Geologic controls on up-dip and along-strike propagation of slip during subduction zone earthquakes from a high-resolution seismic reflection survey across the northern limit of slip during the 2010 Mw 8.8 Maule earthquake, offshore Chile

被引:15
作者
Trehu, Anne M. [1 ]
Hass, Bridget [1 ,4 ]
de Moor, Alexander [1 ,5 ]
Maksymowicz, Andrei [2 ]
Contreras-Reyes, Eduardo [2 ]
Vera, Emilio [2 ]
Tryon, Michael D. [3 ]
机构
[1] Oregon State Univ, Coll Earth Ocean & Atmospher Sci, Corvallis, OR 97331 USA
[2] Univ Chile, Dept Geofis, Fac Ciencias Fis & Math, Santiago, Chile
[3] Scripps Inst Oceanog, La Jolla, CA 92093 USA
[4] Natl Ecol Observ Network, Boulder, CO 80301 USA
[5] Canyonlands Field Inst, Moab, UT 84532 USA
基金
美国国家科学基金会;
关键词
FORE-ARC; MEGATHRUST EARTHQUAKE; MECHANICAL ANALYSIS; LANDWARD VERGENCE; TECTONIC CONTROL; COSEISMIC SLIP; RUPTURE ZONE; M8.8; MAULE; TRENCH; DEFORMATION;
D O I
10.1130/GES02099.1
中图分类号
P [天文学、地球科学];
学科分类号
07 ;
摘要
A grid of closely spaced, high-resolution multichannel seismic (MCS) reflection profiles was acquired in May 2012 over the outer accretionary prism up dip from the patch of greatest slip during the 2010 M-w 8.8 Maule earthquake (offshore Chile) to complement a natural-source seismic experiment designed to monitor the post-earthquake response of the outer accretionary prism. We describe the MCS data and discuss the implications for the response of the accretionary prism during the earthquake and for the long-term evolution of the margin. The most notable observation from the seismic reflection survey is a rapid north-to-south shift over a short distance from nearly total frontal accretion of the trench sediments to nearly total underthrusting of undeformed trench sediments that occurs near the northern edge of slip in the 2010 earthquake. Integrating our structural observations with other geological and geophysical observations, we conclude that sediment subduction beneath a shallow decollement is associated with propagation of slip to the trench during great earthquakes in this region. The lack of resolvable compressive deformation in the trench sediment along this segment of the margin indicates that the plate boundary here is very weak, which allowed the outer prism to shift seaward during the earthquake, driven by large slip down dip. The abrupt shift from sediment subduction to frontal accretion indicates a stepdown in the plate boundary fault, similar to the stepovers that commonly arrest slip propagation in strike-slip faults. We do not detect any variation along strike in the thickness or reflective character of the trench sediments adjacent to the change in deformation front structure. This change, however, is correlated with variations in the morphology and structure of the accretionary prism that extend as far as 40 km landward of the deformation front. We speculate that forearc structural heterogeneity is the result of subduction of an anomalously shallow or rough portion of plate that interacted with and deformed the overlying plate and is now deeply buried. This study highlights need for three-dimensional structural images to understand the interaction between geology and slip during subduction zone earthquakes.
引用
收藏
页码:1751 / 1773
页数:23
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