6:15 PM - 7:30 PM
[SSS26-P03] Temporal velocity changes after the 2014 northern Nagano earthquake, central Japan
Keywords:a large earthquake, seismic interferometry, auto correlation functions, velocity reductions, Hi-net
Around the source area of the northern Nagano earthquake, there are typical six Hi-net stations and six easy Hi-net stations which are composed of only a three-component high-sensitivity and short-period velocity seismograph. Three of them, N.HBAH, N.HKKH, and N.OTNH are on the source region. Using ambient seismic noise of 1-3 Hz bandwidth, we calculated auto-correlation functions (ACFs) of vertical component applying a one-bit normalization correction. Since the relative delay of the ACFs for each lag time corresponds to the relative change of the velocity, the velocity fluctuation for each Hi-net station could be estimated by applying a stretching method to waveforms obtained before and after the earthquake.
The three stations on the source area showed 1 % to 3 % velocity reduction during the earthquake. In addition, N.IGWH at northward and N.MKGH at northeastward from the source area also decreased approximately 0.5 % and 1.5 %, respectively. We could not find clear correlation between the velocity reduction and values such as peak ground acceleration, peak ground velocity, site amplification effect, tilt record, and volumetric strain change by the estimated source fault. After the earthquake, the velocity has recovered approximately by 50% for 2 months except for N.OTNH.