Improvement of back-azimuth estimation in real-time by using a single station record

Abstract

We propose a new approach to improve the accuracy of the back-azimuth estimation in real-time by using a single station record. Compared with the conventional approach in which the length of the time window for the analysis is fixed for all data, the accuracy and speed of the estimation are drastically improved by introducing a variable-length time window which is determined by the first half cycle of the wavelength of the initial P-wave, because this window tends to reduce the influences of trailing scattered waves. The analysis, using the K-NET dataset, shows that the estimation, using this new approach, is improved by 28% and 0.25 s in accuracy and speed, respectively.

<b>Improved Algorithms of Seismic Parameters Estimation and Noise Discrimination in Earthquake Early Warning</b>

“…Accuracy of the estimation was also higher when a data length of a half displacement wavelength after P-wave arrival is used instead of the fixed time window. This new technique was called the variable window method [8]. Half wavelength data length can be detected when the displacement wave reaches the first zero-cross timing after the P-wave arrival.…”

“…There are demands at present to improve the function of EEW systems, in order to raise railway safety during earthquakes. Thus a new algorithm for EEW systems was devised, to improve the accuracy of and shorten the time to obtain seismic parameters [7,8]. Weak initial P-wave vibrations are used typically to estimate seismic parameters, thus it is necessary to discriminate clearly between earthquake motion and other vibrations.…”

<b>Development of Seismograph Equipped with Improved Algorithm for Earthquake Early Warning</b>

“…This time window is applied to the Principal Component Analysis so as to obtain a vibration direction of the P-wave. This improves the accuracy and rapidness by 28 % and 23 % respectively [5]. 4) In addition to displacement amplitude, acceleration amplitude is also used to estimate magnitude.…”

“…3) The conventional fixed-length time window method is replaced with the variable time window method [5] for estimating back-azimuth to the epicenter. The variable time window method uses an optimized length of a time window (0.3-1.0 second) for each seismic wave.…”

<b>New Method for Estimating Earthquake Parameters for Earthquake Early Warning</b>

“…These results demonstrate that utilization of a variable time window improves accuracy by approximately 28% in relation to results obtained through the conventional method or by 14% compared with application of the fixed 0.6 second time window (which achieves the highest level of accuracy among fixed time windows). Other detailed analyses about improvements reached by using variable time windows are discussed in reference document [8].…”