3D Attenuation structure of Long Valley caldera (imaged with coda normalization method)

Abstract:

We model the 3D seismic attenuation structure of Long Valley caldera, California by analyzing more than 8000 vertical waveforms and applying the coda normalization method. The new tomographic model is similar to the 2D scattering attenuation model obtained previously, showing that the main process of energy loss is due to the heterogeneous behavior of the region. We identify high attenuation anomalies in the fluid-rich western and eastern areas of the caldera. From a comparison with other geophysical images (magnetotellurics, seismic tomography) we attribute these anomalies to a hydrothermal system. Low attenuation anomalies in the center-south of the caldera, corresponds to the location of an earthquake swarm in 2014. Average to high attenuation values are also observed at Mammoth Mountain (south-west of the caldera), and may also have a hydrothermal origin. High intrinsic attenuation at low frequencies to the west of the Hartley Springs Fault may be produced by the magmatic system that produced the Inyo craters. Seismic attenuation tomography imaging provides insights into subsurface structures that are complementary to velocity and conductivity images.