What can we learn from aftershocks?

Abstract

From the spatial distribution of aftershocks with respect to the regions of fault slip during the mainshock, information can be gained about the heterogeneous structure within the source volume and about the frictional properties of surrounding faults. Focal mechanisms of aftershocks reveal how stress is redistributed by large earthquakes. While analog data have mainly been used for these studies in the past, a new degree of data quality is obtained with currently available digital recording systems. In addition to the increased accuracy for the determination of purely kinematic data, waveform information can be utilized with digital data. With state-of-the-art signal processing techniques, the contributions of source, path, and site effects on the observed seismic signals can be studied. Provided these effects can be separated, aftershock signals will potentially help us to learn about the properties of fault regions in unprecedented detail. The degree of resolution which can be achieved, however will strongly depend on the number of stations and the geometry of the network employed. Depending on the special scientific problems to be addressed, optimum station geometries may vary. Modern methods in optimization theory, such as simulated annealing, have been successfully used to find optimum station distributions for aftershock monitoring. An additional aspect which has to be addressed is the problem of managing and processing aftershock data. Since high-quality digital data come at the price of huge data volumes, new strategies and concepts for data handling and signal processing have to be developed.