Seismic velocity structure and earthquake relocation for the magmatic system beneath Long Valley Caldera, eastern California

A new three-dimensional (3-D) seismic velocity model and high-precision location catalog for earthquakes between 1984 and 2014 are presented for Long Valley Caldera and its adjacent fault zones in eastern California. The simul2000 tomography algorithm is applied to derive the 3-D V-p and V-p/V-s models using first-arrivals of 1004 composite earthquakes obtained from the original seismic data at the Northern California Earthquake Data Center. The resulting V-p model reflects geological structures and agrees with previous local tomographic studies. The simultaneously resolved V-p/V-s model is a major contribution of this study providing an important complement to the V-p model for the interpretation of structural heterogeneities and physical properties in the study area. The caldera is dominated by low V-p anomalies at shallow depths due to postcaldera fill. High V-p and low V-p/V-s values are resolved from the surface to similar to 3.4 km depth beneath the center of the caldera, corresponding to the structural uplift of the Resurgent Dome. An aseismic body with low V-p and high V-p/V-s anomalies at 4.2-6.2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on V-p models only and the inflation source locations based on geodetic modeling. The Sierran crystalline rocks outside the caldera are generally characterized with high V-p and low V-p/V-s values. The newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high-precision earthquake catalog based on similar-event cluster analysis and waveform cross-correlation data. The fine-scale velocity structure and precise earthquake relocations are useful for investigating magma sources, seismicity and stress interaction and other seismological studies in Long Valley. (C) 2015 Elsevier B.V. All rights reserved.