3D forearc crustal structure in the vicinity of the 2014 Iquique earthquake sequence
Abstract
The 2014 M8.1 earthquake offshore northern Chile has received extensive study because it exhibited a distinct sequence of precursory seismic and aseismic slip and because it ruptured only ~1/3 of a recognized seismic gap that had last ruptured in a major earthquake in 1877. The precursory activity, patch of greatest slip in the mainshock, and southern extent of aftershock activity in this sequence show a striking correlation with residual gravity (i.e. free-air gravity corrected for the effect of water depth and the subducting slab), suggesting that long-lived geologic structure affected the distribution of slip. To better understand the relationship between crustal structure and interplate deformation, we conducted a 3D seismic experiment to image the forearc using multichannel seismic reflection and OBS wide-angle seismic data (cruise MGL1610). Several of the MCS profiles are discussed by Ma et al. in this session. Here we present a 3D P-wave velocity and Moho surface model derived from the grid of airgun shots recorded on ocean bottom and onshore seismometers. The model is based on ~120,000 Pg and PmP picks at a spacing of ~500 m along a grid of 30 source lines spaced ~10 km apart. The footprint of the volume imaged by the data is ~150x150 km, extends up to ~50 km depth, and encompasses the source region of the 2014 earthquake sequence. Preliminary inversions indicate complex structure suggestive of subducted topography in the depth range of 15 to 40 km beneath the seafloor, where Vp is 6.4-7.4 km/s. The position of the Moho surface indicates either that the subducted crust of the Nazca plate is anomalously thick, consistent with results on crustal thickness from a 2D profile across the Iquique Ridge prior to subduction, or that the plate boundary position in the global Slab 2.0 model is underestimated. Efforts are ongoing to refine the model for shallow basin structure, in order to more precisely and accurately resolve the velocity structure of the lower crust and its relationship to seismicity and slow slip.
The PICTURES (Pisagua/Iquique Crustal Tomography to Understand the Region of the Earthquake Source) working group includes scientists from Chile, Germany and the US who are using data acquired during cruise MGL1610 of the R/V Marcus Langseth to study feedbacks between geology and subduction zone dynamics.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMT055...08T
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 3613 Subduction zone processes;
- MINERALOGY AND PETROLOGY;
- 7240 Subduction zones;
- SEISMOLOGY;
- 8170 Subduction zone processes;
- TECTONOPHYSICS