HR: 1340h
AN: S13A-1059    [Abstracts]
TI: Rupture Process of the 2007 Noto Hanto Earthquake Inferred From Local P-wave Records: Second hypocenter, Initial Rupture, Main Rupture, Asperity and Killer Pulse
AU: Yamamoto, Y
EM: yosuke@geor.or.jp
AF: Geo-Research Institute, Itachibori 4-3-2, Osaka, 550-0012, Japan
AU: * Takenaka, H
EM: takenaka@geo.kyushu-u.ac.jp
AF: Dept. of Earth Planet. Sci., Kyushu Univ., Hakozaki 6-10-1, Fukuoka, 812-8581, Japan
AB: The 2007 Noto Hanto earthquake (Mjma6.9; Mw6.7) occurred on 25 March 2007 (JST) in the Noto Peninsula area of central Japan, which shook strongly the near-source region. Many strong-motion stations recorded the seismic motion near the source region. In this study we analyzed the P-wave part of such records. In the waveform a typical characteristic can be seen. That is an emergent onset. The strong-motion records at local stations except the three nearest stations show nearly two seconds of small but increasing amplitude arrival (hereafter, called "initial rupture phase") followed by the onset of the main energy release (hereafter, called "main rupture phase"). Such an emergent onset is seen on strong-motion records of other earthquakes (e.g., the 2000 Western Tottori earthquake; the 2005 West Off Fukuoka Prefecture earthquake; the 2007 Niigataken Chuetsu-oki earthquake). For the three nearest stations, S wave may have masked the main rupture phase with the lager amplitudes. The P- wave part of the records has another remarkable feature. In the first P onset part of the initial rupture phase two events can be seen. The difference between the two arrivals is about 0.5 s. Using a master-event technique (Takenaka et al., 2006, EPS) we determined the location of the second event (hereafter called "the second hypocenter") relative to the location of the first event (i.e. hypocenter), and then estimated the relative location and time of the onset of the main rupture with respect to the second hypocenter. We furthermore mapped the asperity area on the main fault plane using a source imaging technique based on the back-projection (Yamamoto and Takenaka, 2006, AGU Fall Meeting). From these analyses, we derived the following rupture history of this earthquake: The initial rupture plane and the main rupture plane are different as suggested by the focal mechanism solutions of the P-wave polarities (JMA, 2007) and the CMT (F-net, NIED, 2007). The rupture first propagated toward the direction of strike of the initial rupture plane for 0.5 seconds and changed to the main rupture plane, where this changing point is the second hypocenter. It located at about 1 km apart from the hypocenter. The rupture then restarted toward the direction of Wajima City along the main rupture plane. The main rupture (breaking of the asperity) began at a time of 2.4 s after the second hypocenter onset at a position of 1.0 km and 1.4 km in the strike and updip directions, respectively, from the second hypocenter. The asperity distributes along an updip and strike direction from the second hypocenter and the imaging peak locates around the coast near Monzen-cho, Wajima city in the Noto Peninsula. This estimated rupture history is consistent with damage distribution and spatial pattern of the observed killer pulse (forward rupture directivity pulse) in S-wave portion of the strong-motion records. (Acknowledgements) We used the strong-motion records supplied by the National Institute for Earth Science and Disaster Prevention (NIED; K-NET, KiK-net, F-net), and the Japan Meteorological Agency (JMA).
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7215 Earthquake source observations (1240)
SC: Seismology [S]
MN: 2007 Fall Meeting