Keiiti Aki - Böcker

This book provides a unified treatment of seismological methods that will be of use to advanced students, seismologists, and scientists and engineers working in all areas of seismology.

For many centuries people living on volcanoes have known that the outset of seismic activity is often a forerunner of a volcanic eruption. This understand­ ing allowed people living close to the sites of the Mt. Nuovo 1538 eruption at Campi Flegrei, Italy, and of the Mt. Usu 1663 eruption, in Hokkaido, Japan (to quote only two examples) to flee before the eruptions started. During the second half of the 19th century seismographs were installed on some volcanoes, and the link between seismic and eruptive activity started to be assessed on a firmer scientific basis. The first systematic observations of the correlations existing between seismic activity and volcanic eruptions were probably those carried out at Mt. Vesuvius by Luigi Palmieri in 1856. Palmieri was the Director of Osservatorio Vesuviano and built an electromagnetic seismograph with the aim of "making visible the smallest ground motions by recording them on paper and indicating direction, intensity and duration". He was able to show the relationship between earthquakes and the different phases of volcanic activity. He identified the harmonic tremor which he indicated was a precursor of volcanic activity: "the characteristic feature of the ground mo­ tions preceding eruption is its continuity . . . (before the eruption of 1861) the electromagnetic seismograph began to show a continuous tremor". The Palmieri seismograph was also utilized in Japan until 1883, when it was replaced by the new Gray-Milne seismographs, and, later, by the Omori in­ struments.

Geodynamics is concerned with the dynamics of the global motion of the earth, of the motion in the earth's interior and its interaction with surface features, together with the mechanical processes in the deformation and rupture of geological structures. Its final object is to determine the driving mechanism of these motions, which is highly interdisciplinary. In preparing the basic geological, geophysical data required for a comprehensive mechanical analysis, there are also many mechanical problems involved, which means the problem is coupled in a complicated manner with geophysics, rock mechanics, seismology, structural geology, and so forth. This issue is Part I of the Proceedings of an IUTAM/IASPEI Symposium on Mechanics Problems in Geodynamics held in Beijing, September 1994. It addresses different aspects of mechanics problems in geodynamics involving tectonic analyses, lithospheric structures, rheology and the fracture of earth media, and mantle flow, either globally or regionally, and either by forward or inverse analyses or numerical simulation.