Earthquake rupture and seismic hazards - constraints from geophysical observations
Earthquakes occur when the accumulated stress overcomes the frictional resistance. The frequency, location and magnitude of earthquakes hold important information about regional stress field, active fault structures and properties of fault zone materials. To understand the physics of earthquakes, I take advantage of InSAR mapped ground displacements caused by moderate-to-large earthquakes. While static co-seismic deformation offer good constraints on the fault source parameters and static slip distribution, seismic recordings are essential in determining the rupture process. Recent advancements in Earth deformation mapping instruments allow us to see more details into the physics of earthquake rupture.
- Geophysical investigation of the rupture during the 2016 Mw6.6 Muij earthquake, China
Muji fault is part of the complex Pamir fault system that accommodates the India–Asia plate collision. The region is seismically active with several moderate to large earthquakes in recent years. To constrain the fault geometry and slip distribution, we inverted InSAR observations of ground displacements. We inverted regional seismic waveforms for multiple centroid moment tensors and constructed a moment rate function, to reveal the dynamic history of asperity failure.
Our study shows near simultaneous rupture of two fault asperities during the 2016 Mw6.6 Muji earthquake. We found “slip gaps” that were not ruptured by this earthquake. Seismic waveform modelling reveals two asperity failures close in time. This study suggests that near simultaneous failure of multiple asperities close in space and time may cause high seismic hazard, even for a moderate sized earthquake. |
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- InSAR observations of earthquakes in Tibet
Earthquakes included in this poster are Yutian, Nima-Gaize, Zhongba, Damxung, Wenchuan earthquakes in 2008, and Manyi earthquake in 1997 (from left to right).
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InSAR is now widely used in monitoring earthquake and volcano deformation. It provides measurements of ground deformation with high accuracy and wide spatial coverage. Its application has been well extended from coseismic deformation observation into other phases of earthquake cycle, and also other disciplines, such as land subsidence, glacial change and climate change.
Tibetan Plateau is an active tectonic region. In a single year of 2008, several moderate to large earthquakes occurred across the plateau. I produced a synopsis of InSAR observations of some of the earthquakes. The poster was originally used for School Earthquake Workshop organised here in Liverpool every summer. |
- Co-seismic rupture and fault interaction
An improved earthquake rupture model benefits seismic hazard estimation. During my PhD, I improved the non-linear inversion scheme to find an optimal rupture geometry and slip distribution on a fault by incorporating the crustal layering effect. We applied the uniform slip inversion strategy to the study of 2008 Mw6.3 Damxung earthquake. For homogeneous and layered crustal models, the maximum slip of the latter model is smaller and deeper, while the moment release calculated from both models are similar.
Another study focuses on three large earthquakes that occurred in the Ashikule stepover zone, NW Tibet in 2008 (Mw 7.1), 2012 (Mw 6.2) and 2014 (Mw 6.9). We use InSAR data to examine the 2008 event in detail, and place it in the context of both recent/possible future events and regional tectonic environment. To account for the curved rupture trace as mapped in the field, we model the slip on a non-planar fault. This study demonstrates that stepover zone failure can increase stresses on bounding strike-slip faults, which likely has relevance in analogous tectonic environments elsewhere in the world. |
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Relevant publications:
- Bie, L., Ryder, I., Nippress, S. E., & Bürgmann, R. (2014). Coseismic and post-seismic activity associated with the 2008 Mw 6.3 Damxung earthquake, Tibet, constrained by InSAR. Geophysical Journal International, 196(2), 788-803.
- Bie, L., & Ryder, I. (2014). Recent seismic and aseismic activity in the Ashikule stepover zone, NW Tibet. Geophysical Journal International, 198(3), 1632-1643.
- Bie, L., Gonzalez, P., Rietbrock, A. (2017). Slip Distribution of the 2015 Lefkada Earthquake and its Implications for Fault Segmentation. Geophysical Journal International, 210(1), 420–427.
- Bie, L., Hicks, S., Garth, T., Gonzalez, P. & Rietbrock, A., (2018). ‘Two go together’: near-simultaneous moment release of two asperities during the 2016 Mw 6.6 Muji, China earthquake. Earth and Planetary Science Letters, 491, 34-42.