今週のうなぎセミナーについてお知らせいたします。

Here is information of the Unagi-seminar(November, 7).

************** Seminar on Seismology IV B, D /地震学ゼミナールIV B, D (Unagi Seminar) **************

科目：地震学ゼミナールIV B, D / Seminar on Seismology IV B, D（修士・博士）
日時：2024年 11月 7日 (木) 13:30~
場所：京都大学 防災研究所 本館E-232D

Date and Time：2024-11-07, 13:30~
Place：Uji Campus Main Building E232D

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Speaker（発表者）:　Yuki Funabiki

Title（題目）:
Estimating focal mechanism of small earthquakes using S/P amplitude ratio of Distributed Acoustic Sensing records

Abstract（要旨）:
We propose a method for estimating focal mechanisms based on S/P amplitude ratios from Distributed Acoustic Sensing (DAS) records for single earthquakes, and successfully obtained the mechanisms of four events. This method involves identifying Cycle-skipping Channels, relocating epicenter distribution with hypoDD, and searching for the parameters of the focal mechanism with measuring the maximum amplitude ratio between the S-wave and P-wave of DAS records. First, we identified Cycle-skipping Channels focusing on "phase-jumps" of more than +π or less than -π at successive times. Next, we redetermined epicenter location by performing cross-correlation on the same channel for different events, then cross-correlating the obtained cross-correlation functions between nearby channels. The resulting travel-time differences were then introduced into hypoDD. Afterward, we searched for the parameters of the focal mechanism with measuring the maximum amplitude ratio between the S-wave and P-wave of DAS records.
We applied this method to DAS records of four shallow earthquakes ranging from M2.2 to M3.4 that occurred in central Japan. The estimated mechanisms were consistent with the distribution of P-wave polarities from conventional seismometers, despite recording only one component along the cable. This straightforward approach may be effective due to wave scattering caused by near-surface heterogeneities and the varying orientations of cable sections corresponding to the channels. Consequently, the observed scattered waves preserve the overall radiation patterns, allowing us to obtain radiation patterns from a single-component record.

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