日本地球惑星科学連合2016年大会

講演情報

ポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS30] 地震活動

2016年5月25日(水) 17:15 〜 18:30 ポスター会場 (国際展示場 6ホール)

コンビーナ:*林 能成(関西大学社会安全学部)

17:15 〜 18:30

[SSS30-P08] 相互相関を用いた地震波形解析の検出基準の設定

*豊本 大1川方 裕則2平野 史朗2土井 一生3 (1.立命館大学理工学研究科、2.立命館大学理工学部物理科学科、3.京都大学防災研究所)

キーワード:前震、相互相関、検出基準

Recently, small foreshocks have been frequently detected using a cross-correlation technique (e.g., Bouchon et al., 2011, Science). For inland earthquakes, foreshocks whose hypocenters were estimated to be adjacent to the mainshock hypocenter were detected from several tens of minutes before the main shock occurrence (Doi and Kawakata, 2012, GRL; 2013, EPS). Toyomoto et al. (2015, SSJ) tried to detect foreshocks of an M 5.4 earthquake in central Nagano prefecture on June 30, 2011, in a similar manner to Doi and Kawakata (2013). Using the continuous waveforms of the vertical component at N.MWDH (Hi-net) station (the epicentral distance of the mainshock is 4.5 km), they newly detected 14 foreshocks with a cross-correlation criterion of 0.6, in addition to 27 foreshocks listed in the JMA (Japan Meteorological Agency) unified hypocenter catalogs. To efficiently detect small foreshocks for other inland earthquakes, it is necessary to design how to set the cross-correlation detection criterion for foreshock detection.
In this study, we carried out foreshocks detection of the same earthquake in the same method as Toyomoto et al. (2015, SSJ) using the waveform record of N.MNYH (Hi-net) station (epicentral distance of main shock is 5.3km). In this case, the maximum correlation coefficients during one minute tended to be higher than those for records at N.MWDH station, and the result of detection strongly depends on a threshold employed in a cross-correlation method. This indicates that we should not use a universal threshold independent of data. One of alternative way is to use the standard deviation of cross-correlation coefficients. Then, we made a histogram of the cross-correlation coefficients of 1-day data. The histogram of N.MWDH data is Gaussian and the cross-correlation coefficients obey a normal distribution with the average of zero. Although the histogram of N.MNYH data is not Gaussian, so the cross-correlation coefficients have a large-deviation. In such a case, a criterion depending on the standard deviation is inadequate.
Acknowledgments:
We used continuous waveform records of NIED high-sensitivity seismograph network in Japan (Hi-net) and the JMA unified hypocenter catalogs.