THE CASCADIA CREEPING SECTION: STRUCTURAL EVIDENCE FOR HETEROGENEOUS PLATE COUPLING AND LINKAGES TO GEODESY AND PALEOSEISMOLOGY

Abstract The Central Andes experienced major earthquake (Mw =8.2) in April 2014 in a region where the giant 1877 earthquake (Mw=8.8) occurred. The 2014 Iquique earthquake did not break the entire seismic gap zones as previously predicted. Geodetic and seismological observations indicate a highly coupled plate interface. To assess the locking mechanism of plate interfaces beneath Central Andes, a 2.5-D gravity model of the crust and upper mantle structure of the central segment of the subduction zone was developed based on terrestrial and satellite gravity data from the LAGEOS, GRACE and GOCE satellite missions. The densities and major structures of the gravity model are constrained by velocity models from receiver function and seismic tomography. The gravity model defined details of crustal and slab structure necessary to understand the cause of megathrust asperity generation. The densities of the upper and lower crust in the fore-arc (2970 – 3000 kg m−3) are much higher than the average density of continental crust. The high density bodies are interpreted as plutonic or ophiolitic structures emplaced onto continental crust. The plutonic or ophiolitic structures may be exerting pressure on the Nazca slab and lock the plate interfaces beneath the Central Andes subduction zone. Thus, normal pressure exerted by high density fore-arc structures and buoyancy force may control plate coupling in the Central Andes. However, this interpretation does not exclude other possible factors controlling plate coupling in the Central Andes. Seafloor roughness and variations in pore-fluid pressure in sediments along subduction channel can affect plate coupling and asperity generation.

Download Full-text

Observed change in plate coupling close to the rupture initiation area before the occurrence of the 2011 Tohoku earthquake: Implications from an earthquake cycle model

Geophysical Research Letters ◽

10.1002/2013gl058751 ◽

2014 ◽

Vol 41 (6) ◽

pp. 1899-1906 ◽

Cited By ~ 17

Author(s):

Makiko Ohtani ◽

Kazuro Hirahara ◽

Takane Hori ◽

Mamoru Hyodo

Keyword(s):

Tohoku Earthquake ◽

2011 Tohoku Earthquake ◽

Earthquake Cycle ◽

Cycle Model ◽

The 2011 Tohoku Earthquake ◽

Plate Coupling

Download Full-text

Southward expanding plate coupling due to variation in sediment subduction as a cause of Andean growth

Nature Communications ◽

10.1038/s41467-021-27518-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Jiashun Hu ◽

Lijun Liu ◽

Michael Gurnis

Keyword(s):

Sediment Transport ◽

Three Dimensional ◽

Mountain Building ◽

Crustal Shortening ◽

First Order ◽

The Andes ◽

Tectonic Processes ◽

History Of ◽

Plate Coupling ◽

Trench Sediments

AbstractGrowth of the Andes has been attributed to Cenozoic subduction. Although climatic and tectonic processes have been proposed to be first-order mechanisms, their interaction and respective contributions remain largely unclear. Here, we apply three-dimensional, fully-dynamic subduction models to investigate the effect of trench-axial sediment transport and subduction on Andean growth, a mechanism that involves both climatic and tectonic processes. We find that the thickness of trench-fill sediments, a proxy of plate coupling (with less sediments causing stronger coupling), exerts an important influence on the pattern of crustal shortening along the Andes. The southward migrating Juan Fernandez Ridge acts as a barrier to the northward flowing trench sediments, thus expanding the zone of plate coupling southward through time. Consequently, the predicted history of Andean shortening is consistent with observations. Southward expanding crustal shortening matches the kinematic history of inferred compression. These results demonstrate the importance of climate-tectonic interaction on mountain building.

Download Full-text