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2003 | Buch

Modeling earthquakes Kapitel lesen Erstes Kapitel lesen

Earthquake Science and Seismic Risk Reduction

herausgegeben von: Francesco Mulargia, Robert J. Geller

Verlag: Springer Netherlands

Buchreihe : NATO Science Series

Enthalten in: Professional Book Archive

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SUCHEN

Über dieses Buch

What is the first thing that ordinary people, for whom journalists are the proxy, ask when they meet a seismologist? It is certainly nothing technical like "What was the stress drop of the last earthquake in the Imperial Valley?" It is a sim­ ple question, which nevertheless summarizes the real demands that society has for seismology. This question is "Can you predict earthquakes?" Regrettably, notwithstanding the feeling of omnipotence induced by modem technology, the answer at present is the very opposite of "Yes, of course". The primary motivation for the question "Can you predict earthquakes?" is practical. No other natural phenomenon has the tremendous destructive power of a large earthquake, a power which is rivaled only by a large scale war. An earth­ quake in a highly industrialized region is capable of adversely affecting the econ­ omy of the whole world for several years. But another motivation is cognitive. The aim of science is 'understanding' nature, and one of the best ways to show that we understand a phenomenon is the ability to make accurate predictions.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Modeling earthquakes
Abstract
Geophysicists began studying earthquakes long before geophysics existed as a recognized field. Two centuries ago Montessus de Ballore identified crustal faulting as the basic phenomenon of earthquake physics. The picture remained essentially qualitative up to the late 1950s, when Eshelby (1957), Keilis-Borok (1959), Maruyama (1963), Burridge and Knopoff (1964) and Haskell (1964) realized that the faulting problem could be treated quantitatively using methods originally developed by applied mathematicians in the late 1800s to solve engineering problems in metals. The ensuing research progressively developed into the new discipline of ‘quantitative seismology’. This discipline views the crust as a deterministic mechanical system with the following features: (1) the lithosphere is subject to stresses of tectonic and gravitational origin; (2) the lithosphere is brittle, and when these stresses exceed some fixed limit the crust ruptures (i.e., an earthquake occurs), thereby emitting elastic waves; (3) the ruptures are similar to plane dislocations.
Francesco Mulargia, Robert J. Geller
Chapter 2. The classical view of earthquakes
Abstract
The in situ recognition of the evidence of past earthquakes is a task which involves all the branches of geology. Signs of a past earthquake, in fact, can be identified on the landscape morphology and in the rocks generated by fault movements on the fault zone.
Francesco Mulargia, Robert J. Geller
Chapter 3. The physics of complex systems: applications to earthquake
Abstract
We have seen in the previous two chapters that the classical approach to earthquake physics provides an intuitively reasonable model of earthquake occurrence. This theory can be successfully applied to explain the propagation of seismic waves radiated by earthquake sources. However, the classical theory is not able to account globally for the following basic features of earthquake occurrence (cf. section 1.1),
1
Earthquakes are rare events.
 
2
Earthquakes are clustered in both space and time.
 
3
Earthquakes are rupture events which occur mostly on preexisting faults.
 
4
Earthquakes have a quasi-constant stress drop which is, on average, much smaller than ambient stress (Abercrombie and Leary, 1993).
 
5
The external forcing function, i.e. tectonic strain, is small and constant, inducing extremely low strain rates.
 
6
Fault traces are power law distributed in length.
 
7
Faults are rough surfaces, with power law distributed roughness.
 
8
The spatial distribution of hypocentral locations of earthquakes and laboratory acoustic emissions are power law distributed in both space and time (Kagan and Knopoff, 1980; Hirata et al., 1987).
 
9
Earthquakes are power law distributed in size (Gutenberg-Richter law).
 
10
Earthquakes have aftershock sequences that decay with a power law in time (Omori law).
 
11
Seismicity can be induced by stress perturbations smaller than the stress drop of individual events. These may be due to previous earthquakes occurring at relatively great distances (see section 2.6), or to changes in local pore fluid pressure through man-made activity.
 
Francesco Mulargia, Robert J. Geller
Chapter 4. Time-independent hazard
Abstract
Seismic hazard assessment is the estimation of the expected level of ground motion at a site due to the occurrence of possible earthquakes during a fixed future time interval (exposure time). Such estimates require a good knowledge of the relevant seismogenic processes (both in terms of fracture geometries of future earthquakes and of time evolution of tectonic loading), of seismic energy propagation features in the area under study, and of the Earth structure near the site of interest. In fact, the complexity of seismic phenomena requires a modeling capability which is still beyond our reach and would imply in any case the quantification of a large number of relevant parameters dependent on local geological and dynamic conditions. On the other hand, since at least rough seismic hazard estimates are necessary for engineering and regional scale planning in seismic areas, the use of simplified and ‘robust’ approaches is thus necessary.
Francesco Mulargia, Robert J. Geller
Chapter 5. Time-dependent hazard estimates and forecasts, and their uncertainties
Abstract
In section 4.2 we discussed current USGS efforts to estimate both long-term and short-term earthquake probabilities. Here we discuss a number of research topics that may help to improve these probability estimates. While many other topics could be discussed, these are representative of current work at the USGS. All of the work discussed in this section is by USGS authors and their collaborators. This section is not intended as a general review, because a great deal of work done outside the USGS is not covered.
Francesco Mulargia, Robert J. Geller
Chapter 6. Gathering new data
Abstract
Editors’ introduction. We will now discuss how new data may help in solving some of the basic problems that both the classical as well as the PCS (Physics of Complex Systems) approaches leave open. We will analyze separately the time and spatial domains, since palaeoseismic and geodetic techniques allow to tackle them separately. The InSAR geodetic technique, however, is likely to allow to simultaneously resolve the detail in both the time and the spatial domains, at least with regard to the evolution on time scales ranging from a month to several years.
Francesco Mulargia, Robert J. Geller
Chapter 7. Seismic risk mitigation
Abstract
The irregularity and long time intervals between earthquakes are factors contributing to reduced awareness about earthquake risks among the public and government officials and hence to reduced allocation of resources for their mitigation. Moreover, it is not uncommon to see misallocation of resources by non- knowledgeable decision makers and politicians, especially when they act under fear of criticism and public opinion pressures in the aftermath of a catastrophic event. It is therefore up to scientists to help maintain an increased level of awareess about seismic hazards and also to help policy makers understand that seismic risk reduction requires continuous, long-term efforts with a multitude of activities covering all aspects of the problem.
Francesco Mulargia, Robert J. Geller
Chapter 8. Earthquake prediction and public policy
Abstract
As discussed in earlier chapters, estimates of future seismicity are subject to considerable uncertainty. Nevertheless, as earthquakes are a real and present danger to society, governments, companies, and individuals must adopt specific and concrete counter-measures. This is inherently a political process, in that it requires a tradeoff between cost and risk, taking into account the various uncertainties.
Francesco Mulargia, Robert J. Geller
Backmatter
Metadaten
Titel
Earthquake Science and Seismic Risk Reduction
herausgegeben von
Francesco Mulargia
Robert J. Geller
Copyright-Jahr
2003
Verlag
Springer Netherlands
Electronic ISBN
978-94-010-0041-3
Print ISBN
978-1-4020-1778-0
DOI
https://doi.org/10.1007/978-94-010-0041-3