A NEW METHOD OF IDENTIFYING GROUND-BASED ELECTROMAGNETIC ANOMALIES – CASE STUDY OF THE SICHAN LUSHAN 7.0 EARTHQUAKE

摘要

Stereo-observation, being comprised of both ground-andrnspace-based observations, is an important approach forrnlikely making earthquake prediction to break through.rnThe electromagnetic observation is considered as one ofrnthe most important measures in the stereo-observation,rnand should be one of the fields in which breakthrough isrnfirstly and likely made and would be an effective devicernto obtain information for earthquake pre-warning. Newrntechniques of alternating electromagnetic fieldrnobservation, e.g., Controlled-Source Extremely LowrnFrequency (CSELF) and satellite observation, arerngradually applied to the earthquake monitoring, whichrncontain the more abundant information than those mainlyrnobserved in constant electric or magnetic field. This willrnincrease the amount of recorded data greatly andrninevitably require the robust techniques of datarnprocessing and analyzing. Previous analysis techniquesrnmainly utilize the Fourier transform method forrnalternating electromagnetic field data, which cannotrnconsider the information in time and frequency domainsrnsimultaneously. In this study we try to use the waveletrntransform method to process alternating electromagneticrnfield data and carry out a case study, which aims tornobtain the electromagnetic anomaly information in bothrnfrequency- and time-domains. The study is conducted onrnthe data observed for 35 days during the strongrnaftershock period after the Lushan earthquake withrnMs=7.0 in the Sichuan province in China. Thernpreliminary results show that the wavelet transformrnmethod has an advantage and potential for identifyingrnthe electromagnetic anomalies relative to the earthquakernevents.