Using Ambient Noise Seismic Interferometry and Local and Teleseismic Earthquakes to Determine Crustal Thickness and Moho Structure of the Northwestern Gulf of Mexico Margin

The northwestern part of the Gulf of Mexico has undergone two episodes of continental rifting and collision and produced structural artifacts that are now buried under many kilometers of sediments, complicating investigations of the region. The deep sedimentary package precludes outcrops and points to a need for the application of seismic techniques, but low rates of seismicity in the region and sparse seismic monitoring limit the utility of traditional seismic methods. We therefore use diverse data to perform two‐dimensional seismic tomography across the dry land portion of the margin. Data are gleaned from teleseismic and regional earthquakes, postcritical SsPmp arrivals, and direct P wave energy identified with seismic interferometry that were recorded by a broadband, three‐component array and partially overlapping short‐period, vertical‐component array. The Pn and postcritical SsPmp phase help constrain the Moho discontinuity, which a previous receiver function study suggested was absent beneath the seaward portion of this transect. A high‐velocity body is observed in the crust at the same location as the Houston Magnetic Anomaly, possibly marking rocks from the Alleghenian continental assembly. The crust thins from NW to SE, indicating that extension occurred mostly to the south of the Ouachita orogeny. Our model indicates that the margin's sediment package reaches a maximum thickness of ~15 km at the coast and becomes unresolvably thin near the Llano Uplift. Plain Language Summary Structural features buried under the thick sediments in the onshore portion of the Gulf coastal plain may be keys to understanding the process that led to the formation of the present‐day Gulf of Mexico. However, obtaining a model of these structures is challenging for several reasons. First, the Gulf of Mexico has very low rates of seismicity; second, the sediments rapidly reduce seismic energy; third, recording instruments have historically been quite sparse. Together, these limit the use of traditional seismic methods. We therefore use complementary data sets to model the structures, including records of distant earthquakes and local earthquakes plus P arrivals identified with seismic interferometry. We observe a high‐velocity body in the crust that lies beneath the Houston Magnetic anomaly, indicating a possible origin associated with the continental assembly of Africa and North America that occurred approximately 325 to 260 million years ago. Key Points A high seismic