Analysis of Seismic Site Effect Associated with State of Neighboring Fracture Zone

Abstract

An earthquake signal contains data of the source transmission path and site effect around the receiving station Convolution of the three effects could constitute a complete seismogram Different seismic events might cause corresponding source and path effects but for a single station that sees little change in its geological substructures the significant frequency will generally remain unchanged Therefore obtaining the signal features that filter out source and path elements could aid understanding of local geological structures Panzera and Lombardo et al (2013) sort the factors that contribute to the site effect into three major categories: (a) effects linked to topographic and morphologic features; (b) effects linked to typology and geometry of sediments; and (c) effects linked to the presence of water landslides structural discontinuities and cavities Most previous researchers focused on the first two factors Additionally analyzing the seismic resonance frequency associated with the presence of specific subsurface structures has recently become topic of interest However to increase the applicability of the site effect this study aims to determine the resonance frequencies related to structural variations This study is divided into three main sections (1) Crack effects on a slope are investigated in Chunrih Township Pingtung County where a 52 m long 5 m deep crack was produced by the 2009 typhoon Morakot Analysis results show a notable band at 14 5–17 5 Hz after the disaster (2) The fault movement effect is investigated using long-period earthquake data (1995–2010) from the stations around Chelungpu fault analyzing the change of resonance frequency after the Chi-Chi earthquake Stations neighboring the fault show significant disturbances and station TCU129 shows a gradual shift back to the original state over nine years (3) The applicability of computing site response from the background noise at earthquake stations is assessed Results show this signal could reflect peak frequencies as S-wave bands but most data are limited by an insufficient SNR thus practicalities need further discussion This study has demonstrated the potential of these methods in assessing the states of near-field discontinuities directly using earthquake data

Date of Award	2015 Jan 29
Original language	English
Supervisor	Ting-To Yu (Supervisor)