סמינר מחלקתי ביה"ס להנדסה מכאנית Eyal Shalev

School of Mechanical Engineering Seminar
Monday, March 13, 2017 at 14:00
Wolfson Building of Mechanical Engineering, Room 206

Groundwater Level changes induced by teleseismic earthquakes

Eyal Shalev

Geological Survey of Israel

Sustained water levels increase and decrease induced by distant earthquakes were observed in several wells in Israel.  The monitored pressure change in all wells shows significant water level oscillations and sustained water level changes in response to the passage of the seismic waves. The sustained water level changes include short-term (minutes) undrained behavior and longer period (hours and days) drained behavior associated with groundwater flow.  We model the short-term undrained response of water pressure oscillations and sustained change to the distant 2013 Mw7.7 Balochistan earthquake by nonlinear elastic behavior of damaged rocks, accounting for small wave-induced compaction and damage accumulation. We suggest that the rocks are close to failure in most locations and strain oscillations produced by the passing seismic waves periodically push the rock above the yield cap creating compaction when volumetric strain increases and damage when shear strain increases. Compaction increases pore pressure whereas damage accumulation decreases pore pressure by fracture dilation. The dominant process depends on the properties of the rock. For highly damaged rocks, dilatancy is dominant and a sustained pressure decrease is expected. For low-damage rocks, compaction is the dominant process creating sustained water level increase.  We calculate damage and porosity changes associated to the Balochistan earthquake and quantify damage accumulation and compaction during the passage of the seismic waves.