初動の走時から推定される地震波の南関東における伝搬経路

抄録

For the engineering purposes also, the path of the seismic waves must be investigated more clearly. Because, the seismic bedrock that is one of the most important concepts for earthquake engineering, has not been difined finally yet, and incident waves from those seismic bedrock do not always come from just below during earthquakes.
In order to confirm this problem, the crustal structure of the Southern Kanto Region and the path of individual seismic waves during earthquakes were investigated from traveltime tables of the Japan Meteorological Agency. In this paper, earthquakes occurred in the field, that having possibility of bringing earthquake damages in Tokyo Metropolitan area, were taken into consideration.
As results, by using stations on firm ground only, apparent velocities of P-and S-waves were obtained as 6.7km/sec and 3.9km/sec respectively from shallow and near earthquakes, and as 7.5km/sec and 4.3km/sec respectively from rather deep or distant earthquakes. On the other hand, at stations on thick sedimentary layers, systematical delay of travel-time was found. This fact was almost elucidated by existence of sedimentary layers of 2.3km thick, in case of Tokyo.
From these studies, approximate crustal structure of the Southern Kanto Region was obtained and main paths of seismic body waves were confirmed. This result seems to be suggesting about the limitation of subsurface structure, that should be taken into consideration in the field of earthquake engineering.