Seismic Crustal Velocity and Structure of the Texas-Gulf of Mexico Passive Margin From Waveform Inversion Using Global Optimization

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

The Gulf of Mexico (GoM) basin was formed as the Yucatan block rifted away from North America at ~165 Ma. After rifting, seafloor spreading started at ~150 Ma which continued till ~138 Ma. However, due to the thick layers of sediments that now blanket the region, important details, including the style of rifting and degree of extension of the surrounding GoM passive margin, remain unclear. Deep sediments attenuate seismic waves, making it difficult to identify and analyze teleseismic arrivals and rates of local seismicity are quite low.

We use data from the X4 2010-13 seismic array, a transect across the Gulf Coastal Plain. X4 extends across the GoM passive margin from Matagorda Island to the Llano Uplift and consists of 22 broadband, three-component seismometers with Reftek 130 digitizers.

We observe direct S and SsPmp arrivals from a teleseismic earthquake at an epicentral distance of ~60⁰, as is common. The amplitude of postcritical SsPmp tends to be large and easily observed without stacking multiple events. However, we also observe another wave that arrives between direct S and SsPmp, which we interpret to be a P reflection from the basement after an S-to-P conversion and reflection at the surface (SsPbp). SsPbp is expected to have a fairly large amplitude due to a large impedance contrast between. The deep layer of sediments produces good time separation so the three arrivals are distinct. Waveform modeling provides strong constraints on the impedance contrasts of the sediment/basement and the Moho interfaces by matching the waves’ arrival times and amplitudes

Our waveform modeling uses the reflectivity method for forward calculations of waveforms and simulated annealing, a global optimization algorithm, to guide a broad search of locally 1D models. Initial models for the inversion are produced via travel time tomography using local and teleseismic earthquakes and direct waves identified via seismic interferometry performed with a 160-km, 412-geophone short-period array that partly overlaps the X4 array.

Presenting Author: Joseph Thangraj

Authors