Ground‐Motion Forecasting Using a Reference Station and Complex Site‐Response Functions Accounting for the Shallow Geology

Abstract

The distribution of damage due to recent earthquakes has shown that the effects of shallow geological structures on the level of ground shaking represent an important factor in engineering seismology. Whereas many previous studies have estimated site amplification factors in the frequency domain, their application to the realtime modeling of ground motion is not yet fully established. In this article, a method for the real-time correction of frequency-dependent site-response factors is proposed, which accounts not only for the modulus, but also for the changes in the signal phase related to local site conditions. The transformation of the complex standard spectral ratios to a causal recursive filter in the time domain allows for the forecasting of the waveforms for soft-soil sites almost in real time when the signal is recorded earlier at a reference site. When considering travel-time differences of the various seismic phases between the hypocenter and the studied sites, the level of ground motion at soft-soil sites with respect to arrival time, energy, duration, and frequency content can be well constrained, even in cases of a high spatial variability of the amplification patterns.

Real-Time Prediction of Impending Ground Shaking: Review of Wavefield-Based (Ground-Motion-Based) Method for Earthquake Early Warning

“…As | A 2 ( f )/A 1 ( f )| is expressed in the frequency domain, it may be possible to apply a fast Fourie transform (FFT) with a short time interval (i.e., every 1 s or less) to ongoing waveforms at site 1, multiply them by |A 2 ( f )/A 1 ( f )|, and then perform an inverse FFT to predict ongoing waveforms at site 2 (Figure 5). Instead of methods in the frequency domain, a method in the time domain was proposed (Hoshiba, 2013b;Pilz and Parolai, 2016), in which a causal recursive filter, which allows correction of site amplification factors in real time, is used. The time domain filter alleviates computational workload of the system, comparing with that of the frequency domain analysis, and makes it easy to estimate continuously sitecorrected waveforms regardless of whether earthquakes are occurring or not.…”

“…Ogiso et al (2016) evaluated the relative site amplification factors of more than 2,200 stations in Japan and obtained their IIR filters, and Xie et al (2019) also applied this technique. Pilz and Parolai (2016) extended this method to include phase characteristics.…”

Basin-edge generated Rayleigh waves in the Almaty basin and corresponding consequences for ground motion amplification

“…In turn, the measured group delay depends slightly on the nature and amplitude of the signal but, more significantly, on its SNR. Further details can be found, for example, in Beauval et al (2003) and Pilz & Parolai (2016).…”