Frequently Asked Questions
1) Why should geophysical surveys be performed?
Geophysical surveys should be performed to aid in locating and/or avoiding particular subsurface objects, to map geologic hazards such as earthquake faults and landslides, to delineate the location, depth, and lateral extent of subsurface contamination, to evaluate geologic resources for mining and groundwater development, to measure foundation parameters for large structures, and to aid in the planning of other investigations such as the strategic placement of test borings for environmental investigations.
2) How do you plan a geophysical survey?
We plan geophysical surveys by working with our clients to gather information on the local and regional geology, the specific site conditions and site access, the objectives of the survey, how the geophysical information will be used by them and others, and by applying our extensive experience regarding the use of geophysical techniques in similar applications.
3) How long do geophysical surveys take?
Geophysical surveys can require anywhere from several hours to several weeks to complete depending upon the size of the area of interest, the depth of investigation, the geophysical method used, and the amount of survey coverage required. Typical Bay Area geophysical surveys conducted by NORCAL take about 1 to 3 days to complete.
4) How much do geophysical surveys cost?
The cost of geophysical surveys is directly related to how long they take, the distance of the job site from our Cotati, California office, the size of the geophysical crew required to conduct the survey, and the number and complexity of the geophysical instruments that are utilized. Consequently, geophysical surveys can range in cost from less than $1,000 to over $100,000. However, typical Bay Area geophysical surveys that take one to three days to complete range in cost from about $2500 to $7500.
5) How do you determine the best geophysical method to use for a particular survey?
The decision regarding which geophysical methods are selected for a given project is based primarily on the experience that we have gained over decades of conducting geophysical surveys throughout the United States and in several foreign countries. Specifically, we base our selection on our knowledge of the local and regional geology, the local site conditions, and the size and depth of the target. We also work with our clients to derive an approach that can best suit their objectives without exceeding their budgetary constraints.
6) Do I need to hire a licensed geophysicist to perform geophysical surveys?
Section 7832 of the California Business & Professions Code provides that any person who practices or offers to practice geology or geophysics for others in the State of California is subject to the provisions of the Geologists and Geophysicists Act. This act requires that persons practicing geophysics in the State of California must be licensed by the Board for Geologists and Geophysicists. Furthermore, any licensee who signs a report involving the use of geophysics must be in “Responsible Charge of the Work”. This term means that the licensee signing the report must be in independent control and direction by the use of initiative, skill and independent judgment of geophysical work or the supervision of such work.