Active Tectonics
Overview
CoSeismic Deformation
The Complexity of the 2018 Mw 6.4 Hualien Earthquake in East Taiwan
We use seismic and geodetic measurements to optimize the fault geometry as well as coseismic slip distribution from the 2018 Mw 6.4 Hualien earthquake. We find that at least three faults were involved in the earthquake. The earthquake initiated from a south-dipping fault in offshore Hualien, and slip transferred into the main west-dipping oblique fault. The slip finally triggered movement of the east-dipping Milun fault at shallower depth and caused surface rupture. Although there is no offshore data constraints, our inverted slip distribution shows that the majority of slip occurred between 5- and 10-km depth on the main west-dipping fault, and 1- to 3-m slip on the shallower part of the Milun fault. Additionally, we process 5 months of postseismic deformation time series and find more than 5-cm postseismic displacement occurred along the Milun fault but is insignificant near the Coastal Range located south of the Hualien City.
The 2016 earthquake sequence in Central Apennines, Italy
The Central Apennines in Italy have had multiple moderate-size but damaging shallow earthquakes. In this study, we optimize the fault geometry and invert for fault slip based on coseismic GPS and Interferometric Synthetic Aperture Radar (InSAR) for the 2016 Mw 6.2 Amatrice earthquake in Italy. Our results show nearly all the fault slip occurred between 3 and 6 km depth but extends 20 km along strike. There was less than 4 cm static surface displacement at the town Amatrice where the most devastating damage occurred. Landslides triggered by earthquake ground shaking are not uncommon, but triggered landslides with sub-meter movement are challenging to be observed in the field. We find evidence of coseismically triggered deep-seated landslides northwest and northeast of the epicenter where coseismic peak ground acceleration was estimated > 0.5 g. By combining ascending and descending InSAR data, we are able to estimate the landslide thickness as at least 100 and 80 m near Mt. Vettore and west of Castelluccio, respectively. The landslide near Mt. Vettore terminates on the pre-existing fault Mt. Vettore Fault (MVEF) scarp. Our results imply that the long-term fault slip rate of MVEF estimated based on paleoseismic studies could potentially have errors due to triggered landslides from nearby earthquake events.
The 2016 Mw 6.4 MeiNong earthquake in SW Taiwan
Rapid shortening in convergent mountain belts is often accommodated by slip on faults at multiple levels in upper crust, but no geodetic observation of slip at multiple levels within hours of a moderate earthquake has been shown before. Here we show clear evidence of fault slip within a shallower thrust at 5–10 km depth in SW Taiwan triggered by the 2016 Mw 6.4 MeiNong earthquake at 15–20 km depth. We constrain the primary coseismic fault slip with kinematic modeling of seismic and geodetic measurements and constrain the triggered slip and fault geometry using synthetic aperture radar interferometry. The shallower thrust coincides with a proposed duplex located in a region of high fluid pressure and high interseismic uplift rate, and may be sensitive to stress perturbations. Our results imply that under tectonic conditions such as high-background stress level and high fluid pressure, a moderate lower crustal earthquake can trigger faults at shallower depth.
PostSeismic Deformation
Probing Lithospheric Rheology of eastern Tibetan Plateau from the 2008 Mw 7.9 Wenchuan earthquake postseismic deformation
The fundamental geological structure, geodynamics, and rheology of the Tibetan Plateau have been debated for decades. Two end-member models have been proposed: (1) the deformation of Tibet is broadly distributed and associated with ductile flow in the mantle and middle or lower crust, (2) the Tibetan Plateau formed during interactions between rigid lithospheric blocks with localization of deformation along major faults. The nature and distribution of continental deformation are governed by the varying rheology of rocks and faults in the lithosphere. Insights into lithospheric rheology can be gained from observations of postseismic deformation, which represents the response of the Earth’s interior to coseismic stress changes. Here we use up to 2 years of InSAR and GPS measurements to investigate postseismic displacements following the 2008 Mw 7.9 Wenchuan earthquake in eastern Tibet and probe the differences in rheological properties across the edge of the Plateau. We find that near-field displacements can be explained by shallow afterslip on the Beichuan Fault, which is anti-correlated with the coseismic slip distribution. Far-field displacements cannot be explained by a homogeneous rheology, but instead require a viscoelastic lower crust (from 45 to 60 km depth) beneath Tibet with an initial effective viscosity of 4.4×1017 Pas and a long-term viscosity of 1018 Pas, whereas the Sichuan Basin block has a high-viscosity upper mantle (>1020 Pa s) underlying an elastic 35-km-thick crust. The inferred strong contrast in lithospheric rheologies between the Tibetan Plateau and the Sichuan Basin is consistent with models of ductile lower crustal flow that predict maximum topographic gradients across the Plateau margins where viscosity differences are greatest.
