Using Ground-based Magnetics and VLF Surveying to Characterize Potential Fault Zones Near Bonanza Springs, California

Peter A. Flores, & Jascha Polet

Published August 12, 2019, SCEC Contribution #9461, 2019 SCEC Annual Meeting Poster #111

Bonanza Springs is a rare natural watering spot and riparian environment in the eastern Mojave fed by a local aquifer. Like many desert oases in this area, faulting plays a large role in the local hydrology and flow of groundwater in the subsurface. A report on the spring, published by a private company, has suggested that two fault zones, one trending northwest and the other trending northeast, meet just north of Bonanza Springs. The convergence of these proposed fault systems may contribute to the structural controls of groundwater flow to the spring. However, there is limited literature available on the geology of the area and no detailed geophysical surveys have been performed. This study aims to investigate the presence of the two reported fault zones and to enhance our understanding of groundwater flow to the spring and any connection to adjacent aquifer systems. To this end, we used a GEM proton procession magnetometer to collect total magnetic field intensity data within the study area around Bonanza Springs. The multiple volcanic units of the area provide for clear magnetic signals, thus magnetic anomalies help locate linear features that coincide with fault zones. Additionally, a VLF (Very Low Frequency) attachment was used with the magnetometer to help identify conductive bodies in the subsurface. Numerous VLF profiles were measured across the proposed northwest and northeast trending fault zones. The existence of magnetic anomalies indicates a linear feature corresponding with the previously identified northwest trending fault. However, no feature in this data suggests a northeast trending fault. Similarly, several highs in the VLF data support the proposed location of the northwest trending fault, but not the location of the northeast trending fault, in agreement with similar results in the magnetic dataset. To further investigate the presence of the fault zones, future work will include several DC (Direct Current) resistivity surveys to determine if a discontinuous conductive zone can be found that would indicate a barrier to groundwater flow, such as a fault.

Citation
Flores, P. A., & Polet, J. (2019, 08). Using Ground-based Magnetics and VLF Surveying to Characterize Potential Fault Zones Near Bonanza Springs, California. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology