Field Measurement of P- and S-Wave Velocities for Wyoming Trona Deposit

Abstract

A detailed field investigation of P- and S-wave velocities was carried out for the Wyoming trona deposit. The velocity measurement was performed at two field sites and included 11 transmission surveys. A total of 97 independent ray paths were generated from these surveys and utilized for the velocity calculation. The test sites consisted of two large pillars. The average travel distance of the signals utilized for the survey was 100 m. A high resolution data acquisition system was used with the sampling rate set at 50 kHz. The sensors were high sensitive accelerometers, with a flat response range of 50–5,000 Hz. These sensors were installed in the boreholes to avoid the attenuation problem caused by the fractured pillar surface. A special sensor installation technique was employed for reliable sensor installation in boreholes which could be oriented in any directions. The signals acquired from the transmission surveys were of very high quality. The frequencies of these signals were very high, ranged from 2,500 to 5,000 Hz, with 5,000 Hz being most typical. The P- and S-waves were well defined and separated. The timing error was estimated within 0.05 ms. The velocities calculated for all 97 survey lines were very consistent. The average P- and S-wave velocities were 5,108 and 2,640 m/s, respectively. The mean standard deviations were small, only 2.4 and 1.9 % for the P- and S-wave velocities. The 95 % two-sided confidence interval for the true P-wave velocity was 5,108 ± 24 m/s and for the S-wave velocity was 2,640 ± 10 m/s. With the consideration of the test conditions associated with this investigation, including multiple test sites, large pillars, excellent signal quality, a very large database, and extremely consistent results, we believe that the P- and S-wave velocities determined from this investigation are accurate, reliable and representative for the Wyoming trona deposit.