Impact and Solutions of Seawater Heterogeneity on Wide-Angle Tomographic Inversion of Crustal Velocities in Deep Marine Environments—Numerical Studies

Abstract

The seawater column is typically taken as a homogeneous velocity layer in wide-angle crustal seismic surveys in marine environments. However, heterogeneities in salinity and temperature throughout the seawater layer result insignificant lateral variations in its seismic velocity, especially in deep marine environments. Failure to compensate for these velocity inhomogeneities will introduce significant artifacts in constructing crustal velocity models using seismic tomography. In this study, we conduct numerical experiments to investigate the impact of heterogeneous seismic velocities in seawater on tomographic inversion for crustal velocity models. Experiments that include lateral variation in seawater velocity demonstrated that the modeled crustal velocities were contaminated by artifacts from tomographic inversions when assuming a homogeneous water layer. To suppress such artifacts, we propose two strategies: 1) simultaneous inversion of water velocities and the crustal velocities; 2) layer-stripping inversion during which to first invert for seawater velocity and then correct the travel times before inverting for crustal velocities. The layer-stripping inversion significantly improves the modeling of variation in seawater velocity when preformed with seismic sensors deployed on the ocean bottom and in the water column. Such strategies improve crustal modeling via wide-angle seismic surveys in deep-marine environment.

Keywords

deep water / seismic tomography / wide-angle seismic survey / water heterogeneity / OBS / vertical cable

References

[1] Armi L., Hebert D., Oakey N., . Two Years in the Life of a Mediterranean Salt Lens. Journal of Physical Oceanography, 1989, 19(3): 354-370.

[2] Bertrand A., MacBeth C. Seawater Velocity Variations and Real-Time Reservoir Monitoring. The Leading Edge, 2003, 22(4): 351-355.

[3] Bian A. F., Yu W. H. Layer-Stripping Full Waveform Inversion with Damped Seismic Reflection Data. Journal of Earth Science, 2011, 22(2): 241-249.

[4] Bian A. F., Zou Z. H., Zhou H. W., . Evaluation of Multi-Scale Full Waveform Inversion with Marine Vertical Cable Data. Journal of Earth Science, 2015, 26(4): 481-486.

[5] Biescas B., Sallarès V., Pelegrí J. L., . Imaging Meddy Finestructure Using Multichannel Seismic Reflection Data. Geophysical Research Letters, 2008, 35 11 L11609

[6] Biescas B., Ruddick B. R., Nedimovic M. R., . Recovery of Temperature, Salinity, and Potential Density from Ocean Reflectivity. Journal of Geophysical Research: Oceans, 2014, 119(5): 3171-3184.

[7] Bornstein G., Biescas B., Sallarès V., . Direct Temperature and Salinity Acoustic Full Waveform Inversion. Geophysical Research Letters, 2013, 40(16): 4344-4348.

[8] Chen H., Xie X., Mao K. Deep-Water Contourite Depositional System in Vicinity of Yi’tong Shoal on Northern Margin of the South China Sea. Earth Science—Journal of China University of Geosciences, 2015, 40(4): 733-743.

[9] Eakin D., Holbrook W. S., Fer I. Seismic Reflection Imaging of Large-Amplitude Lee Waves in the Caribbean Sea. Geophysical Research Letters, 2011, 38 21 L21601

[10] Gailler A., Klingelhoefer F., Olivet J. L., . Crustal Structure of a Young Margin Pair: New Results Across the Liguro–Provencal Basin from Wide-Angle Seismic Tomography. Earth and Planetary Science Letters, 2009, 286(1/2): 333-345.

[11] Han F. X., Sun J. G., Wang K. The Influence of Sea Water Velocity Variation on Seismic Traveltimes, Ray Paths, and Amplitude. Applied Geophysics, 2012, 9(3): 319-325.

[12] Holbrook W. S., Fer I., Schmitt R. W., . Estimating Oceanic Turbulence Dissipation from Seismic Images. Journal of Atmospheric and Oceanic Technology, 2013, 30(8): 1767-1788.

[13] Holbrook W. S. Thermohaline Fine Structure in an Oceanographic Front from Seismic Reflection Profiling. Science, 2003, 301(5634): 821-824.

