Based On High-frequency Tiltmeter And Strainmeter Recorded Seismic Waves Phase Identification And Research

The development of observation technology has made the traditional ground observation methods to high-frequency.The low-frequency solid tide observations have been used to observe the ground tilt and ground strain observations for a long time.In recent years,the observation frequency band have widen to high-frequency.In the "Plate Boundary Observation"(PBO),the United States has deployed a variety of observation programs including GNSS,seismograph,strainmeter,tiltmeter,and InSAR along the west coast plate boundary in order to study the deformation of the western boundary of the North American continent.In this paper,based on the PBO comprehensive borehole observation data and the full knowing of the PBO borehole deformation observation instrument,combined the high-frequency ground tilt and ground strain observation data with the same-site seismic observation data,realized the deformation observation data high-frequency signal extraction,phase identification and time-frequency analysis.Taking the M8.1 earthquake in Mexico as an example,the data of 14 high-frequency deformation observation instruments and seismometers observed at the same site were analyzed,and the seismic signal extraction,the coseismic self-test of the component borehole strainmeters,the seismic wave travel time analysis and the coseismic strain main direction solution were completed.The results show that the seismic wave recorded by the high-frequency deformation instruments accord with the seismic ray propagation law.Using the S transformation of the observation data of different epicentral distances,the obtained spectrum shows that the strainmeters can identify seismic wave signals with a frequency between 0.02-0.25 Hz,which is in good agreement with the seismograph records.Limited by 1sps,the PBO borehole strainmeter has a significantly lower recording capacity in the body wave band than its surface wave response.The surface wave can be recorded more completely in the strainmeter observation,which is more advantageous than the seismograph observation.The crustal structure can be studied by combining the strain gauge and the seismograph surface wave data.In the teleseismic record,the main direction of the coseismic strain recorded by the PBO borehole strainmeters point to the epicenter,indicating that the main body of the signal recorded by the strainmeters when the seismic wave propagates to the borehole is the deformation caused by the seismic wave.