Estimation of slip rate and fault displacement during shallow earthquake rupture in the Nankai subduction zone

Abstract

Enormous earthquakes repeatedly occur in subduction zones, and the slips along megathrusts, in particular those propagating to the toe of the forearc wedge, generate ruinous tsunamis. Quantitative evaluation of slip parameters (i.e., slip velocity, rise time and slip distance) of past slip events at shallow, tsunamigenic part of the fault is critical to characterize such earthquakes. Here, we attempt to quantify these parameters of slips that may have occurred along the shallow megasplay fault and the plate boundary décollement in the Nankai Trough, off southwest Japan. We apply a kinetic modeling to vitrinite reflectance profiles on the two fault rock samples obtained from Integrated Ocean Drilling Program (IODP). This approach constitutes two calculation procedures: heat generation and numerical profile fitting of vitrinite reflectance data. For the purpose of obtaining optimal slip parameters, residue calculation is implemented to estimate fitting accuracy. As the result, the measured distribution of vitrinite reflectance is reasonably fitted with heat generation rate _ Q À Á and slip duration (t r ) of 16,600 J/s/m 2 and 6,250 s, respectively, for the megasplay and 23,200 J/s/m 2 and 2,350 s, respectively, for the frontal décollement, implying slow and long-term slips. The estimated slip parameters are then compared with previous reports. The maximum temperature, Tmax, for the Nankai megasplay fault is consistent with the temperature constraint suggested by a previous work. Slow slip velocity, long-term rise time, and large displacement are recognized in these fault zones (both of the megasplay, the frontal décollement). These parameters are longer and slower than typical coseismic slip, but are rather consistent with rapid afterslip.

Strain decoupling reveals variable seismogenic risk in SEJapan (Nankai Trough)

“…The frontal part of the imbricate-thrust zone and the megasplay are revealed as the regions of highest fault activity and, potentially, largest seismogenic risk-if assuming coseismic slip for most of the structures interpreted in the study area. This assumption is valid in light of recent data in Hamada et al [2015], which recognized slow slip velocity, long-term rise time, and large displacement are recognized both the megasplay fault zone and the frontal d ecollement. These parameters were considered by the authors to be longer and slower than typical coseismic slip, but are rather consistent with rapid afterslip.…”

“…This assumption is valid in light of recent data in Hamada et al . [], which recognized slow slip velocity, long‐term rise time, and large displacement are recognized both the megasplay fault zone and the frontal décollement. These parameters were considered by the authors to be longer and slower than typical coseismic slip, but are rather consistent with rapid afterslip.…”

“…In the interpreted 3-D seismic volume, branches of the megasplay fault are visible cutting through the outer accretionary prism (Figure 2a). Coseismic slip occurs along some of the branches of the megasplay fault, including outward from the plate boundary mega-thrust into the frontal d ecollement, to produce a number of great earthquakes [Fukao, 1979;Baba et al, 2006;Hamada et al, 2015]. In fact, the outer accretionary prism of Nankai exhibits a long history of seismogenesis [Byrne et al, 2009] and associated tsunamis [Ando, 1975].…”

Three‐dimensional texture of natural pseudotachylyte: Pseudotachylyte formation mechanism in hydrous accretionary complex

“…Recently, several geological approaches have revealed evidence of both seismic and slow slips from the fault rocks of on‐land fossilized faults (Hamada, Hirono, & Ishikawa, ; Ujiie & Kimura, ; Ujiie, Yamaguchi, Kimura, & Toh, ) and from drilled faults in the modern subduction zone (Hamada et al, , and references therein). These approaches focus on the traces of frictional heat imprinted as chemical reactions along the fault.…”

Kinetic effect of heating rate on the thermal maturity of carbonaceous material as an indicator of frictional heat during earthquakes

“…In particular, the thermal maturity of carbonaceous material (CM) has received considerable attention as a new temperature proxy (e.g., Savage et al 2014;Hirono et al 2015;Kaneki et al 2016;Rabinowitz et al 2017) because the organochemical characteristics of CM, including its elemental compositions and molecular structures, change irreversibly with increasing temperature (e.g., Beyssac et al 2002). The frictional heat recorded by CM in both natural and experimental fault rocks has been investigated by spectroscopic analyses (e.g., Furuichi et al 2015;Hirono et al 2015;Kaneki et al 2016Kaneki et al , 2018Ito et al 2017;Kouketsu et al 2017;Kuo et al 2017) and by determining elemental compositions (Kaneki et al 2016), biomarker indexes (Polissar et al 2011;Savage et al 2014;Sheppard et al 2015;Rabinowitz et al 2017), and vitrinite reflectance (e.g., O'Hara 2004;Sakaguchi et al 2011;Kitamura et al 2012;Maekawa et al 2014;Hamada et al 2015). Several studies have succeeded in inferring slip behaviors on natural faults during past earthquakes from estimations of maximum temperatures recorded by CM (Savage et al 2014;Hirono et al 2015;Kaneki et al 2016;Mukoyoshi et al 2018).…”