American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 3643827 bytes)    Cited by

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, B05408, doi:10.1029/2005JB003901, 2006

Inference of postseismic deformation mechanisms of the 1923 Kanto earthquake

Fred F. Pollitz

U.S. Geological Survey, Menlo Park, California, USA


Marleen Nyst

U.S. Geological Survey, Menlo Park, California, USA


Takuya Nishimura

Geographical Survey Institute, Tsukuba, Japan


Wayne Thatcher

U.S. Geological Survey, Menlo Park, California, USA


Abstract

Coseismic slip associated with the M7.9, 1923 Kanto earthquake is fairly well understood, involving slip of up to 8 m along the Philippine Sea–Honshu interplate boundary under Sagami Bay and its onland extension. Postseismic deformation after the 1923 earthquake, however, is relatively poorly understood. We revisit the available deformation data in order to constrain possible mechanisms of postseismic deformation and to examine the consequences for associated stress changes in the surrounding crust. Data from two leveling lines and one tide gage station over the first 7–8 years postseismic period are of much greater amplitude than the corresponding expected interseismic deformation during the same period, making these data suitable for isolating the signal from postseismic deformation. We consider both viscoelastic models of asthenosphere relaxation and afterslip models. A distributed coseismic slip model presented by Pollitz et al. (2005), combined with prescribed parameters of a viscoelastic Earth model, yields predicted postseismic deformation that agrees with observed deformation on mainland Honshu from Tokyo to the Izu peninsula. Elsewhere (southern Miura peninsula; Boso peninsula), the considered viscoelastic models fail to predict observed deformation, and a model of ∼1 m shallow afterslip in the offshore region south of the Boso peninsula, with equivalent moment magnitude M w = 7.0, adequately accounts for the observed deformation. Using the distributed coseismic slip model, layered viscoelastic structure, and a model of interseismic strain accumulation, we evaluate the post-1923 stress evolution, including both the coseismic and accumulated postseismic stress changes and those stresses contributed by interseismic loading. We find that if account is made for the varying tectonic regime in the region, the occurrence of both immediate (first month) post-1923 crustal aftershocks as well as recent regional crustal seismicity is consistent with the predicted stress pattern. This suggests that the influence of the 1923 earthquake on regional seismicity is fairly predictable and has persisted for at least seven decades following the earthquake.

Received 23 June 2005; accepted 18 January 2006; published 18 May 2006.

Keywords: Japan; postseismic.

Index Terms: 1207 Geodesy and Gravity: Transient deformation (6924, 7230, 7240); 1242 Geodesy and Gravity: Seismic cycle related deformations (6924, 7209, 7223, 7230); 8162 Tectonophysics: Rheology: mantle (8033).

Read Full Article (file size: 3643827 bytes)    Cited by

Citation: Pollitz, F. F., M. Nyst, T. Nishimura, and W. Thatcher (2006), Inference of postseismic deformation mechanisms of the 1923 Kanto earthquake, J. Geophys. Res., 111, B05408, doi:10.1029/2005JB003901.