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Shear wave velocities from down‐hole measurements
Author(s) -
Beeston H. E.,
McEvilly T. V.
Publication year - 1977
Publication title -
earthquake engineering and structural dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.218
H-Index - 127
eISSN - 1096-9845
pISSN - 0098-8847
DOI - 10.1002/eqe.4290050206
Subject(s) - geophone , seismometer , geology , hammer , shear (geology) , seismology , shear waves , seismic wave , geotechnical engineering , structural engineering , engineering , petrology
Shear wave velocities of soils, which provide shear moduli for earthquake response calculations, can be measured clearly and accurately using the down‐hole method. Such a method has been used at a number of sites in California with good results to depths of 200 ft. Seismic waves from hammer blows, delivered to the ends of a heavy plank loaded by the front wheels of a vehicle, are received by a three‐component geophone in a carefully prepared vertical hole and recorded at 1 mm/ms with a six‐channel seismograph. A series of records are obtained at various measured depths in the hole, allowing calculation of interval velocities. Shear waves are easily identified by a clear 180 degrees phase difference between waves generated by blows on the opposite ends of the plank. Compressional waves are routinely logged by a vertical hammer blow at each recording depth. Shear velocities are reproducible to about 5 per cent in surveys of neighbouring holes. The reading uncertainty of ± 1 msec for the S arrival gives a resolution sufficient to detect a buried layer 5–10 ft thick with a velocity contrast of only 20 per cent.