Geophysics in Pomona encompasses a suite of non-invasive subsurface investigation techniques that measure physical properties of soil and rock to guide engineering, environmental, and construction decisions. These methods, including MASW / VS30 (shear wave velocity) profiling, electrical resistivity / VES (Vertical Electrical Sounding), and seismic tomography (refraction/reflection), provide critical data without the need for extensive drilling or excavation. In a seismically active region like Southern California, understanding the dynamic behavior of near-surface materials is essential for public safety and regulatory compliance.
Pomona sits within the Los Angeles Basin, a geologically complex area characterized by deep alluvial deposits, ancient river channels, and proximity to active fault systems such as the San Jose Fault and the larger Puente Hills Thrust. The local subsurface often consists of interbedded sands, silts, and gravels overlying older sedimentary formations, with groundwater tables that can vary significantly by season and location. These conditions create site-specific challenges, including variable bearing capacity, liquefaction potential, and amplified seismic shaking, making targeted geophysical surveys indispensable for accurate site characterization.
Local and national regulations heavily influence geophysical work in Pomona. The California Building Code (CBC), which adopts and amends the International Building Code (IBC), mandates site-specific seismic hazard evaluations for many structures. Chapter 16 of the CBC requires determination of the Site Class based on the average shear wave velocity in the upper 30 meters (VS30), a parameter directly measured through MASW / VS30 (shear wave velocity) surveys. Additionally, ASCE 7-16 standards, referenced by the CBC, dictate the use of seismic refraction and resistivity data for liquefaction assessment and foundation design, ensuring that projects meet rigorous safety thresholds.
Projects in Pomona that typically require geophysical services range from mid-rise commercial developments and school expansions to infrastructure upgrades and environmental remediation. Structural engineers rely on seismic refraction and MASW to model ground motion and design earthquake-resistant foundations, while geotechnical engineers use electrical resistivity to map groundwater, locate buried utilities, or delineate contaminant plumes. Municipal agencies and developers increasingly integrate these methods early in the design phase to reduce geotechnical uncertainty, avoid costly surprises, and comply with the stringent review processes of the City of Pomona Building and Safety Division.
Geophysics provides non-invasive subsurface data essential for seismic design, foundation engineering, and environmental assessment. In Pomona, it helps identify soil stiffness, depth to bedrock, groundwater, and hidden anomalies, enabling compliance with California Building Code requirements and reducing geotechnical risks before excavation begins.
VS30 is the primary parameter used to classify site soil types per CBC and ASCE 7-16 for seismic design. Pomona's alluvial soils can vary sharply, affecting ground motion amplification. Accurate VS30 profiling through methods like MASW directly determines the seismic design category and foundation requirements for a project.
Yes, the California Building Code and City of Pomona standards often mandate seismic site classification and liquefaction studies for new buildings, schools, and hospitals. These studies typically rely on geophysical methods such as MASW and seismic refraction to derive the necessary VS30 and dynamic soil properties for regulatory approval.
Pomona is underlain by complex alluvial basins and is near active faults, leading to variable soil profiles, shallow groundwater, and potential liquefaction zones. Geophysical surveys effectively map these lateral and vertical changes, identifying soft zones, bedrock depth, and water saturation that impact construction safety and cost.