2:45 PM - 3:00 PM
[J05-1-06] Frictional strength of plate interfaces inferred from numerical simulations of stress fields for oceanic plates: Application to the North American-Pacific plate interface off northeast Japan
Steady plate subduction along a curved interface brings about stress changes at constant rates in the surrounding lithosphere (Fukahata and Matsu'ura, 2016). So, in subduction zones, not only frictional resistance at plate interfaces but also steady plate subduction causes tectonic stress fields. The stress field caused by frictional resistance is basically compressive, but that caused by steady plate subduction is basically tensile in a seismogenic depth-range. Comparing these stress patterns with the actual tectonic stress fields, we can obtain information about the absolute frictional strength of plate interfaces on the same idea as Terakawa and Matsu'ura (2009).
In northeast Japan, the Pacific plate is descending beneath the North American plate. Before the 2011 Tohoku-oki earthquake, the focal mechanisms of seismic events at and around the plate interface were thrust-fault type (e.g., Asano et al., 2011), indicating that the compressive stress field due to frictional resistance was dominant there. The drastic increase of normal-fault type events after the Tohoku-oki earthquake could be interpreted as the change in stress regime from compression to tension. In this study, we estimate the lower limit of frictional strength at the plate interface through the 2-D numerical simulations of stress fields for descending oceanic plates. The advantages of oceanic plates are, it passes through the plate-to-plate interaction zone within a limited time (1-2Ma), and its rheological property is much simpler than the overriding plate (Matsu'ura et al., 2017 JpGU-AGU Joint Meeting). The results of numerical simulations show that the tensile stress in the upper part of the oceanic lithosphere reaches 200 MPa at the depth-range of 10-20km. We will show the downdip variation of frictional strength to reproduce the pre-seismic compressive stress field at and around the plate interface.
In northeast Japan, the Pacific plate is descending beneath the North American plate. Before the 2011 Tohoku-oki earthquake, the focal mechanisms of seismic events at and around the plate interface were thrust-fault type (e.g., Asano et al., 2011), indicating that the compressive stress field due to frictional resistance was dominant there. The drastic increase of normal-fault type events after the Tohoku-oki earthquake could be interpreted as the change in stress regime from compression to tension. In this study, we estimate the lower limit of frictional strength at the plate interface through the 2-D numerical simulations of stress fields for descending oceanic plates. The advantages of oceanic plates are, it passes through the plate-to-plate interaction zone within a limited time (1-2Ma), and its rheological property is much simpler than the overriding plate (Matsu'ura et al., 2017 JpGU-AGU Joint Meeting). The results of numerical simulations show that the tensile stress in the upper part of the oceanic lithosphere reaches 200 MPa at the depth-range of 10-20km. We will show the downdip variation of frictional strength to reproduce the pre-seismic compressive stress field at and around the plate interface.