Aftershock distribution of the 2004 Mid Niigata Prefecture Earthquake derived from a combined analysis of temporary online observations and permanent observations

Abstract

The 2004 Mid Niigata Prefecture Earthquake (Mj = 6.8) occurred on 23 October 2004 in the northeastern part of the Niigata-Kobe Tectonic Zone where large contraction rates were observed. The mainshock was followed by an anomalously intense aftershock activity that included nine Mj ≥ 5.5 aftershocks. We deployed three temporary online seismic stations in the aftershock area from 27 October, combined data from the temporary stations with those from permanent stations located around the aftershock area, and determined the hypocenters of the mainshock and aftershocks with a joint hypocenter determination (JHD) technique. The resulting aftershock distribution showed that major events such as the mainshock, the largest aftershock (Mj = 6.5), the aftershock on 27 October (Mj = 6.1), etc. occurred on different fault planes that were located nearly parallel or perpendicular to each other. This might be due to heterogeneous structure in the source region. The strain energy was considered to have been enough accumulated on the individual fault planes. These features are probably a cause of the anomalous intensity of the aftershock activity.

Seismic scaling relations and aftershock activity from the sequences of the 2004 mid Niigata and the 2005 west off Fukuoka earthquakes (MW 6.6) in Japan

“…[25] Figure 12 shows the distribution of analyzed foreshocks and aftershocks of the MNPE sequence that are distinguished in five groups based on the proximity of their locations to several faults identified by Shibutani et al [2005]. Here the event locations are shown by the symbols of different color in five groups on a map view (top) and on a vertical cross section along profile X-X 0 (bottom).…”

“…We also analyze six large (M W ! 5.5) events (E1, E3, E4, E5, E6 and E7 in Figure 2 and Table 1 summarizes the parameters of the selected events, e.g., the hypocenters relocated by Shibutani et al [2005], the origin times determined by Japan Meteorological Agency (JMA) and the focal mechanism solutions and M W 's provided by the NIED F-net operation.…”

Why do aftershocks occur? Relationship between mainshock rupture and aftershock sequence based on highly resolved hypocenter and focal mechanism distributions

“…Thus, a number of previous studies estimated the subsurface structure of the mainshock fault plane based on the aftershock distribution (e.g., Shibutani et al 2005a;Kato 2005). On the other Open Access *Correspondence: yukutake@onken.odawara.kanagawa.jp 1 Hot Springs Research Institute of Kanagawa Prefectural Government, Odawara, Japan Full list of author information is available at the end of the article hand, field observation of an exhumed outcrop has demonstrated that a fault damage zone is developed around a fault core that is the localized slip zone and contains high-strain products, such as gouges, cataclasites, and ultracataclasites (Mitchell and Faulkner 2009).…”

Coseismic deformation of the Mid Niigata prefecture Earthquake in 2004 detected by RADARSAT/InSAR

“…GPS results and the aftershock distribution suggested that several fault planes had been ruptured in this series of earthquakes. For example, the largest aftershock ruptured the parallel plane to the main shock fault, and the aftershock that occurred on October 27 ruptured the conjugate plane (e.g., Hirata et al, 2005;Kato et al, 2005;Sakai et al, 2005;Shibutani et al, 2005). To investigate such a complex fault mechanism, more spatially detailed deformation data is useful, thus we applied a synthetic aperture radar interferometry (InSAR) technique around the epicentral area.…”