Éditeur(s) : HAL CCSD Société géologique de France
Résumé : The mechanical equilibrium of an orogenic wedge is maintained thanks to interactions between tectonic processes and surface processes. To better constrain the influence of erosion and sedimentation on the evolution of orogens, we performed a series of analogue models based on the tapered wedge principle, varying the amounts of erosion and sedimentation. The models develop by frontal accretion in the foreland basin and by simple underthrusting and subsequent underplating in the hinterland. The variations in rates of erosion and sedimentation strongly modify the extent, the morphology, the structures, the timing of development and the material paths in the different models. Under certain conditions, entire structural units can be formed and subsequently eroded out of the geological record, leading to important underestimations when restoring sections. Particles located in the converging lower-plate or in the upper-plate show complex uplift paths related to tectonic stages. The correlation between models and three Alpine tectonic cross-sections emphasizes the role of erosion and sedimentation on the dynamics and development of the orogen and adjacent Molasse basin. Along strike changes in the present structure of the orogen could be explained in part by differences in surface processes.
EISSN: 1777-5817

hal-00411140
https://hal.archives-ouvertes.fr/hal-00411140
DOI : 10.2113/gssgfbull.3.297

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : TECTO LITHO
On the basis of a section across the northwestern Alpine wedge and foreland basin, analogue modeling is used to investigate the impact of surface processes on the orogenic evolution. The basis model takes into account both structural and lithological heritages of the wedge. During shortening, erosion and sedimentation are performed to maintain a critical wedge. Frontal accretion leads to the development of a foreland thrust belt; underplating leads to the formation of an antiformal nappe stack in the internal zones. Important volumes of analogue materials are eroded out of the geological record, which in the case of the Alps suggests that the original lengths and volumes may be underestimated. The foreland basin evolves differently depending on the amounts of erosion/sedimentation. Its evolution and internal structuring is governed by the wedge mechanics, thought to be the main controlling mechanism in the development of the Molasse basin in a feedback interaction with surface processes.
ISSN: 0278-7407

hal-00404424
https://hal.archives-ouvertes.fr/hal-00404424
DOI : 10.1029/2006TC002048

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events. It is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault-offset landforms. However, the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault, so that they rarely allow recovering the slip distributions and largest slips of these earthquakes. We acquired ~1 m resolution airborne lidar data on a 30 km stretch of a fast-slipping strike-slip fault (eastern Hope Fault, New Zealand) located in a region of high alluvial dynamics where landforms are rapidly evolving. Data analysis reveals >200 offset landforms; only 30% allow a good to moderate quality offset measurement. From these good to moderate quality measures, we recover the slip-length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4–6 prior events. The record suggests that large earthquake slip recurred in multiples of about 4 m along the 30 km stretch. Although they have larger uncertainties, the more numerous lower-quality offsets that we also measured reveal a similar earthquake slip record. This shows that, although offset landforms are partly degraded in dynamically active landscapes, they store valuable information on paleoearthquake slips. This information might be recovered provided that the morphology is analyzed at high resolution and " continuously " over a significant fault length. Remote lidar data are powerful to perform such analyses.
ISSN: 2169-9313

insu-01469219
https://hal-insu.archives-ouvertes.fr/insu-01469219
https://hal-insu.archives-ouvertes.fr/insu-01469219/document
https://hal-insu.archives-ouvertes.fr/insu-01469219/file/Manighetti_et_al-2015-Journalsur Geophysical_Research__Solid_Earth.pdf
DOI : 10.1002/2014JB011787

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Sandbox experiments, using a two-dimensional and a three-dimensional approach, are used to study the deformation of margins in response to seamount subduction. Successive mechanisms of deformation are activated during the subduction of conical seamounts. First, reactivation of the frontal thrusts and compaction of the accretionary wedge is observed. Then, back thrusting and, conjugate strike-slip faulting develops above the leading slope of the subducted seamount. The basal d6collement is deflected upward in the wake of the subducting high, and a large shadow zone develops behind the seamount trailing slope. Consequently, frontal accretion is inhibited and part of the frontal margin is dragged into the subduction zone. When the main d6collement returns to its basal level in the wake of the seamount, the margin records a rapid subsidence and a new accretionary wedge develops, closing the margin reentrant. The sediments underthrusted in the wake of the seamount into the shadow zone, are underplated beneath the rear part of the accretionary wedge. Substantial shortening and thickening of the deformable seaward termination of the upper plate basement, associated with basal erosion is observed. Seamount subduction induces significant material transfer within the accretionary wedge, favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin. The subduction and underplating of relatively undeformed, water-ladden sediments, associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal ddcollement. Consequently, significant variations of the effective basal friction and local mechanical coupling between the two plates could be expected around the subducting seamount.
ISSN: 0278-7407

hal-01261523
https://hal.archives-ouvertes.fr/hal-01261523
https://hal.archives-ouvertes.fr/hal-01261523/document
https://hal.archives-ouvertes.fr/hal-01261523/file/Dominguez2000-Tectonics.pdf
DOI : 10.1029/1999TC900055

