Premium
Weighted sum method for calculating ground force: an evaluation by using a portable vibrator system
Author(s) -
Van Der Veen Michiel,
Brouwer Jan,
Helbig Klaus
Publication year - 1999
Publication title -
geophysical prospecting
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.735
H-Index - 79
eISSN - 1365-2478
pISSN - 0016-8025
DOI - 10.1046/j.1365-2478.1999.00133.x
Subject(s) - seismic vibrator , vibrator (electronic) , acoustics , acceleration , displacement (psychology) , electrical impedance , amplitude , base (topology) , geology , impedance parameters , physics , optics , mathematics , mathematical analysis , classical mechanics , psychology , quantum mechanics , psychotherapist
Using a lightweight portable vibrator, we have evaluated the accuracy of the ‘weighted sum’ method for calculating ground force. Experiments in which the vibrator was suspended elastically have shown that, contrary to expectations based on standard theory, the amplitude of the weighted sum ground force was significantly above zero at high frequencies (> 500 Hz). Complementary investigations with load cells confirmed these results. If not accounted for, these deviations may introduce significant ‘vibroseis‐correlation noise’ in processed records. Furthermore, we have demonstrated that ground force and base‐plate velocity can be used to estimate the radiation impedance, which describes the interaction of (vibratory) sources with the ground. Using the mechanical characteristics of the system (i.e. maximum displacement, maximum velocity and maximum acceleration of the base‐plate) and the radiation impedance, the behaviour of the portable vibrator on typical Dutch soil types was evaluated. We found that for the same sweep, more high‐frequency energy could be generated on hard grounds (e.g. concrete) characterized by a higher radiation impedance than on softer grounds (e.g. clay or sand). Knowledge of this behaviour may provide important information for use in data interpretation.