09:15 〜 09:30
[SCG63-26] 地震，測地，地形データから推定される島弧地殻の変形速度
キーワード：島弧地殻、変形速度、非弾性歪み、地震データ、測地データ、地形データ
Steady plate subduction brings about steady uplift of the island-arc lithosphere [1]. This process is simply explained as convex upward bending of an elastic plate by the effect of gravity [2]. So, there is no analogy in mechanism between the steady uplift and steady horizontal shortening or stretching of island-arc crust. The island-arc crust is basically elastic, but it includes a number of defects. Brittle fracture and/or plastic flow at these defects, which occur so as to release the overall elastic strain energy produced by mechanical interaction at plate interfaces, cause the horizontal shortening or stretching of island-arc crust [3]. To sum up, the crustal shortening or stretching is a purely inelastic deformation process. In northeast Japan, for example, the evidence of crustal shortening has been reported from seismic, geodetic, and geomorphic data [4, 5]. The point is a discrepancy in its rates. One of the reasons is difference in the length of observation periods. Actually, geodetic observation is too short to cover the entire cycle of large earthquakes. Another, more essential, reason is that different kinds of data provide different information about crustal deformation; that is, seismic and geomorphic data provide information about purely inelastic crustal deformation, whereas geodetic data provide information about total (elastic + inelastic) crustal deformation. So, we cannot directly compare the crustal shortening rates from geodetic data with those from seismic and geomorphic data unless geodetically observed deformation is divided into the elastic and inelastic parts [3].
References
[1] Matsu’ura, M. and T. Sato (1989), A dislocation model for the earthquake cycle at convergent plate boundaries, Geophys. J. Int., 96, 23-32.
[2] Fukahata, Y. and M. Matsu’ura (2016), Characteristics of island arc deformation due to steady plate subduction, Geophys. J. Int., 204, 825-840.
[3] Noda, A. and M. Matsu’ura (2010), Physics-based GPS data inversion to estimate 3-D elastic and inelastic strain fields, Geophys. J. Int., 182, 513-530.
[4] Wesnousky, S.G., C.H. Scholz, and K. Shimazaki (1982), Deformation of island arc: Rates of moment release and crustal shortening in intraplate Japan determined from seismicity and Quaternary fault data, J. Geophys. Res., 87, 6829-6852.
[5] Ikeda, Y., S. Okada, and M. Tajikara (2012), Long-term strain buildup in the Northeast Japan arc-trench system and its implications for gigantic strain-release events, J. Geol. Soc. Jpn., 118, 294-312.
References
[1] Matsu’ura, M. and T. Sato (1989), A dislocation model for the earthquake cycle at convergent plate boundaries, Geophys. J. Int., 96, 23-32.
[2] Fukahata, Y. and M. Matsu’ura (2016), Characteristics of island arc deformation due to steady plate subduction, Geophys. J. Int., 204, 825-840.
[3] Noda, A. and M. Matsu’ura (2010), Physics-based GPS data inversion to estimate 3-D elastic and inelastic strain fields, Geophys. J. Int., 182, 513-530.
[4] Wesnousky, S.G., C.H. Scholz, and K. Shimazaki (1982), Deformation of island arc: Rates of moment release and crustal shortening in intraplate Japan determined from seismicity and Quaternary fault data, J. Geophys. Res., 87, 6829-6852.
[5] Ikeda, Y., S. Okada, and M. Tajikara (2012), Long-term strain buildup in the Northeast Japan arc-trench system and its implications for gigantic strain-release events, J. Geol. Soc. Jpn., 118, 294-312.