Vertically propagating shear waves reflected from a thin reservoir permeated by a single oriented system of open vertical fractures contain information about the fracture density. The outer perimeter of the hodogram constructed from shear waves polarized in the fast and slow directions in the natural coordinate system is approximately elliptical. The polarization is defined as the angle which the major axis of the ellipse makes with the natural coordinate. Over a range of layer thickness which extends well above and below the tuning frequency, the polarization does not deviate from its value for an infinitely thick layer, [Formula: see text], by more than a few degrees. [Formula: see text] and [Formula: see text] are the reflection coefficients in the fast and slow directions. [Formula: see text] is independent of the fracture density, but ψ, [Formula: see text], and the anisotropy η all depend on the fracture density. [Formula: see text], [Formula: see text], and η are related by [Formula: see text]. Analysis of the constant‐anisotropy hyperbolas derived from this equation reveals conditions under which ψ is extremely sensitive to variations in anisotropy. As η increases by 20 percent, the change in ψ approaches 135 degrees for small negative [Formula: see text] and 45 degrees for small positive [Formula: see text]. The ellipse is also characterized by an aspect ratio which is significantly different from zero over a range of layer thickness that extends above and below the tuning frequency. Aspect ratio versus polarization (ARP) curves can be constructed from multi component field data. Each curve is constructed for fixed [Formula: see text] and [Formula: see text] (the two‐way traveltime across the layer for the fast polarization). [Formula: see text] and [Formula: see text] are independent of lateral changes in fracture density. Consequently, points on ARP curves correspond to different values of the anisotropy. If [Formula: see text] is known from well measurements, [Formula: see text] can be determined and a value of anisotropy assigned to each point where there is a field measurement.

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was studied for the earthquakes that occurred from November, 2008 to May, 2013. The analysis was based on the data collected from seismic networks in Korea and China. Fault plane solutions were obtained from P and SH wave polarities and SH/P amplitude ratioes. Most earthquakes exhibited predominantly strike-slip fault characteristics with NNE-SSW or WNW-ESE nodal planes. The P-axes trends are mainly NE-SW or ENE-WSW direction in the northern part of the Yellow Sea and inland area of North Korea except some areas in the Hwanghae province. Fault plane solutions and main axis of stress field in the study region were similar to those observed in the southern part of the Korean Peninsula.

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