Effect of ice sheet growth and melting on the slip evolution of thrust faults

Field investigations suggest that postglacial unloading and rebound led to the formation or re-activation of reverse faults even in continental shields like Scandinavia. Here we use finite-element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading. The model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation. The magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet, the viscosity of the lithospheric layers and the long-term shortening rate. In contrast, the width of the ice sheet, the rate of deglaciation or the fault dip have an only minor influence on the slip evolution. In all experiments, the slip rate variations are caused by changes in the differential stress. The modelled deglaciation-induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the Fennoscandian ice sheet, which led to the formation of spectacular fault scarps in particular in the Lapland Fault Province. Furthermore, our model results support the idea that the low level of seismicity in currently glaciated regions like Greenland and Antarctica is caused by the presence of the ice sheets. Based on our models we expect that the decay of the Greenland and Antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions.     

The Contribution of Landslide Susceptibility Factors Through the Use of Rock Engineering System (RES) to the Prognosis of Slope Failures: An Application in Panagopoula and Malakasa Landslide Areas in Greece

This paper presents an application of the rock engineering system (RES) in an attempt to assess the proper landslide parameters and estimate the instability index, using two disastrous landslides in Greece which took place in Panagopoula (1971) and Malakasa (1995). RES has been developed by Hudson (Rock engineering systems: theory and practice. Ellis Horwood Limited, 1992) to determine interaction of a number of parameters in rock engineering design and calculate instability index for rock slopes. In this paper, an attempt is made to prove, how RES can be implemented in large-scale instability areas where natural slopes are associated with a variety of geomaterials (soils, rocks, weathering mantle, etc.), by selecting each time the most appropriate parameters that are relevant to the ad hoc potential slope failure and which can be quantified easiest than those of time and money consuming ones. RES approach allows the utilization of those parameters which are particularly active at the site, evaluates the importance of their interactions, taking into account the particular problems at any investigated site. The instability index for both study areas were calculated and found 89.47 for Panagopoula site and 81.59 for Malakasa (out of 100). According to the classification for landslide susceptibility by Brabb et al. (Landslide susceptibility in San Mateo County, California, 1972), both the examined case studies are classified as landslides, approving their existence as two serious slope failures. Thus, RES could be a simple and efficient tool in calculating the instability index and consequently in getting the prognosis of a potential slope failure in landslide susceptible areas, for land use and development planning processes.     

Application of MODFLOW for simulating groundwater flow in the Trifilia karst aquifer, Greece

Karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features. As a result, a three-dimensional finite-difference groundwater flow model (equivalent porous media) may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated. Statistical analysis of karst hydrographs of the Trifilia aquifer in Greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow. An equivalent porous media model was developed to simulate the Trifilia karst aquifer using MODFLOW. Steady state and transient state calibration gave encouraging results for the equivalent porous media approach, which does not consider pipe flow or turbulence. Detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent; and flux to/from the aquifer. Only hydraulic conductivity and specific yield were adjusted during calibration, as the flux to/from the system was considered known and applied as boundary conditions. Small mean absolute and RMS piezometric head error of the model under both steady and transient state conditions were achieved.