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Hydrologic Precursors to Earthquakes

Hydrologic Precursors to Earthquakes. Watching the Water…. By Laura Maharaj. Confined and Unconfined Aquifers. Piezometers, Hydraulic Head and Hydraulic Pressure. Hp. Hydraulic Head. Screen. Z. The General Trend. A gradual lowering of water levels of a period of months or years

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Hydrologic Precursors to Earthquakes

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  1. Hydrologic Precursors to Earthquakes Watching the Water… By Laura Maharaj

  2. Confined and Unconfined Aquifers

  3. Piezometers, Hydraulic Head and Hydraulic Pressure Hp Hydraulic Head Screen Z

  4. The General Trend • A gradual lowering of water levels of a period of months or years • An accelerated lowering of water levels (rate often exponential) in the final few months or weeks preceding the earthquake. • A “rebound” where water levels begin to increase rapidly in the last few days or hours before the main shock.

  5. Water Level Changes due to Crustal Strain(Confined Aquifers) Pressure change as a result of crustal strain Δp = -(2GB/3)[(1 + vu)/(1 - 2vu)]Δε Δp= Δhpg Water level changes due to Crustal strain Δh = -(1/pg)(2GB/3)[(1 + vu)/(1 - 2vu)]Δε Δp – Change in Hydraulic Pressure Δε – Increment of volumetric strain in the aquifer G – Shear Modulus B – Skempton’s Coefficient Vu – undrained Poisson’s Ratio

  6. Water Level Changes due to Barometric Pressure (Confined Aquifers) Pressure changes as a result of Barometric pressure Δp = (B/3)[(1 + vu)/(1 - vu)]Δb Water level changes due to barometric pressure Δh = -(1/pg)[1 - (B/3)(1 + vu)/(1 - vu)]Δb

  7. Barometric Pressure Changes

  8. Other influences on Changes in Water Levels Tidal Response Δh = Δε /(βwnpwg) Rainfall

  9. Difficulties in Earthquake Prediction • Numerous Environmental Variables • No Anticipated Earthquakes • Contradicting Results • Sensitivity of monitoring wells Variation • Instrument Failure • Lack of Understanding in Underlying Mechanisms

  10. Recorded Earthquakes September 21, 1999 The Chi-Chi earthquake was the largest and most disastrous earthquake of the 20th century in Taiwan • Ranging in depth from 14 to 300 m • 188 groundwater-monitoring wells • Barometric Pressures • Rapid changes in groundwater • Seasonal, Trend-Cycle and Irregular

  11. March 16, 1997 Tono Mines, Japan • 16 closely clustered wells • 6 Month Water level drop • Sensitivity due to High permeability aquifer • Located on either side of the fault • Leak and Slug tests preformed to detect Anomalies

  12. Improvement Recommendations • Knowing the Depth of the Wells • Record of rainfall for at least one year • Record of barometric pressure, measured at least once every three hours • Response to earth tides • Greater information about surrounding wells and their distances from the epicenter • Detailed Geographical Strata analyses • Co seismic response of water levels to earthquake • Descriptions of the type of fault of the earthquake

  13. THE END

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