A Refraction Statics Method for Mapping Bedrock

The bedrock surface beneath unconsolidated eolian sand and garbage at the active Casper, Wyoming landfill was successfully imaged using a refraction statics method. The method employed the summation of common‐detector refraction seismic traces in a manner analogous to common midpoint (CMP) reflection seismic methods. The method produces a seismic time section that is interpreted in much the same way as reflection seismic time sections. The method was very robust in imaging the bedrock surface, even when the refractions were poorly defined on both unprocessed and filtered shot records. Processing of a refraction statics data set is less expensive than CMP high‐resultion reflection processing and does not rely on the detailed graphical constructs of the more commonly used refraction seismic analysis methods. This alternative to more commonly used refraction and reflection seismic methods should be applicable in noisy and otherwise difficult data acquisition areas where the resolution of first breaks and/or reflections is difficult. The summation of data traces enhances the signal to noise ratio allowing direct observation of the bedrock image on the time section. A depth section can be calculated from the final time section. In poor data quality settings, the enhancement of the refraction signal by summation of multiple, common‐detector data traces is the significant advantage of the refraction statics method over other refraction seismic interpretation methods which are dependent on accurately picking refracted arrivals on individual data traces. An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.