Seismic Tomography (Refraction/Reflection) in Hampton, Virginia

With a sledgehammer source and a 115-meter spread, we typically image 25–35 meters deep in the saturated sands and clays of the Tabb and Yorktown formations. Switching to an accelerated weight drop extends that to 60–80 meters, which is enough to reach the top of the crystalline basement in most parts of Hampton. The actual depth depends on the velocity gradient—the denser shell beds in the Yorktown transmit energy efficiently, so we often get better penetration here than in the looser upland soils farther west on the Peninsula.

Yes, and this is one of the strongest applications in Hampton. Solution cavities in the Yorktown Formation create a velocity shadow—first arrivals are delayed because the wave has to diffract around the void. Tomographic inversion turns those delays into a low-velocity anomaly that we can map in plan and cross-section. We've identified cavities as small as 1.5 meters across at 10–15 meters depth. For high-resolution cavity imaging, we often combine refraction tomography with a targeted reflection line over the anomaly.

A single refraction line with 24 geophones, sledgehammer source, and full tomographic processing runs between US$2,510 and US$4,700 depending on line length, number of shot points, and whether we're shooting P-wave, SH-wave, or both. Reflection surveys with CMP acquisition cost more because of the tighter station spacing and processing time. Every proposal includes a site-specific scope based on your target depth and the site access conditions we assess during the walkover.

Aircraft noise is a reality on the Peninsula, especially near the base. We stack shots—typically 5 to 10 impacts per shot point—to improve signal-to-noise ratio, and we use geophones with a 14 Hz natural frequency that roll off low-frequency jet rumble. Our processing software also applies bandpass filtering and first-arrival muting to clean up the records. The result is a usable refraction dataset even with F-22s overhead, which we've proven on multiple sites within 2 miles of the runway.