Interseismic Deformation & Structural Geology
Geodetically Constrained Interseismic Deformation in Taiwan
Plate convergence at more than 83 mm/yr makes Taiwan one of the most active tectonic regions in the world, as this strain is accommodated on a complex network strike-slip and thrust faulting. (a) Geologic setting of Taiwan. (b, c) We use Sentinel-1 ascending and descending Interferometric Synthetic Aperture Radar (InSAR) data as well as GNSS measurements to reveal interseismic deformation in Taiwan. We combine InSAR and GNSSS measurements from 2016 to 2021. (d) Based on the horizontal interseismic velocities, we can calculate surface strain rate as 2nd invariant, to highlight regions subject to greater surface deformatiom, which is likely due to fault creep.
Publications (since 2018)
Franklin, K.R.*, and Huang, M.-H., 2022, Revealing crustal deformation and strain rate in Taiwan using InSAR and GNSS. Geophysical Research Letters, 49, e2022GL101306. https://doi.org/10.1029/2022GL101306
Huang, M.-H., K. Morell, A. Duvall, S. F. Gallen, and G. E. Hilley, 2022, Exploring subduction zone geohazards on land and at sea, Eos, 103, https://doi.org/10.1029/2022EO220159.
Chong, J.-H.*, and Huang, M.-H., 2021, Refining the 2018 Mw 7.5 Papua New Guinea Earthquake Fault Slip Model Using Sub-Pixel Offset, accepted in Bull. Seismol. Soc. Am., 111, 1032-1042, https://doi.org/10.1785/0120200250
Hsu, Y.-F., Huang, H.-H., Huang, M.-H., Tsai, V. C., Chuang, R. Y., Feng, K.-F., and Lin, S.-H., 2020, Evidence for fluid migration during the 2016 Meinong Taiwan aftershock sequence, J. Geophys. Res: Solid Earth., 125, e2020JB019994. https://doi.org/10.1029/2020JB019994
Huang, M.-H. and Evans, E.L., 2019, Total variation regularization of geodetically constrained block models in southwest Taiwan. J. Geophys. Res: Solid Earth, 124. https://doi.org/10.1029/2019JB018076
Le Béon, M., Marc, O., Suppe, J., Huang, M.-H., Huang, S.‐T., & Chen, W.‐S., 2019, Structure and deformation history of the rapidly growing Tainan anticline at the deformation front of the Taiwan mountain belt. Tectonics, 38. https://doi.org/10.1029/2019TC005510Huang, M.-H. and Huang, H.-H., 2018, The complexity of the 2018 Mw 6.4 Hualien earthquake in east Taiwan, Geophysics. Res. Lett., 45, 13249-13257, https://doi.org/10.1029/2018GL080821.
Dickinson-Lovell, H., Huang, M.-H., Freed, A.M., Fielding, E.J., Bürgmann, R., and Andronicos, C., 2018, Inferred rheologic structure and mantle conditions from postseismic deformation following the 2010 Mw 7.2 El Mayor-Cucapah earthquake, Geophys. J. Int., 213, 1720-1730, doi:10.1093/gji/ggx546.