Three‐Dimensional S Velocity Structure of the Mantle Transition Zone Beneath Central America and the Gulf of Mexico Inferred Using Waveform Inversion

Abstract

Travel time tomography studies have reported various modes of subduction of slabs around the mantle transition zone, but the causes of this variability are still controversial. In order to place additional constraints on the style of subduction in and near the mantle transition zone, we apply waveform inversion to S wave triplications due to the 410‐ and 660‐km discontinuities, and infer the regional three‐dimensional S velocity structure in the depth range 370–820 km beneath Central America and the Gulf of Mexico. We use ~3,400 transverse component records at epicentral distances 17–30° from 20 intermediate focus earthquakes beneath Central America recorded at stations of the USArray and other smaller networks. We filter the records between 20 and 100 s, and use the portions of the waveforms from 10 s before to ~40–80 s after the arrival of the direct S wave, thereby including the S wave triplications while excluding the sS depth phase. We correct the data for the structure above our target region using previous S velocity models, and we show that the results of the inversion do not depend heavily on which correction is used. Resolution tests confirm that we can resolve small‐scale structure in the target region. Our inferred models show that the Cocos slab penetrates into the lower mantle, but with important variations along the Middle America Trench in the subduction style of the slab. We suggest that this variability could be due to the thermal structure of the Cocos slab, and to the interaction of the slab with a possible lower mantle plume.

The theory of compression–shear coupled composite wave propagation in rock

“…The internal structure and composition of the Earth and terrestrial planets have always been a matter of great concern to the natural science community. Due to the limitations of drilling equipment and the environment of high temperature and pressure in the deep crust, inversion analysis based on seismic wave signals has always been the main method to study the internal structure and composition of the Earth (Borgeaud et al, 2019; Kanna & Gupta, 2021; Mesimeri et al, 2021) as well as the Mars (Banerdt et al, 2020; Giardini et al, 2020; Khan et al, 2021; Knapmeyer‐Endrun et al, 2021; Stähler et al, 2021). Seismic wave signals could be used to analyze the geometric information of continental plate faults and ruptures, and to determine the location of hypocenters and the earthquake mechanism.…”