Towards an Understanding of the Geometry of the Hilton Creek Fault System Within the Long Valley Caldera, Using Ground-Based Magnetics and High-Resolution Topographic Profiles

Jason De Cristofaro, & Jascha Polet

Submitted August 14, 2017, SCEC Contribution #7684, 2017 SCEC Annual Meeting Poster #108

The eastern escarpment of California’s Sierra Nevada mountains is defined by a series of high-relief down-to-the-East normal faults including the Owens Valley, Round Valley, Hilton Creek and Hartley Springs faults. These faults separate the Sierra Nevada to the West from the Basin and Range province to the East. The Long Valley Caldera (LVC), an area of active volcanism that most notably erupted 760 ka, exists along this boundary at the left step between the Hilton Creek Fault (HCF) and the Hartley Springs Fault (HSF). The HCF is well mapped along its main trace to the south of the LVC, but the location and nature of its northern terminus is poorly constrained. The fault terminates within the caldera as a series of left-stepping splays. The timing of the most recent motion on these fault splays is debated, as is the threat posed by this section of the Hilton Creek Fault. The Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3) model depicts the HCF as a single strand projecting up to 12km into the LVC. However, Bailey (1989) and Hill and Montgomery-Brown (2015) have argued against this model, suggesting that extensional faulting within the Caldera has been accommodated by the ongoing volcanic uplift and thus the intra-caldera section of the HCF has not experienced motion since prior to caldera formation.

To better assess the rupture history and potential of the fault in this area, we intend to map the intracaldera fault splays and model their shallow subsurface characteristics. This goal will be accomplished using high-resolution topography and subsurface geophysical methods, including ground-based magnetics. Preliminary work was performed using high-precision Nikon Nivo 5C total stations to generate elevation profiles and a backpack mounted GEM proton precession magnetometer. The initial results reveal a correlation between magnetic anomalies and topography. East-West topographic profiles show terrace-like steps, sub-meter in height, which correlate to anomalies in the magnetic data. Analysis and modeling of the magnetic data using Oasis Montaj 3D modeling software is planned. Additionally, we intend to prepare a high-resolution terrain model using structure-from-motion techniques with imagery acquired by a small UAV and ground control points measured with realtime kinematic GPS receivers. This terrain model will be combined with subsurface geophysical data to form a comprehensive model of the geometry of the intra-caldera fault splays.

Key Words
Long Valley Caldera, Hilton Creek Fault, Basin and Range, Sierra Nevada, fault splay, magnetics, topography, structure from motion, SfM, drone, UAV

Citation
De Cristofaro, J., & Polet, J. (2017, 08). Towards an Understanding of the Geometry of the Hilton Creek Fault System Within the Long Valley Caldera, Using Ground-Based Magnetics and High-Resolution Topographic Profiles. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Tectonic Geodesy