Nested Regional-Global Seismic Tomography and Precise Earthquake Relocation Along the Aleutian-Alaska Subduction Zone

Abstract:

The dominant mechanism involved in the genesis of intermediate depth earthquakes is an unresolved question. Several hypotheses have been proposed including dehydration and fluid related embrittlement, geometric unbending of the slab and thermal shear instability. Our study aims to investigate seismic characteristics along the Aleutian-Alaska subduction zone using high-resolution techniques. We obtain phase-arrival data from the International Seismological Centre (ISC) and waveform data from Incorporated Research Institutions for Seismology (IRIS). We apply the teletomoDD algorithm that uses a nested regional-global parameterization with a fine-grid regional model embedded in a coarse-grid global model. The resulting 3-D P-wave velocity model is used for absolute earthquake location improvements. A differential-time relocation method based on waveform cross-correlation is then applied to further improve the accuracy of hypocenters by resolving relative locations. In our preliminary model, a low P-wave velocity body juxtaposes on top of a subducting pacific slab with high Vp anomaly (~ 8.5 km/s) to the northeast of the subduction zone. This low Vp zone starts at ∼40 km depth and terminates at ∼100 km depth, correlates with the Yakutat slab location, and also follows the seismicity pattern. This low P-wave velocity starts to disappear moving to the west. Beneath Cook Inlet, the high Vp subducting pacific slab (above 8.5 km/s) correlates with seismicity. The seismicity pattern and P wave velocity change along the strike of the subduction zone. The patterns of seismicity and velocity anomalies will help provide insights about mechanisms involved in slab deformation. In the light of these observations and slab properties (e.g., slab age, thermal parameter and convergence rate), we hope to provide a better understanding of the seismogenic processes responsible for the genesis and distribution of intermediate-depth earthquakes in our study area.