Volcanic Processes Inferred from GPS Geodesy, Dominica, Lesser An8lles. A Lecture to Learn Some Kids up Good Stephen James

Transcription

1 Volcanic Processes Inferred from GPS Geodesy, Dominica, Lesser An8lles A Lecture to Learn Some Kids up Good Stephen James

2 Where are we? Image courtesy of 2004 CIA Factbook

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5 What are we doing? GPS Geodesy Field Precision mounted antenna receives data and transmits to receiver over 3 4 days. Lab GIPSY/OASIS II (a collec8on of sosware from JPL) is used along with precise clocks and orbits to determine a precise posi8on.

6 Site Rate Diagrams

7 Site Veloci8es Error estimates are almost all greater than site velocities. Three possibilities exist. Small residual velocities are due to motion with stable Caribbean Plate Measurements are too immature to yield statistically robust residual velocities. Magnitude of the error has been overestimated.

8 Are our veloci8es Random? Vectors show grouping and gaps. Gap between 120 and 210 Group between 345 and 15 Group on bearing of 120 and 300 With exception of GUIG there s a gap between 15 and 80 (GUIG is an immature site and may be effected by structural instability of a road cut).

9 Is Dominica really moving with the stable Caribbean Plate? Only sites with at least 3 epochs of observation were considered. Average velocities are significantly less than average error in the horizontal components of motion. With 95% confidence, Dominica is moving with the stable Caribbean Plate.

10 Mao et al., 1999 Error estimates were too high, but not significantly. This made only a minor difference with respect to how many sites had a greater residual velocity than their estimated error. Geologic map from Roobol and Smith 2004 via Lindsay et al., 2005

11 Into the Models Northern Dike Model Parameters: Strike: Dip: 90 Depth: 0.82 km Width: 1.52 km Length: km SS Disp: 0 mm/yr DS Disp.: 0 mm/yr Tens. Disp mm/yr Horizontal Deformation Field Vertical Deformation Field

12 WaX Mountain Dike Model Parameters: Strike: 59 Dip: N Depth: 3.17 km Width: 8.8 km Length: km SS Disp: 0 mm/yr DS Disp.: 0 mm/yr Tens. Disp mm/yr Horizontal Deformation Field Vertical Deformation Field

13 Morne Anglais Mogi Model Parameters: Depth: 0.67 km ΔV: m3 Horizontal Deformation Field Vertical Deformation Field

14 West Coast Fault Model Parameters: Strike: Dip: 68 W Depth: 0 km Width: 0.7 km Length: 58 km SS Disp: 4.12 mm/yr DS Disp.: mm/yr Tens. Disp. 5.6 mm/yr Horizontal Deformation Field Vertical Deformation Field

15 WaX Mountain Mogi Model Parameters: Depth: 0.3 km ΔV: m3 Horizontal Deformation Field Vertical Deformation Field

16 Combined Models Watt Mountain Dike Watt Mountain Mogi West Coast Fault Horizontal Deformation Field Vertical Deformation Field

17 Watt Mountain Dike Morne Anglais Mogi Lindsay et al., 2005 proposed that the seismic swarm in the south was the result of magmatic intrusion at Morne Anglais causing motion on faults in southern Dominica. Horizontal Deformation Field Vertical Deformation Field

18 All Models Combined Horizontal Deformation Field Vertical Deformation Field

19 Checking the Models F Test Bevington, 1969

20 The Boiling Lake of Dominica All Boiling Lake images courtesy of Arlington James via natureisland.com

21 Weird Stuff Happens

22 Fournier et al., 2008

23 Boiling Lake Level Below Normal Feet Below 20 Normal Lake Level Days

24 WaX Mountain Mogi Model Parameters: Depth: 0.3 km ΔV: m3 Horizontal Deformation Field Vertical Deformation Field

25 Never trust Austrians or Spaniards, they might go swimming in your Boiling Lake

26 References Bevington, P. R., 1969, Data Reduc8on and Error Analysis for the Physical Sciences: McGraw Hill, Inc. Byrne, D., Davis, D.M., and L. Sykes,1988, Loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduc8on zones. Tectonics, v. 7, p Central Intelligence Agency, 2004, CIA World Factbook. Fournier, N., Witham, F., Moreau-Fournier, M., and Bardou, L., 2008, The Boiling Lake of Dominica, West Indies: high-temperature volcanic crater lake dynamics,: Journal of Geophysical Research, v. 114, B02203, doi: /2008JB Lindsay, J.M., Smith, A.L., Roobol, M.J. & Stasiuk, M.V., 2005, Dominica. In: Lindsay, J.M., Robertson, R.E.A., Shepherd, J.B. & Ali, S. (eds) Volcanic Hazard Atlas of the Lesser Antilles. Seismic Research Unit, The University of the West Indies, Trinidad and Tobago, W.I. p Mao, Ailin, Harrison, Christopher G. A., Dixon, Timothy H., 1999, Noise in GPS Coordinate Time Series: Journal of Geophysical Research, v. 104, no. B2, p