![]() MSM is based on the theory of stationary stochastic processes. These methods, which are founded on the same principle, are collectively called the (SPAC). In addition, the extended spatial autocorrelation method (ESPAC) has been developed, in which the geophones are freely arranged. The spatial autocorrelation method (SPAC) in the microtremor survey was proposed by Aki in 1957 and according to its array arrangement method, the original geophones are arranged in circles or nested triangles, as shown in Figure 1. Although the amplitude and shape of the microtremor signal changed over time and space, there is statistical stability within a range, which can be described by a stationary stochastic process in time and space. A schematic diagram of MSM is shown in Figure 1. It is caused by two types of sources: Natural noise, such as noise due to air pressure, wind speed, ocean wave, and tidal changes (signal frequency 1 Hz). This type of vibration phenomenon is extremely irregular in time and space. Microtremor signals are composed mainly of body waves (primary and secondary waves) and surface waves (Rayleigh and Love waves) and the energy of the surface wave is the main component (more than 70 %) of the total energy. ![]() The applicability of the system is evaluated using field data, according to which the integrated energy-efficient wireless sensor node is convenient and effective for MSM. Therefore, it provides substantial support for the effective data acquisition over long measurement durations in microtremor exploration processes. According to the results of a series of in situ tests and field measurements, the noise level of the system was 0.7 μ Hz with 0 dB attenuation and 220 mW power consumption of the system in the autonomous data acquisition mode. The data quality monitoring system solves the closed technical flaws between the acquisition systems and the control center via 4G wireless monitoring technologies. Dynamic frequency selection technology (DFS) and dynamic power management technology (DPM) are used to design an energy-efficient mode. ![]() A high-precision AD chip and noise matching technology are used to develop a low-noise design for the sensor node. In this study, we combined a 2 Hz moving coil geophone with advanced acquisition systems to develop a new integrated energy-efficient wireless sensor node for microtremor exploration. However, the existing microtremor exploration equipment has been unable to satisfy the requirements of the MSM, which suffers from low data accuracy, long measurement time, and blind acquisition. The microtremor survey method (MSM) has the potential to be an important geophysical method for identifying the strata velocity structure and detecting the buried fault structures.
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