Advances in Earthquake Prediction

Since the beginning of seismology 100 years ago it has been the hope of seismologists to be able to predict earthquakes in order to help populations across the globe avoid destruction and casualties. Nonetheless, earthquakes continue to occur without warning.

The decision to set up an international earthquake prediction research project in Iceland was taken in the 1986–1988 timeframe, a period characterized by growing pessimism worldwide about the possibilities for earthquake prediction research.

The multiplicity of observable crustal processes in Iceland has made the country a good natural laboratory for multinational earthquake prediction research. Using Iceland as a natural laboratory for such research is based on the favorable geological or tectonic conditions found in Iceland. Little by little, the availability of the necessary technology for observations and the high level of geological and geophysical research is being built up to complement the natural facilities.

This chapter comprises 11 sections describing large earthquakes that occurred in the South Iceland Seismic Zone in 2000. The chapter looks at how they were predicted and how they could have been predicted. Section 4.12 describes an earthquake in 2008 also in the SISZ.

Stefánsson and Halldórsson (1988) proposed that there was interplay between local intrusions of fluids from below the brittle crust in the South Iceland Seismic Zone (SISZ) and strain buildup by plate motion and release in earthquakes. This was called the ‘‘dual-mechanism model’’ (described briefly in Chapter 3). This made a lot of sense for Iceland with its volcanism. However, in volcanic rift zones earthquakes are frequent, but small, rarely larger than around magnitude 5. Dyke intrusions there result in land deformation, volcanic eruptions, and areas of fumarolic high-temperature activity, which quickly and effectively release strains at seismogenic depths in the crust and do not lead to large earthquakes. This was in stark contrast with the non-volcanic transverse zones of Iceland where day-to-day seismicity is low but large earthquakes occur at long intervals. The dual-mechanism model could explain many observed seismic patterns in the transverse zones but it was not well constrained physically. It was revived at a meeting of the PRENLAB group in 1999 (Stefánsson, 1999) as it was considered to be a more robust physical model.

Efforts to predict earthquakes started long before seismology and seismometers. Earthquakes were like monsters hiding deep below the surface, waking up, and breaking out of their grottos when we least expected them. Often they were preceded by tremors which were felt by people or animals (which are more sensitive to tremors) or some other phenomena related to the waking up of the giant. For thousands of years stories were told over and over again about such phenomena. When people sensed phenomena like those described in the stories they feared an earthquake was approaching and sometimes reacted to save themselves from its effects. These predictions were not based on physical understanding of the causes of the earthquakes, but on observing similar phenomena as had been observed before in relation to earthquakes.

Warnings of impending earthquakes are made on various timescales and for various purposes. In some cases a warning may lead to better observation of a particular area. In other cases a warning may lead to rescuing people from houses that may be vulnerable to the expected hazard. In countries where destructive earthquakes are the norm, there needs to be continuous interactive communication between geoscientists and government bodies regarding observation, prediction, and selection of the most appropriate steps to be taken to mitigate risks. Warnings may involve assessing the effects of a destructive earthquake in a particular area. Earthquake warning may involve assessing which fault will most probably rupture next inside a seismic zone. Warnings may be time-dependent (i.e., indicating on a short-term or long-term basis the imminence of an earthquake).

Since 1988 the South Iceland Seismic Zone (SISZ) has been a test area for multinational and multidisciplinary earthquake prediction research. The basic objective of various research projects has been to study the physical processes leading to large earthquakes. Chapter 2 contains a short overview of the projects. The hope is that the experience gained in the SISZ will be applied at the many places of the world prone to dangerous earthquakes.