Analysis on several factors of periodic air pressure wave affecting crustal strain field

Crustal strain field is usually measured by borehole volumetric strainmeters. It is a long-erm influence that short-eriod air pressure waves with period of a few minutes to several hours affect the work of volumetric strainmeters. Evertson and others derived a model that volume strain was disturbed by short-eriod air pressure. Based on their work this paper made a theoretical study on the relation between the influence coefficient of air pressure on volume strain and the air pressure cycle, rock elastic modulus and borehole depth. Since there is a coupling effect between strainmeter and borehole, we established the equation for calculating the borehole coupling coefficient under the vertical atmosphere loads. The difference between the theoretical air pressure coefficient and the true value of non porous rock under the action of multiple factors was examined, and compared with the Sacks volume strain observed data at Laishui, Shunyi, Dong Sanqi and Changping station. The study result is of practical significance for exploring basic micro-dynamic variation of possible earthquake precursors.