- Our Research
My research focuses on studying the earthquake cycle deformation of the continental thrust faults and megathrust faults at subduction zones. I use GNSS (Global Navigation Satellite System), seismic, and geological data to investigate fault coupling, frictional properties, fault zone rheology, and slow-moving landslides. In particular, active deformation at subduction zones mostly lies beneath the seafloor and is poorly resolved by terrestrial geodetic techniques. My research group and I have investigated different seafloor geodetic techniques including GNSS-acoustic observations and ocean-bottom absolute pressure gauge, aiming at establish a geodetic observatory network in the Taiwan plate boundary zone to study the spatial extent of the locked zone and transient slip events on the subduction megathrust. In addition, delineation of physical factors that contribute to earthquake triggering is a challenging issue in seismology. Taking advantages of high seismicity and geodetic strain rates, and the densely-distributed seismic, groundwater level, and geodetic networks in Taiwan, we quantify the relationship between the hydrological cycle, crustal motion, and earthquake seasonality. Studying seismicity driven by different forces with various stressing periods provides important clues to earthquake nucleation.
Chen, H.Y., Y. J. Hsu*, R. Ikuta, H. Tung, C. S. Ku, H. H Su, C. H. Tang, M. Ando and T. Tsujii, (2022), Strain partitioning in the southern Ryukyu margin revealed by seafloor geodetic and seismological observations, Geophys. Res. Lett., 46, https://doi.org/10.1029/2022GL098218
Jiang, Z., Y. J. Hsu, L. Yuan, M. Tang, X. Yang, and X. Yang (2022), Hydrological drought characterization based on GNSS Imaging of vertical crustal deformation across the contiguous United States, Sci. Total Environ., 823, https://doi.org/10.1016/j.scitotenv.2022.153663.
Jiang, Z. S. Y. J. Hsu, L. G. Yuan, S. Cheng, W. Fang, M. Tang, and X. G. Yang (2021), Insights into hydrological drought characteristics using GNSS-inferred large-scale terrestrial water storage deficits, Earth Planet. Sci. Lett., https://doi.org/10.1016/j.epsl.2021.117294
Hsu, Y. J. *, H. Kao, R. Bürgmann, Y. T. Lee, H. H. Huang, Y. F. Hsu, Y. M. Wu, and J. Zhuang (2021), Synchronized and asynchronous modulation of seismicity by hydrological loading: A case study in Taiwan, Sci. Adv. 16, eabf7282, doi:10.1126/sciadv.abf7282.
Jiang, Z. S. Y. J. Hsu, L. G. Yuan, and D. F. Huang (2021), Monitoring time-varying continental water storage changes using daily GNSS measurements in Yunnan, southwest China, Remote Sen. Enviro., 254, doi:10.1016/j.rse.2020.112249
Hsu, Y. J.*, Y. Fu, R. Bürgmann, S. Y. Hsu, C. C. Lin, C. H. Tang, and Y. M. Wu (2020), Assessing seasonal and interannual water storage variations in Taiwan using geodetic and hydrological data, Earth Planet. Sci. Lett., 550, doi: 10.1016/j.epsl.2020.116532
Tang, C.-H., Y. J. Hsu, S. Barbot, J. D. P. Moore, W.-L. Chang (2019), Lower-crustal rheology and thermal gradient in the Taiwan orogenic belt illuminated by the 1999 Chi-Chi earthquake, Sci. Adv., 5, eaav3287.
Synchronized and asynchronous modulation of seismicity by hydrological loading I analyzed hydrological modulation of seismicity in Taiwan using groundwater level data and GNSS time series. In western Taiwan, the seismicity rate reaches peak levels in February-April and drops to its lowest values in July-September, exhibiting a direct correlation with annual water unloading. The elastic hydrological load cycle may be the primary driving mechanism for the observed synchronized modulation of earthquakes, as also evidenced by deep earthquakes in eastern Taiwan. However, shallow earthquakes in eastern Taiwan (<18 km) are anti-correlated with water unloading, which is not well explained by either hydrological loading, fluid transport or pore pressure changes, and suggests other time-dependent processes. The moderate correlation between stacked monthly trends of large historic earthquakes and present-day seismicity implies a modestly higher seismic hazard during the time of low annual hydrological loading.
Lower-crustal rheology and thermal gradient in the Taiwan orogenic belt The strength of the lithosphere controls tectonic evolution and seismic cycles, but how rocks deform under stress in their natural settings is usually unclear. We constrain the rheological properties beneath the Taiwan orogenic belt using the stress perturbation following the 1999 Chi-Chi earthquake and fourteen-year postseismic geodetic observations. The evolution of stress and strain rate in the lower crust is best explained by a power-law Burgers rheology with rapid increases in effective viscosities from ~1017 to ~1019 Pa s within a year. The short-term modulation of the lower-crustal strength during the seismic cycle may alter the energy budget of mountain building. Incorporating the laboratory data and associated uncertainties, inferred thermal gradients suggest an eastward increase from 19.5±2.5°C/km in the Coastal Plain to 32±3°C/km in the Central Range. Geodetic observations may bridge the gap between laboratory and lithospheric scales to investigate crustal rheology and tectonic evolution.