Abstract
Strainmeters have been used to detect earthquake precursory anomalies in many countries. An innovated four-component strainmeter with four sensing units set at 45 degrees intervals, named SKZ strainmeter, was developed and used in China. The design, with a few unique features, allows high-sensitivity monitoring of the regime of the crustal strain field, as well as the self-consistencies of the instrument. One of the most difficult problems in the earthquake precursory investigation is to efficiently detect anomalies from large amount of data. Pattern recognition of waveforms is widely used, but it is time-consuming and relies more or less investigator’s experience and decision. In this study, the consistency factors of the paired components were firstly shown to be utilized to detect anomalies possibly related with imminent earthquakes. Here, rather than using the consistency factors, the correlation coefficients of the two orthogonal strain data were used to detect. SKZ strainmeters have been installed at more than ten sites in China, exhibited high efficiency and reliability in precursory monitoring since. Anomalous variations from a few stations during two recent earthquakes in south China were analyzed. During normal stages, diurnal earth tides could be clearly observed with very little urban noises. Though the consistency factors may have near constant bias, their correlation coefficients remain near 1.0, greater than 0.99. During the imminent preparatory stage of earthquake occurrence, non-planar strain may appear and the correlation coefficients drop noticeably. The analysis showed that the correlation coefficient between the two orthogonal components is a useful parameter in post-processing of the strain data to detect precursory anomalies. The resultant resolving power is shown to be some one-order larger compared with previous methods.
Highlights
Crustal strain monitoring using borehole strain meter has been widely conducted in China, Japan, USA, and Russia to detect anomalous precursory variations
The analysis showed that the correlation coefficient between the two orthogonal components is a useful parameter in post-processing of the strain data to detect precursory anomalies
The crustal deformation measurement related to earthquakes, volcanic eruption and plate movement has been conducted by using those kinds of strainmeters, borehole ground tilt meters, volumetric strainmeters (Agnew, 1986 [7]), and continuous Global Positioning System (GPS) (e.g., Rikitake, 1976 [8]; Su, 1977 [9]; Okada, 1985 [10]; Agnew, 1986 [7]; Qiu et al, 2011 [11])
Summary
Crustal strain monitoring using borehole strain meter has been widely conducted in China, Japan, USA, and Russia to detect anomalous precursory variations. The crustal deformation measurement related to earthquakes, volcanic eruption and plate movement has been conducted by using those kinds of strainmeters, borehole ground tilt meters, volumetric strainmeters (Agnew, 1986 [7]), and continuous Global Positioning System (GPS) (e.g., Rikitake, 1976 [8]; Su, 1977 [9]; Okada, 1985 [10]; Agnew, 1986 [7]; Qiu et al, 2011 [11]). As for the earthquake prediction, the evaluation of candidate precursory anomalies relies on large amount of monitoring data from dozens or hundreds of sites in any countries as China, Japan, and USA along. Automatic effective post-processing methods are greatly needed to identify candidate precursory phenomena using huge amount of data
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