[14] Huang X. H., Song H. B., Luis M. P., . Ocean Temperature and Salinity Distributions Inverted from Combined Reflection Seismic and XBT Data. Chinese Journal of Geophysics, 2011, 54(3): 307-314.

[15] Ji L. L., Lin M. Numerical Analysis of the Effect of Mesoscale Eddies on Seismic Imaging. Pure and Applied Geophysics, 2013, 170(3): 259-270.

[16] Liu H., Zhou H. W., Liu W. G., . Tomographic Velocity Model Building of the near Surface with Velocity-Inversion Interfaces: A Test Using the Yilmaz Model. Geophysics, 2010, 75(6): U39-U47.

[17] Ma X. H., Jing Z., Chang P., . Western Boundary Currents Regulated by Interaction between Ocean Eddies and the Atmosphere. Nature, 2016, 535(7613): 533-537.

[18] MacKay S., Fried J. Removing Distortions Caused by Water Velocity Variations: Method for Dynamic Correction. SEG Technical Program Expanded Abstracts, 2002, 21: 2074-2077.

[19] MacKay S., Fried J., Carvill C. The Impact of Water-Velocity Variations on Deepwater Seismic Data. The Leading Edge, 2003, 22(4): 344-350.

[20] Makris J., Papoulia J., McPherson S., . Mapping of Sediments and Crust Offshore Kenya, East Africa: A Wide Aperture Refraction/Reflection Survey. SEG Technical Program Expanded Abstracts, 2012, 31: 1-5.

[21] Moser T. J. Shortest Path Calculation of Seismic Rays. Geophysics, 1991, 56(1): 59-67.

[22] Richardson P. L., Bower A. S., Zenk W. A Census of Meddies Tracked by Floats. Progress in Oceanography, 2000, 45(2): 209-250.

[23] Richardson P. L., Price J. F., Walsh D., . Tracking Three Meddies with SOFAR Floats. Journal of Physical Oceanography, 1989, 19(3): 371-383.

[24] Ritter G. L. D. S. Water Velocity Estimation Using Inversion Methods. Geophysics, 2010, 75(1): U1-U8.

[25] Song H. B., Luis P., Wang D. X., . Seismic Images of Ocean Meso-Scale Eddies and Internal Waves. Chinese Journal of Geophysics, 2009, 52(6): 1251-1257.

[26] Tian W., He M., Yang Y., . Complex Linkage and Transformation of Boundary Faults of Northern Huizhou Sag in Pearl River Mouth Basin. Earth Science—Journal of China University of Geosciences, 2015, 40(12): 2037-2051.

[27] Yang Y., He G., Zhu K., . Classification of Seafloor Geological Types of Qianyu Seamount from Mid Pacific Seamounts Using Multibeam Backscatter Intensity Data. Earth Science—Journal of China University of Geosciences, 2016, 41(4): 718-728.

[28] Zelt C. A. Modelling Strategies and Model Assessment for Wide-Angle Seismic Traveltime Data. Geophysical Journal International, 1999, 139(1): 183-204.

[29] Zhou H. W. A High-Resolution P wave Model for the Top 1 200 km of the Mantle. Journal of Geophysical Research: Solid Earth, 1996, 101(B12): 27791-27810.

[30] Zhou H. W. Multiscale Traveltime Tomography. Geophysics, 2003, 68(5): 1639-1649.

[31] Zhou H. W. Multiscale Deformable-Layer Tomography. Geophysics, 2006, 71(3): R11-R19.

[32] Zhou H. W. On the Layering Artifacts in Seismic Imageries. Journal of Earth Science, 2011, 22(2): 182-194.

[33] Zhu X. H., Angstman B. G., Sixta D. P. Overthrust Imaging with Tomo-Datuming: A Case Study. Geophysics, 1998, 63(1): 25-38.

[34] Zou Z. H., Liu K., Zhao W., . Upper Crustal Structure beneath the Northern South Yellow Sea Revealed by Wide-Angle Seismic Tomography and Joint Interpretation of Geophysical Data. Geological Journal, 2016, 51(4): 108-122.