Thanks to Alessandro I came across this incredible video of liquefaction occuring in the Tokyo Central Park during the M9.0 Japan earthquake. We can see a lot of very interesting features. First, cracks are opening, perfectly visible on the paved road and the cobble. Then we see the differential moving along those cracks, they are widening and narrowing and there’s vertical movement as well. Soon, the first ruptures appear in the meadows, despite the soft sediment there.
Video doesn’t work? Watch it here.
When liquefaction starts, the first thing to recognize is water coming out of the meadows, where there are small depressions. Suddenly, there’s water everywhere and we see fountains of mud being ejected from the cracks which still are in motion. As we expected, the soils gets more liquified the longer the shaking continues.
Obviously, we should not only think about ground motion, PGA and PGV when we discuss anti-seismic measures and building standards. Liquefaction happens with low intensities also and this may be the reason for structural damage that you didn’t expect. Your house may still be in shape, but it might have turned over…
If you’ve never seen how liquefaction works, this is the perfect example. Learn more about liquefaction here.
Papers on liquefaction:
Bouhadad, Y., Benhamouche, A., Maouche, S., Belhai, D. (2009): Evidence for Quaternary liquefaction-induced features in the epicentral area of the 21 May 2003 Zemmouri earthquake (Algeria, Mw = 6.8), Journal of Seismology, 13-1, 161-172, doi:10.1007/s10950-008-9134-y.
Goy, J. L., Zazo, C., Mörner, N.-A., Hoyos, M., Somoza, L., Lario, J., Bardají, T., Silva, P. G.,
Dabrio, J. C. (1994): Pop up-like deformation of a Roman floor and liquefaction structures in SW Spain as possible paleoseismic indicators, Bulletin of the INQUA Neotectonics Commission, 17, 42-44.
Idriss, I. M., Boulanger, R. W. (2004): Semi-empirical procedures for evaluating liquefaction potential during earthquakes, Soil Dynamics and Earthquake Engineering, 26, 2-4, 115-130.
Lekkas, E., Lozios, S., Skourtsos, E., Kranis, H. (1996): Liquefaction, ground fissures, and
coastline change during the Egio earthquake (15 June 1995: Central Greece), Terra Nova, 8, 648-654.
Obermeier, S. F. (1996): Use of liquefaction-induced features for paleoseismic analysis – An
overview of how seismic liquefaction features can be distinguished from other features and
how their regional distribution and properties of source sediment can be used to infer the
location and strength of Holocene paleo-earthquakes, Engineering Geology, 44, 1-76, doi:
10.1016/S0013-7952(96)00040-3.
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