Response of Alaskan wells to near and distant large earthquakes

Abstract

We observed water level changes in groundwater wells in Alaska following the large 2002 Nenana Mountain and the Denali fault earthquakes. Multiple mechanisms must be responsible for the variable temporal pattern and the magnitude of the observed water level changes. For the wells in a consolidated confined aquifer system, poroelastic theory explains the water level changes. However for the wells in a partially confined unconsolidated aquifer, 1) fracture formation due to an earthquake which changes the permeability of the aquifer, or 2) consolidation of the unconfined aquifer in host rock by earthquake induced dynamic strain (liquefaction) are both important mechanisms. For each well the dominant mechanisms are the same for both earthquakes. For the group of wells where dynamic strain is the cause of water level changes, we also observed water level changes due to the 2004 great Sumatra-Andaman earthquakes. Though more than 10000 km away, the Sumatra earthquake induced water level changes that are very consistent with the changes due to the local large earthquakes. Along with the determination of the mechanics of the well water level changes in Alaska, we also determined general hydrological parameters of the wells which can be helpful for future studies.