Possible Physical Models of Harmonic Tremor Source in Lascar Volcano, Chile
Presenter: Cholisina Anik Perwita (¬_˛ú®R)
Date: 2012/10/11Abstract
Harmonic tremor was observed in Lascar Volcano, Chile, in April 1994. This kind of tremor signal has fundamental frequency 0,63Hz and more than 25 overtones at exact integer multiples lasting 18 hour. Power spectra in all components have similiarities in four stations recorded, so that the frequency of harmonic tremor must be attributed to mechanism at or near the source. The source system might not be resonance of organ pipe, might not come from crack/small fracture, but must be in the volcanic fluids or gases. There are three proposed models as a source of resonance to explain the harmonic tremor mechanism : eddy shading, turbulent slug flow, soda bottle model. These model explain different characteristic in possibility fluid that might be present in order to have appropriate Reynold number, dimension conduit and flow velocity. For source tremor in eddy shedding model, Reynold number between 102-104, with possibility conduit around 0,1m-100m. Slug flow model can be applied if there are turbulent slug that occur in laminar flow in the conduit. Turbulent slug occurs when ratio of lenght of pipe and diameter is about 50. From itermittancy factor, it give that Reynold number in this case is about 2700 and possible conduit is 0,01m-100 meter with most possible fluid is steam, water and gas rather than magma. Soda Bottle model assume that fluid inside conduit are saturated with gas. Kind of fluid that appropriate with this model are low in viscosity, and most likely to be water ?near the surface at relative overpressure. All three models agreed that source of harmonic tremor must be produce by movement of water or gas, generated near the surface at close to athmospheric presure (probably in active crater), and change frequency tremor are caused by small, easily reversible changes in flow velocity.
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