The gray whale will avoid its regular migratory and feeding grounds by >30 km in areas of seismic testing. Similarly the breathing of gray whales was shown to be more rapid, indicating discomfort and panic in the whale. It is circumstantial evidence such as this that has led researchers to believe that avoidance and panic might be responsible for increased whale beachings although research is ongoing into these questions. Offering another point of view, a joint paper from the International Association of Geophysical Contractors (IAGC) and the International Association of Oil and Gas Producers (IOGP) argue that the noise created by marine seismic surveys is comparable to natural sources of seismic noise, stating:  "The sound produced during seismic surveys is comparable in magnitude to many naturally occurring and other man-made sound sources. Furthermore, the specific characteristics of seismic sounds and the operational procedures employed during seismic surveys are such that the resulting risks to marine mammals are expected to be exceptionally low. In fact, three decades of world-wide seismic surveying activity and a variety of research projects have shown no evidence which would suggest that sound from E&P seismic activities has resulted in any physical or auditory injury to any marine mammal species."In 2017, IOGP recommended that, to avoid disturbance whilst surveying:    The following books cover important topics in reflection seismology. Most require some knowledge of mathematics, geology, and/or physics at the university level or above. Further research in reflection seismology may be found particularly in books and journals of the Society of Exploration Geophysicists, the American Geophysical Union, and the European Association of Geoscientists and Engineers.