Vein structures, like ripple marks, are formed by short-wavelength shear waves

Abstract

Vein structure, a distinctive structure in deep-sea hemipelagic clayey and siliceous mudstones at convergent plate boundaries, consists of closely spaced mud-filled veins forming an array usually parallel to the bedding plane. This structure has been regarded as a seismite that formed during earthquake shaking by resonance of fractures. Our detailed field observations and shaking model experiments verified that both basic (first-stage) and advanced (developed-stage) vein structures can be explained by a systematic theory. Essentially, a vein structure forms in an array of fractures as a result of shearing, not by push waves but by shear waves of very short wavelength, by a mechanism very similar to that which forms ripple marks. We found the height of a vein array (H) to be systematically related to vein spacing (S) such that H = 5S, suggesting that the shear strength of the sediment is proportional to the thickness of the standing wave part of a sediment layer. Shear or oscillatory flow occurs in the top part of a sediment layer, under which standing waves with wavelengths on the order of millimeters to centimeters lead to vein structure formation. Vein structure can develop not only in response to earthquake shaking but also by propagation of shear waves along a large fault or by other kinds of shears associated with density or debris flows, landsliding, or faulting.

Site C0009

“…Vein structures were also found in slope apron and slope basin deposits of the Middle America Trench off Guatemala (Cowan, 1982) and Peru (Lindsley-Griffin et al, 1990). Brothers et al (1996) and Ohsumi and Ogawa (2008) have shown that vein structures have a relationship between height and spacing and are interpreted as forming by oscillatory deformation such as shaking of incohesive sediments (e.g., resulting from an earthquake or a debris flow).…”

Syndepositional tectonic activity in an epicontinental basin revealed by deformation of subaqueous carbonate laminites and evaporites: Seismites in Red River strata (Upper Ordovician) of southern Saskatchewan, Canada

“…Pratt, unpublished data). Vein arrays form by short wavelength shear waves which segregate the finer particles (Brothers et al, 1996;Ohsumi and Ogawa, 2008).…”

Episodic seafloor mud brecciation due to great subduction zone earthquakes

“…Several geologic signatures have been used to reconstruct ancient earthquake and tsunami records. These include sand dikes and sills rooted in liquefi able sandy layers under low-permeability sediments (e.g., Ettenshon et al, 2002), shaking-induced grain-fi lled veins (Ogawa, 1980;Brothers et al, 1996;Ohsumi and Ogawa, 2008), and turbidite and debris fl ow deposits inferred to result from collapse of unstable submarine slopes during earthquakes (e.g., Goldfi nger et al 2003;Noda et al, 2008).…”