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

Xuan You, Deng Yahong, Chang Jiang, Mu Huandong, Cao Ge

Acta Geophysica

2022

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

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

Acta Geophysica

2018

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.