The seismic wave speed structure of the Ontong Java Plateau determined from joint ambient noise and earthquake waveform data

Abstract:

The Ontong Java Plateau (OJP) represents the result of a significant event in the Earth's geologic history. Limited geophysical and geochemical data, as well as the plateau's relative isolation in the Pacific Ocean, have made interpretation of the modern day geologic structure and its 120 Ma formation history difficult.

Here we present the highest resolution images to date of the wave speed structure of the OJP region. We use an iterative finite-frequency tomography methodology and a unique data set that combines empirical Green’s functions extracted from ambient noise and earthquake waveforms. The uniqueness and combination of datasets allow us to best exploit the limited station distribution in the Pacific and image wave speed structures between 35 km and greater than 250 km into the Earth.

We image a region of fast shear wave speeds, greater than 4.75 km/s, that extends to greater than 100 km beneath the plateau. The wave speeds are similar to as observed in cratonic environments and are consistent with a compositional anomaly likely a result of eclogite entrainment during the plateau's formation.