## 1 Introduction  
Earth fissures are linear tensile fissures with a certain extension length that develop on the Earth's surface and may be accompanied by vertical fissures. They are affected by various complex factors such as internal and external forces and human activities [1]. Earth fissures have developed widely around the world and occur in the United States, Mexico, Africa, Europe, and throughout most of China [2, 3]. Thus, the formation and development of earth fissures seriously affect infrastructure construction and restrict national economies [4]. The study of earth fissures began in 1929 [5, 6], and humans have been studying earth fissures for a century. The first step in preventing and controlling earth fissure hazards is to identify the mechanisms of their formation and evolution. There are many factors affecting the formation of earth fissures, and the explanations of the formation mechanisms of earth fissures by domestic and foreign scholars can mainly be divided into three categories: ground subsidence induced by tectonic genesis [7, 8], groundwater genesis [9, 10, 11], and structural and groundwater compound genesis [12, 13, 14]. Among them, China is one of the countries whose earth fissures have an enormous scale of development, the broadest distribution, and the most substantial phenomenon of surface damage caused by earth fissures. Since 2000, more than 5000 earth fissures have been discovered in China, mainly in the Fenwei Basin, the Hebei Plain, and the Su-Xi-Chang area (Figure 1) [15]. Compared to the other two regions, the planar spread of the earth fissures within the Fenwei Basin is the longest and most active. There have been many excellent results and consensus on the distribution pattern, activity characteristics, and genesis mechanisms of fissures in the Fenwei Basin [16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28]. The existence and activity of earth fissures do not only cause direct damage to surrounding structures, but when an earthquake occurs, the presence of earth fissures can change and even increase the seismic response of the site, causing the structures near the earth fissures to suffer severe damage or even be destroyed. Thus far, research on the development, distribution characteristics, and formation mechanisms of earth fissures all over the world has produced results, but our understanding of the dynamic effects of earth fissure sites is insufficient. Several studies have investigated the dynamic effects of earth fissures under earthquake loads based on numerical simulations [29; 30], and others have used indoor simulation experiments to explore the influence of earth fissures on the dynamic response of a site [31; 32; 33; 34; 35], but the existing results are few and unsystematic and are not sufficient to guide engineering practice. Therefore, in terms of the specifications for site investigation and engineering design on Xi'an ground fractures (DBJ61-6-2006), [36] only regards the seismic effects of earth fissure sites as a general site threat in accordance with the code for the seismic design of buildings (GB50011-2010) [37]. Furthermore, because there are no systematic measurement data on the seismic response of earth fissure sites, in order to study this problem it is necessary to develop new ideas and appropriate methods. A microtremor is a kind of constant micro-movement that has no specific seismic source and can be observed at any time, and its amplitude is generally only a few microns. Microtremor studies originated in the 1950s. [PERSON] and [PERSON] [38] quantitatively analyzed the nature of microtremor surface waves. After this, many research works were carried out on the microtremor sources, formation mechanisms, and waveforms of microtremors [39; 40; 41; 42]. In the late 1960s, [PERSON] and [PERSON] used a seismic network to separate, extract, and analyze the various periodic components of microtremors [43; 44] and reported on the components of the different bands of the microtremors and their possible causes.