Simulation of recurring earthquakes along the Nankai trough and their relationship to the Tokai long‐term slow slip events taking into account the effect of locally elevated pore pressure and subducting ridges

Abstract

[1] Many earthquakes of moment magnitudes greater than 8 associated with subduction of the Philippine Sea plate under Japan have occurred along the Nankai trough with a recurrence interval of 90-150 years. A large-scale rupture of the Tokai fault segment is believed to be imminent because that segment did not rupture during the most recent Tonankai earthquake in 1944. Recurring long-term slow slip events (LSSEs) have recently been observed in the Tokai region. To investigate the current stress state in the Tokai region, we numerically simulated earthquake cycles using a three-dimensional model consisting of triangular cells based on the rate-and state-dependent friction law. Our numerical simulations successfully modeled the Tokai segment not ruptured during the 1944 Tonankai earthquake as well as the recurring LSSEs in the Tokai region. We found that a large characteristic displacement (L) and effective normal stress (σ) in areas of subducted ridges are essential to avoid rupture of the Tokai segment during the 1944 Tonankai earthquake. We also demonstrated that we can reproduce the recurring LSSEs by assigning low values of σ and L to the area beneath Lake Hamana without introducing a velocity-strengthening friction law at high slip rate. Our simulation showed that the amplitudes of the LSSEs increased following the earthquakes that did not rupture the Tokai segment, which suggests that the recent LSSEs may be related to the accumulation of stresses in the Tokai segment because it did not rupture during the 1944 earthquake.Citation: Hirose, F., and K. Maeda (2013), Simulation of recurring earthquakes along the Nankai trough and their relationship to the Tokai long-term slow slip events taking into account the effect of locally elevated pore pressure and subducting ridges,

An estimate of tidal and non-tidal modulations of plate subduction speed in the transition zone in the Tokai district

“…In the current study, this idea is generalized under the assumption that plate subduction speed in the transition zone, including in slow slip areas, changes due to external forces. However, to prove that fluctuations in subduction speed below the seismogenic zone can trigger earthquakes, quantitative simulations, such as those made by Hirose and Maeda (2013), would be necessary to calculate the 3-D stress distribution on the plate interface. The stress behaviors would strongly depend on given frictional parameters, and enormous efforts are needed to reveal the parameter sensitivity.…”

“…65 and 66 in Geographical Information Authority of Japan 2015). Recurrence intervals of~10 years can be reproduced by numerical simulation (Hirose and Maeda 2013). However, why these slips occurred during these periods has not been explained.…”

“…where K 1i denotes the elastic Green's function (e.g., Hirose and Maeda 2013). Of the four terms on the right-hand side of Eq.…”

“…(1) was 2-3 kPa in almost all of the tremor zones in the Nankai Trough. By contrast, A − B in the slow slip area was set to −17 kPa by Hirose and Maeda (2013) to simulate SSE recurrence and the main ruptures in the Tokai area, which were based on a rate-and statedependent law. However, the chosen A − B magnitude is not unique because slip behaviors also depend on the characteristic distances discussed above.…”

A possible scenario for earlier occurrence of the next Nankai earthquake due to triggering by an earthquake at Hyuga-nada, off southwest Japan

“…Moreover, aseismic events recently observed in the Nankai Trough region have also been successfully modeled in the framework of quasi-dynamic earthquake cycle model. Long-term slow slip event (SSE) beneath Tokai, eastern part of the Nankai trough region, was reproduced with M w 8-class Nankai Trough earthquakes (Hirose and Maeda 2013). As for the western side of the Nankai Trough, Shibazaki et al (2010) and Matsuzawa et al (2010) modeled SSEs, occurring in the deeper part of the seismogenic zone of the M w 8-class earthquake beneath Shikoku, by using a modified version of the rate-and state-dependent friction laws.…”