Presentation Title

The Geometry and Hazard of the Hilton Creek Fault System near the Long Valley Caldera

Start Date

November 2016

End Date

November 2016

Location

HUB 302-#113

Type of Presentation

Poster

Abstract

The Hilton Creek Fault System (HCF) is a collection of faults near the Long Valley Caldera. This caldera, a large depression caused by the sudden emptying of a magma chamber ~760,000 years ago, sits between the Basin and Range Province and the Sierra Nevada. The faults that make up the HCF are not mapped in detail, and their location and geometry is disputed. Hill and Montgomery-Brown (2015) argue that the HCF does not penetrate the caldera, and that the normal faulting within the caldera is a series of graben structures associated with post-caldera magmatism instead of displacements consistent with range-front faulting. The resulting reduction in the total length of the fault would significantly decrease the predicted shaking intensity near the town of Mammoth Lakes. Elevation profiles across these structures can help determine the nature of the faulting within the caldera: a staircase-like shape across these features would indicate range-front faulting while uplifted mounds would indicate post-caldera magmatism. We have generated three high-resolution elevation profiles using total stations. Our preliminary results suggest that the shape of these elevation profiles is indicative of post-caldera magmatism. We used structure-from-motion techniques to generate a complete topography map of the study area. We also used magnetometers to measure variations in the strength of Earth’s magnetic field. Magnetic anomalies may be generated by offsets between rock units with different magnetic properties in the subsurface, created by faulting. We aim to integrate the results from these techniques to help develop a model of the HCF geometry.

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The Geometry and Hazard of the Hilton Creek Fault System near the Long Valley Caldera

HUB 302-#113

The Hilton Creek Fault System (HCF) is a collection of faults near the Long Valley Caldera. This caldera, a large depression caused by the sudden emptying of a magma chamber ~760,000 years ago, sits between the Basin and Range Province and the Sierra Nevada. The faults that make up the HCF are not mapped in detail, and their location and geometry is disputed. Hill and Montgomery-Brown (2015) argue that the HCF does not penetrate the caldera, and that the normal faulting within the caldera is a series of graben structures associated with post-caldera magmatism instead of displacements consistent with range-front faulting. The resulting reduction in the total length of the fault would significantly decrease the predicted shaking intensity near the town of Mammoth Lakes. Elevation profiles across these structures can help determine the nature of the faulting within the caldera: a staircase-like shape across these features would indicate range-front faulting while uplifted mounds would indicate post-caldera magmatism. We have generated three high-resolution elevation profiles using total stations. Our preliminary results suggest that the shape of these elevation profiles is indicative of post-caldera magmatism. We used structure-from-motion techniques to generate a complete topography map of the study area. We also used magnetometers to measure variations in the strength of Earth’s magnetic field. Magnetic anomalies may be generated by offsets between rock units with different magnetic properties in the subsurface, created by faulting. We aim to integrate the results from these techniques to help develop a model of the HCF geometry.