We present the abundance analysis of 97 nearby metal-poor ( -3.3 < [ Fe/H ] < -0.5 ) stars having kinematics characteristics of the Milky Way ( MW ) thick disk , inner , and outer stellar halos .
The high-resolution , high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope .
Abundances of Fe , Mg , Si , Ca and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres .
By assigning membership of the sample stars to the thick disk , inner or outer halo components based on their orbital parameters , we examine abundance ratios as a function of [ Fe/H ] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges .

We show that , in the metallicity range of -1.5 < [ Fe/H ] \leq - 0.5 , the thick disk stars show constantly high mean [ Mg/Fe ] and [ Si/Fe ] ratios with small scatter .
In contrast , the inner , and the outer halo stars show lower mean values of these abundance ratios with larger scatter .
The [ Mg/Fe ] , [ Si/Fe ] and [ Ca/Fe ] for the inner and the outer halo stars also show weak decreasing trends with [ Fe/H ] in the range [ Fe/H ] > -2 .
These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars , while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales .