Development of a mechanical optical seismometer

Abstract

Seismometers are instruments that record the seismic waves, these waves are generated by the movement of tectonic plates, sea waves, explosions, human activity, among other sources. The importance of these instruments allows geoscientists to study the interior of the earth. This study also allows for instance to know the characteristics of the earth's crust and so be able to identify sources of minerals, water, hydrocarbons and other resources. The first seismometers have been constructed entirely mechanical and consisted of a mass and a spring and sometimes a bumper, or a mass subject by a thread and that oscillates by vibration. In 1922, Harry Wood and John Anderson built a seismometer known as Wood-Anderson seismometer. A light source illuminates a mirror that is on a mass suspended by a vertical wire which acts as a torsion spring. The reflected light on a drum records the seismic signal. This seismometer operated in Southern California by the year 1980 and was used by Charles Francis Richter in defining the magnitude of the earthquake in 1930. These instruments are of a single degree of freedom and physically large volume and in case of a system of three degrees of freedom, the seismometer occupy a larger volume. For the case of mapping larger areas and placing several seismometers it is necessary that the seismometer is smaller. This facilitates a more continuous barrido. With the advancement in electronics and fine mechanics, the seismometers over time have become more sophisticated and achieving greater sensitivities and shrinking smaller and smaller in size. The advances that have occurred in recent years in the areas of microelectronics (now nanoelectronics), optics and precision mechanics; They have stimulated the development of new types of seismometers, based on new technologies such as laser and optics, with the main objective to increase the sensitivity, bandwidth, power consumption and miniaturization. Currently, Brazil has achieved great achievements and international reputation with regard to terrestrial seismology. This achievement has been possible thanks to financial support from development agencies in Brazil and by research groups from universities and institutes, synergy that led to the formation of the Brazilian Seismograph Network. Despite all this progress, so far what we perceive is the lack of research groups in these institutions and / or companies in Brazil, aimed at seismological instrumentation, specifically in the development and construction of broadband seismometers and high sensitivity, different to what happens in other countries. Thus it is proposed to this research project, development and innovation (RD & I): Development of a mechanical-optical seismometer, for the purpose of suprirmos local demand and we cover local technological gap by the lack of this type of solutions. Aims to show in this project phase-1 scientific and technical feasibility for further development of a seismometer high sensitivity optical-mechanical prototype and performance measurement of seismic waves long and short. For the optical part, we will test two optical techniques, interferometric technique and technique with Bragg grating fiber optic (fiber Bragg grating FBG). On the mechanics will test systems composed of springs and dampers. The broadband seismometers commercial values are measured in a few thousand dollars, then increase to higher sensitivity sensors and coverage on the long band range. The optical-mechanical seismometer will be used primarily for: meet the national demand of the seismology research groups and related fields from universities and research centers; meet the national demand of companies to microssísmico monitoring studies of hydroelectric, hydrocarbon reservoirs and mines; Passive seismic for exploration onshore hydrocarbons, seismic microzonation, among others. (AU)