The dynamic response of sites with earth fissures as revealed by microtremor analysis——A case study in the Linfen Basin, China

Abstract

Earth fissures are a major cause for concern worldwide, and an ever-increasing number of geohazards are being caused by fissures. However, the dynamic response of sites with earth fissures is still unclear. With the aim of providing previously lacking advice regarding earthquake fortification in proximity to fissures, this study employed microtremors to estimate the effect of fissures on the dynamic response of a site, taking fissures in the Linfen Basin as its example. Survey lines were laid across four earth fissures in three different regions: the Linfen depression, the Houma depression, and the piedmont of Lvliang Mountain. The time-history acceleration of microtremors was transformed into the Fourier amplitude spectrum, response acceleration, Arias intensity, and H/V spectral ratio. The results show that the frequency contents, including the spectral pattern, bandwidth, and spectral area, are consistent with the conditions in each region. The Fourier amplitude, peak acceleration, Arias intensity and H/V ratio amplitude are significantly elevated near the fissure, falling to the background value by 20 m away from it, whereas the predominant frequencies are independent of distance from the fissure. This change in the amplification factors confirms that earth fissures amplify the dynamic response of the site. A larger range of influence and greater amplification were detected on the hanging side of the fissure. Results from different regions show that the amplification and range of influence vary between regions. On the basis of the results, it is suggested that a higher seismic fortification intensity and a greater setback distance should be adopted at sites with earth fissures.