Earthquake Early Warning System in Israel—Towards an Operational Stage

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 Mw 7.5 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.

Harnessing Distributed Acoustic Sensing for Earthquake Early Warning: Magnitude Estimation and Ground Motion Prediction

“…The same analysis for the largest earthquake in the dataset, a magnitude 5.7, is shown in Supplementary Fig. (2); for this earthquake, strain-rate amplitudes exhibit some saturation (See Discussion). The real-time slant-stack approach resolves the apparent velocities of the different seismic phases:…”

“…Stress drop, Δτ, is a fundamental earthquake source parameter that strongly affects ground motion intensities 36,[39][40][41] (See "The relation between earthquake source parameters and ground motions" in Methods). For optimal ground motion prediction, both magnitude and stress drop should be determined, as demonstrated by recent studies 2,30,32,36 . Since in this framework we only use one ground motion metric, i.e., ground accelerations rms, Arms, we may only estimate the magnitude (see "Magnitude estimation from bandlimited ground accelerations" in Methods)…”

“…While earthquake prediction remains out of reach, continuous seismic monitoring has enabled earthquake early warning (EEW) systems that provide alerts to population centers and critical infrastructure seconds to tens of seconds before intense ground shaking is felt [1][2][3][4] .…”

Accurate Magnitude and Stress Drop Using the Spectral Ratios Method Applied to Distributed Acoustic Sensing

“…The inversion produced stable earthquake specific seismic moments (Figure S4 in Supporting Information S1). Stress drops were then estimated via Equation 2 using the different corner frequencies, k = 0.21 (Madariaga, 1976) and Cs = 3.2 km/s (Nof et al, 2021). Event averaged source parameters are listed in Table S1 in Supporting Information S1.…”

Improved Resolution and Cost Performance of Low-Cost MEMS Seismic Sensor through Parallel Acquisition

“…The propagation of the local undamped motion (PLUM) algorithm [ 9 ] has undergone substantial refinement and testing in Japan [ 2 ]. Mexico, Japan, South Korea, and Taiwan have all established earthquake early warning systems (EEW systems) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]; Turkey, Romania, Italy, China, Israel, and southwestern Iberia are on the verge of developing and testing their own seismic intensity rapid reporting systems [ 10 , 14 , 23 , 24 , 25 , 26 , 27 , 28 ]. The working principle of an EEW system is usually based on the idea that P-waves are faster than destructive S-waves.…”