Spectral Analysis of Subduction Zone Earthquakes for Coastal Stations and Applications to Stochastic Finite-Fault Simulation Method

Abstract

Accelerograms of 58 subduction zone earthquakes recorded by 25 K-NET coastal stations located in Sagami Bay and its adjacent regions were used to analyze the spectral properties of the source, propagation path, and site effects by using the generalized inversion technique. The inverted [Formula: see text] values vary from 1.7[Formula: see text]MPa to 17.4[Formula: see text]MPa, with an average value of 4.89[Formula: see text]MPa and a standard deviation of [Formula: see text]. Although the depths of the selected earthquakes are confined to 30 km, which is similar to those of the crustal earthquakes, this study obtains an average [Formula: see text] which coincides with the plate-boundary earthquakes rather than the crustal earthquakes. It implies that the stress condition of the plate-boundary region varies from the inland crust. The obtained [Formula: see text] is similar to the previous studies. The [Formula: see text] of the selected stations varies from 0.0479[Formula: see text]s to 0.0904[Formula: see text]s, indicating high-frequency attenuation for the coastal area. The inverted site response shows the systematic tendency for different site classes. The amplification levels of class A sites fluctuate around one between 1[Formula: see text]Hz and 10[Formula: see text]Hz. Class B sites indicate peak amplification at the resonant frequency distributed between 3[Formula: see text]Hz and 10[Formula: see text]Hz. Most of the Classes D and E sites have peak amplification below about 4[Formula: see text]Hz. Using the inversion results as the input parameters of the stochastic finite-fault method, an [Formula: see text] subduction zone earthquake was simulated. The resulting response spectra corresponded to the observations and confirmed that the inverted parameters are reasonable.