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SUMMARY:3D tomographic constraints on upper-plate elastic structure and in
 ter-plate geometry offshore the Ecuadorian-Colombian margin - Manel Prada 
 -- Institute of Marine Sciences\, Spanish National Research Council (CSIC)
DTSTART:20250305T140000Z
DTEND:20250305T150000Z
UID:TALK229057@talks.cam.ac.uk
CONTACT:ChuanChuan Lu
DESCRIPTION:In subduction zones\, upper-plate elastic rock properties play
  a major role in controlling megathrust fault dynamics (Sallarès & Ranero
  2019\; Prada et al.\, 2021\; Ulrich et al.\, 2022). The variations of the
 se properties in the downdip direction are influenced by increasing confin
 ing pressure with depth\, forming a global depth-dependent pattern (Sallar
 ès & Ranero 2019). However\, the understanding of how these properties va
 ry along-strike\, especially above the interplate\, where elastic energy i
 s stored during interseismic cycle\, remains unclear. Here we present 3D t
 omographic constraints on the velocity structure of the upper plate as wel
 l as the inter-plate geometry offshore the Ecuadorian-Colombian margin. Th
 e study area has been the locus of large megathrust tsunamigenic earthquak
 es\, including the seventh largest in history (1906 Mw~8.8 Esmeraldas)\, b
 ut elastic properties above the megathrust are not mapped hitherto. Here w
 e use 3D wide-angle seismic (WAS) dataset acquired in 2005 during the ESME
 RALDAS survey and multichannel seismic (MCS) lines to integrate tectonic i
 nformation to our tomographic results. WAS data were acquired with 26 ocea
 n bottom seismometers from which we picked travel times of P-waves refract
 ed through the upper and lower plates\, as well as P-wave reflections at t
 he interplate. We invert travel times with a 3D joint reflection and refra
 ction travel time method (Melendez et al.\, 2015) following a Monte Carlo 
 approach to provide uncertainties on model parameters.The resulting model 
 shows the 3D P-wave velocity (Vp) structure of the upper and lower plates 
 as well as the geometry of the interplate reflector. Additional elastic pa
 rameters such as rigidity (i.e.\, shear modulus) were derived using empiri
 cal relationships between Vp\, Vs\, and density. Downdip variations in rig
 idity align with the inferred global trend. However\, rather than being la
 terally consistent\, elastic properties exhibit remarkable variations alon
 g-strike within the rupture area of the largest recorded earthquakes. MCS 
 sections in the study area depict a complex interaction between crustal-sc
 ale faults. This interaction has been proposed to control the seismogenic 
 behavior of the subduction zone in this region\, promoting the occurrence 
 of confined ruptures (Collot et al.\, 2004). A comparison between MCS refl
 ection lines and tomographic results reveals a correlation between localiz
 ed low-rigidity upper-plate regions and the interaction of such crustal-sc
 ale faulting. The presence of low rigidity areas above the interplate may 
 enhance coseismic slip\, while locally damaged regions in the upper-plate 
 may favour inelastic deformation during coseismic events\, promoting local
 ised seafloor uplift. In contrast to downdip elastic rock variations above
  the upper-plate\, our results indicate that along-strike variations are d
 ependent on the interaction of crustal-scale structures and\, consequently
 \, on local geology.
LOCATION:Wolfson Lecture Theatre
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