An experimental study on the excitation of large volume airguns in a small volume body of water

A large volume airgun array is effective in generating seismic waves, which is extensively used in large volume bodies of water such as oceans, lakes and reservoirs. So far, the application of large volume airguns is subject to the distribution of large volume bodies of water. This paper reports an attempt to utilize large volume airguns in a small body of water as a seismic source for seismotectonic studies. We carried out a field experiment in Mapaoquan pond, Fangshan district, Beijing, during the period 25–30 May 2009. Bolt LL1500 airguns, each with volumes of 2000 in3, the largest commercial airguns available today, were used in this experiment. We tested the excitation of the airgun array with one or two guns. The airgun array was placed 7–11 m below the water's surface. The near- and far-field seismic motions induced by the airgun source were recorded by a 100 km long seismic profile composed of 16 portable seismometers and a 100 m long strong motion seismograph profile, respectively. The following conclusions can be drawn from this experiment. First, it is feasible to excite large volume airguns in a small volume body of water. Second, seismic signals from a single shot of one airgun can be recognized at the offset up to 15 km. Taking advantage of high source repeatability, we stacked records from 128 shots to enhance the signal-to-noise ratio, and direct P-waves can be easily identified at the offset ~50 km in stacked records. Third, no detectable damage to fish or near-field constructions was caused by the airgun shots. Those results suggest that large volume airguns excited in small bodies of water can be used as a routinely operated seismic source for mid-scale (tens of kilometres) subsurface explorations and monitoring under various running conditions.

[1]  Yong Chen,et al.  Using an airgun array in a land reservoir as the seismic source for seismotectonic studies in northern China: experiments and preliminary results , 2008 .

[2]  Chen Yong,et al.  The application of large volume airgun sources to the onshore-offshore seismic surveys: implication of the experimental results in northern South China Sea , 2007 .

[3]  Jie Zheng,et al.  Construction of the Technical System of Data Backup Centre for China Seismograph Network and Its Support to Wenchuan Earthquake Researches , 2009 .

[4]  P. Leary,et al.  Systematic monitoring of millisecond travel time variations near Palmdale, California , 1979 .

[5]  Christoph Sens-Schönfelder,et al.  Passive image interferometry and seasonal variations of seismic velocities at Merapi Volcano, Indonesia , 2006 .

[6]  Yong Chen,et al.  A new way to generate seismic waves for continental crustal exploration , 2007 .

[7]  Paul G. Richards,et al.  Seismological evidence for differential rotation of the Earth's inner core , 1996, Nature.

[8]  Keiiti Aki,et al.  A precise, continuous measurement of seismic velocity for monitoring in situ stress , 1974 .

[9]  D. Okaya,et al.  Double-sided onshore–offshore seismic imaging of a plate boundary: “super-gathers” across South Island, New Zealand , 2002 .

[10]  Hongqiao Hu,et al.  Ionospheric foF2 Reconstruction and its Application to the Short-Term Forecasting in China Region , 2008 .

[11]  Kazunori Kobayashi,et al.  A trial for monitoring temporal variation of seismic velocity using an ACROSS system , 2001 .

[12]  Jack Caldwell,et al.  A brief overview of seismic air-gun arrays , 2000 .

[13]  P. Leary,et al.  Millisecond accurate monitoring of seismic travel times over 13‐ and 18‐kilometer baselines , 1982 .

[14]  Liang Jian,et al.  Technical system construction of Data Backup Centre for China Seismograph Network and the data support to researches on the Wenchuan earthquake , 2009 .