Portal de Periódicos da CAPES

P and S velocity structure of the Yellowstone volcanic field from local earthquake and controlled‐source tomography

1999; American Geophysical Union; Volume: 104; Issue: B7 Linguagem: Inglês

10.1029/1998jb900095

2156-2202

Douglas S. Miller, Robert B. Smith,

Geological and Geochemical Analysis

The three‐dimensional P and S velocity (from V p /V s ratios) distribution and improved hypocenters for the Yellowstone volcanic field have been determined from inversion of first arrival times from 7942 local earthquakes and 16 controlled‐source explosions. The P velocity model has an rms residual of ±0.09 s, whereas the V p /V s ratio model (calculated from 511 earthquakes) has an rms residual of ±0.29 s. High P and S velocities outside the Yellowstone caldera represent thermally undisturbed basement and sedimentary rocks. A caldera‐wide 15% decrease from regional P velocities at depths of 6 to 12 km is coincident with a −60 mGal gravity anomaly and is interpreted as a hot, subsolidus, granitic batholith with a quasi‐plastic rheology. Localized 30% reductions from regional seismic velocities and higher V p /V s ratios 8 km beneath Yellowstone's resurgent domes are interpreted as partial melts and vestigial magma systems associated with youthful (less than 2 Ma) silicic volcanism. Additional low seismic velocities and V p /V s ratios and a 20 mGal gravity low less than 4 km beneath the northeast caldera rim are interpreted as a hydrothermal fracture zone thermally driven by underlying partial melt. Hypocenters relocated with the three‐dimensional P velocity model show subparallel alignment with NW‐SE trending postcaldera volcanic vents and normal faults northwest of the caldera. Focal depths of relocated earthquakes decrease from more than 11 km outside the caldera to less than 6 km within the caldera, reflecting thinning and heating of the seismogenic crust.