Structural and seismic stratigraphic framework of the NanTroSEIZE Stage 1 transect

Abstract

The location of the Integrated Ocean Drilling Program's (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) was based on regional two-dimensional seismic reflection surveys carried out by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Final site locations were chosen based on a three-dimensional (3-D) seismic reflection survey acquired across the seaward margin of Kumano Basin and the accretionary prism from the basin to the deformation front. This survey covered a region 12 km wide (approximately parallel to the regional structural strike) and 56 km long (approximately perpendicular to the regional strike) and provided detailed images of the structure and seismic stratigraphy of the drill sites. Sites were drilled in the frontal thrust zone at the toe of the accretionary prism, the frontal region of the megasplay fault zone, and the forearc basin. The 3-D seismic data volume images a main frontal thrust at the prism toe with the hanging wall thrust at least 7.5 km seaward over the trench. This configuration is different from that in other parts of the Nankai prism. At the shallow end of the megasplay, the data images a complex thrust system that truncates older structures in the underlying accretionary prism and shows that the hanging wall block has overridden more than 1250 m of young slope sediments. At the forearc basin site, we interpret landward-dipping forearc basin strata onlapping older slope sediments, which in turn overlie an older part of the accretionary prism.

Late Oligocene–early Miocene olistostromes (sedimentary mélanges) as tectono-stratigraphic constraints to the geodynamic evolution of the exhumed Ligurian accretionary complex (Northern Apennines, NW Italy)

“…In this framework, mass-transport processes are leading agents in maintaining the dynamic equilibrium by reshaping the accretionary wedge topography and producing high concentration of small-to medium-scale submarine landslide accumulations (McAdoo et al 2004;Mosher et al 2008;Camerlenghi et al 2009;Moore et al 2009;Harders et al 2011;Strasser et al 2011) and megaslides (Moore et al 1976;Golfinger et al 2000;Cochonat et al 2002;von Huene et al 2004;Hühnerbach et al 2005;von Huene, 2008;Yamada et al 2010). Earthquake shaking, as well as long-term causal factors (i.e., sea level variations, rate of sedimentation, gas-hydrates instability, tectonic oversteepening), may exert a primary role in triggering slope failures (e.g., Keefer 1984;Hampton et al 1996;Cochonat et al 2002).…”

“…Although recent studies in modern accretionary wedges provided excellent results on the comprehension of the complex interplay between tectonic and submarine mass-transport processes (e.g., Moore et al 2009;Kawamura et al 2009Kawamura et al , 2011Strasser et al 2011), some complexities still exist in defining entirely the conditions, structures and processes leading to stratal disruption and mélange and chaotic rock formation, as well as the triggering factors and mechanisms for slope failure. In particular, the internal structure of the deposits from mass transport (hereafter defined as mass-transport deposits, or MTDs, and mass-transport complexes, or MTCs when they consist of different superposed MTDs, see, e.g., Ogata et al 2012b) is commonly difficult to be deciphered in detail mainly because of the acoustic transparency and the small-scale of the related features (meters to tens of meters) that is below the standard seismic resolution.…”

NanTroSEIZE Stage 1 Expeditions 314, 315, and 316: First Drilling Proram of the Nankai Trough Seismogenic Zone Experiment

“…2, 3; Moore et al, 2009). Most of the thrusts inferred from the seismic profiles and LWD data were confirmed through age reversals, fault zones sampled in cores, and repetition of specific strata, but some additional faults were also defined during Expedition 316 drilling.…”

“…2; Moore et al, 2009). A series of sites targeted the thrust sheet, fault zone, and footwall of the lower of these branches, which was judged to be the most active and most significant of the seismically imaged splays (Tobin and Kinoshita, 2006b;Moore et al, 2009). …”

Quantification of free gas in the Kumano fore-arc basin detected from borehole physical properties: IODP NanTroSEIZE drilling Site C0009

“…The NanTroSEIZE project aims to understand the formation of the Nankai fore arc and its seismogenic zone [e.g., Kinoshita et al, 2006]. Extensive seismic studies conducted in advance of drilling provide evidence of gas within sediments filling the Kumano fore-arc basin (Figure 1, see also Moore et al [2009]). For example, a laterally extensive horizontal bottomsimulating reflector (BSR) extends throughout the basin, marking the base of the gas hydrate stability zone.…”