Analysis of afterslip distribution following the 2007 September 12 southern Sumatra earthquake using poroelastic and viscoelastic media

Lubis, Ashar Muda; Hashima, Akinori; Sato, Toshinori

doi:10.1093/gji/ggs020

Cited by 31 publications

(25 citation statements)

References 71 publications

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“…A conventional way to derive the distribution of the afterslip is to invert the surface deformation observed mostly on land with or without removing the effects of the viscoelastic relaxation of the upper mantle in an elastic half space [ Okada , ] or layered Earth [ R. Wang et al ., ]. This approach ignores the viscoelastic response to time‐dependent afterslip, which is significant and usually results in large estimates of afterslip at greater depths [e.g., Sato et al ., ; Bedford et al ., ; Lubis et al ., ; Sato et al ., ; Diao et al ., ]…”

Section: Model Setupmentioning

confidence: 95%

“…[], they obtained afterslip in a reversed direction in areas in the vicinities of the coseismic rupture area. It has been a common feature in other models inverting for afterslip in an elastic half space or in a layered Earth that afterslip takes place to great depths [e.g., Ozawa et al ., ; Bedford et al ., ; Lubis et al ., ; Nishimura et al ., ]. Johnson et al .…”

Section: Introductionmentioning

confidence: 98%

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Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

et al. 2016

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Understanding of postseismic deformation following great subduction zone earthquakes is complicated by the combined effects of viscoelastic relaxation of earthquake‐induced stresses in the upper mantle and time‐dependent afterslip on the megathrust. We integrate geodetic observations and constraints on afterslip from small repeating earthquakes on the megathrust to better distinguish contributions from these two postseismic processes. We have developed a three‐dimensional, spherical viscoelastic finite element model to study the postseismic deformation of the 2011 Mw9.0 Tohoku earthquake that has been recorded at unprecedented high resolution in space and time. We model stress‐driven afterslip in a 2 km thick weak shear zone away from historic rupture zones on the megathrust. We model both the viscoelastic relaxation of the upper mantle and shear zone deformation with a transient Burgers body rheology. The transient Kelvin viscosity is assumed to be one order of magnitude lower than that of the Maxwell viscosity. Viscoelastic relaxation of the mantle wedge alone causes postseismic uplift and seaward motion in the upper plate, opposite to the pattern from relaxation of just the oceanic upper mantle. Afterslip on the fault produces uplift updip of the afterslip zone and subsidence over its downdip edge and mostly seaward motion above the afterslip zone. The best fit Maxwell viscosity of the shear zone at depths ≤50 km is 1017 Pa s, constrained by afterslip estimates from repeating earthquakes. The optimal viscosities of the deep weak shear zone, continental mantle wedge, and oceanic upper mantle are determined to be 5 × 1017 Pa s, 3 × 1019 Pa s, and 5 × 1019 Pa s, respectively. The stress‐driven afterslip in the shear zone is up to ~3.5 m in the first 2 years after the earthquake, equivalent to an Mw8.4. Our model reproduces the first‐order pattern of the GPS observations both in horizontal and in vertical directions. Seafloor geodetic observations of subsidence and landward motions near the high‐slip zone of the earthquake provide evidence for a low‐viscosity asthenosphere below the oceanic lithosphere.

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Section: Model Setupmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 98%

Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

et al. 2016

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“…(14) as a simple inverse problem of estimating the fault-slip increment Dw K ðgÞ at the K-th time step. Lubis et al (2013) have also used a similar sequential procedure to estimate afterslip distribution following the 2007 southern Sumatra earthquake (M w 8.5) from postseismic GPS data. However, the sequential procedure described above has a weak point that the misfits between the data and the theoretical values at one time step are carried over 564 A. Noda et al Pure Appl.…”

Section: Sequential Stepwise Inversionmentioning

confidence: 99%

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

Noda

Kawasato

Matsu’ura

2017

Pure Appl. Geophys.

