Attenuation Characteristics of Earthquake Ground Motion for Large Volume Airgun

In order to further deepen the understanding of seismic wave propagation characteristics induced by the large volume airgun source,experimental data from multiple fixed excitation points in Fujian Province were used to obtain the equivalent single excitation high signal-to-noise ratio velocity and displacement records through linear stacking and simulation techniques.Then the peak displacements of different epicentral distances were used to calculate the equivalent magnitude of the airgun source excitation at different fixed excitation points so as to establish the attenuation relationship between equivalent magnitude,epicenter distance and velocity peak.Our results show that:①Within 270 km of epicentral distance,for the large-volume airgun’s single shot,the peak velocity range is about 700-4 nm/s,and the peak displacement range is about 200.0-0.2 nm;②The equivalent magnitude of the P-wave from the airgun source with a total capacity of 8,000 in 3 is 0.181-0.760,and the equivalent magnitude of the S-wave is 0.294-0.832.By contrast,the equivalent magnitude of the P-wave from the airgun source with a total capacity of 12,000 in 3 is 0.533-0.896,and the equivalent magnitude of the S-wave is 0.611-0.946.The S-wave energy is greater than the P-wave energy,and the excitation efficiency varies greatly with different excitation environment;③The peak velocity increases with the equivalent magnitude,and decreases with the epicentral distance.The vertical component of the P-wave peak velocity is the largest among those three components,while the S-wave has the smallest vertical component and similar horizontal components.Hence,our research can provide an important basis for the quantitative judgment of the seismic wave propagation distance using the airgun and the design of the observation system in deep exploration or monitoring with airgun.