Constraints on Volcanic Tremor Source Models from Worldwide Measurements of Tremor Amplitudes, Frequencies, Wave Types and Durations

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9418219 McNutt This project will support a post-doctoral investigator to complete an existing database ion volcanic tremor from more thal 160 volcanoes around the world. The most important parameter to be investigated is the amplitude of tremor which is normalized to reduced displacement. This problem is as fundamental as the determination of earthquake magnitudes. Preliminary results show that tremor reduced displacements during eruptions are proportional to the Volcano Explosivity Index (VEI), which is proportional to the tephra volume. We propose to test the hypothesis that the energy of volcanic tremor is directly proportional to the volume of magma and its contained volatiles. We will measure the seismic efficiencies of tremor, and we show preliminary data that suggest there are different efficiencies for different eruptive mechanisms. This project is complementary to many theoretical studies. It is broad and wide ranging because it includes data from all known seismically monitored volcanoes worldwide. Although the chief value of the project is scientific, several components, especially reduced displacement versus VEI, also have a direct bearing on volcanic hazards assessment and forecasting.