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Dynamic characteristics of fault-controlled earth fissure sites in Jingyang County, Weihe Basin, China

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Xuan Y. , Deng Y. , Chang J. , Mu H. , Cao G.

Acta Geophysica

2022

tom Vol. 70, no 4

1687--1700

Jingyang County is located in the northern part of the Weihe Basin, which is an important part of the Fen-Wei graben system. Nearly half of earth fissures located in northern Jingyang County have East–West orientations that match the orientation of the nearby Kouzhen–Guanshan active fault. In order to analyze the superficial structures and dynamic characteristics of earth fissures, we conducted trenching and microtremor testing at two earth fissure sites that are largely controlled by activity along the Kouzhen–Guanshan fault. Our main results are as follows: (1) The presence of earth fissures has little to no effect on the predominant frequencies and natural periods that excite the maximum response acceleration during a microtremor. (2) Three specific amplitudes, including the Fourier amplitude at the predominant frequency, the maximum response acceleration, and the Arias intensity, are smaller at site 1 than they are at site 2. (3) Amplification occurs at both earth fissure sites. These three amplitudes have high values at distances less than ~6 m from the crack, attenuated values at distances of ~6–20 m from the crack, and low stable values at distances greater than~20 m away from the crack. (4) We calculated the amplification factors for these two earth fissure sites and identified regions that experience varying degrees of this amplification. Based on our analysis, we recommend seismic fortification for buildings in areas affected by these earth fissure sites.

Simulation of the Microtremor H/V Spectrum Based on the Theory of Surface Wave Propagation in a Layered Half-space

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Zhang Z. , Chen X. , Gao M. , Li Z. , Li Q.

Acta Geophysica

2018

tom Vol. 66, no. 2

121--130

Subsurface velocity structures must be estimated to predict longperiod ground motions and seismic hazards. Subsurface velocity structures can be constructed via an inversion of the horizontal-to-vertical (H/V) spectral ratio of microtremor (MHV) curves; thus, a method of simulating the MHV curves is key. In this study, we use the H/V spectral ratio of the surface wave (SHV) based on the surface wave propagation theory in a layered half-space to simulate the MHV curves at sites A and B of the Yuxi basin. Then, we attempt to analyze the features of the SHV curves. We find the H/V ratio of the microtremor loading source to be independent of the peak frequency of the SHV curve, but it has some relation to the amplitude of the SHV curve. Moreover, to reduce the error in subsurface velocity structures obtained by the MHV curves, we suggest that the SHV curves at near-peak frequencies should not be considered in the inversion, because the amplitude deviation is higher at the peak frequency of the MHV curve. In addition, the best frequency ranges for the inversion of the microtremor H/V spectrum are between the peak and trough frequencies of the microtremor H/V spectrum.

Geophysical investigation on the subsoil characteristics of the Dendam Tak Sudah Lake site in Bengkulu City, Indonesia

84%

Mase L. Z. , Amri K. , Ueda K. , Apriani R. , Utami F. , Tobita T. , Likitlersuang S.

Acta Geophysica

2024

tom Vol. 72, no. 2

893--913

Bengkulu City in Indonesia is one of the areas prone to earthquakes, yet it has developed increasingly in the last five years. One of the prospective areas in Bengkulu City, called Singaran Pati, is located close to the Dendam Tak Sudah Lake, a natural tropical lake. This research aims to interpret geological characteristics for the spatial plan development in the study area. Microtremor measurement and site investigation are implemented to observe the geophysical and geological characteristics of the study site. Inversion analysis using Monte Carlo simulated annealing is conducted to generate a shear wave velocity profile. Based on the shear wave velocity, the identified bedrock surface is illustrated in a 3D geological model. A simple analysis of the natural period to estimate allowable structural building storeys is also performed. Results show that the depth of the bedrock surface is around 4.5-147 m. The study area is dominantly categorised as Site Classes C and D. Low- to medium-rise buildings are appropriate to construct based on the geophysical and geotechnical information. The findings can provide preliminary guidelines on geotechnical and geological information for the seismic site conditions in the study area in Bengkulu City.