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Crustal Deformation Process in the Mid‐Niigata Region of the Niigata‐Kobe Tectonic Zone as Observed by Dense GPS Network Before, During, and After the Tohoku‐Oki Earthquake
Author(s) -
MenesesGutierrez A.,
Sagiya T.,
Sekine S.
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 - 10.1029/2018jb015567
Subject(s) - geology , crust , seismology , deformation (meteorology) , tectonics , slip (aerodynamics) , fault (geology) , wavelength , geodesy , geophysics , oceanography , physics , thermodynamics , optoelectronics
We evaluate response of Mid‐Niigata during the preseismic, coseismic, and postseismic periods of the 2011 Mw9.0 Tohoku‐oki earthquake by analyzing strain distributions based on a dense Global Positioning System network. Decomposition of the coseismic E‐W strain according to its wavelength shows localized elastic extension, while persistent localized contraction in the short‐wavelength component within a narrow zone of 40‐ to 60‐km width is significant before and after the event, implying the persistence of an inelastic process. Differences in the amplitude and horizontal location of the localized deformation suggest that elastic heterogeneities of the crust, acting in different sense before and after the earthquake, affect the deformation in Mid‐Niigata as well. We model localized deformation in the preseismic and postseismic period considering an aseismic fault slip and a weak elastic zone as deformation sources. Our kinematic models suggest vertical decoupling between the weak elastic layer and the basement rock, implying that the preseismic and postseismic strain rate patterns represent direct effects of the shallow portion of the crust in Mid‐Niigata. Although model parameters are not well constrained, we find that faults cutting the lower crust and a part of the upper crust, and an anomalously weak zone of a 40‐ to 60‐km width located above the fault explain the data. Our simple model shows that both inelastic and elastic sources are essential in the deformation mechanism of the Mid‐Niigata area in northern Niigata‐Kobe Tectonic Zone.