ATTENUATION TOMOGRAPHY OF NIIGATA PREFECTURE, JAPAN

Abstract

A three-dimensional (3-D) seismic attenuation structure of region lies within Niigata prefecture is determined by inversion of strong motion data by damped least square method proposed by Hashida and Shimazaki (1984) and later modified by Joshi (2006). The study of ,attenuation of seismic waves is one of the basic physical parameter can be used to correlate seismicity and tectonic activity of the region by which we can do Hazard analysis. In. this work I have used two data set each contain four earthquakes digitally recorded on strong motion network (KIK-net) across of all Japan with magnitude ranging from 3.1 to 4.7 and depth ranging from 8 to 15 Km. Study area lies between latitude 35.2N to 36.2N and longitude 136.8E to 137.8E. I compute characteristics of seismic attenuation in Niigata region using data set 1 and 2 by dividing the entire area into twenty-five three-dimensional blocks of uniform thickness (0-5) Km, (5-10) Km and (10-15) Km having different frequency dependent shear wave quality factor in each block. Shear wave quality factor have been computed at frequencies of 2.5, 7 and 10 Hz, respectively. The obtained attenuation structure reveals that upper layer have low Q (high attenuation) value means tectonically more active provenance with shallow earthquake and deeper layer have high Q (low attenuation) value means it's found under old oceanic crust and continental shield. I have compared obtained attenuation structure with geological feature of area and found it is capable to resolve the geology.