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Abstract-On the 11th March 2011, a megathrust event, called the Tohoku-oki earthquake, occurred at the North American-Pacific plate interface off northeast Japan. Transient crustal movements following this earthquake were clearly observed by a dense GPS network (GEONET) on land and a sparse GPS/Acoustic positioning network on seafloor. The observed crustal movements are in accordance with ordinary expectations on land, but not on seafloor; that is, slowly decaying landward movements above the main rupture area and rapidly decaying trench-ward movements in its southern extension. To reveal the cause of such curious offshore crustal movements, we analyzed the coseismic and postseismic GPS array data on land with a sequential stepwise inversion method considering viscoelastic stress relaxation in the asthenosphere, and obtained the following results: The afterslip of the Tohoku-oki earthquake rapidly proceeds for the first 1 year on a high-angle downdip extension of the main rupture, which occurred on the low-angle offshore plate interface. The theoretical patterns of seafloor horizontal movements due to the afterslip and the viscoelastic relaxation of coseismic stress changes in the asthenosphere are essentially different both in space and time; inshore trench-ward movements and offshore landward movements for the afterslip, while overall landward movements for the viscoelastic stress relaxation. General agreement between the computed horizontal movements and the GPS/Acoustic observations demonstrates that the postseismic curious offshore crustal movements can be ascribed to the combined effect of afterslip on a high-angle downdip extension of the main rupture and viscoelastic stress relaxation in the asthenosphere.

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“…To address these questions, we study postseismic time series that span multiple years following the earthquake. Even though a previous study examined the afterslip following the Bengkulu earthquake, the maximum time period of their data spans only 15 months after the earthquake [ Lubis et al , ]. To the best of our knowledge, postseismic deformation spanning longer time periods after the earthquake have not yet been studied.…”

Section: Introductionmentioning

confidence: 99%

Afterslip following the 2007 M_w 8.4 Bengkulu earthquake in Sumatra loaded the 2010 M_w 7.8 Mentawai tsunami earthquake rupture zone

et al. 2016

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The 12 September 2007 Mw 8.4 Bengkulu earthquake in Sumatra marked the first in a modern series of large earthquakes along the Mentawai section of the Sunda megathrust. Understanding the spatial distribution of coseismic slip and ensuing afterslip is important for assessing seismic hazard in neighboring unruptured regions of the megathrust. We reestimate the spatial distribution of coseismic slip during this earthquake with improved coseismic offsets from the Sumatran GPS Array (SuGAr) and estimate afterslip following this earthquake with SuGAr postseismic time series spanning ∼6.3 years after the earthquake. We invert for the spatiotemporal distribution of afterslip with the principal component analysis‐based inversion method (PCAIM), and we take into account viscoelastic deformation by incorporating into the inversion the estimation of strain within ductile deforming blocks located at asthenospheric depths. Our results suggest cumulative afterslip concentrated within, updip, and downdip of the 2007 coseismic rupture area and shallow afterslip that borders and overlaps the 2010 Mw 7.8 Mentawai earthquake rupture zone. The cumulative contribution of stress changes due to the coseismic event and the ensuing afterslip likely increased strain rates in the shallow portion of the megathrust adjacent to the Mentawai earthquake rupture area, potentially promoting its rupture in 2010.

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Analysis of afterslip distribution following the 2007 September 12 southern Sumatra earthquake using poroelastic and viscoelastic media

Cited by 31 publications

References 71 publications

Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

Afterslip following the 2007 M_w 8.4 Bengkulu earthquake in Sumatra loaded the 2010 M_w 7.8 Mentawai tsunami earthquake rupture zone

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Analysis of afterslip distribution following the 2007 September 12 southern Sumatra earthquake using poroelastic and viscoelastic media

Cited by 31 publications

References 71 publications

Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

Stress‐driven relaxation of heterogeneous upper mantle and time‐dependent afterslip following the 2011 Tohoku earthquake

Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation

Afterslip following the 2007 Mw 8.4 Bengkulu earthquake in Sumatra loaded the 2010 Mw 7.8 Mentawai tsunami earthquake rupture zone

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Afterslip following the 2007 M_w 8.4 Bengkulu earthquake in Sumatra loaded the 2010 M_w 7.8 Mentawai tsunami earthquake rupture zone