Liquefaction in the coastal environment: An analysis of case histories

Extensive soft-sediment deformation structures in the early Darriwilian (Middle Ordovician) shallow marine siliciclastic sediments formed on the Baltoscandian carbonate ramp, northwestern Estonia

“…Therefore, pressure fluctuations either due to turbulent surge or a storm (Molina et al, 1998;Alfaro et al, 2002;Chen et al, 2009) are not applicable in this case. Considering the extremely flat palaeo-relief of the region, spontaneous liquefaction on slopes ranging from 22 to 27° ( Chaney and Fang, 1991) is not likely to occur. Furthermore, there is no indication of lateral stress within the observed deformation structures (i.e.…”

“…Where the fluid pressure exceeded the strength of the overlying semi-permeable layers, forceful (brittle or semi-brittle) rupture occurred and the watersediment slurry was forced to the surface of the Pakri Formation. This process results in the erosion and mobilization of sediment from the liquefied zones leaving voids in the underlying horizons, which can then collapse due to overburden weight and cause further distortion and brecciation of the surface (Chaney and Fang, 1991). Such a deformation path is exceptionally preserved on Osmussaar Island (deformation zone I) where the Pakri Formation together with the underlying sediments are brecciated and penetrated by large sedimentary dykes.…”

“…On the other hand, earthquake-induced shear waves propagate upwards from lower level in the ground involving a larger volume of material than non-earthquake wave loading (Chaney and Fang, 1991). The clear zonality of the deformation structures in the Pakri Formation indicates deformative energies resulting from a single concentrated source, which also strongly favors their seismic origin .…”

“…Such planes of weakness may have been introduced during the deformation process (i.e. brittle cracks can be generated by preceding earthquake or oscillatory storm wave loading) before fluidization commenced a few minutes after the end of cyclic loading (Chaney and Fang, 1991). The following observations support liquefaction mechanism of the large sedimentary dykes [rather than filling of the open fissures from above as discussed by Puura and Tuuling (1988) and Suuroja et al (1999)]: 1) upwardnarrowing mouths of the dykes; 2) breccia clasts are cut off from the existing, earlier deposited sediments and transported upwards within the dykes along with the fluidized sediments; 3) flow signs and laminations are parallel to the dyke walls with no indications of normal sedimentary laminations at any places within the dykes; and 4) smaller dykes are shooting off and narrowing upwards rather than downwards from the major 'feeder' dykes ( Fig.…”

“…Some of the high-energy processes can induce gradual build-up of hydrostatic pressure within water saturated near-surface sediments due to the application of shock or cyclic loading (Chaney and Fang, 1991). Increase in pressure can ultimately lead to rapid loss of shear resistance and collapse of grain framework which enables sediments to temporarily behave like a liquid (hence the 'liquefaction') until granular strength is regained (Ambraseys and Sarma, 1969).…”