With the help of numerical simulations we show that the established Olami-Feder-Christensen earthquake model exhibits sequences of foreshocks and aftershocks; this behavior has not been recognized in previous studies. Our results are consistent with Omori's empirical law, but the exponents predicted by the model are lower than observed in nature. The occurrence of foreshocks and aftershocks can be attributed to the nonconservative character of the Olami-Feder-Christensen model.

Abstract.From landslide mapping it is known that the frequency of landslide occurence as a function of their magnitude can be described by a power law in many regions. In order to investigate the magnitude distribution of landslides from a theoretical point of view, we present a physically based landslide model combining aspects of slope stability and mass movement. If the long term driving processes (fluvial or tectonic) are integrated, the model shows self-organized criticality (sac). The results coincide with results obtained from landslide mapping, so that our model suggests that landsliding may be seen as a sac process. In contrast to other models showing sac that are mostly based on cellular automata, our model is based on partial differential equations. The results show that SOC is not a fashion of cellular automata, but can also occur in differential equation models.

[1] Hydraulic lift is the transport of water from moist into drier soil layers through plant root systems: Plant roots sometimes do not only take up water but also release water if the soil is dry. Hydraulic lift has been shown for a relatively small number of species, but it is believed to be a more general phenomenon. We model numerically water uptake and two-dimensional water transport through the soil and through the root system as coupled processes. Both water uptake and transport through the root system are considered to be hydraulic processes; osmotic effects are neglected. The model is capable of tracing hydraulic lift; the simulated amount of shifted water is consistent with experimental data. This supports the theory that hydraulic lift is a pure hydraulic process without an osmotic component. Furthermore, we discuss how far hydraulic lift could be an optimized strategy for the plant.

[1] In continental rift zones, thermal anomalies and enhanced occurrence of mantlederived fluids in groundwaters often coincide on a continental but rarely on the local scale. For areas of recent intraplate volcanism this suggests a time shift between the transport of mantle-derived volatiles and heat to the Earth's surface. As a particularly illustrative example, we studied the central European Rhine graben, which is distinguished by extensional tectonics, high seismicity, young, Upper Tertiary volcanism, abundant mineral water springs, and a heat flow anomaly. A combination of thermal, helium isotope, and major element data of mineral waters with numerical simulations of flow and heat transport leads to a profound understanding of crustal-scale transport processes and allows a clear distinction between diffusion and flow dominated regimes. The simulations show that for a crustal-scale system the transition between these two regimes occurs within one decade of permeability (10 À16 -10 À17 m 2 ). Flow is likely to be strongly controlled by fault systems both in the lower and upper crust. While thermal anomalies highlight fluid circulation within the upper brittle crust, mantle-derived volatiles provide information on transport phenomena from lower crustal sections. The thermal and hydro-chemical anomalies in the Upper Rhine graben are directly related to mass flow rates. Therefore lack of thermal anomalies around the Kaiserstuhl volcano suggests that mass flow rates must be very small, while positive thermal anomalies in the central part of the graben can directly be related to advection of fluids into basin sediments and to redistribution of heat within these sediments. Citation: Clauser, C., E. Griesshaber, and H. J. Neugebauer, Decoupled thermal and mantle helium anomalies: Implications for the transport regime in continental rift zones,

We present a cellular automaton approach involving two variables and investigate its behavior with respect to self-organized criticality ͑SOC͒. It can be seen as a generalization of the Bak-Tang-Wiesenfeld and OlamiFeder-Christensen models and exhibits SOC behavior, too. In contrast to these models it leads to a power law distribution of the cluster sizes with an exponent close to one, as it occurs in earthquakes and landsliding processes, without any tuning.PACS number͑s͒: 05.65.ϩb, 0.5.45.Df, 91.30.Px