# Mapping the Basement along the Northern Ecuadorian Margin using Refraction and Reflexion Data from the HIPER Experiment.

Arnaud Delsuc, A. Galvé, Mireille Laigle, Andreas Rietbrock, Laure Schenini, Alessandra Ribodetti, B. Marcaillou, Scientific Crew Hiper

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Arnaud Delsuc, A. Galvé, Mireille Laigle, Andreas Rietbrock, Laure Schenini, et al. Mapping the Basement along the Northern Ecuadorian Margin using Refraction and Reflexion Data from the HIPER Experiment. American Geophysical Union, Fall Meeting 2024 (AGU 2024), Dec 2024, Washington DC, United States. hal-04920497

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Submitted on 8 Dec 2025

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# Mapping the Basement along the Northern Ecuadorian Margin using Refraction and Reflexion Data from the HIPER Experiment

Delsuc, A.(1,2), Galve, A.(1), Laigle, M.(1), Rietbrock, A.(2), Schenini, L.(1), Ribodetti, A.(1), Marcaillou, B.(1), and scientific crew of HIPER2 : Pelleau, P.(3), Oregioni, D.(1), Ferrant, A.(3), Soto, E.(1), Paulatto, M.(5), Vaca, S.(4), Moreno Piña, M.(6), Muñoz Muñoz, M.(6), Skrubej, A.(1), Acosta, V.(4)
(1) Université Côte d'Azur, IRD,CNRS, Observatoire de la Côte d'Azur, Géoazur, 06560 Valbonne, France; (2) Karlsruhe Institute of Technology, Geophysical Institute, Karlsruhe, 76187, Germany; (3) Geo-Ocean, Université Brest, CNRS, Brest, France; (4) Instituto Geofisico, Escuela Politécnica Nacional, Quito, 170525, Ecuador;
(5) Imperial College London, Earth Science and Engineering, Prince Consort Road, London SW7 2BP, UK; (6) Instituto Oceanográfico y Antártico de la Armada (INOCAR), Avenida 25 de Julio via Puerto Marítimo, Base Naval Sur, Guayaquil, Ecuador

Email: arnaud.delsuc@geoazur.unice.fr

## 1- INTRODUCTION & OBJECTIVES :

* Major earthquakes in 20th century

* 2016 Mw 7.8 Pedernales earthquake

* Megathrust fault at shallow depth

* Carnegie Ridge -> thicker oceanic crust

* Many different slip behaviors observed

* Forearc crust from accreted oceanic terranes (Hernadez et al. 2020)

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

* Image velocity structures of the crustal part of the Ecuadorian margin

* Mapping the forearc basement

## 2- DATA :

### HIPER1 (2020)

### campaign :

* 47 OBS (Géoazur & AWI)

* 1 dense WAS profile

* 3 MCS profiles

### HIPER2 (2022)

### campaign :

* 43 OBS (IFREMER)

* 100 land stations

* 14 000 shots

* Source of 4990 cu.inch

* Vessel : L'Atalante

* ~55000 first breaks picked

* 6 trench parallel profiles

* 9 trench normal profiles

* 3 dense WAS profiles

<figure><img src="image_4.png" /></figure>

## 3- METHOD & RESOLUTION : Bayesian Tomo2D (Korenaga et al. 2012)

### First application on a subduction zone

* Bayesian approach of tomo2D

* 13 a priori ranges of model parameters

* Automatically build initial model from inputs parameters

* Analysis of output velocity model using data misfit (log(χ²)) and model roughness (R)

<figure><img src="image_5.png" /></figure>

* (A-B) Distribution of log(χ²) and R over iteration → adaptive importance sampling.

* (C-D) Selection of two of the 13 model parameters

<figure><img src="image_6.png" /></figure>

## 4- RESULTS

### 2D Vp models

<figure><img src="image_7.png" /></figure>

### Line 3

<figure><img src="image_8.png" /></figure>

### Line A

<figure><img src="image_9.png" /></figure>

### Comparison with Previous studies :

<figure><img src="image_10.png" /></figure>

### Gradient 2D models

<figure><img src="image_11.png" /></figure>

### Line 4

<figure><img src="image_12.png" /></figure>

### Line A

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

## 5- INTERPRETATION & CONCLUSION :

* High vertical Vp gradient mapping the forearc basement (>0.85 km/s/km, green area)

* LV1 interpretation (Line A) : faulted oceanic plate ?

<figure><img src="image_15.png" /></figure>

* LV2 interpreted as fracturation/alteration of the outer crustal wedge near the deformation front (similar to Garcia-Cano et al., 2014)

* Successful application of the Bayesian approach of Tomo2D at a subduction zone setting

Next step => 3D Inversion

### References :

Korenaga et al. (2000). Crustal structure of the southeast Greenland margin from joint refraction and reflection seismic tomography. *Journal of Geophysical Research: Solid Earth*, 105(B9), 21591-21614.

Korenaga, J., & Sager, W. W. (2012). Seismic tomography of Shatsky Rise by adaptive importance sampling. *Journal of Geophysical Research: Solid Earth*, 117(B8).

Marcaillou et al. (2016). Seamount subduction at the North-Ecuadorian convergent margin: Effects on structures, inter-seismic coupling and seismogenesis. *Earth and Planetary Science Letters*, 433, 146-158.

León-Rios et al. (2021). 3D local earthquake tomography of the Ecuadorian margin in the source area of the 2016 Mw 7.8 Pedernales earthquake. *Journal of Geophysical Research: Solid Earth*, 126(B3), e2020JB020701.

Font et al. (2013). Seismicity patterns along the Ecuadorian subduction zone: new constraints from earthquake location in a 3-D a priori velocity model. *Geophysical Journal International*, 193(1), 263-286.

Gonzalez, M. (2018). Nature and origin of sedimentary deposits in the Ecuador subduction trench: Paleoseismological implications (Doctoral dissertation, Université de Rennes).

García Cano et al. (2014). Three-dimensional velocity structure of the outer fore arc of the Colombia-Ecuador subduction zone and implications for the 1958 megathrust earthquake rupture zone.

Sallarés et al. (2003). Seismic structure of Cocos and Malpelo Volcanic Ridges and implications for hot spot-ridge interaction. *Journal of Geophysical Research: Solid Earth*, 108(B12).

Sallarés et al. (2005). Seismic structure of the Carnegie ridge and the nature of the Galápagos hotspot. *Geophysical Journal International*, 161(3), 763-788.

Grevemeyer et al. (2018). Structure of oceanic crust and serpentinization at subduction trenches. *Geosphere*, 14(2), 395-418.