One of the successes of the PRENLAB project was development of methods for subcrustal mapping of faults based on the algorithm by Slunga et al. (1995). Location of groups of similar, well correlated microearthquakes with relative accuracy of the order of 10 m, even at great depth in the crust, made it possible to map with a great accuracy complicated network of faults within active fault zones. The method has been further developed within PRENLAB-2, with applications in some areas of Iceland, where comparison has been made with geological studies. This method together with the fault plane solutions of microearthquakes is also the basis for using microearthquakes to study crustal instability in fault zones.
A new way of handling the multievent locations has been designed within the PRENLAB-2 project, which makes it possible to treat a large mass of data from a complicated fault system.
This method is suited for automatic on-line analysis where the new incoming microearth-quake events are located in groups together with the previously located events and where the previous results are used. The analysis of the new events may improve all previous locations successively. This new algorithm consists of three main software programs. One correlates the new event with the previously analyzed and defines the group of events based on both location and signal correlation. The second performs the multievent location based on arrival time differences from the correlations and on the absolute arrival times. The third program fits the absolute locations to the previously achieved absolute locations and stores the results in a library.
This method has been installed for testing and routine application at IMOR.DG.