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Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography

Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography
Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography
Knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures. Observations of aftershocks that followed the 2010 MwMw 8.8 Maule, Chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone. We manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3-D velocity model of the rupture zone using local earthquake tomography. From the trench to the magmatic arc, our velocity model illuminates the main features within the subduction zone. We interpret an east-dipping high P-wave velocity anomaly (>6.9 km/s) as the subducting oceanic crust and a low P-wave velocity (<6.25 km/s) in the marine forearc as the accretionary complex. We find two large P-wave velocity anomalies (?7.8 km/s) beneath the coastline. These velocities indicate an ultramafic composition, possibly related to extension and a mantle upwelling during the Triassic.

We assess the role played by physical heterogeneity in governing megathrust behaviour. Greatest slip during the Maule earthquake occurred in areas of moderate P-wave velocity (6.5–7.5 km/s), where the interface is structurally more uniform. At shallow depths, high fluid pressure likely influenced the up-dip limit of seismic activity. The high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity. The northern velocity anomaly may have acted as a structural discontinuity within the forearc, influencing the pronounced crustal seismicity in the Pichilemu region. Our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts.
Maule earthquake, Chile, subduction, seismic zone, seismic tomography, OBS
0012-821X
142-155
Hicks, Stephen P.
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Rietbrock, Andreas
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Ryder, Isabelle M.A.
e4db9c08-f27a-41a8-bbcc-0b6f9c472aad
Lee, Chao-Shing
9c335151-cca0-48d8-8056-48b3cf5d7672
Miller, Matthew
c9764ebd-1cdd-4db9-93b3-d6bbadba4bab
Hicks, Stephen P.
036d1b3b-bb7a-4a22-b2ce-71618a1723a3
Rietbrock, Andreas
e4656f22-06be-40fe-8f98-7f88c351c434
Ryder, Isabelle M.A.
e4db9c08-f27a-41a8-bbcc-0b6f9c472aad
Lee, Chao-Shing
9c335151-cca0-48d8-8056-48b3cf5d7672
Miller, Matthew
c9764ebd-1cdd-4db9-93b3-d6bbadba4bab

Hicks, Stephen P., Rietbrock, Andreas, Ryder, Isabelle M.A., Lee, Chao-Shing and Miller, Matthew (2014) Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography. Earth and Planetary Science Letters, 405, 142-155. (doi:10.1016/j.epsl.2014.08.028).

Record type: Article

Abstract

Knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures. Observations of aftershocks that followed the 2010 MwMw 8.8 Maule, Chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone. We manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3-D velocity model of the rupture zone using local earthquake tomography. From the trench to the magmatic arc, our velocity model illuminates the main features within the subduction zone. We interpret an east-dipping high P-wave velocity anomaly (>6.9 km/s) as the subducting oceanic crust and a low P-wave velocity (<6.25 km/s) in the marine forearc as the accretionary complex. We find two large P-wave velocity anomalies (?7.8 km/s) beneath the coastline. These velocities indicate an ultramafic composition, possibly related to extension and a mantle upwelling during the Triassic.

We assess the role played by physical heterogeneity in governing megathrust behaviour. Greatest slip during the Maule earthquake occurred in areas of moderate P-wave velocity (6.5–7.5 km/s), where the interface is structurally more uniform. At shallow depths, high fluid pressure likely influenced the up-dip limit of seismic activity. The high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity. The northern velocity anomaly may have acted as a structural discontinuity within the forearc, influencing the pronounced crustal seismicity in the Pichilemu region. Our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts.

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Accepted/In Press date: 26 August 2014
Published date: 1 November 2014
Keywords: Maule earthquake, Chile, subduction, seismic zone, seismic tomography, OBS
Organisations: Ocean and Earth Science, Geology & Geophysics

Identifiers

Local EPrints ID: 405577
URI: http://eprints.soton.ac.uk/id/eprint/405577
ISSN: 0012-821X
PURE UUID: 21dc0672-d3a0-4d11-9511-9306d59baf21
ORCID for Stephen P. Hicks: ORCID iD orcid.org/0000-0002-7476-3284

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Date deposited: 06 Feb 2017 15:04
Last modified: 22 Oct 2019 00:27

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Contributors

Author: Stephen P. Hicks ORCID iD
Author: Andreas Rietbrock
Author: Isabelle M.A. Ryder
Author: Chao-Shing Lee
Author: Matthew Miller

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