Abstract
The Geological Survey of Israel has upgraded and expanded the national Israeli Seismic Network (ISN), with more than 110 stations country-wide, as part of the implementation of a governmental decision to build a national Earthquake Early Warning (EEW) system named TRUAA. This upgraded seismic network exhibits a high station density and fast telemetry. The stations are distributed mainly along the main fault systems, the Dead Sea Transform, and the Carmel-Zfira Fault, which may potentially produce Mw7.5 earthquakes. The system has recently entered a limited operational phase, allowing for initial performance estimation. Real-time performance during eight months of operation (41 earthquakes) matches expectations. Alert delays (interval between origin-time and Earthquake Early Warning alert time) are reduced to as low as 3 s, and source parameter errorstatistics are within expected values found in previous works using historical data playbacks. An evolutionary alert policy is implemented based on a magnitude threshold of Mw 4.2 and peak ground accelerations exceeding 2 cm/s2. A comparison between different ground motion prediction equations (GMPE) is presented for earthquakes from Israel and California using median ground motion prediction equations values. This analysis shows that a theoretical GMPE produced the best agreement with observed ground motions, with less bias and lower uncertainties. The performance of this GMPE was found to improve when an earthquake specific stress drop is implemented.
Highlights
Earthquake Early Warning Systems (EEWS) are a tool to reduce earthquake risk
The results show that the EEW algorithm performance in real-time is as expected and that decision makers may rely on these findings to determine the alert approach for Israel
We focus on the median predictions of the ground motion prediction equations (GMPE), neglecting their uncertainties, since the EEW alerts are binary—either alert or not and these GMPEs uncertainties cannot be considered in real-time
Summary
Earthquake Early Warning Systems (EEWS) are a tool to reduce earthquake risk. Their basic approach is to issue an alert as soon as possible following the occurrence of an earthquake, before damaging seismic waves arrive at a target. We attempt to assess the expected performance of the EEWS in terms of alert-delays and source parameter accuracy (location, origin-time and magnitude) by analyzing statistics of the available data between May 2020 and January 2021.
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