Chicxulub revealed with new seismic and gravity data Jo Morgan, Anneka Smith, Elinor Styles, Imperial College London, UK Anusha Surendra, Penny Barton,

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