Chicxulub revealed with new seismic and gravity data
Jo Morgan, Anneka Smith, Elinor Styles, Imperial College London, UKAnusha Surendra, Penny Barton, University of Cambridge, UK
Some observationsPreliminary travel-time inversionCorrelation between reflection, velocity, gravity and magnetic data
Model assessmentPurpose: to examine model reliability
Details 2005 seismic and gravity experiment
New seismic data
New gravity data
Funded by NERC and NSF
Data examples
Clear arrivals – small uncertainty
Refraction data3,800,000 travel-times
first-arrivals for 1/3 of data picked to-date
Reflection dataProcessing complete
Re
duc
ed
tra
vel-
time
(se
cs)
TW
TT
(se
cs)
0
2
0
2
Horizontal distance (~10 km)Tertiary
Peak ring
Dipping reflectors
Seismic inversion Determine a velocity model
that “best-fits” the travel-times
Blue dots: land stationsRed are ray paths (looking from above)
80 k
m
65 km
Anneka Smith
Subset of rays into western land stations
Anusha Surendra
ExamplePart of inverted velocity model from marine seismometers
Green surface is 6 kms-1 velocity boundary
Peak ring is visible on marine reflection profiles
Topographic peak ring is directly above a low-velocity-zone at depth
Structures visible on marine reflection profiles showrelationship to velocitygravity and magnetic data
Bouguer gravity Horizontal gradient gravity Magnetic data
E. Styles E. Styles M. Pilkington
innermost slumped block peak ring
Problem: Non-uniquenessA range of models will fit the data equally as well
Solution: Model assessmentIn final model, need to distinguish between structure that is required by the data and structure that is consistent with the data
Model assessment
“Basic” model assessmentUse ray coverage to indicate areas in the model that are well constrained (dark shading)
“Better” model assessment: Checkerboard TestingAdd checkerboard of high and low velocity anomalies to final velocity model Determine travel-times through this “checkerboard” modelUse inversion to recover the checkerboard
Determine how well checkerboard is
recovered (semblance)
Identify areas of good recovery (dark)
Gradually decrease size of checkerboard until it
is too small to recover
More model assessmentTest effect of starting model starting model, inversion parameters etcTest for uncertainties in parametersRun synthetics tests to investigate resolution – example below
Finally get “reliable” velocity modelCan identify parts of model required by data
Peggy Vermeesch
synthetic model central uplift inverted model (1996 data)
Use drill core, reliable velocity model, and other geophysical data to:Obtain well-constrained structural/lithological modelMelt volume, sample stratigraphic uplift, determine nature of peak ring…
ICDP/IODP workshop – future drilling of ChicxulubPostdam 11-12 September 2006 Call for participants
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