Segmentation and Holocene surface faulting on the Median Tectonic Line, southwest Japan

Abstract

The Median Tectonic Line (MTL) active fault system is a 300-km-long, arc-parallel, right-lateral strike-slip fault related to oblique subduction of the Philippine Sea plate beneath the Eurasian plate at the Nankai trough, southwest Japan. The fault on Shikoku Island has a slip rate of 5-10 mm/yr, one of the highest in onshore Japan. We identified 12 geometric segments along the MTL separated by discontinuities such as en echelon steps, bends, changes in strike, and gaps in the surface trace. A chronology of latest Holocene surface faulting on the MTL was constructed based on previously published and new work including trenching, geomorphic mapping, and acoustic profiling and piston coring of the submarine extension of the fault zone. The MTL probably does not rupture along its entire length in a single earthquake but instead consists of multiple "earthquake segments" that rupture independently of one another. The recurrence interval and surficial offset for surface-rupturing earthquakes at four individual sites on the MTL in Shikoku Island are 1000-3000 years and 5-8 m, respectively. The relatively long recurrence interval and large surficial offset per earthquake suggest large seismic moment release during surface-mpturing earthquakes on the MTL, as commonly observed for Japanese moderate to large intraplate earthquakes. Because the predicted rupture lengths based on empirical relations between surface displacement and rupture length are considerably larger than those of individual segments, large earthquakes on the MTL probably rupture multiple geometrically defined segments. The fault was previously thought to be unruptured at least in the past 1000 years based on the absence of historical evidence for destructive earthquakes. However, trench excavations show that part of the MTL mptured most recently during or after the 16th century A.D. with at least 6.9 + 0.7 m of slip along the main fault trace. This rupture may be correlated to the 1596 Keicho-Kinki earthquake, but further geological and historical investigations are needed to confirm this hypothesis. Nevertheless, a detailed model of the rupture process of this earthquake based on inversion of geodetic, geologic, and Paper number 95JB01913. 0148.0227/96/95JB.01913505.00 seismographic data suggests that the two principal en echelon steps are related to retardation of the propagating ruptures [Wald and Heaton, 1994]. As we learn more about the dynamic rupture processes of modern earthquakes, we also need to look at historic and late Quaternary earthquakes for rupture patterns along a fault through multiple earthquake cycles. In this paper, we describe the late Holocene behavior of the Median Tectonic Line (MTL), a large strike-slip fault in southwest Japan. The MTL is an arc-parallel, right-lateral strike-slip fault (Figure 1) related to oblique subduction of the Philippine Sea plate beneath the Eurasian plate along the Nankai trough [Fitch, 1972]. Arc-parallel strike-slip faults are capable of generating moderate to large earthquakes such as the 1892 Tapa...

Source rupture processes of the foreshock and mainshock in the 2016 Kumamoto earthquake sequence estimated from the kinematic waveform inversion of strong motion data

“…This fault system is thought to be part of the western extension of the Median Tectonic Line, which is the longest active right-lateral strike-slip fault in Japan (e.g., Chida 1992;Okada 1980;Yeats 2012). The average horizontal slip rate of the Futagawa-Hinagu fault system has been 0.88 mm/year in the late Quaternary (Tsutsumi and Okada 1996). Surface breaks caused by the mainshock were found along the Futagawa-Hinagu fault system by emergency field surveys (e.g., Geological Survey of Japan 2016; Okada and Toda 2016).…”

Subsurface structure and faulting of the Median Tectonic Line, southwest Japan inferred from GPS velocity field

“…Current seismic activity is relatively low so that no linear distribution of microearthquakes is found along the MTL (Okano and Kimura, 1996). Though recent trench excavations have suggested a partial rupture at the end of 16th century (Tsutsumi and Okada, 1996), most of the MTL has the potential to rupture in a large event in the future.…”

Interaction between Transform Faults and Rift Systems: A Combined Field and Experimental Approach

“…Moreover, several mechanisms have been proposed to describe how such strike-slip faults terminate, but they are poorly resolved in several cases. More detailed data on transform fault terminations have been collected and studied on-land, especially in regard to the transition to reverse fault/trench systems (e.g., Davis and Burchfiel, 1973;Bellier and Sebrier, 1995;Quebral et al, 1996;Tsutsumi and Okada, 1996;Freymueller et al, 1999;Norris and Cooper, 2000), while fewer are related to on-land rift zones (e.g., Joffe and Garfunkel, 1987;Mouslopoulou et al, 2007a).…”