Small- to intermediate-scale mantle heterogeneity from observations of seismic scattering
Abstract
Observations of PKP precursors in the 0.7 to 2.5 Hz frequency band suggest the presence of small-scale (~10 km) compositional heterogeneity distributed throughout the lowermost mantle. We stack amplitudes of over 10,000 PKP precursor waveforms, culled from broadband global seismic data with source-receiver distances between 120 and 145 degrees recorded from 1990 to 2012. Forward modeling the stacked amplitudes using a Monte Carlo 'seismic phonon' approach, we find that a mantle with 0.1% r.m.s. velocity perturbations and a correlation length of 6 km fits the data reasonably well, in agreement with Margerin and Nolet (2003). To better understand what the global PKP precursor stack represents, we explore the statistical distribution of the amplitudes and look for particular ray paths that exhibit stronger or weaker scattering than average. To address the question of larger scale lengths, we compare long-period seismic records (17 to 150 s) with SPECFEM3D GLOBE synthetics and find that the data exhibit more power between the main phases (e.g., P, PP), hinting at the presence of greater intermediate-scale (50-200 km) heterogeneity than accounted for by 3D global tomography models. We also observe a significant amount of surface-wave scattering in the data that is not seen in the SPECFEM3D GLOBE synthetics. We preliminarily model amplitude stacks of the long-period records with the 'seismic phonon' code but ultimately plan to check the accuracy of this approach by adding random media to a SPECFEM3D GLOBE calculation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.S31D..08M
- Keywords:
-
- 7208 SEISMOLOGY Mantle;
- 7203 SEISMOLOGY Body waves