Events

Fall Semester Classes Begin

UTIG Seminar Series: Bhargav Boddupalli, UTIG

Speaker: Bhargav Boddupalli, Postdoctoral Fellow, UTIG

Host: Shuoshuo Han

Title: Imaging of the Deep Galicia margin using ocean bottom seismic data

Abstract: Continental rifting and breakup is the first order tectonic process that initiates the plate tectonic cycle and results in the formation of passive rifted margins. The Galicia margin, west of Iberia, is archetypical for magma-poor rifted margins where a number of key concepts of rifting processes have been developed and tested. Seismic imaging has been instrumental in understanding rifting in the Galicia margin. In this talk, I present a high-resolution P-wave velocity model of the Deep Galicia margin (DGM) where the final breakup of the continental crust happened. The velocity model is derived employing a 3D acoustic full waveform inversion (FWI) technique in the time domain using sparsely acquired wide-angle ocean bottom seismometer (OBS) data. Comparison of the 3D FWI model result with 2D result derived along a profile through the 3D seismic volume highlighted the differences between the imaging methods in a real world setting. Differences in the data residuals of the 2-D, 2.5-D and 3-D inversions suggest that 2-D inversion can be prone to overfitting when using a sparse data set. Using the 3D FWI velocity model of hyper-thinned crust at the Deep Galicia Margin (DGM), we constrain the nature of the crust at this margin by comparing its velocity structure with those in other similar tectonic settings. Our velocity model also shows evidence for exhumation of the lower crust under the footwalls of fault blocks to accommodate the extension. We used our model to generate a serpentinization map for the uppermost mantle at the DGM, at a depth of 100 ms (~340m) below the S-reflector, a low-angle detachment that marks the base of the crust at this margin. Based on this map, we propose that serpentinization began during rifting and continued into a post-rift phase until the faults were sealed. We find a poor correlation between the fault heaves and the degree of serpentinization beneath the hanging- and foot-wall blocks, indicating that serpentinization was controlled by a complex mechanism during and after rifting. A good match between topographic highs of S and local highly serpentinized areas of mantle suggests that the serpentinization process resulted in variable uplift of the S-surface.

First-order multiples from the OBS data can be used to develop seismic images using a technique called mirror imaging. We developed seismic images of the DGM in time and depth domains using mirror imaging. In this technique, the seafloor along with the OBS is mirror imaged with respect to the sea-surface and placed at a depth of twice the water column depth. Such an adjustment allows incorporation of the multiples in to migration algorithms just like primary reflections. Mirror imaging can become a standard processing step in studies where no multichannel data are available.

Soft Rock Seminar: Zach Sickmann

Accelerating sand mining for Bangladesh development threatens the sand chars of the Ganges

Dr. Zach Sickmann (UTIG)

Monday, August 30th 12-1 pm 

Zoom link: https://utexas.zoom.us/j/94967658238

UTIG Discussion Hour: Gail Christeson, UTIG

Speaker: Gail Christeson, Senior Research Scientist / Associate Director, UTIG

Title: South Atlantic Transect Project: Pre-Expedition Drilling during Covid-19 Pandemic