Constraining subducted slab properties with deep earthquakes
Abstract
The discovery of deep earthquakes and Wadati-Benioff zone was a critical piece in the early history of plate tectonics. Today, deep earthquakes continue to serve as important markers/probes of subducted slab geometry, structure, and stress state. Here we discuss three examples in which we have recently used deep earthquakes to provide new insights to subducted slab properties. In the first application, we investigate the slab morphology and stress regimes under different trench motion histories with geodynamic models. We find that the isolation of the 2015 Mw 7.9 Bonin Islands deep earthquake from the background Wadati-Benioff zone may be explained as a result of Pacific slab buckling in response to the slow trench retreat. Additionally, subducted slab is inherently heterogeneous due to non-linear viscosity, contributing to the occurrences of isolated deep earthquakes. In the second application, we quantify the coda waveform differences from nearby deep earthquakes to image fine-scale slab structures. We find that large metastable olivine wedge suggested by several previous studies can not fit our observations. Therefore, the effects of metastable olivine on slab dynamics should be re-assessed. In the third application, we take advantage of P and S differential travel times from deep earthquake clusters to isolate signatures of Vp/Vs ratios within slabs from ambient mantle. We observe substantial deviations of slab Vp/Vs from that in 1D reference Earth models, and even possible lateral variations. This sheds light on potential difference in slab temperature or water content. All three applications underscore that deep earthquakes are still incredibly useful in informing us more about subducted slabs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMDI41B..08Z
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRY;
- 3999 General or miscellaneous;
- MINERAL PHYSICS;
- 7240 Subduction zones;
- SEISMOLOGY;
- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS