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Nodal Arrays for Improved Tomography Imaging of the Ecuadorian Forearc and Insights Into Slip Behavior Controlling Process

Description: 

Large subduction earthquakes (Mw > 7.7) often occur along the Ecuadorian subduction zone where the Nazca plate converges towards the South American plate. In 2016, the Pedernales megathrust earthquake (Mw 7.8) led to nearly 60 temporary stations being deployed. Data from this international response and the permanent network run by IG-EPN showed that subducted seafloor topography, accreted terranes, and inherited structures control the slip behavior along the margin. However, the role of fluids in the stress build-up and the influence of a large rupture on the distribution of fluids remain open questions. For that reason, nodal arrays were installed in the northern Ecuadorian forearc in 2020 and 2022, overlapping with the rupture area of the Pedernales earthquake. The second array overlaps with 60 broadband stations deployed from 2021 to 2022 from the foothill of the Andes to the coast. Using Deep-Learning phase picking on continuous recordings, we derived a seismicity catalog of over 3,000 earthquakes made of 300,000 P and S arrivals. Both P and S-wave velocity models were derived from a 3D travel time tomography inversion. The models were then used to infer fluid saturation and crack density.

The velocity model derived from the nodal arrays shows higher resolution features than tomography inversion, which used broadband stations only. We identified a slower and narrower velocity area overlaying with the rupture extent of the 2016 Pedernales earthquake and more focused high-velocity and high Vp/Vs structures. The velocity model shows structures associated with higher amplitude peaks in the over-thickened oceanic crust of the downgoing plate. The nodal arrays offer insights into the controls of slip behavior around the plate interface. The subducting plate appears more cracked and saturated with fluids than the overriding plate. The plate interface is highly fractured which suggests that cracks may consist of fluid migration pathways. The fluid circulation may cause seismicity on subducting faults while the seepage on the plate interface could trigger subduction earthquakes.

Session: Innovative Applications of Seismic Nodal Technology for Hazard Mitigation and Earth System Monitoring - I

Type: Oral

Date: 4/15/2025

Presentation Time: 02:30 PM (local time)

Presenting Author: Alexander

Student Presenter: No

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