Presentation Title

Where's the Magma: An Analysis of the Subsurface of Long Valley Caldera Based on Earthquake Statistics

Start Date

November 2016

End Date

November 2016

Location

HUB 265

Type of Presentation

Oral Talk

Abstract

The Hilton Creek Fault System (HCFS) is characterized as a single normal fault from the western side of Davis Lake until it penetrates the southern rim of the Long Valley Caldera. Once in the caldera, the fault appears to splay into numerous parallel faults, eventually intercepting the resurgent dome. Increased activity in the area began in May 1980 when four 6.0+ earthquakes occurred, resulting in massive earthquake swarms that coincided with periodic vertical uplift of the caldera floor. Significant seismic activity continues to this day. We will present the results of our study of the HCFS to determine the seismic behavior of the fault splays in the north, within the caldera, and compare and contrast these results with those of the southern part of the fault system. This study is conducted by generating maps of the area that show the spatial variation in the ratio of small earthquakes to large earthquakes, referred to as the “b-value”. Typical b-values in California are roughly around 1.0. Small b-values may indicate high stress buildup, while large b-values may indicate the presence of magma. Our maps indicate a cluster of high b-values near the resurgent dome of the caldera, which has historically experienced vertical uplift, and areas of low b-values in the Sierra Nevada Block Region, southwest of the caldera, which may indicate that there is an accumulation of stress in this area. We plan to expand this research to investigate variations in b-value with depth, and with time.

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Nov 12th, 2:00 PM Nov 12th, 2:15 PM

Where's the Magma: An Analysis of the Subsurface of Long Valley Caldera Based on Earthquake Statistics

HUB 265

The Hilton Creek Fault System (HCFS) is characterized as a single normal fault from the western side of Davis Lake until it penetrates the southern rim of the Long Valley Caldera. Once in the caldera, the fault appears to splay into numerous parallel faults, eventually intercepting the resurgent dome. Increased activity in the area began in May 1980 when four 6.0+ earthquakes occurred, resulting in massive earthquake swarms that coincided with periodic vertical uplift of the caldera floor. Significant seismic activity continues to this day. We will present the results of our study of the HCFS to determine the seismic behavior of the fault splays in the north, within the caldera, and compare and contrast these results with those of the southern part of the fault system. This study is conducted by generating maps of the area that show the spatial variation in the ratio of small earthquakes to large earthquakes, referred to as the “b-value”. Typical b-values in California are roughly around 1.0. Small b-values may indicate high stress buildup, while large b-values may indicate the presence of magma. Our maps indicate a cluster of high b-values near the resurgent dome of the caldera, which has historically experienced vertical uplift, and areas of low b-values in the Sierra Nevada Block Region, southwest of the caldera, which may indicate that there is an accumulation of stress in this area. We plan to expand this research to investigate variations in b-value with depth, and with time.