The horizontal stresses are greater than the vertical stress, indicating a thrust faulting regime at all tested locations.
This approach is supported by the work of Ito et al. (2004), who pointed out that the mechanisms of the aftershocks, distributed along the boundary between the Pacific and the North American plates, are similar to that of the main event, indicating a thrust fault with a nodal plane dipping to the northwest.
Both indicate a thrust-fault mechanism with a strike, dip, and rake angles varying from about 200° to 209°, 45° to 59°, and 42° to 50°, respectively, and with a moment magnitude of about 6.2.
The distribution of the slip vectors indicates that a thrust fault mechanism with a small left-lateral strike-slip component (assuming the NE-SW plane is the active plane) occurred near the hypocenter and in deep parts.
Meanwhile, rifle bullets fell into the International Settlement behind British and American lines, indicating a Japanese thrust toward that section.
A seismic inversion of long-period P and SH body-wave seismograms indicated a rupture on a thrust fault that dips 49 degrees to the southwest and had a centroid depth of roughly 10 km.
The focal mechanisms of the down-dip earthquakes indicate a NE-SW thrust-faulting system, whereas the earthquakes in the up-dip portion indicate an extensional-faulting component, with a T-axis oriented in a roughly E-W direction (Fig. 2(b)) (Kato et al., 2011).
That the two strike-slip events followed a thrust event indicated a strong coupling of stresses at the North American and Gorda plate boundaries, and underscored the convoluted nature of the interconnected faults in that area.
Recent studies on Riasi Thrust indicate a cumulative vertical separation of 272 ± 10 m and shortening rate of 5.6 ± 2.8 7.1 ± 4.06 mm/year in last 100 ka (Gavillot et al. 2016).
