HF).

Further details in Dal Moro (2014) and Dal Moro et al., 2015b).

MAAM (Miniature Array Analysis of Microtremors) [Cho et al., 2013]

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

The site (NW Italy urban area)

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

The acquisition parameters

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

sampling rate 4 ms (Nyquist frequency 125 Hz)acquisition length 30 min

radius 2 + 5 msensors four vertical 4.5Hz geophones

MAAM acquisition parameters

sampling rate 1 ms (1000 Hz)acquisition length 1 s

offset (m) 40sensor one 3-component 2Hz geophonestack 4

HS acquisition parameters

HVSR data

stable

no directivity

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

HVSR data

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

MAAM data and analysis (Rayleigh-wave effective dispersion curve)

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

MAAM (passive seismics): a) acquisition setting (in this case the four

vertical-component geophones are along a 2m-radius circle); b) Rayleigh-

wave effective dispersion curve (vertical component) determined while

considered the data acquired for the present case study.

Validation: comparing MAAM and ESAC

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

ESAC acquisition and velocity spectrum

Validation: comparing MAAM and ESAC

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

In the background the

ESAC velocity spectrum

and, overlaying, the MAAM

(effective) dispersion curve.

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Joint (Multi-Objective) Analysis:

HVSR: alfa (α) parameters as variable

Active data (Rayleigh- and Love-wave group velocity spectra): FVS approach

Effective dispersion from MAAM: effective Z-component (Tokimatsu et al., 1992)

Critical points in the MAAM analysis:

- Acquisition: necesary a very low amount of “electronic” noise

- Choosing the maximum amplitude of the considered segments

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Considered Data

HVSR

Rayleigh-wave effective dispersion curve (Z component) from MAAM

THF – Love waves(group velocity spectrum)

Z R T

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Joint analysis of the five here-considered components: a) acquired active traces (vertical, radial

and transversal components); b) field and synthetic HVSR curves; c) field (from MAAM) and

synthetic Rayleigh-wave (vertical component) effective dispersion curves; d) field (background

colors) and synthetic (overlain black contour lines) Love-wave group velocity spectra from the

active acquisition (FVS analysis). Also shown the ZVF and RVF velocity spectra.

Few Final Remarks

- “Component” versus “number of geophones”

- A light equipment (a 4-channel system + one 3C geophone +

four vertical geophones) for efficiently acquire active & passive

data to jointly analyze up to 6 (now actually 7) components

- RVSR and RPM

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

versus

- Thanks to the large number of considered components we avoid

pitfalls and do no need for a priori geological information

- Joint Analysis as compromise

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Some References

Arai H. and Tokimatsu K.; 2004: S-wave velocity profiling by inversion of microtremor H/V spectrum.

Bull. Seism. Soc. Am, 94, 53–63.

Arai H. and Tokimatsu K.; 2005: S-Wave velocity profiling by joint inversion of microtremor dispersion

curve and horizontal-to-vertical (H/V) spectrum. Bull. Seism. Soc. Am., 95: 1766-1778

Cho I., Senna S. and Fujiwara H.; 2013: Miniature array analysis of microtremors. Geophysics, 78,

KS13–KS23.

Dal Moro G., Moura R.M. and Moustafa S.R.; 2015c: Multi-component Joint Analysis of Surface

Waves. J. Appl. Geophysics, 119, 128-138.

Dal Moro G., Moustafa S.R. and Al-Arifi N.; 2015b: Efficient acquisition and holistic analysis of Rayleigh

waves, Proceedings of the Near-Surface EAGE 2015 (Turin - Italy)

Dal Moro G., Keller L. and Poggi V.; 2015a: A Comprehensive Seismic Characterization via Multi-

Component Analysis of Active and Passive Data. First Break, 33, 45-53.

Dal Moro G.; 2014: Surface Wave Analysis for Near Surface Applications. Elsevier, ISBN

9780128007709, 252pp

Ohori M., Nobata, A. and Wakamatsu K.; 2002: A comparison of ESAC and FK methods of estimating

phase velocity using arbitrarily shaped microtremor analysis. Bull. Seism. Soc. Am., 92, 2323–2332.

Tokimatsu K., Tamura S. and Kojima H.; 1992: Effects of Multiple Modes on Rayleigh Wave Dispersion

Characteristics. Journal of Geotechnical Engineering, 118, 1529-1543.

Less is More (Dal Moro et al., 2015) – GNGTS 17-19 November 2015 – Trieste (Italy)

Acknowledgements

The present work was partially supported by the Visiting Professor

Program of the King Saud University (Riyadh, Saudi Arabia) and the

authors are grateful to the Deanship of the Scientific Research of the King

Saud University (Riyadh, Saudi Arabia) for the financial support (PRG-

1436-06 Research Grant).

thanks