BUBBLE COLLAPSE AS THE SOURCE OF TREMOR AT OLD-FAITHFUL GEYSER

Old Faithful Geyser, Yellowstone, was used as a natural laboratory for fluid-flow-induced seismic activity. Pressure measurements within the geyser's water column, obtained simultaneously with seismic measureme nts on the surface, demonstrated that the tremor observed at Old Faith ful results from impulsive events in the geyser. Tremor intensity is c ontrolled by the rate of occurrence of these impulsive events. There i s no resonance observed within the water column. The impulsive events are modeled by a collapse of a spherical bubble, including the effects of residual non-condensible gas and damping. The pressure data can be explained by a collapse of a similar to 5 cm radius bubble driven by a pressure difference of Delta P = 0.3 x 10(5) Pa and effective viscos ity v(E)=0.04 m(2)/s. Using a quasi-static geyser model, we treat the individual bubble collapses as cooling events that occur when the wate r column reaches a critical temperature. Their rate of occurrence is c ontrolled by the heating rate dT/dt of the water column. As a result, the intensity of the hydrothermal and seismic activities is determined by the heat and mass input rate into the geyser. It is demonstrated t hat a sharp widening of the conduit can cause the number of events per unit time to drop (as observed) while the water level is still rising and heat is being input, and thus the tremor intensity can be modulat ed by variations in the conduit shape.