DSX-08 Saariselka June 8-13, 2008 IMAGING & INTERPRETING CONTINENTAL LOWER CRUST: FROM POTENTIAL...

DSX-08 Saariselka June 8-13, 2008DSX-08 Saariselka June 8-13, 2008

IMAGING & INTERPRETINGCONTINENTAL LOWER CRUST:

FROM POTENTIAL PROBLEMS TO PROBABLE PROCESSES

Kabir Roy-ChowdhuryUtrecht University, The Netherlands

KRC, Department of Earth Sciences DSX-08: Saariselka, June 8-13, 2008

Imaging & Interpreting CLC Deterministic Probabilistic

Fellow Travellers• Quarry Blasters at Univ Hamburg: Menzel

• The Instt. Of Geophysics, Kiev

• The DSS group at N.G.R.I. Hyderabad

• Geo-Sciences, Princeton: Phinney, Kong, Hansen

• Geo-Sciences, Utrecht: Douma, Carpentier

• Levander, Hurich, Holliger and many others …

• And also Geologists like Smithson, Rutter, …



Late ’60s – early ’70s• Recording quarry blasts with MARS recorders

• Sporadic locations with 3 channels @ 500 m

• Phase correlations of refracted arrivals

• Modelling (scattered) wave-forms from MOHO

• Transition zone? Linear gradient? Lamellae?



Indo – Soviet collaboration (1972 -)• Kiev group had contoured Moho below Ukraine!

• 660 km Kavali – Udipi profile in Indian Shield

• 50-1500 Kg source, 100 m spacing, analogue rec

• Human-intensive processing …



Processing DSS records



Indo – Soviet collaboration (1972 -)• Kiev group had contoured Moho below Ukraine!

• 660 km Kavali – Udipi profile in Indian Shield

• 50-1500 Kg source, 100 m spacing, analogue rec

• Human-intensive processing

• Reciprocal (Deep) Reflection Segments Helped

• First Danger Signals for Interpretation

• Vertical vs.Horizontal Tectonics …



Gibbs, 1986



1980s: CERP at Princeton• Try to Objectivise the Ubiquitous Line-Drawing

• Coherency Filter (Kong et al, 1985) …



Kong et al, 1985



1980s: CERP at Princeton• Objectivise the Ubiquitous Line-Drawing


• The USGS Long-Island line as a benchmark …



Phinney & Roy-Chowdhury, 1989



COCORP Georgia Lines 1 (above) and 5 (below)

Phinney & Roy-Chowdhury, 1989






• Sign Filter (Hansen et al, 1988) …



Hansen et al, 1988






• Sign Filter (Hansen et al, 1988) …

• Second Danger Signal for interpretation

• Look beyond Phase … to Amplitudes too

• Black/White problem (Seismix88 in Canberra)



Enigma of Lower Crustal Reflectivity• Exposures exhibit multi-scale structure

• Compositional and Evolutionary causes

• Banded reflectivity at mid/lower- crustal depths

• Compute Response of a Random Bi-modal Stack

• Vertical Reflection Coefficient could be ~ 0.7!

• Classify Regions based upon Back-Scattering

Roy-Chowdhury et al, 1988



1990s: let’s go stochastic• An explosion of people and papers

• Random Layering gives Banded Reflectivity

• Crustal Exposures show von Karman structure

• Difficult to estimate the relevant parameters

• Quantitative? Interpretation of Deep Seismic Data

Gibson, Holliger, Hurich, Levander, Pullammanappallil, …



Picking up the thread again• Multiple Scattering in a Multi-Scale Medium

• Layer-Cake model with von Karman structure

• Bi-modal material property (impedance)

• Vertical Incidence of P-waves (no conversions)

• Can Single-Scattering based Processing work?



Douma & Roy-Chowdhury, 2001



The Estimation Problem• 2-D von Karman Medium with ax , az and

• Bi-Modal Lithology (back to the BW problem)

• Full-wave seismic response is von Karman too

• Medium parameters may be back-estimated

Carpentier and Roy-Chowdhury



The (under)Estimation Problem• Getting Reflectivity from Impedance lowers ax

• Estimated ax may be upscaled, is less robust

• Source deconvolution needed to estimate az

• Dip Scan improves Estimation for Rotated Blocks

Carpentier and Roy-Chowdhury



Carpentier et al

Dip Scan using a Data-window from the Lithoprobe AG-48 line improves the estimation



Got Curious? Visit our Poster (# 72)• Method tried on two Deep Reflection Datasets

• Lithoprobe Abitibi-Grenville (AG-48) line

• DOBRE 2000/2001 lines in Ukraine! (world is round!)

• Results similar to earlier Interpretations

• Some interesting differences though

• Should help constrain Tectono-Thermal History

Thanks!



Carpentier et al

AG-48



Carpentier et al

DOBRE 2000/1

DSX-08 Saariselka June 8-13, 2008 IMAGING & INTERPRETING CONTINENTAL LOWER CRUST: FROM POTENTIAL...

Documents

Transcript of DSX-08 Saariselka June 8-13, 2008 IMAGING & INTERPRETING CONTINENTAL LOWER CRUST: FROM POTENTIAL...