A geophone spread cable rolls out across a vacant tract near Buffalo Bayou: 24-channel arrays with 4.5 Hz vertical-component receivers, connected to a 24-bit seismograph that records first arrivals and reflections at sub-millisecond sampling intervals. In Houston, seismic tomography tackles a specific problem—the thick, unconsolidated Beaumont Formation clays and Pleistocene terrace deposits that blanket the metropolitan area from Katy to Baytown. These sediments, often exceeding 600 meters in depth before reaching competent bedrock, mask buried faults, paleochannels, and abrupt facies changes that affect foundation design. The refraction method maps the compressional-wave velocity (Vp) of successive layers by analyzing critically refracted head waves, while the reflection technique images deeper impedance contrasts tied to the Fleming Formation and underlying Vicksburg Group. Together, they produce a continuous velocity model of the subsurface that no drilling program alone can supply across the spatial scales required for large Houston developments. When a high-resolution stratigraphic profile is needed before committing to a deep boring plan, the team often runs a preliminary MASW survey to constrain shear-wave velocities in the upper 30 meters, then extends the imaging depth with refraction tomography.
A well-constrained seismic velocity model turns a single boring log into a calibrated cross-section spanning hundreds of meters—essential in Houston's faulted, laterally variable geology.
