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Determination of dynamic shear modulus in situ has been an increasingly important source of data for ground response analysis for earthquake design studies. Historically, shear modulus is calculated from in situ measurement of seismic shear-wave velocity. A downhole impact energy source has been developed which maximizes the shear-wave energy produced and minimizes compressional-wave energy for purposes of crosshole in situ seismic shear-wave velocity measurements. The geometry of the energy source permits reversal of the polarity of shear-wave arrivals without changing the polarity of compressional-wave arrivals.
The energy source is described and in situ measurement data are presented. Based on more than three years experience using the downhole source, a procedure for in situ measurement of seismic shear-wave velocity is suggested.
earthquakes, measurements, velocity, shear stress, soils
Project engineer-geologist, Woodward-Clyde Consultants, New York, N.Y.
Project geophysicist, Woodward-Cycle Consultants, San Francisco, Calif.
President, Bison Instruments. Inc., Minneapolis, Minn.