Baltimore sits on a complex mix of coastal plain sediments and Piedmont bedrock. For any project above 5 stories, ASCE 7-22 requires site-specific seismic response analysis. Our seismic tomography surveys map the subsurface velocity structure down to 50 meters. We use 24-channel seismographs with 4.5 Hz geophones. This method identifies soil layers, bedrock depth, and potential fault zones. It is especially relevant in Baltimore’s Inner Harbor area where old fill and soft clays overlie irregular rock. Before drilling piles, we combine refraction tomography with MASW-Vs30 to obtain shear-wave velocity profiles for site class determination. The data directly feeds into IBC Chapter 16 seismic design parameters.
Refraction tomography in Baltimore’s coastal plain routinely images bedrock at 15–30 meters, critical for pile length optimization.
Method and coverage
Regional considerations
Baltimore has over 620,000 residents and sits in Seismic Zone 2A. The last damaging earthquake was the 2011 M5.8 Virginia event, felt strongly in the city. Old brick buildings and soft soils amplify ground motion. Without seismic tomography, you risk designing for wrong site class. Overestimating soil stiffness leads to under-designed foundations. Underestimating it wastes concrete and steel. The 2018 Baltimore City Building Code now mandates site-specific response for all essential facilities. Our surveys reduce that risk. We map Vs30 profiles to confirm site class A through E. This avoids the 40% cost penalty of an overly conservative default class D assumption. The data also identifies liquefaction-prone zones in the Patapsco River basin.
Standards that apply
ASCE 7-22 Seismic Site Class, ASTM D5777-18 (Refraction), ASTM D7128-18 (Reflection), IBC 2021 Chapter 16, NEHRP Recommended Provisions
Related services
Refraction Tomography
Uses first-arrival P-wave travel times to invert for velocity layers. Best for depth to bedrock, fill thickness, and rippability assessments. Typical depth range 5–50 m.
Reflection Tomography
Imaging of deep stratigraphy, faults, and dipping contacts using reflected P- and S-waves. Applied for tunnel alignments, deep foundations, and seismic hazard studies. Depth range 20–100 m.
Typical parameters
Common questions
What is the difference between refraction and reflection tomography?
Refraction uses first-arrival times to map velocity layers and bedrock depth. Reflection uses reflected waves to image discontinuities like faults and dipping strata. Refraction is shallower (up to 50 m) and faster; reflection goes deeper (up to 100 m) and gives more structural detail.
How much does seismic tomography cost in Baltimore?
A typical refraction survey for a half-acre site costs between US$2,880 and US$4,850 including field work, processing, and a report with velocity profiles. Larger projects or reflection surveys may cost more depending on line length and shot count.
How long does a field survey take?
A 180-meter refraction line with 24 geophones takes about 4–6 hours in the field. Processing and interpretation add another 2–3 working days. Reflection surveys require 8–12 hours per line due to longer offsets and more shots.
Do I need seismic tomography for a residential basement in Baltimore?
Not always. For a typical 2-story house on stable ground, a simple test pit and soil classification may suffice. But if you are building a deep basement in areas like Fells Point or Canton where fill depth varies, tomography can prevent surprises and extra excavation costs.