A five component land seismic sensor for measuring lateral gradients of the wavefield

Abstract

We built a five‐component (5C) land seismic sensor that measures both the three‐component (3C) particle acceleration and two vertical gradients of the horizontal wavefield through a pair of 3C microelectromechanical accelerometers. The sensor is a small cylindrical device planted vertically just below the earth's surface. We show that seismic acquisition and processing 5C sensor data has the potential to replace conventional seismic acquisition with analogue geophone groups by single 5C sensors placed at the same station interval when combined with a suitable aliased ground roll attenuation algorithm. The 5C sensor, therefore, allows for sparser, more efficient, data acquisition. The accuracy of the 5C sensor wavefield gradients depends on the 3C accelerometers, their sensitivity, self‐noise and their separation. These sensor component specifications are derived from various modelling studies. The design principles of the 5C sensor are validated using test data from purpose‐built prototypes. The final prototype was constructed with a pair of 3C accelerometers separated by 20 cm and with a self‐noise of 35 ng Hz−1/2. Results from a two‐dimensional seismic line show that the seismic image of 5C sensor data with ground roll attenuated using 5C sensor gradient data was comparable to simulated analogue group data as is the standard in the industry. This field example shows that up to three times aliased ground roll was attenuated. The 5C sensor also allows for correcting vertical component accelerometer data for sensor tilt. It is shown that a vertical component sensor that is misaligned with the vertical direction by 10° introduces an error in the seismic data of around –20 dB with respect to the seismic signal, which can be fully corrected. Advances in sensor specifications and processing algorithms are expected to lead to even more effective ground roll attenuation, enabling a reduction in the receiver density resulting in a smaller number of sensors that must be deployed and, therefore, improving the operational efficiency while maintaining image quality.

Seismic responses of high‐rise structure under multiple‐component ground motions

“…The most significant drawback of these instruments and devices is their size and cost, 26 and improvement for the device is now in progress. Muyzert et al 27 proposed a cheap sensor rotation placed below the surface to solve some of the problems of an insufficient sensor. The first portable rotary sensor specifically designed for seismology came out in 2018, 28 and it promotes the acquisition for rocking ground motion to a certain extent.…”

Seismological Processing of Six Degree-of-Freedom Ground-Motion Data

“…Since signal levels are expected to be much higher in seismic exploration than in global seismology, due to the proximity to the source [21], smaller and less sensitive devices with an analog output should be envisaged. Innovative rotation sensors based on the principles of conventional geophones, such as described by Muyzert et al [78], could prove a valuable alternative to expensive fibre-optic gyroscope for wide-spread use in land-seismic exploration. Figure 9.…”

“…Their sensor, called rotaphone, has since successfully recorded rotational ground-motions in tectonically active regions around the globe [130]. Muyzert et al [78] proposed a rotational sensor consisting of a pair of 3C microelectromechanical accelerometers that are vertically placed a few centimeters apart within a cylindrical housing. If this sensor is planted vertically just below the Earth's surface, the vertical gradient between the two sensors is enough to measure the two horizontal components of rotational motions due to the free surface boundary condition (Equation (19)).…”