ESTIMATION OF SHEAR WAVE VELOCITY STRUCTURE USING SURFACE WAVES ON THE AEROPUERTO FAULT, MANAGUA, NICARAGUA
Supervisor: Toshiaki YOKOI, Takumi HAYASHIDA
Shear wave velocity (Vs) structure is one of the most important
information for ground motion estimation and seismic microzonation. In this
study, I estimated the Vs structure around the Aeropuerto Fault Zone, in the
eastern part of Managua city, Nicaragua, using microtremors (ambient
vibrations) and surface wave data, and investigated the effectiveness,
limitations and advantages of each method as a tool for seismic microzonation.
I used array observation data with the multichannel analysis of surface waves
(MASW) and the spatial autocorrelation (SPAC) methods as well as single station
microtremor data with the Horizontal-to-Vertical spectral ratios (H/V) method.
The MASW method provides shallow subsurface Vs structure (0~8 m) at four sites
while the SPAC method provides deep Vs structure (14~60 m) at five sites. These
results indicate that the depth of engineering rock is shallower than 20 m in
the target area and there could be the differences of the deep structure
between east and west in the target area. Finally, I estimated physical
parameters of velocity structures for the unknown layer between shallow and
deep portion in consideration of dominant periods of microtremor H/V spectral ratios.
The study has shown that the combination of the different surveys is an
effective approach for estimation of Vs structure, where there is little
available information regarding subsurface soil structure.