ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
A method is developed for estimation and interpolation of b-values in space. A 3-D spline function is considered for the logarithm of the b-values at each location in the space. Since many parameters for the spline coefficients are required to obtain a sensible estimate of the spatial variation of b-values, we consider the penalized log-likelihood with the standard roughness penalties for the spline function. Further the error bands of the b-value estimation at each location can be calculated. Using the current method, the spatial distribution of b-values beneath the Kanto District down to the depth of 100 km is determined based on hypocentral data of microearthquakes from the Kanto-Tokai Observational Network of the National Research Center for Disaster Prevention. the stability of the estimated pattern is checked by comparing with the results using alternative cut-off magnitudes. This is further ensured by comparison with the result obtained by an alternative model using equally divided blocks. On the whole, the vertical change in b-value is greater than the horizontal one. It is high in the crust of the Eurasian plate, especially above the upper boundary of the subducting Pacific plate and in the northwest part, or the volcanic area, in the Kanto District. A steep decrease of the b-values is seen to take place in perpendicular direction to the subducting Pacific plate boundary. Also, a similar change is seen in the boundary between the Eurasian and Philippine Sea plates, especially beneath the southern part of the Kanto Plain. the b-value is low in the upper boundary of the subducting plates, but high in the lower plane of the double seismic zone in the Pacific plate. It appears that, even within a narrow area of aftershocks, the b-value can change significantly. It is also found that the variation of the b-value estimate is in good agreement with the structure of seismic wave fractional velocity perturbations. the regions of high and low b-values correspond, respectively, to the lower and higher parts of the P-wave velocity. the similar relationship is seen with the spatial structure of the seismic wave attenuation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1991.tb02499.x
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