Inversion forPandSwave attenuation structure, Long Valley caldera, California

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Abstract
PandSwave amplitude data from digital, three‐component seismograms of local earthquakes recorded on a temporary seismic array have been used to tomographically invert for the three‐dimensional attenuation structure in the upper crust of Long Valley caldera, California. Differential attenuation (∂Q−1) values are obtained through the use of a spectral ratio technique that minimizes the site effect on the spectral ratios. The spectral ratios are inverted for ∂Q−1using the LSQR algorithm. Zones of high, positivePwave ∂Q−1(greaterPwave attenuation) are observed at a depth of 4–5 km beneath the east flank of Mammoth Mountain and at 6–8 km beneath the southwestern edge of the resurgent dome. A region of positiveSwave ∂Q−1is seen at 7–8 km beneath the southern edge of the resurgent dome, whereas at 6–7 km, theSwave results are near average. The region of positive S wave ∂Q−1at 7–8 km beneath the resurgent dome may indicate the roof of a magmatic system. The positivePwave ∂Q−1at 4–5 km beneath Mammoth Mountain and 6–8 km beneath the resurgent dome may be due to the presence of a compressible fluid such as supercritical water. These zones may represent some of the source regions for the Long Valley geothermal system.