Paper No. 17
Presentation Time: 1:00 PM


WEYMER, Bradley A.1, EVERETT, Mark E.2, HOUSER, Chris3, BARRINEAU, Patrick4, GIARDINO, John R.5 and BISHOP, Michael P.3, (1)Geology and Geophysics, Texas A&M University, College Station, TX 77840, (2)Geology/Geophysics, Texas A&M Univ, 3115 TAMU, Halbouty Bldg, College Station, TX 77843, (3)Department of Geography, Texas A&M University, 810 O&M Building, College Station, TX 77843, (4)Department of Geography, Texas A&M University, 810 O&M Building, College Station, TX 77840, (5)High Alpine and Arctic Research Program (HAARP), Department of Geology and Geophysics and Water Management and Hydrological Sci, Texas A&M University, College Station, TX 77843-3115,

The use of EM to detect subsurface stratigraphic features in coastal environments has not been explored in great detail. Unlike ground-penetrating radar (GPR), which images subsurface features directly, the EM method requires complex numerical and statistical modeling to invert apparent conductivity (σA) values into interpretable depth profiles. This work explores the utility of non-invasive EM induction for reconstructing the geomorphic history of the Laguna Madre wind-tidal flats in south Texas.

The Laguna Madre wind-tidal flats and adjacent barrier island (Padre Island National Seashore) are highly-conductive environments (upwards of 3,800 mS/m) that offer a unique opportunity to test the capability of EM to differentiate a variety of coastal depositional environments. For this study, we used a multi-frequency GSSI EMP-400 EM Profiler™ to conduct a series of transects extending across the barrier into the wind-tidal flats. Three shore-normal surveys were taken along the southern, central and northern portions of the sand sheet at a total distance of 10 km, 9 km and 7 km, respectively. In addition, a 20 km long shore-parallel survey intersected the three shore-normal transects along the central portion of the island. For each survey, the EM profiler was oriented to the in-line horizontal dipole mode (HDM) at a 5 m sampling interval. Responses were recorded at three discrete frequencies: 1 kHz, 8 kHz, and 15 kHz, corresponding to skin depths of ~16 m, 10 m and 5 m, respectively. To invert the EM data, we used a Markov Chain Monte Carlo (MCMC) 1D inversion model to distinguish different geoelectric layers. Additionally, wavelet and spectral estimation of the non-stationary time series was performed. Preliminary results suggest that by taking the inverse of the EM data, inflection points become visible, which enables one to distinguish the main stratigraphic features of the barrier and wind-tidal flat system. Further research is currently in progress to incorporate morphometric analyses from a companion study to establish relationships between surface morphometry and subsurface EM results.