HR: 1400h
AN: T43A-04    [Abstracts]
TI: The Mw 8.8, 1906 Colombia-Ecuador Subduction Earthquake: Seismic Structure and Thermal Regime of the Plate Boundary.
AU: * Collot, J
EM: collot@geoazur.obs-vlfr.fr
AF: IRD, UMR Géosciences Azur, BP 48, Villefranche s/mer, 06235, France
AU: * Collot, J
EM: collot@geoazur.obs-vlfr.fr
AF: Instituto Geofisico, Escual Politecnica Nacionale, Ladron de Guevara, Quito, Ecuador
AU: Marcaillou, B
EM: Boris.Marcaillou@geoazur.obs-vlfr.fr
AF: UPMC, UMR Géosciences Azur, BP 48, Villefranche s/mer, 06235, France
AU: Agudelo, W
EM: agudelo_w@yahoo.com
AF: IRD, UMR Géosciences Azur, BP 48, Villefranche s/mer, 06235, France
AU: Agudelo, W
EM: agudelo_w@yahoo.com
AF: UPMC, UMR Géosciences Azur, BP 48, Villefranche s/mer, 06235, France
AU: Ribodetti, A
EM: ribodeti@geoazur.obs-vlfr.fr
AF: IRD, UMR Géosciences Azur, BP 48, Villefranche s/mer, 06235, France
AU: d'Acremont, E
EM: elia.dacremont@lgs.jussieu.fr
AF: UPMC, Laboratoire de Tectonique, T46-00, Case 129, 4 place Jussieu, Paris, 75252, France
AB: The North Ecuador-SW Colombia active margin underwent four great subduction earthquakes in 1906 (Mw8.8), 1942(Mw7.8), 1958 (Mw7.7) and 1979(Mw8.2). The resulting seismotectonic segmentation of the margin may be a consequence of variable mass transfer, remarkable down-going plate basement relief, and margin transverse and along strike crustal faults. The margin basement consists of accreted oceanic terranes, and is underthrust by the northern flank of the19-km thick Carnegie Ridge, and 7-km-thick and structurally complex, Miocene Malpelo- Yaquina-Buenaventura spreading-transform system of the northern Nazca plate. The oceanic crust is covered by turbidite that strongly vary in thickness along the trench. South of 1°30'N, the oceanic crust shows N35- 75° and N120° faults and lineaments, and a N-trending chain of small seamounts, which delineate en-échelon, small pounded trench basins containing up to 500 m of turbidites. The steep adjacent inner trench slope is devoid of an accretionary wedge, but shows evidences for slope instabilities and mass wasting deposits. A 1-km thick subduction channel that is continuous with the hemipelagic cover of the oceanic crust is imaged landward, over a 30-km distance from the trench. This region shows evidence for thinning of the margin basement by seamount subduction, and correlates with the hypocenter of the 1942 subduction earthquake. North of 1°30'N, an up-to 4-km-thick deep-sea turbidite system has developed in the Colombia trench. The turbidite system is fed by the major Esmeraldas and Patia-Mira canyons and rivers, and dammed to the South by the Galera seamounts. This thick trenchfill appears to be dominantly subducting beneath an erosional margin basement between 1°30'N and 2°30'N, thus forming a km-thick subduction channel that is modulated by the subduction of a buried, large horst and graben structure. This region of thick sediment and rough oceanic crust subduction coincides with the hypocenters of the1958 and1979 subduction earthquakes, which occurred beneath the subsiding fore-arc basin. North of latitude 2°30'N, although the trench fill is thinner (~2 km), the Colombian accretionary wedge has developed and reaches 30 km in width at 3°30'N. The zones where each of the 1942, 1958 and 1979 earthquake rupture zones meet with the adjacent rupture zone have been shown to correlate with along strike changes in the fore-arc tectonic regime from uplift (1942) to subsidence (1958), and oblique compression (1979), and with transverse crustal faults that segment the margin. In addition, a fault-bounded outer basement high and a major splay fault that branches upward from the plate interface may control the seaward limit of the 1958 earthquake rupture zone. Thermal modeling, matching bottom simulating reflector (BSR)-derived heat flow, and heat flow measurements, suggests that the 1958 and 1979 earthquakes nucleated within a central to shallow portion of the seismogenic zone, at temperatures estimated to be ~160°C and that the updip limit of the seismogenic zone is controlled by low temperature (60-70°C) processes, with the exception of the 1958 event, where the updip limit is more likely related to prominent structural features fronting the margin.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3025 Marine seismics (0935, 7294)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly