Application of Seismic Array Processing to Earthquake Early Warning

Abstract

Earthquake early warning (EEW) systems that issue warnings prior to the arrival of strong shaking are essential in mitigating earthquake hazard. Currently operating EEW systems work on point-source assumptions and are of limited effectiveness for large events, for which ignoring finite-source effects result in magnitude underestimation. Here, we explore the concept of characterizing rupture dimensions in real time for EEW using small-aperture seismic arrays located near active faults. Back tracing array waveforms allow estimation of the extent of the rupture front (as a proxy of the rupture size) and directivity in real time, providing complementary EEW capabilities for M > 7 earthquakes to existing EEW systems. We implement it in a simulated realtime environment and analyze the 2004 M 6 Parkfield, California, earthquake recordings by the U.S. Geological Survey Parkfield dense Seismograph ARray (UPSAR) array and the 2010 M 7.2 El Mayor-Cucapah earthquake recordings by strong-motion sensors in San Diego, California. We find it important to correct for the bias in back azimuth induced by dipping structures beneath the UPSAR array, based on data from smaller events. Our estimated rupture length is 30% shorter than those inferred from other studies but still reasonable for EEW purposes. We attribute this difference to rupture directivity effects and the limited field of view of a single array. The accuracy of the approach may be improved with a network of arrays with overlapping fields of view. We demonstrate this by tracking the 2011 Tohoku earthquake rupture with two clusters of Hi-net stations in Kyushu and northern Hokkaido. The obtained results are consistent with teleseismic back-projection results and yield reasonable estimates of rupture length and directivity. Compared with other proposed finite-fault EEW approaches, the array method is less affected by the coarseness of a Global Positioning System or seismic network and provides a high-frequency characterization of the rupture that yields more suitable predictors of ground shaking for certain structures.

A High‐Frequency Distance Metric in Ground‐Motion Prediction Equations Based on Seismic Array Backprojections

“…Second, BP algorithms (such as beamforming) are simple and do not require heavy computations, such as large‐scale matrix inversions or wave‐propagation simulations. Therefore, BP is easily automated (e.g., IRIS BP products) and well suited for implementation in real time for the purpose of rapid seismic hazard assessment or earthquake/tsunami early warning (An & Meng, ; Meng et al, ). Third, since BP does not attempt to deterministically fit seismic waves and relies only on the coherent phase of seismic array signals, it does not require the detailed knowledge of the Green's functions.…”

Application based seismological array design by seismicity scenario modelling

“…Arrays have a variety of applications, particularly when the signal enhancement is a prerequisite to detect seismic events, and in situations where installing and maintaining sparse networks around the source is impractical. Study and monitoring of nuclear and chemical explosions (Baumgardt & Der 1998;Kim et al 1998), volcanic and non-volcanic tremors (Saccorotti & Del Pezzo 2000;La Rocca et al 2008;Ghosh et al 2009), earthquake swarms (Hiemer et al 2012) and real-time monitoring and early warning systems of active faults (Meng et al 2014) are examples of array applications.…”

A frequency-based parameter for rapid estimation of magnitude

“…Given the occurrence of destructive earthquakes in seismically intensive regions, the resultant human and financial losses, and the scientific inability to predict earthquakes, investigations into earthquake early warning systems (EEWSs), and their development are critical requirements. Accordingly, researchers have recently proposed many approaches to improving EEWS performance [1,3,4,12,14,15,17,26,27,29]. Earthquake records generally contain valuable information on seismic sources [20]; records of the first waves of an earthquake contain information on magnitude, and those of second waves carry information on energy [2,12].…”