Tau-p Depropagation of Five Regional Earthquakes Recorded by the Earthscope Usarray to Constrain the 410-km Discontinuity Veloci

Tau-p Depropagation of Five Regional Earthquakes Recorded by the Earthscope Usarray to Constrain the 410-km Discontinuity Velocity Gradient Baja California earthquake P-wave recorded by the Transportable array.
<p>
Seismic recordings by the EarthScope USArray from three Queen Charlotte region earthquakes and two southern Baja Mexico earthquakes are transformed to the Tau-P domain and the post-critical P-wave branches are picked. Five one dimensional velocity models are formed via depropagation of the picked Tau-P curves. All five models are in good agreement with the ak135 reference model velocity gradients both above and below the 410 km discontinuity and the observed 410 P-wave velocity step is within 10% of ak135. The 410 velocity gradients for three of the models are sharp (<5 km) and for two of the models are gradational (25-30 km). The maximum 410 velocity gradient is found at depths of 392-443 km. From this small sample set, no correlation between the 410 widths and depths is observed. All five models have 2-4% higher velocities in the 50-100 km depth interval above the 660 km discontinuity which may manifest stagnated slabs. The two models with a large 410 gradient can be explained by up to 500 ppm by mass hydration levels.</p>

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