Nanoseismicity forecasts sinkhole collapse in the Dead Sea coast years in advance

摘要

The human-induced desiccation of the Dead Sea has led to the formation of more than 6000 collapse sinkholes along its western coast during the past 20 yr, causing severe infrastructural damage. This desiccation led to intrusion of fresh groundwater from the Judaean Mountains to the west; the groundwater dissolves a 10-70-m-deep salt layer, forming subsurface cavities. The coastal sediments overlying these cavities become unstable until their final collapse to develop sinkholes. Here we show results of seismic monitoring that identified subsurface instabilities several years before sinkhole collapse. The survey, which included a network of five borehole geophones buried at depths between 11 and 25 m, detected 82 nanoseismic events, 75 of which were in a magnitude range between -2 and -3. The hypocenter depths range upward from the base of the salt layer, and the plan-view distribution agrees with a salt dissolution propagation front. Therefore, these nanoseismic signals are likely due to deformation that precedes the surface collapse of sinkholes. During the monitoring period there were no indications of subtle land subsidence at the surface above most of the nanoseismic events, as we show from interferometric synthetic aperture radar. The first sinkhole collapse occurred 2.5 yr after the nanoseismic events, and seven additional sinkholes formed in 2016, suggesting that the zone of nanoseismicity is prone to further collapse in the coming years.