Abstract
In order to study the seismic wave attenuation characteristics of complex plate tectonics in and around the Kanto Basin, based on the focal mechanism and Slab1.0 model, the research area is divided into four regions. The one-step non-parametric generalized inversion technique was used to analyze the seismic wave attenuation characteristics of each region separately. The results show that the seismic path attenuation of earthquakes occurring in the shallow crust (Reg.1) is weak, and the seismic wave refraction at the crust–mantle boundary leads to almost no attenuation over a long hypocentral distance (>60 km), the frequency–dependent inelastic attenuation is also weak with the 0.5–20 Hz quality factor Q = 92.33f1.87. The seismic path attenuation of the upper mantle earthquakes occurring in the Kanto Basin (Reg.2) is strong, and the attenuation curve decreases with the increase of hypocentral distance, which is approximately parallel to the geometric diffusion R−2.0, the frequency–dependent inelastic attenuation is stronger with the quality factor Q = 27.75f1.08. The seismic path attenuation of subduction zone earthquakes (Reg.3 and Reg.4) is more obvious in the high–frequency band and has a frequency correlation, indicating that the attenuation of subduction zone earthquakes includes more inelastic attenuation. The frequency–dependent inelastic attenuation Q of Reg.3 and Reg.4 are 52.58f0.95 and 58.07f0.89, respectively.
Highlights
The regional geological structure of the subduction zone is complex and accompanied by frequent crust–mantle activities
The attenuation curves with a hypocentral distance less than 60 km show a downward trend, and the slope is close to R−0.5
The path attenuation of Reg.2 is stronger than that of Reg.1, mainly because the seismic waves generated by the earthquake in Reg.2 pass through the upper mantle and crustal layers when received by the surface station, and its propagation path is more complex and longer than that of Reg
Summary
The regional geological structure of the subduction zone is complex and accompanied by frequent crust–mantle activities. The rapid release of energy in the activity leads to the subduction zone being prone to rare earthquakes, and causes a series of secondary disasters such as tsunamis and fires. The Kanto Basin is the most densely populated area in Japan, and it is the area with the most complex subsurface structure. The friction and torsion between the Philippine plate and the Eurasian plate, the compression of the Pacific plate as it sinks beneath the Philippine plate, and the interactions between the three plates have caused many large earthquakes [6]. Complex geological structure and frequent seismic activity lead to high seismic risk in the Kanto Basin [9–11], which makes it an ideal place for studying seismic attenuation characteristics of complex plate tectonics
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