Premium
Absolute Stress Fields in the Source Region of the 1992 Landers Earthquake
Author(s) -
Terakawa Toshiko,
Hauksson Egill
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb015765
Subject(s) - geology , stress field , focal mechanism , hypocenter , seismology , aftershock , shear stress , stress (linguistics) , geodesy , pore water pressure , cauchy stress tensor , hydrostatic equilibrium , fault plane , shear (geology) , fault (geology) , induced seismicity , mechanics , mathematics , geotechnical engineering , physics , petrology , mathematical analysis , linguistics , philosophy , quantum mechanics , finite element method , thermodynamics
Earthquake focal mechanisms are often inverted to obtain the deviatoric stress field. Because shear stress is equal to the frictional strength of the fault at the time of an earthquake, six components of the absolute stress tensor at the hypocenter can be obtained from a focal mechanism by combining deviatoric stress fields with the Coulomb failure criterion. For a data set of focal mechanisms determined for southern California earthquakes, including the 1992 Landers earthquake sequence, we calculated the absolute stress tensors at their hypocenters using a standard intrinsic friction coefficient under three pore pressure conditions, parameterized by the reference pore pressure at the optimally oriented faults to the stress field. Three absolute stress fields were obtained for southern California immediately before the Landers main shock by applying each data set of the stress tensors to an inversion scheme based on Bayesian statistical inference and Akaike's Bayesian Information Criterion. The coseismic stress field was calculated to obtain the absolute stress fields immediately after the main shock. The variations of the coseismic stress rotation were related to the reference pore pressure. Comparing this relation with that obtained through stress inversion, we determined the absolute stress field and the most plausible reference pore pressure to be hydrostatic. On average, the maximum shear stresses immediately before the main shock were 44 ± 15 and 79 ± 24 MPa at depths of 5 and 10 km, respectively. Earthquakes on the off‐plate boundary faults in southern California occur on faults that are loaded by Anderson‐Byerlee stress conditions.