## 1 Introduction
[5] investigated the effect of the salinity interface on the seismoelectric logging by acoustic monopole source, and the results show that the inducing electric waves have a complicated response law to salinity. The salinity interface formed between the borehole fluid and the formation has a significant effect on the induced electric fields. When using the seismoelectric effect for logging, the electromagnetic wave interface response generated by the acoustic waves hitting the medium interface is important information. Since the amplitude of the interface converted electromagnetic wave is relatively small, when the geological structure of the formation is complex, the electric field full-wave sometimes cannot fully reflect the interface response properties. The method of complex analysis can be used to solve a single component of the wave field, where the secant integral method is an effective tool for solving the interface response in the seismoelectric effect [50; 51; 52; 53]. In addition, the component wave analysis of the seismoelectric wave fields by using the pole residue can have a deeper understanding of the propagation characteristics of the mode waves and their accompanying electric field [54]. In this article, we will discuss the influence of the interface, across which the electrical properties differ, on the seismoelectric wave fields, and focus on the response mechanism of the interface radiated electromagnetic waves. Besides, there are few studies on the use of seismoelectric wave fields to detect borehole-side interface position. Here, we propose an interface position inversion method combining slowness-time coherence (STC) [55; 56; 57] and the time-domain waveforms. At the same time, the feasibility of using the borehole SH-TE wavefields to invert the position of the salinity interface next to the borehole is also discussed. The SH-TE acoustoelectric coupling waves have been widely used in shallow exploration [58; 59; 60; 61; 62; 63]. The results show that when the SH waves pass through the interface of the horizontally layered formations, interface responses appear. The electromagnetic waves generated at the interface reach different receivers almost simultaneously. The differences in elasticity, consolidation, and electrical properties between the two sides of the interface are important factors that influence the strength of the interface response [64]. In addition, the high signal-to-noise ratio is also an advantage of using SH-TE waves for exploration [65]. [PERSON] [66] first proposed the idea of using the pure SH waves for logging and performed some simple calculations for homogenous elastic media. A subsequent study showed that layered structure media complicates the borehole SH wave composition since the multi-order and dispersive mode waves are excited [67]. As for the borehole SH-TE waves, [PERSON] et al. [68] simulated the SH-TE acoustoelectric coupling fields of a homogeneous porous medium. Similar to the borehole SH wave, when the nature of the formation is discontinuous, the dispersive accompanying electric fields are also excited. In addition, the electromagnetic interface response becomes complicated [53]. Then in a later work [PERSON] et al. [52] discussed the response law of borehole SH-TE waves in partially saturated soil. Although this work also examined the influence of pore fluid salinity on the electric field, it did not investigate in detail its influence mechanism. To further understand the seismoelectric coupling phenomenon in the reservoir and investigate the application potential of the borehole SH-TE wave fields in exploration, here we study the influence of fluid salinity on SH-TE waves in a borehole and explore the influence mechanism. The composition of the article is as follows: In Section 2, we derive the analytical expressions of the field quantities in each region.