Abstract
The spatiotemporal stress states in the aftershock region of the 2005 West Off Fukuoka Prefecture Earthquake are examined via an analysis of the b values and focal mechanism solutions. The aftershocks are aligned roughly NW–SE, with the southeastern part of the aftershock region believed to correspond to the Kego Fault, which extends beneath the Fukuoka metropolitan area. This study reveals depth-dependent b values in the focal region, where the b values (b = 0.7–1.4) are generally higher above the mainshock depth (9.5 km) and lower (b = 0.5–1.0) at greater depths. The shallower region possesses a significant temporal increase in b values, whereas a lateral b value heterogeneity is observed in the deeper region. The b values (b ~ 1.0) near the mainshock are relatively high, whereas the northwestern and southeastern edges of the deep region have lower b values (b = 0.5–0.7). On the other hand, many of the focal mechanisms for the $$M\ge 3.5$$ events are located in the low b value area of the deep region. The stress tensor inversion results reveal a change in stress state from strike-slip to strike-slip/normal faulting. These findings imply that the stress state remains high and/or slightly decreased in the northwestern and southeastern parts of the deep region. These results and the findings of previous research on this earthquake sequence suggest that the likelihood of future large earthquakes along the southeastern part of the aftershock region should be considered relatively high.
Highlights
The 2005 West Off Fukuoka Prefecture Earthquake (MJ 7.0) occurred in Genkai-nada, Fukuoka Prefecture, northern Kyushu, Japan, on 20 March 2005 (e.g., Shimizu et al 2006; Uehira et al.2006)
The spatiotemporal b-value distributions are highly heterogeneous in the aftershock region of the 2005 West Off Fukuoka Prefecture Earthquake, with the stress-tensor inversion results indicating that the stress state below 9.5 km depth changed from a strike-slip-dominated to strike-slip/normal faulting regime
This study examined the spatiotemporal b-value distributions in the aftershock region of the
Summary
The 2005 West Off Fukuoka Prefecture Earthquake (MJ 7.0) occurred in Genkai-nada, Fukuoka Prefecture, northern Kyushu, Japan, on 20 March 2005 (e.g., Shimizu et al 2006; Uehira et al.2006). Numerous research studies have investigated the coseismic slip distribution of the mainshock, spatial distribution of static stress drops, postseismic deformation, and attenuation structure in the focal region of the 2005 West Off Fukuoka. Iio et al (2006) have provided important details for hazard assessments in the focal region via an investigation of the static stress drop distribution of the aftershocks using the waveforms from temporary seismic stations; they highlighted the possibility of a large stress concentration around the southeastern end of the aftershock area, which includes the largest aftershock Prefecture Earthquake (e.g., Asano and Iwata 2006; Horikawa 2006; Iio et al 2006; Matsumoto, S. et al.2009; Nakao et al 2006; Nishimura et al 2006). Iio et al (2006) have provided important details for hazard assessments in the focal region via an investigation of the static stress drop distribution of the aftershocks using the waveforms from temporary seismic stations; they highlighted the possibility of a large stress concentration around the southeastern end of the aftershock area, which includes the largest aftershock
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