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The island of Taiwan is located on the convergent boundary between the Philippine Sea plate and the Chinese continental margin. It offers very active mountain building and collapsing processes well illustrated by the rugged topography, rapid uplift and denudation, young tectonic landforms, active faulting and numerous earthquakes. In this paper, using simple models, we have estimated vertical movements and associated absolute gravity variations which can be expected along a profile crossing the southern part of the island and probably suffering the highest rates of rising. The two different tectonic styles proposed for the island, thin-skinned and thick-skinned, were taken into account. Horizontal and vertical movements were modeled by an elastic deformation code. Gravity variations due to these deformations are then modeled at a second step. They are dominated by plate and free-air effects, i.e. elevation of the topography, with several mu Gal yr(-1). By comparison, gravity changes generated by mass transfers are weak: maximum 0.1 mu Gal yr(-1) with the thin-skinned tectonic and 0.3 mu Gal yr(-1) with the thick-skinned tectonic. Though elastic rheology has limitations, this modeling offers interesting results on what gravity signal can be expected from the AGTO project (Absolute Gravity in the Taiwanese Orogen), which proposes to study the dynamic of these mountain ranges using absolute gravimetry (AG) and also including relative gravimetry (RG) and GPS measurements.
ISSN: 0264-3707

hal-00456035
https://hal.archives-ouvertes.fr/hal-00456035
DOI : 10.1016/j.jog.2009.09.004

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We conducted a laser-equipped analog experiment aimed at quasi-continuously monitoring the growth of a dense population of normal faults in homogeneous conditions. To further understand the way geological faults progressively gain in slip and length as they accumulate more strain, we measured with great precision the incremental slip and length changes that the analog faults sustain as they grow. These measurements show that the analog faults share common features with the natural ones. In particular, during their growth, the faults develop and maintain cumulative slip profiles that are generally triangular and asymmetric. The growth takes place through two distinct phases: an initial, short period of rapid lateral lengthening, followed by a longer phase of slip accumulation with little or no lengthening. The incremental slip is found to be highly variable in both space (along the faults) and time, resulting in variable slip rates. In particular, ‘short- and long-term' slip rates are markedly different. We also find that slip measurements at local points on fault traces do not contain clear information on the slip increment repeat mode. Finally, while the fault growth process is highly heterogeneous when considered at the scale of a few slip events, it appears homogeneous and self-similar at longer time scales which integrate many slip increments. This is likely to be the result of a feedback between stress heterogeneities and slip development. The long-term scale homogeneity also implies that the long-term faulting process is primarily insensitive to the short-term heterogeneities that are rapidly smoothed or redistributed. We propose a new conceptual scenario of fault growth that integrates the above observations and we suggest that faults grow in a bimodal way as a result of a self-driven and self-sustaining process.
ISSN: 0012-821X

Droits : info:eu-repo/semantics/OpenAccess
insu-00351998
https://hal-insu.archives-ouvertes.fr/insu-00351998
https://hal-insu.archives-ouvertes.fr/insu-00351998/document
https://hal-insu.archives-ouvertes.fr/insu-00351998/file/SchlagenhaufEtAl2008_EPSL_author.pdf
DOI : 10.1016/j.epsl.2008.06.042

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Past earthquake slips on faults are commonly determined by measuring morphological offsets at current ground surface. Because those offsets might not always be well preserved, we examine whether the first 10 m below ground surface contains relevant information to complement them. We focus on the Te Marua site, New Zealand, where 11 alluvial terraces have been dextrally offset by the Wellington fault. We investigated the site using pseudo-3D Ground Penetrating Radar and also produced a high-resolution digital elevation model (DEM) of the zone to constrain the surface slip record. The GPR data reveal additional information: (1) they image the 3D stratigraphic architecture of the seven youngest terraces and show that they are strath terraces carved into graywacke bedrock. Each strath surface is overlain by 3-5 m of horizontally bedded gravel sheets, including two pronounced and traceable reflectors; (2) thanks to the multilayer architecture, terrace risers and channels are imaged at three depths and their lateral offsets can be measured three to four times, constraining respective offsets and their uncertainties more reliably; and (3) the offsets are better preserved in the subsurface than at the ground surface, likely due to subsequent erosion-deposition on the latter. From surface and subsurface data, we infer that Te Marua has recorded six cumulative offsets of 2.9, 7.6, 18, 23.2, 26, and 31 m (± 1-2 m). Large earthquakes on southern Wellington fault might produce 3-5 m of slip, slightly less than previously proposed. Pseudo-3D GPR thus provides a novel paleoseismological tool to complement and refine surface investigations
ISSN: 2169-9313

hal-00873350
https://hal.archives-ouvertes.fr/hal-00873350
DOI : 10.1002/jgrb.50317

Éditeur(s) : HAL CCSD
Bolletino di Geofisica teorica ed applicata

hal-00411455
https://hal.archives-ouvertes.fr/hal-00411455