Outer rise seismicity related to the Maule, Chile 2010 mega-thrust earthquake and hydration of the incoming oceanic lithosphere

Abstract

ABSTRACT. Most of the recent published geodetic models of the 2010 Maule, Chile mega-thrust earthquake (Mw=8.8) show a pronounced slip maximum of 15-20 m offshore Iloca (~35°S), indicating that co-seismic slip was largest north of the epicenter of the earthquake rupture area. A secondary slip maximum 8-10 m appears south of the epicenter west of the Arauco Peninsula. During the first weeks following the main shock and seaward of the main slip maximum, an outer rise seismic cluster of >450 events, mainly extensional, with magnitudes Mw=4-6 was formed. In contrast, the outer rise located seaward of the secondary slip maximum presents little seismicity. This observation suggests that outer rise seismicity following the Maule earthquake is strongly correlated with the heterogeneous coseismic slip distribution of the main megathrust event. In particular, the formation of the outer-rise seismic cluster in the north, which spatially correlates with the main maximum slip, is likely linked to strong extensional stresses transfered from the large slip of the subducting oceanic plate. In addition, high resolution bathymetric data reveals that bending-related faulting is more intense seaward of the main maximum slip, where well developed extensional faults strike parallel to the trench axis. Also published seismic constraints reveal reduced P-wave velocities in the uppermost mantle at the trench-outer rise region (7.5-7.8 km/s), which suggest serpentinization of the uppermost mantle. Seawater percolation up to mantle depths is likely driven by bending related-faulting at the outer rise. Water percolation into the upper mantle is expected to be more efficient during the co-seismic and early post-seismic periods of large megathrust earthquakes when intense extensional faulting of the oceanic lithosphere facilitates water infiltration seaward of the trench. RESUMEN. Sismicidad ʻouter rise' relacionada con el mega terremoto de Maule, Chile en el 2010 e hidratación de la litósfera oceánica subductante. La mayoría de los modelos geodésicos del terremoto de 2010 en la Región del Maule, Chile (Mw=8.8) muestran un pronunciado deslizamiento máximo de 15-20 m frente a las costas de Iloca (~35°S), indicando que el mayor deslizamiento cosísmico fue en la parte norte del área de ruptura. Un deslizamiento secundario, con un máximo de 8-10 m aparece al sur del epicentro, localizado al sur de la península de Arauco. Durante las semanas siguientes al evento principal y frente al área de máximo deslizamiento, se formó un enjambre sísmico de más de 450 eventos, con mecanismo de foco mayoritariamente extensional y de magnitudes Mw, oscilando entre los 4 y 6 grados. En contraste con ello, el área del ʻouter rise', ubicada frente a la zona sur de deslizamiento máximo, presenta baja sismicidad. Esta observación sugiere que la sismicidad ʻouter rise' posterior al evento principal del terremoto del Maule está fuertemente correlacionada con la distribución heterogénea de deslizamiento cosísmico. En particular, la formación del enjambre de sismicidad ...

Outer rise seismicity boosted by the Maule 2010 Mw 8.8 megathrust earthquake

“…Failure of the whole brittle upper part of the oceanic lithosphere is also consistent with previous studies that show that the oceanic Nazca plate in the region is highly fractured as a consequence of bending related faulting (Contreras-Reyes et al, 2008;Moscoso and Contreras-Reyes, 2012). Active seismic investigations have found evidence for active deformation on north-south trending faults, probably resulting from the reactivation of the tectonic fabric of the seafloor (Contreras-Reyes et al, 2008;Moscoso and Contreras-Reyes, 2012).…”

“…(B) Cross-section A-B shows the best source depth estimated in this study. Brown line is the top of the oceanic subducting slab, purple dashed line is the Moho discontinuity, and blue solid line is the bathymetry (Moscoso and Contreras-Reyes, 2012). The black dashed, red lines, and black dotted lines are the 350°C, 450°C and 600°C isotherms, respectively, computed for the subducting oceanic slab based on the cooling of a semi-infinite half-space model (e.g.…”

“…Active seismic investigations have found evidence for active deformation on north-south trending faults, probably resulting from the reactivation of the tectonic fabric of the seafloor (Contreras-Reyes et al, 2008;Moscoso and Contreras-Reyes, 2012). In particular, at~36.5°S and~38.5°S, Diaz-Naveas (1999) and Grevemeyer et al (2005) imaged bending faults with seismic reflection data that cut at least~6 km into the uppermost mantle.…”

“…However, the seafloor spreading fabric is perturbed/ modified in the outer rise region due to existence of cross-cutting normal faults caused by plate bending (e.g. Contreras-Reyes et al, 2008;Moscoso and Contreras-Reyes, 2012). The study area is bounded by the presence of two prominent bathymetric features: the Juan Fernández Ridge (JFR) and the oceanic Mocha FZ in the north and south, respectively ( Fig.…”

Seismotectonic deformation in the contact area of the Nazca and South American lithospheric plates in relation to the February 27, 2010 Mw 8.8 Maule earthquake

“…Особенности в поведении сейсмичности до и по-сле землетрясения Мауле к западу от желоба, в области океанического поднятия, для которой в целом характерны механизмы очагов сбросового типа и, соответственно, деформации удлинения в крест простирания желоба, рассматривались в ра-боте [Moscoso, Contreras-Reyes, 2012]. Наши данные о сейсмотектонических деформациях подтверждают наличие этого явления и позволяют предложить для него уточненную блоковую модель, которая включает блок континентальной литосферы с за-цеплением вследствие высокоскоростного подня-тия [Hicks et al, 2012] в океанической литосфере.…”