Abstract
Due to changes in the Earth’s climate, the Earth has experienced colder periods, which generated the growth of continental ice sheets at higher latitudes. The build up of an ice sheet induces flexural stresses in the lithosphere and mantle affecting the stability of pre-existing faults. During and after the end of deglaciation, these faults are activated and the flexural stresses are released as earthquakes. The last ice sheet in North America started to melt 20ka ago, and was gone by 6ka. Here, (re-)activated faults were found, which show vertical fault scarps of up to 100m. As moderate seismicity is observed in North America now, it is of major societal and economic importance to investigate the relationship of this activity to the ongoing rebound.
The extended seismological network in northeastern Canada gives us the possibility to analyze local seismicity in more detail than previously possible. Thrust-faulting mechanisms are estimated for five moderate earthquakes that occurred in northern Hudson Bay, and the related stress is NW-SE directed. Comparing this stress direction to results from rebound models and the general background stress field with NE-SW directions, a large difference is found, which might be due to a local fault zone disturbing the main stress field.
This study presents an improved two-dimensional rebound model including a fault, which is able to move in a stress field consisting of rebound stress, and horizontal and vertical background stresses. The sensitivity of this fault is tested regarding lithospheric and crustal thickness, viscosity structure of upper and lower mantle, ice-sheet thickness and width, and fault parameters including coefficient of friction, depth, angle and location. Fault throws of up to 64m are obtained using a fault of 30° dipping below the ice-sheet centre. Thicknesses of the crust and lithosphere are two of the major parameters affecting the total fault throw. The ice-sheet width has an impact on the activation time. Even steep-angle faults can be activated. Most faults start to move close to the end of deglaciation, and movement stops after one thrusting/reverse earthquake. However, certain conditions may also lead to several fault movements after the end of glaciation.
