Rotary Actuated Seismic Source And Methods For Continuous Direct-push Downhole Seismic Testing

Abstract

Remotely operated rotary actuated shear wave generating apparatus and methods that generate horizontally polarized vertically propagating shear waves for use in down-hole shear wave velocity measurements. Seismic signals are generated by an offset mass rotating in a plane perpendicular to the surface of the ground, which impacts an impact member coupled to the ground. The energy of impact is transmitted to the ground parallel to the surface of the ground. The apparatus uses a spring-loaded rotating mass that has a rotary motion. Because acceleration of the mass is not horizontal, reaction forces caused by acceleration of the mass create less horizontal shear stress in the ground prior to the desired time (impact). Reaction forces of the accelerated rotating mass does not generate undesirable waves that obscure the desirable waves caused by impact with the impact member. The source generates transient shear waves repeatedly at constant intervals. Wave motions are recorded by a probe as it is advanced into the ground, without pause.