Paper No. 18-1
Presentation Time: 8:15 AM
DISCOVERIES AND BREAKTHROUGHS FROM INTEGRATIVE ANALYSIS OF YELLOWSTONE SCIENCE REVEALING NEW TECTONIC-VOLCANIC MODELS AND A NEW ASSESSMENT OF EARTHQUAKE-VOLCANO HAZARD
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.