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

Abstract

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 network can be divided into three categories. (1) Single-station analysis performed 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-station analysis done at the center, using the phase reports from the stations and producing information about all detected events including estimates of location, magnitude and fault plane solutions. (3) Alert reporting to notify the operators of the network in cases of a priori defined changes in parameters derived from the single- and multi-station analysis. The system is designed for maximum automatic operation and minimum operational cost and has shown to be capable of automatic evaluation of more then 1000 earthquakes per day or episodically several earthquakes per minute. While no attempt is made to detect and locate teleseismic events, teleseismic data is automatically saved, based on e-mail messages from global seismological networks. Groups of events are analyzed using correlation techniques to obtain accurate 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 regarding the automatic operation of the network. A geographically indexed data base will be created where different classes of earthquakes are 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 first motion direction picks from there. The algorithm is planned to be implemented in late 1999. New methods have been developed to estimate the stress tensor based only on the microearthquake focal mechanisms and accurate relative locations. This is planned to be implemented into the automatic on-line procedures. Methods and related software are being developed for real-time monitoring of fault movements based on the high accuracy locations and fault plane solutions.