Paper No. 18-1
Presentation Time: 8:15 AM


SMITH, Robert B.1, FARRELL, Jamie1, MASSIN, Fred2, PUSKAS, Christine3, CHANG, W.L.4, SHELLY, David5, and SHELLY, David5, (1) Geology and Geophysics, University of Utah, 155 S. 1460 E, Salt Lake City, UT 84112,, (2) University of French West Indies Seismological Data Center, French Lesser Antilles, Guadeloupe, (3) Unavco, Boulder, CO 80301, (4) Earth Sciences, National Central University, Jhongli City, 32001, Taiwan, (5) U.S. Geological Survey, Menlo Park, CA
We integrate multiple datasets to formulate new geodynamic models of the active processes and hazard implication of the Yellowstone system. 1) The Yellowstone plume extends ~1500 km deep into the lower mantle and tilts NW from 80 km to ~600 km, then tilts SE, as a result of being entrenched in the eastward upper mantle return flow. 2) Using seismic and electrical tomography, the Yellowstone plume is now shown to have a high conductivity annulus of mineralized fluids surrounding the upper mantle part of the plume “doubling its previously imaged width” to ~150 km; 3) New local earthquake tomography shows that the Yellowstone crustal magma reservoir is now imaged “to be 50% larger” than originally thought. It extends ~90 km NE-SW and shallows markedly from ~15 km beneath the caldera to less than ~2 km NE of the caldera. 4) This geometry is consistent with a southwest N. American Plate motion of ~20 km over the Yellowstone plume in the last 640,000 years producing the progressive northeast spatial progression of the magma reservoir; 5) Earthquake swarms are the dominant mode of Yellowstone seismic energy release and account for ~47% of the seismicity. This includes earthquakes that “repeat themselves” as multiplets on time scales of seconds to decades for which we suggest “Yellowstone is always shaking”; 6) The strong E-W band of northern Yellowstone earthquakes is shown to result from post-seismic viscoelastic stress contagion from the M7.3 1959 Hebgen Lake earthquake. In contrast, caldera seismicity reflects regional NE-SW extension of up to 4 mm/yr. on NS zones of weakness that are associated with episodic caldera magmatic/hydrothermal injection, migration, and deflation; 7) The largest Yellowstone earthquake swarms are shown to coincide with a change from caldera uplift to subsidence reflecting the lateral release of magmatic fluids out of the caldera. We hypothesize this process reflects a “pressure relief valve” maintaining an equilibrium flux of magmatic fluids into and out of the magma reservoir; and 8) Integrated probabilistic hazard assessment shows that the biggest Yellowstone Plateau threat is from large M7+ earthquakes, not from volcanic or supervolcano eruptions, contrary to what has been commonly thought and conveyed to the public.