Understanding subduction-zone rheology and crustal deformation in earthquake cycles
| dc.contributor.author | Luo, Haipeng | |
| dc.contributor.supervisor | Wang, Kelin | |
| dc.contributor.supervisor | Nissen, Edwin | |
| dc.date.accessioned | 2021-12-02T21:42:19Z | |
| dc.date.available | 2021-12-02T21:42:19Z | |
| dc.date.copyright | 2021 | en_US |
| dc.date.issued | 2021-12-02 | |
| dc.degree.department | School of Earth and Ocean Sciences | en_US |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | My PhD program is focused on how earthquake cycle deformation in subduction zones is governed by the rheology of the asthenosphere and lithosphere. The method of research is numerical modelling of deformation processes constrained by geodetic observations. This dissertation includes research results on the three deformation phases of earthquake cycles, namely the coseismic, postseismic, and interseismic phases. Coseismic: Tension cracks were produced by megathrust earthquakes in the Chile-Peru forearc, seemingly challenging the elastic rebound theory. We explain the cracks as the consequence of less or no interseismic stress accumulation in the near-surface material due to its viscoelastic behaviour, in contrast to the deeper elastic crust. Elastic rebound of the deeper crust during earthquakes induces more stress in the near-surface material than has been accumulated and thus generates the tensile failure. The results confirm the validity of the elastic rebound theory and highlight the importance of understanding the heterogeneity of lithosphere rheology. Postseismic: A sharp contrast between the cold forearc and hot arc and backarc, considered fundamental to subduction dynamics, indicates the presence of a cold mantle wedge nose, but direct evidence is limited. The cold nose, if present, should behave elastically for the time scale of earthquake cycles. Through modelling postseismic vertical motion following great subduction earthquakes, we propose and demonstrate that global observations of postseismic uplift just seaward of the volcanic arc provide a geodetic signature of the cold nose. This finding helps to establish a link between the relatively short-term earthquake cycle deformation with long-term thermo-petrologic processes. It also solves a mystery that has puzzled the scientific community for six decades regarding crustal deformation caused by the largest recorded earthquake on Earth – the1960 moment magnitude (Mw) 9.5 Chile earthquake. Interseismic: In the southern area of the 1960 Mw 9.5 Chile earthquake, regional geodetic measurements in the 21st century show a rapid systematic landward increase in the velocity of station motion that cannot be explained by the standard viscoelastic earthquake cycle model. We propose that the velocity increase is due to a sudden downdip widening of the zone of megathrust locking. This finding not only raises new theoretical questions for the study of megathrust fault mechanics but also has important implications to assessing seismic hazard in the subduction zone environment. In addition to the earthquake cycle deformation studies, we explore along-strike viscosity variations in a slab window associated with the Chile triple junction which terminated the southward rupture propagation of the 1960 Chile earthquake. We model geodetically observed ongoing surface uplift due to recent climatically induced mass loss at the Patagonian icefields that are situated just above the slab window. The results suggest an order of magnitude viscosity contrast within the slab window, with the younger and thus warmer northern part being much less viscous. This case study provides an example for how the anatomy of an active tectonic system can be geodetically “imaged” using non-tectonic signals. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.bibliographicCitation | Russo, R.M., Luo, H., Wang, K., Ambrosius, B., Mocanu, V., He, J., James, T., Bevis, M. & Fernandes, R. (2021). Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields, Geology, doi: 10.1130/G49388.1. | en_US |
| dc.identifier.bibliographicCitation | Luo, H. & Wang, K. (2021). Postseismic geodetic signature of cold forearc mantle in subduction zones, Nature Geoscience, 14, 104-109, doi: 10.1038/s41561-020-00679-9. | en_US |
| dc.identifier.bibliographicCitation | Luo, H., Ambrosius, B., Russo, R.M., Mocanu, V., Wang, K., Bevis, M. & Fernandes, R. (2020). A recent increase in megathrust locking in the southernmost rupture area of the giant 1960 Chile earthquake. Earth and Planetary Science Letters, 537, 116200, doi: 10.1016/j.epsl.2020.116200. | en_US |
| dc.identifier.bibliographicCitation | Luo, H., Wang, K., Sone, H. & He, J. (2019). A model of shallow viscoelastic relaxation for seismically induced tension cracks in the Chile‐Peru forearc. Geophysical Research Letters, 46(19), 10773-10781, doi: 10.1029/2019GL084536. | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/13562 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.subject | Mantle rheology | en_US |
| dc.subject | Earthquake cycle deformation | en_US |
| dc.subject | Postseismic vertical | en_US |
| dc.subject | cold mantle wedge corner | en_US |
| dc.subject | GIA | en_US |
| dc.subject | Megathrust earthquakes | en_US |
| dc.subject | viscoelastic relaxation | en_US |
| dc.subject | tension cracks | en_US |
| dc.subject | elastic rebound theory | en_US |
| dc.subject | Megathrust locking | en_US |
| dc.subject | Interseismic deformation | en_US |
| dc.subject | Coseismic deformation | en_US |
| dc.subject | Slab window | en_US |
| dc.subject | Subduction Zone | en_US |
| dc.subject | 1960 Mw 9.5 Chile earthquake | en_US |
| dc.subject | 2011 Mw 9 Tohoku-oki earthquake | en_US |
| dc.title | Understanding subduction-zone rheology and crustal deformation in earthquake cycles | en_US |
| dc.type | Thesis | en_US |