Natural hazards and self-organized criticality

Several natural hazards, e.g., earthquakes, landslides, rockfalls and forest fires, have strikingly similar frequency- magnitude relations (event size statistics), namely power-law distributions. The similar frequency-magnitude relations of these obviously different phenomena suggest that there is a unifying concept on a more fundamental level. The framework of self-organized criticality (SOC) which was introduced nearly 20 years ago seems to be the most promising candidate for such a unifying concept. SOC has been recognized in some rather simple computer models. The three most widespread models of SOC may be related to earthquakes, rockfalls and forest fires which supports the idea of SOC as a unifying concept behind several natural hazards. These models show some degree of universality, which means that the frequency- magnitude relations hardly depend on process parameters and boundary conditions. However, this result hinges on self-organization, which means that, independent of the initial conditions, the system organizes towards a certain (critical) state (adjusted to parameters and boundary conditions) where a certain frequency-magnitude is maintained. In theoretical research on SOC systems only this state is considered, but this is not necessarily reasonable with respect to natural hazards. If parameters or boundary conditions (e.g. climate) change, it takes some time (perhaps up to several thousand years) until the system has reorganized to recover its original frequency-magnitude relation. During the phase of reorganization, the frequency-magnitude relation of the occurring events may strongly deviate from the expected one. The project concerns these phases of reorganization by means of numerical simulations of the three most widespread models of SOC. As a result, variations in the frequency-magnitude relation arising from different types of changes in boundary conditions and parameters are determined. Finally, the results shall help to find out how frequency-magnitude relations of several natural hazards may evolve in future, and what actually observed distributions tell us about parameter changes in the past.

Several natural hazards, e.g., earthquakes, landslides, rockfalls and forest fires, have strikingly similar frequency- magnitude relations (event size statistics), namely power-law distributions. The similar frequency-magnitude relations of these obviously different phenomena suggest that there is a unifying concept on a more fundamental level. The framework of self-organized criticality (SOC) which was introduced nearly 20 years ago seems to be the most promising candidate for such a unifying concept. SOC has been recognized in some rather simple computer models. The three most widespread models of SOC may be related to earthquakes, rockfalls and forest fires which supports the idea of SOC as a unifying concept behind several natural hazards. These models show some degree of universality, which means that the frequency- magnitude relations hardly depend on process parameters and boundary conditions. However, this result hinges on self-organization, which means that, independent of the initial conditions, the system organizes towards a certain (critical) state (adjusted to parameters and boundary conditions) where a certain frequency-magnitude is maintained. In theoretical research on SOC systems only this state is considered, but this is not necessarily reasonable with respect to natural hazards. If parameters or boundary conditions (e.g. climate) change, it takes some time (perhaps up to several thousand years) until the system has reorganized to recover its original frequency-magnitude relation. During the phase of reorganization, the frequency-magnitude relation of the occurring events may strongly deviate from the expected one. The project concerns these phases of reorganization by means of numerical simulations of the three most widespread models of SOC. As a result, variations in the frequency-magnitude relation arising from different types of changes in boundary conditions and parameters are determined. Finally, the results shall help to find out how frequency-magnitude relations of several natural hazards may evolve in future, and what actually observed distributions tell us about parameter changes in the past.