Regional Variation of Fine-Scale Structure of Earth's Inner Core
Abstract
Fine-scale (~1-10 km) heterogeneity in Earth's inner core has been reported in several studies over the last 20 years based on the observation of emergent, spindle-shaped codas following pre-critical PKiKP. However, the detail structure of fine-scale heterogeneity in the inner core is poorly constrained. To better understand the geodynamic evolution of the inner core, it is important to develop an end-to-end approach including data acquisition, observation, analyses, modeling, and interpretation for the inner core heterogeneity. Here, we develop an array processing python package, gPar, and apply it to data from seven small-aperture International Monitoring System (IMS) arrays, of which five are in North America and two are in Australia. We search the gCMT catalog for earthquakes that occurred from 1996 to 2018 in the distance range of 50°-75°, where the codas are least affected by structure in the crust and mantle. We identify a total of 654 earthquakes for ASAR, 746 earthquakes for ILAR, 678 earthquakes for NVAR, 542 earthquakes for PDAR, 644 earthquakes for TXAR, 612 earthquakes for WRA, and 766 earthquakes for YKA. We use gPar to perform standard array processing to enhance the coda signal and remove the background scattered energy from the crust and mantle. The preliminary results show that the PKiKP coda energy scattered from different regions have distinct shapes, suggesting there could be regional variations in inner core scattering structure. As the coda shape is indicative of the scatterer properties such as depth, grain size, and scattering strength, we characterize the properties of the observed PKiKP codas using a multi-scattering phonon simulation code. We find it difficult to fit the observations with a single layer model of uniform scattering strength within the inner core. A two-layer scattering model provides a significantly better fit to our observations, implying a change in scattering strength with depth for at least some regions of the inner core under the Pacific Ocean and North America.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMDI23B0051P
- Keywords:
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- 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 7207 Core;
- SEISMOLOGY