Constraining the geometry of small-scale mantle heterogeneities: A case study from the Mariana region

Abstract:

A new array-based method for seismic waveform data is developed to not only detect small-scale heterogeneities in the mantle but also constrain their possible geometries. Detecting small-scale heterogeneities using scattered waves has been challenging because scattered phases usually suffer from low signal-to-noise ratios, and determining the shapes of such heterogeneities is even more difficult because of isochronal artifacts. In the proposed method, the problem of the low signal-to-noise ratio is addressed by adopting dual bootstrap stack, which can detect weak signals even with a limited number of channels, as well as by ensuring reproducibility among different events. The geometries of detected scatterers are then estimated using a new kind of hierarchical cluster analysis that could minimize the effect of isochronal artifacts. The new method is applied to a previously analyzed data set of Mariana earthquakes to facilitate a comparison with conventional methods. In the mantle beneath the Mariana trench region, a total of 39 scatterers are identified, with their potential volumes ranging from ~8x10^4 to ~1x10^6 km^3.