## 1 Introduction  
In unconventional reservoirs with low matrix permeability, fractures can be the main conduits for the flow of pore fluids [1; 2]. Fracture detection and characterization are very important in the context of oil/gas exploration and production [3; 4]. As a result, analyses of fracture physical characteristics (scale, aperture, orientation) and their influences on seismic propagation have attracted considerable interest in academia and industry [5; 6; 7]. Equivalent medium theories have been used to bridge the rock physics relationships between rock, fracture, and fluid properties and seismic velocity, attenuation, and anisotropy. Traditionally, the theories of [PERSON] (1988) [8; 9], [PERSON] (1995) [10], and [PERSON] (2003) [11] have been applied. However, these models have strict frequency limitations because of the assumptions in their derivation processes. The model of [PERSON] (1988) is usually referred to as a linear-slip model and is limited to a high-frequency regime wherein fluid is isolated in fractures, whereas the [PERSON] model is limited to a low-frequency regime with fluid allowed to flow between fractures and quant pores. The [PERSON] model provides different expressions in low- and high-frequency regimes, respectively. These three models neglect the dispersion effect and cannot be used to obtain the frequency-dependent moduli of fractured rocks. [PERSON] et al. extended the [PERSON] model and derived an analytical solution for P-wave dispersion [12; 13]. [PERSON] and [PERSON] provided a unified model by branching function approximation [14; 15; 16]. This approximation has similar behavior to asymptotic analytical solutions at low and high frequencies and satisfies causality, turning out to be very accurate and useful. We refer to the [PERSON] and [PERSON] (2015) model as the [PERSON] model. Validation of these theoretical models through well-designed laboratory experiments is desirable [17; 18; 19; 20; 21]. Unfortunately, the fractures are unknown and cannot be quantitatively controlled in natural rocks. Thus, artificial sandstones with controlled fractures are frequently used to study seismic wave propagation in fractured rocks by conducting laboratory experiments. [PERSON] (1995) provided P- and S-wave velocity results in artificial fractured sandstones bounded by epoxy [22], and the data set confirmed the nature of seismic anisotropy in porous rocks with aligned penny-shaped fractures. The measured results were compared with predictions of the [PERSON] model [23; 24] and [PERSON] model, and the results demonstrated significant effects of fluid flow on seismic velocity and anisotropy. [PERSON] (2012, 2014) investigated the feasibility of the [PERSON] model in predicting seismic velocity and anisotropy in silica-cemented artificial rocks [25; 26]. [PERSON] (2017, 2018, 2020) experimentally investigated the effects of fracture density and scale on seismic velocity anisotropy [27; 28; 29]; the results were compared with those of the [PERSON] model [30; 31; 32] and good fits were found between the measured data and theoretical predictions. However, as previous experimental studies based on artificial fractured sandstones were often conducted in the high-porosity range (>29%), there are, so far, few experimental studies that address the reliability of equivalent medium theories of low-porosity fractured rocks, despite the fact that unconventional reservoirs are usually characterized by low porosity and low permeability. In this work, we aimed to investigate the application of the Galvin model for low-porosity artificial fractured sandstones. We constructed three artificial fractured sandstone samples with the same background matrix porosity (11.7% \(\pm\) 1.2%) but different fracture densities (0%, 3.12%, and 6.24%). The P- and S-wave velocities as well as the anisotropic parameters were measured by an ultrasonic bench-top pulse transmission system in dry and water-saturated conditions. Results were compared with the predictions of the Galvin model.