Using ambient seismic noise to image the mantle transition zone

Abstract

Imaging of the mantle transition zone, the part of the Earth’s mantle bound by the 410 and 660km discontinuities, has long been confined to earthquake data only. Recent studies demonstrated that the mantle transition zone can also be imaged with seismic interferometry, a method to approximate the Green’s function between receiver pairs by cross-correlating ambient seismic noise. Retrieving body waves that have travelled through the deep Earth with this method remains challenging, because surface waves are the dominant signals in ambient seismic noise records. Our study investigates if mantle transition zone reflections can be observed in California, using ambient seismic noise. Four years of seismic data (2018–2021) for 251 stations is retrieved, preprocessed, crosscorrelated and stacked in variable time windows. The results are dependent on many factors, such as frequency range, season and interstation distance. The mantle transition zone reflections are best observed between June and August, because in these months useful microseismic noise is generated in the Southern Ocean, close to the antipode of the array. The frequency range giving the best reflections is 0.07–0.15 Hz, including both the primary and secondary microseisms.