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(October, 31).

************** 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 10月 31日 (木) 13:30~
場所：京都大学 防災研究所 本館E-232D

Date and Time：2024-10-31, 13:30~
Place：Uji Campus Main Building E232D

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Speaker（発表者）1:　Ketzallina Flores Ibarra

Title（題目）:
Study of scaled energy: Mexico, Central America, South America and Noto peninsula

Abstract（要旨）:
Subduction zones are regions where one tectonic plate slides beneath another. This phenomenon generates a variety of earthquakes: interplate, tsunami, intraplate, and deep earthquakes. The different types of subduction zone earthquakes exhibit variations in the frequency content of the seismic energy released (Venkataraman and Kanamori, 2004). For example, tsunami earthquakes (Kanamori, 1972; Polet and Kanamori, 2000) occur in the shallow portions of the subduction zone. Despite their seismological similarities, there is currently no commonly accepted model that describes the structural or morphological conditions around these faults that are conducive to large tsunamis with little ground motion.
Newman and Okal (1998) demonstrated that the scaled energy calculated from observed waveforms is one of the most powerful discriminants for tsunami earthquakes. Tsunami earthquakes typically show scaled energy values ranging from to (Venkataraman and Kanamori, 2004).
The seismic moment and the radiated seismic energy are among the most fundamental macroscopic parameters for understanding the physical processes of earthquake sources. Seismic energy reflects the dynamic characteristics of the earthquake source, while seismic moment captures the static characteristics. The ratio of seismic energy to seismic moment, or scaled energy, can be interpreted as the radiated energy per unit area and per unit slip on the fault plane (Izutani and Kanamori, 2001).
We estimate the radiated seismic energy from teleseismic P-waves using the methodology proposed by Perez-Campos et al. (2003). We calculated the scaled energy of events close to the subduction zones in Mexico, Central America, and South America. Additionally, we estimated the scaled energy for the Noto event (January 1, 2024) and crustal events in the Noto Peninsula. We compared these results to better understand the factors that control scaled energy.

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Speaker（発表者）2:　Yihuan Ruan

Title（題目）:
Investigation of Seismic Velocity Structure beneath Shikoku Island and its Anisotropy by Receiver Function and Ambient Noise

Abstract（要旨）:
Deep low-frequency tremor was first detected in the Nankai subduction zone in south-west Japan. It was found that the broad family of observations associated with slow earthquakes are distributed in the subduction system all over the world. To understand their generation mechanisms and role during the seismic cycle, one way to get a better understanding of the tremor activity and other phenomena is to investigate the Earth's internal structure and anisotropy property in this region. Receiver function (RF) analysis and shear wave splitting are able to estimate the fast polarization direction (FPD) and split time are treated as key parameters for inferring anisotropic properties. However, the intrinsic shortcoming of RF inevitably results in a trade-off between the seismic velocity difference and the thickness between velocity discontinuities. In addition, when RF analysis is used with higher frequency signals, reverb from shallow structures must have an effect on the discontinuity depth, velocity structure and anisotropic property results. The dense distribution of Hi-net stations makes it possible to apply ambient noise surface wave tomography, a technique in seismic interferometry that extracts seismic wave propagation between pairs of stations by cross-correlating the seismic records. We used 2 years of continuous records for the ambient noise analysis to reduce the seasonal effect as much as possible. Due to the nature of the Hi-net sensor, tomography is limited and more sensitive to the shallow velocity structure.

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