| Home | Highlights | Intro | Objective | System | More |

Contributions from the Geophysical Approach to Seismic Hazards Reduction

The goal of the geophysical community generally is to provide so-called free-field measurements of seismic activity. Ideally, these data should reflect exclusively the behavior of the ground and not its interaction with large structures. Sites must be selected carefully in order to avoid influence from the built environment (effects of resonance) on the ground motion.

Most of today´s seismic networks can provide data of this sort in near real time. Based on these free-field data, shake maps can be created for a specific event. From these maps, together with databases on the built environment, probabilistic conclusions about the amount of damage to the built environment can be drawn. This is their real value for dispatching safety and rescue squads and sizing and directing regional and national response efforts. Additionally, the threat of landslides and the liquefaction risk can be judged.

Aftershock monitoring

Another side of the geophysical approach is aftershock monitoring. Major earthquakes are followed by numerous aftershocks, of course. Such events typically can be observed with decreasing size and frequency for several weeks or even years. As a rule-of-thumb, earthquakes with a magnitude as high as one point less than the original event´s rating are quite likely in the early days.

With a dense array of seismometers in place, the observation of this prolonged activity along an active fault opens a unique window for the research community. Whenever researchers succeed in collecting these aftershock sequences with a large number of properly placed field instruments, they should be able to extract very precise, three-dimensional information about what is happening below the earth´s surface across the area affected by the events.

Aftershock monitoring offers a chance to better our understanding of the reasons behind and the effects of local seismic activity, thus contributing significantly to preparedness for future earthquakes. This is why seismologists immediately begin to deploy hundreds of field instruments very quickly whenever a major earthquake has occurred somewhere on the globe.

There are other, even more valuable contributions to earthqake hazards reduction originating in geophysics. However, the explanations given so far should provide enough depth for outsiders.

Further information can be obtained from several different websites related to earthquakes.