Research of CRP-based irregular 2D seismic acquisition

Seismic exploration in the mountainous areas of western Chinese is extremely difficult because of the complexity of the surface and subsurface, which results in shooting difficulties, seismic data with low signal-to-noise ratio, and strong interference. The complexity of the subsurface structure leads to strong scattering of the refl ection points; thus, the curved-line acquisition method has been used. However, the actual subsurface structural characteristics have been rarely considered. We propose a design method for irregular acquisition based on common refl ection points（CRP） to avoid difficult-to-shoot areas, while considering the structural characteristics and CRP positions and optimizing the surfacereceiving line position. We arrange the positions of the receiving points to ensure as little dispersion of subsurface CRP as possible to improve the signal-to-noise ratio of the seismic data. We verify the applicability of the method using actual data from a site in Sichuan Basin. The proposed method apparently solves the problem of seismic data acquisition and facilitates seismic exploration in structurally complex areas.

A new type of fiber Bragg grating based seismic geophone

Aimed at the poor performance of conventional geophones in exploration for deeper and complex targets, we present the principle and theoretical design of a new geophone based on the optical fiber Bragg grating （FBG） sensing technology. The important parameters such as response functions are calculated theoretically. Because of the advantages of FBG sensing technology, the new FBG geophone has a high dynamic range of 94dB at （10-200 Hz）. This new generation of geophones will have wide use in seismic prospecting due to its higher sensitivity, lighter weight, and lower cost.

High-resolution data acquisition technique in broadband seismic observation systems

The dynamic range of the currently most widely used 24-bit seismic data acquisition devices is 10–20 d B lower than that of broadband seismometers, and this can affect the completeness of seismic waveform recordings under certain conditions. However, this problem is not easy to solve because of the lack of analog to digital converter(ADC) chips with more than 24 bits in the market. In this paper, we propose a method in which an adder, an integrator, a digital to analog converter chip, a field-programmable gate array, and an existing low-resolution ADC chip are used to build a third-order 16-bit oversampling delta-sigma modulator. This modulator is equipped with a digital decimation filter, thus facilitating higher resolution and larger dynamic range seismic data acquisition. Experimental results show that, within the 0.1–40 Hz frequency range, the circuit board's dynamic range reaches 158.2 d B, its resolution reaches 25.99 bits, and its linearity error is below 2.5 ppm, which is better than what is achieved by the commercial 24-bit ADC chips ADS1281 and CS5371. This demonstrates that the proposed method may alleviate or even completely resolve the amplitude-limitation problem that so commonly occurs with broadband observation instruments during strong earthquakes.