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Laser strainmeter and gravity-inertial instruments in prevention of earthquake disaster
by
M.N. Dubrov
Institute of Radio-engineering and Electronics of RAS, Fryazino, Russia
Coauthors: V.A. Alyoshin (Institute of Radio-engineering and Electronics of RAS, Fryazino, Russia), V.A. Volkov (Institute of Physics of the Earth of RAS, Moscow, Russia), A.V. Kalinina (Institute of Physics of the Earth of RAS, Moscow, Russia), S.A. Moiseenko (Institute of Physics of the Earth of RAS, Moscow, Russia)
Two different kinds of precise geophysical instruments are concerned owing to their valuables for seismic risk mitigation problem development. The comparison has been performed in a scope of the geological medium parameters estimation. The laser strainmeter gives the data on deformation tensor of elastic body while the gravity-inertial instrument output is the reaction to the whole body’s displacements and to the tilts or to the gravity field variations. Such complementary information seems to be very important when the safety factors of a ground or building foundations are to be determined. Natural and artificial geological processes are in consideration. We present a number of experimental results obtained during last few years. The strains of underground constructions due to traffic motion and water well operation are presented too. The precise laser interferometric strainmeters and accurate pendulum seismic-gravimeters and tiltmeters have been used. The laser strainmeter measures horizontal and vertical relative displacements of two points at the earth surface or buildings on which the interferometer is anchored. The accuracy of the order of 10(-2)-10(-3) nm is achieved at basis 1-300 m. The seismic-gravimeter devices have resolution of 0, 5 uGal to vertical biases about 1 um in a seismic frequency band. Tiltmeter resolution is estimated as 0.1 msec of arc in tide channel and 0.01 msec in seismic-accelerometer channel. The linear deformations of a ground due to load affection of the earth surface by activity of the traffic motion have been investigated. They are accompanied by 3-D spatial strains: vertical and horizontal tensions from which elastic modules of the medium are defined. We have found that operation of underground water wells causes the velocity of ground strains up to 10-20 um per hour. A heavy debit of underground waters can give in a raise of hazard from such phenomena as the sedimentary of building bases, development of landslips etc. Intensive variations of atmospheric pressure and motions of the earth surface are explored on distances between observation sites of 45-140 km. The synchronous records of pressure, earth strains, and gravity acceleration revealed the dynamic perturbations in the atmosphere and lithosphere. They have undular microstructure of horizontal and vertical earth surface motions with clear delineated phases spreading along the atmosphere-earth boundary with the velocities of 30-50 km per hour. The intensity of atmosphere-lithosphere interaction has been often accompanied by the Earth’s seismic activity. We have observed the essential growth of 0.4-5 hour period disturbances during 1-2 days before the strong earthquakes (M =7.0-7.9). Earth-strain signals accompanying earthquakes were recorded in the form of large tilts and period oscillations as long as 1.5 hours. The large spike-shaped pre-seismic and post-seismic strains have been observed for some remote earthquakes. The detailed mechanism of the atmosphere and the solid Earth interaction is a proper signal for study of geological media. Such technique would be useful for the evaluation of seismic territorial vulnerability and could promote the applied research and engineering aimed at seismic risk mitigation. This work is supported by the Russian Foundation of Basic Research, Projects N02-05-64720.
Date received: July 22, 2004
Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caon-20.