Title of research project: Application of Dynamical Systems to Earthquake Prediction

Number of grant: EAR-9423818

Period of performance: 3 year; from 1 April 1995 to 31 March 1998

Project Coordinator: Prof. D. Turcotte (Cornell University)

Principal Investigator: Prof. V. Keilis-Borok

Executive Summary:

MATHEMATICAL MODELS

- It was proved that the theoretical curves of scaling exponents in turbulence for the Kolmogorov inertial range have a bifurcation point, because the ergodic hypothesis breaks down.

- Hierarchical models displaying different kinds of self- organized criticality (SOC) were investigated. For simple hierarchical models various combinations of SOC, catastrophe and stability were observed and described. Also, the predictability of strongest events in a hierarchical model with two types of movement was investigated. This predictability essentially depends on parameters of the model.

MODELS AND PHENOMENOLOGY

- It was found by analysis of the aftershocks of large earthquakes of the Southern California and Japan that the aftershocks behave in a much more complex manner over time than required by the well-known Omori law and the models proposed by Ogata (1988) and their actual sequences had a fractal structure.

- Main patterns in the characteristics of synthetic seismicity produced by simulating simple types of tectonic movements were detected.

- Effects of viscous flow, phase transition, and dehydration on the stress in the relic slab were studied to explain the intermediate-depth seismic activity in the Vrancea region.

- Synthetic seismicity was simulated by numerical modelling of block structure dynamics for three groups of formal structures with increasing of structure separateness inside each group by self-similar way. Two types of boundary movements were considered. When structure separateness increases, the following changes in seismicity features occur for one type of the boundary movement: the total number of events and the number of small events increase; the number of large events decreases; the b-value increases. When the boundary movement of another type are specified, the character of this dependence is altered drastically and is at variance with the accepted opinion.

- Realistic block structures are considered for the Vrancea (Romania) region and for the Western Alps. For the Vrancea region the model parameters, which supply a synthetic earthquake catalog with the space distribution of epicentres close to the one observed in the Vrancea region and the Gutenberg-Richter curve similar to the one obtained with the real catalog were determined. The result of variation of these parameters allow us to state that it is possible to use the procedure of the block- structure dynamics modelling to reconstruct the ranges of some parameters used to describe the real tectonics of the region. It is found for the Western Alps that the change of the direction of motion of the boundary between the Western Alps and the North Apennines has a strong influence on the features of the synthetic seismicity.

- The SOFT (scaling organization and fracture tectonics) model of earthquakes was developed. The Omori law of aftershock rate decay and the seismic cycle were obtained due to the introduction of the redistribution of energy by creep.

- It is shown that seismicity on the Pacific Rim during 1950- 1960s started in the Tonga-New Guinea regions, migrated clockwise along the Pacific Rim with a mean velocity about 2000 km/yr and culminated in the 1960 Chile earthquake. The migration is statistically significant.

TEST OF PREDICTION ALGORITHMS

- It was found by using a modification for lower seismic rate areas of the algorithm known as M8 that large earthquakes in Italy were preceded by a specific activation which could be diagnosed by the algorithm. The analysis of the results from different approaches to earthquake prediction which claimed high probability of large earthquake in advance of Delarof islands earthquake (10 June 1996) was carried out.

- A systematic approach to the assessment of earthquake hazard on a global basis was proposed: the data on earthquakes of magnitude 4 and above and the Gutenberg-Richter frequency- magnitude scaling are utilized to estimate the probability of occurrence of larger earthquakes.

- A tentative intermediate-term earthquake prediction algorithm base on observable transformations in the Gutenberg-Richter law was developed and successively applied to predict great earthquakes along the Pacific ring. An optimal magnitude range of predicting events was found by examination of results from a monitoring of the CN algorithm as applied to 22 seismic regions.

SEISMIC RISK

- A new hierarchical approach is put forward to describe the frequency-magnitude (FM) relation in problems of seismic risk analysis and has been implemented for Italy and the Caucasus. The approach calls for seismic zonation at different scales which are related to the conditions for similarity of seismic events and to the linearity of the FM relation in the relevant magnitude range.

SEISMIC SOURCE AND THE STRESS FIELD

- New methods in the determination of seismic source parameters from body and surface waves spectra were developed, translated to computer codes and applied to a few recent large earthquakes in some regions of FSU.

GEODYNAMIC MODELS AND RECONSTRUCTIONS

- Mechanisms by which the earth's surface subsides to form basins in the East-European platform were studied. On the basis of observed data it was shown that magmatism-eclogitization mantle flow mechanism is likely to be responsible for the post-Devonian subsidence of the basins. Tectonic subsidence and a model of the Ionian basin evolution were studied.

- For the study of the problem of possible great displacements in ancient subduction zones, a new method for the inverse problem (with limitations) of the reconstruction of plate motion from paleomagnetic data was developed. The estimated speeds of absolute motions of ancient subduction zones could reach 15 cm/yr.