Coseismic fault‐related fold model, growth structure, and the historic multisegment blind thrust earthquake on the basement‐involved Yoro thrust, central Japan

Abstract

[ 1 ] We use high-resolution seismic reflection profiles, boring transects, and mapping of fold scarps that deform late Quaternary and Holocene sediments to define the kinematic evolution, subsurface geometry,c oseismic behavior,a nd fault slip rates for an active, basement-involved blind thrust system in central Japan. Coseismic fold scarps on the Yoro basement-involved fold are defined by narrow fold limbs and angular hinges on seismic profiles, suggesting that at least 3.9 km of fault slip is consumed by wedge thrust folding in the upper 10 km of the crust. The close coincidence and kinematic link between folded horizons and the underlying thrust geometry indicate that the Yoro basementinvolved fold has accommodated slip at an average rate of 3.2 ±0.1 mm/yr on ashallowly west dipping thrust fault since early Pleistocene time. Past large-magnitude earthquakes, including an historic M 7.7 event in A.D. 1586 that occurred on the Yoro blind thrust, are shown to have produced discrete folding by curved hinge kink band migration above the eastward propagating tip of the wedge thrust. Coseismic fold scarps formed during the A.D. 1586 earthquake can be traced along the en echelon active folds that extend for at least 60 km, in spite of different styles of folding along the apparently hard-linked Nobi-Ise blind thrust system. We thus emphasize the importance of this multisegment earthquake rupture across these structures and the potential risk for similar future events in en echelon active fold and thrust belts.Citation: Ishiyama, T., K. Mueller, H. Sato, and M. Togo (2007), Coseismic fault-related fold model, growth structure, and the historic multisegmentb lind thrust earthquake on the basement-involved Yoro thrust, central Japan,

Diverse rupture modes for surface-deforming upper plate earthquakes in the southern Puget Lowland of Washington State

“…Although upper plate structure eastward from the Saddle Mountain deformation zone remains unclear, we hesitate to exclude such a possibility, given some unexpected multifault ruptures of the past approximately two decades (e.g., Sieh et al, 1993;Xu et al, 2009). Earlier historical examples of such ruptures include the en echelon folds >60 km long that grew during the 1586 M~7.7 earthquake on the Yoro blind thrust of central Japan (Ishiyama et al, 2007). Above subduction zone megathrusts, backthrusts tens of kilometers arcward of the megathrust have ruptured during and after great earthquakes (McCalpin and Carver, 2009;Berryman et al, 2011;Wiseman et al, 2011) However, the >20 km distance between the surface projections of the Seattle and Tacoma master-ramp thrusts (Fig.…”

“…1C) is greater than the distance between adjacent intraplate faults that have ruptured during the same earthquake (Rubin, 1996;Wesnousky, 2008). How Coulomb stress changes infl uence the interactions of nearby thrusts depends on many factors in addition to fault proximity, including fault orientations, prior earthquake timing and magnitudes, and whether thrusts are blind (Stein and Yeats, 1989;Lin and Stein, 2004;Ishiyama et al, 2007;Schwartz et al, 2012). Rupture modeling of thrust faults (e.g., Wang and Chen, 2001;Lin and Stein, 2004), and of central Seattle fault deformation during the Restoration Point earthquake (ten Brink et al, 2006), do not directly address simultaneous rupture on thrusts so far apart.…”

“…A common theme is that even for well-studied modern earthquakes with tens to hundreds of kilometers of complex fault and fold scarps (e.g., 1988 M s 7 Spitak, Armenia; 2008 M w 7.9 Wenchuan, China), some slip on blind thrusts must be invoked to fully explain patterns of surface deformation (e.g., Hull, 1990;Rubin, 1996;Ishiyama et al, 2007;de Michele et al, 2010). Slip on blind thrusts during earthquakes as large as M w 7.7 has produced too little surface evidence of deformation to be preserved for more than decades (e.g., McCalpin and Thakkar, 2003).…”

“…Preliminary tree-ring correlations date stumps killed by fl ooding, a result of surface rupture on the Saddle Mountain faults, to >50 yr before the Restoration Point earthquake (Hughes, 2005;Snook, 2011). At heights as great as 7-8 m, the Catfi sh lake scarps within the Tacoma fault zone are too high to have formed entirely during a single large earthquake (e.g., Ishiyama et al, 2007), and the 6-m-high scarp at 1 site (Cedars trench, Nelson et al, 2008, sheet Two consequences of forearc structure that the Puget Lowland shares with intraplate thrust fault systems cloud estimates of the frequency and degree of clustering of large earthquakes in the lowland: uncertain structural relations among faults and probable blind thrusting. Evidence from 2 short backthrusts in the central Seattle fault zone records a cluster of at least 4 late Holocene earthquakes after 2.7 ka.…”

Fine fault structure of a moderate earthquake in the 2007 earthquake sequence of Northern Mie, Japan

“…The northern part of the Yokkaichi Fault was ruptured by the historical large earthCopyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB. quake that occurred in 1586 (Ishiyama et al, 2007). The hypocenter of the main shock in the 2007 earthquake sequence of Northern Mie is also located at the base of the seismogenic zone (Fig.…”