Absolute Tectonic Stress Inversion in the 2016 Mw 7.0 Kumamoto Earthquake Source Region Using Topography and Rupture Models. Issue 8 (4th August 2022)

• Record Type: Journal Article
• Authors: Yun, Naidan; Yue, Han; Zhou, Shiyong; Xu, Wuchuan
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-04
• Subjects: absolute stress -- Bayesian probability -- finite fault model -- topographic stress; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB023204
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Absolute tectonic stress estimation is of fundamental importance to investigating regional earthquake hazards, while traditional algorithms only invert relative stress and its orientations. We use topography data and rupture models to invert the absolute tectonic stress in the source region of the 2016 M w 7.0 Kumamoto earthquake. We adopt a basic assumption that the slip direction of each sub‐fault is in the shear direction of the total stress tensor, which is a combination of tectonic and topographic stresses. We use the Bayesian theorem to describe the probability density function of stress parameters and perform a grid search for the optimal values and uncertainties of stress parameters. Our synthetic test shows that the true parameters can be reliably estimated over a broad range of tectonic stress magnitudes. In the application to the Kumamoto earthquake, we find that the optimal tectonic stress is uniaxial tensional with a magnitude of 35 MPa and orientation of N6.5°W, which is at an angle of ∼47.5° to the fault strike. The average total shear stress on the fault plane is 16 MPa on the fault plane. With the inverted stress parameters, we evaluate the pore pressure based on the absolute stress field, the result of which is within a range of 0.3–0.45 of the lithostatic stress. Plain Language Summary: We estimate the absolute stress of the 2016 Kumamoto earthquake source region using rupture models and ground topography. We assume the overall slip direction is controlled by the tectonic stress loading, while the topographic stresses introduce spatial variation of slip directions. The tectonic stress field in the Kumamoto source region is estimated as uniaxial‐tensional stress of about 35 Mpa close the north‐south direction. This estimation is slightly higher than the previous estimations using other assumptions. Key Points: We develop an algorithm to invert for the absolute tectonic stress in the Kumamoto earthquake region We obtain a tectonic stress in uniaxial tension with magnitude 35 MPa and orientation N6.5°W We estimate that the pore‐pressure above 5 km depth is about 0.3–0.45 times lithostatic stress, which is close to a drained system