An Investigation into the Eastern Extent of the Garlock Fault using Ground-based Magnetics and Seismotectonic Analysis

Brad Ruddy, & Jascha Polet

Published August 15, 2016, SCEC Contribution #6942, 2016 SCEC Annual Meeting Poster #245 (PDF)

The character of the Garlock fault has been a topic of contention among geologists since its discovery in 1910. The 250 km long Garlock fault strikes roughly east-west and its current surface expression is located between the San Andreas fault and the Death Valley fault zone. Initially, it was believed that the Garlock fault had only 8 km of displacement and that the eastern portion of the Garlock turned south, turning into a westward dipping fault underneath the Avawatz mountains. Later work done in the 1970’s determined that the displacement was much larger (48-64 km) than previously suggested. This new data prompted the hypothesis that the Garlock fault extends east of the Death Valley fault zone. Magnetic and gravity measurements by Plescia and Henyey (1982) across the extension of the fault suggested the existence of an eastern limb of the fault, located in Kingston wash. Their data showed contrasting magnetic basement patterns: a gentle gradient to the north of the proposed fault trace, with areas south of the fault exhibiting various highs and lows, likely corresponding to buried horsts and grabens. The purpose of our study is to confirm whether the Garlock fault does continue east into Kingston wash, through the creation and analysis of a walking magnetometer dataset at a much shorter sampling distance. At present, four 8 km transects have been surveyed with plans to collect 8-10 more over a 45 km2 study area. This collected data confirms a large magnetic gradient in a similar location as was established by Plescia and Henyey (1982), which may represent the proposed eastern extension of the Garlock fault. In addition to the magnetic data, 3-4 Very Low Frequency Electromagnetics (VLF) walking transects will be performed, in locations based on the preliminary analysis of the magnetic data, to help create resistivity profiles. We plan to develop a three-dimensional model to characterize the eastwards extension of the fault at depth as well as the strike on the surface. We also will generate maps and cross-sections of the earthquake focal mechanism catalog by Yang et al. (2012) and the relocated earthquake location catalog by Hauksson et al. (2012) to assess whether any micro-seismicity corresponds to the suggested strike and dip of the potential eastern extension of the Garlock fault.

Key Words
Garlock, Magnetics, Seismotectonics, VLF, tectonics

Citation
Ruddy, B., & Polet, J. (2016, 08). An Investigation into the Eastern Extent of the Garlock Fault using Ground-based Magnetics and Seismotectonic Analysis. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology