The SIL data acquisition system - at present and beyond year 2000

The South Iceland Lowland (SIL) data acquisition system presently consists of 33 digital, three component seismic stations connected to a common data center. The automatic, on-line, earthquake analysis performed by the SIL ne twork can be divided into three categories. (1) Single-station analysis per formed at the site stations producing information about all incoming phases . A short message with data on the phase is sent to the center. (2) Multi-s tation analysis done at the center, using the phase reports from the statio ns and producing information about all detected events including estimates of location, magnitude and fault plane solutions. (3) Alert reporting to no tify the operators of the network in cases of a priori defined changes in p arameters derived from the single- and multi-station analysis. The system i s designed for maximum automatic operation and minimum operational cost and has shown to be capable of automatic evaluation of more then 1000 earthqua kes per day or episodically several earthquakes per minute. While no attemp t is made to detect and locate teleseismic events, teleseismic data is auto matically saved, based on e-mail messages from global seismological network s. Groups of events are analyzed using correlation techniques to obtain acc urate absolute and relative locations of earthquakes with similar waveforms . In some areas within the network, most of the earthquakes correlate very highly with each other. Based on this a new approach is being taken regardi ng the automatic operation of the network. A geographically indexed data ba se will be created where different classes of earthquakes an stored. As new earthquakes are recorded by the network the system automatically looks for similar waveforms in this data base and, if found, takes the onset and fir st motion direction picks from there. The algorithm is planned to be implem ented in late 1999. New methods have been developed to estimate the stress tensor based only on the microearthquake focal mechanisms and accurate rela tive locations. This is planned to be implemented into the automatic on-lin e procedures. Methods and related software are being developed for real-tim e monitoring of fault movements based on the high accuracy locations and fa ult plane solutions. (C) 1999 Elsevier Science B.V. All rights reserved.