scholarly journals Fluid-faulting evolution in high definition: Connecting fault structure and frequency-magnitude variations during the 2014 Long Valley Caldera, California, earthquake swarm

2016 ◽  
Vol 121 (3) ◽  
pp. 1776-1795 ◽  
Author(s):  
David R. Shelly ◽  
William L. Ellsworth ◽  
David P. Hill
Keyword(s):  
Earthquake Swarm ◽  
High Definition ◽  
Long Valley Caldera ◽  
Fault Structure ◽  
Long Valley ◽  
Frequency Magnitude

3-D seismic attenuation structure of Long Valley caldera: looking for melt bodies in the shallow crust

2019 ◽  
Vol 220 (3) ◽  
pp. 1677-1686 ◽  
Author(s):  
Janire Prudencio ◽  
Michael Manga
Keyword(s):  
Earthquake Swarm ◽  
Vertical Component ◽  
Seismic Attenuation ◽  
Hydrothermal Systems ◽  
Magma Body ◽  
Long Valley Caldera ◽  
High Attenuation ◽  
Coda Normalization ◽  
Long Valley ◽  
Attenuation Structure

SUMMARY Unrest at Long Valley caldera (California) during the past few decades has been attributed to the ascent of hydrothermal fluids or magma recharge. The difference is critical for assessing volcanic hazard. To better constrain subsurface structures in the upper crust and to help distinguish between these two competing hypotheses for the origin of unrest, we model the 3-D seismic attenuation structure because attenuation is particularly sensitive to the presence of melt. We analyse more than 47 000 vertical component waveforms recorded from January 2000 through November 2016 obtained from the Northern California Earthquake Data Center. We then inverted the S-to-coda energy ratios using the coda normalization method and obtained an average Q of 250. Low attenuation anomalies are imaged in the fluid-rich western and eastern areas of the caldera, one of which corresponds to the location of an earthquake swarm that occurred in 2014. From a comparison with other geophysical images (magnetotellurics, seismic tomography) we attribute the high attenuation anomalies to hydrothermal systems. Average to high attenuation values are also observed at Mammoth Mountain (southwest of the caldera), and may also have a hydrothermal origin. A large high attenuation anomaly within the caldera extends from the surface to the depths we can resolve at 9 km. Shallow rocks here are cold and this is where earthquakes occur. Together, these observations imply that the high attenuation region is not imaging a large magma body at shallow depths nor do we image any isolated high attenuation bodies in the upper ≈8 km that would be clear-cut evidence for partially molten bodies such as sills or other magma bodies.

Bibliography of literature pertaining to Long Valley Caldera and associated volcanic fields

2005 ◽  
Author(s):  
John W. Ewert ◽  
Christopher J. Harpel ◽  
Suzanna K. Brooks
Keyword(s):  
Long Valley Caldera ◽  
Long Valley ◽  
Volcanic Fields
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