Large earthquakes around faults earthquakes come in

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Large earthquakes around faults. Earthquakes come in various flavors Deep EQs: From far away from volcano - they have sharp arrivals and high frequency Shallow EQs: Less than 3 km that have with medium to low frequency, and less sharp arrivals Surface events: Rockfall, steam, and gas eruptions, snow avalanches Harmonic tremor: Long lasting, very rhythmic signal associated with volcanoes Seismograms Tectonic like earthquakes - Deep Earthquakes - high frequency Shallow Volcanic Earthquakes - Shallow EQs - medium to low frequency (bubbles breaking). Less sharp arrival Surface Events - Small explosive events, rockfalls, snow and rock avalanches Harmonic Tremor - Long-lasting rhythmic signal - movement of fluid beneath volcano Sources of Local Earthquakes
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Moving magma and fluids trigger shallow EQs MOST volcanic Eqs: SMALL magnitude (less than M. 2-3) SHALLOW (less than ~10 km below volcano) Moving magma has a specific seismic signature Seismometers are placed near volcanoes for more precise monitoring Epicenter - Location on ground surface ABOVE site of EQ Focus - Actual location of EQ, in the ground MSH Seismicity, 1980-2004 1980 eruption Earthquakes across all depths Low frequency events concentrated at shallower depths (magma moving) 1980-86 Eruptive period 1987-2004 Quiescence Measuring Ground Deformation (on the volcanos) EDM (Electronic Distance Measuring) Standard Surveying tool Shoots a light beam from a station to a benchmark Measures the distance Effective at MSH as a method to monitor dome growth (seen at right) Effective to see how magma is moving into system Tilt Meters Records deformation at a single station Continually monitors by itself Actually measures the tilt of the instrument Tilt related to deformation, which is related to magma movement GPS Measures the position of a station with respect to a 24 satellite network More accurate, provides vertical movement, more convenient (fairly mobile) Issue: Needs a clear view of the sky. Cloudy sky makes it difficult to connect with satellite Thermal infrared Monitoring Works under cloud cover High Sample Rates Constant Viewing geometry Good for rapid processes Combine with infrasonics Interferometric Synthetic Aperture Radar Satellite Radar captures entire field of deformation, as opposed to discrete points Takes a “picture: of ground surface that can then be compared Creates an image with concentric colored circles Each full colored band from blue to red represents 2.8 cm of ground movement in the direction of the satellite. InSAR at Three SIsters, Oregon Huge colored circles of deformation at North Sister 4 bands indicate 11 cm of deformation between 1996-2000 Probably magma accumulating in the crust
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Problem: Picks up first highly elevated thing (tree/person) which thinks its ground LIDAR (Light Detection and Ranging) Laser shot from airplane to the ground 30,000 points per second at ~15cm accuracy Problem: Expensive $500/sq mi Airplane GPS, Camera, laser scanner Extensive automated, filtering of the data to remove tree canopy (Virtual deforestation) Each laser pulse can produce multiple consecutive measurements from reflections off several surfaces in its path
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  • Spring '09
  • Bergantz
  • Volcano, lahar

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